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Isothermal transformations in eutectoid zirconium-biobium alloys. Finlayson, Malcolm John 1957

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ISOTHERMAL TRANSFORMATIONS  IN EUTECTOID  ZIRCONIUM-NIOBIUM ALLOYS by MALCOLM JOHN FINLAYSON  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n th© Department of MINING AND METALLURGY  We accept t h i s thesis as conforming to the standard required from candidates f o r the degree of MASTER OF APPLIED SCIENCE.  Members o f the Department of Mining and Metallurgy  THE UNIVERSITY OF BRITISH COLUMBIA  November, 1957-  ABSTRACT  Isothermal transformations i n eutectoid zirconium-niobium a l l o y s have been s t u d i e d by r e s i s t o m e t r i c techniques at high temperature, and by room-temperature hardness measurements, metallography, and X-ray methods, Room-temperature measurements were performed on specimens which had been heat-treated i n evacuated vycor capsules.  The r e s i s t o m e t r i c method gave  data which were not i n agreement w i t h data obtained by room-temperature measurements.  A T-T-T curve e s t a b l i s h e d by room-temperature hardness and  metallography was found t o be s i m i l a r t o one obtained by a previous i n v e s t i gator.  The l a c k of agreement between measurements made a t high temperature  and those made at room temperature suggests that a s t r u c t u r a l change i s o c c u r r i n g i n these a l l o y s during the quench from the transformation temperature.  For t h i s reason, room temperature metallography i s u n s a t i s f a c t o r y f o r  f o l l o w i n g transformations i n these a l l o y s .  The a n a l y s i s of micro-structure  i s complicated by the presence of a n e e d l e - l i k e •phase' which was not i d e n t i f i a b l e by the X-ray techniques employed. I t i s shown t h a t the r e s i s t o m e t r i c technique i s a s e n s i t i v e method f o r observing transformations i n zirconium-niobium a l l o y s .  In p r e s e n t i n g the  t h i s t h e s i s In p a r t i a l f u l f i l m e n t  requirements f o r an advanced degree at the  of  University  of B r i t i s h Columbia, I agree t h a t the  L i b r a r y s h a l l make  it  study.  freely available  agree that  for reference  and  I  further  permission f o r e x t e n s i v e copying of t h i s t h e s i s  f o r s c h o l a r l y purposes may  be granted by the Head o f  Department or by h i s r e p r e s e n t a t i v e .  my  I t i s understood  t h a t copying or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not  Department of  be allowed without my  ML^^.^ <^~<J  The U n i v e r s i t y of B r i t i s h Vancouver 5\ Canada. Date  7 M  7  written  tod/,^j^  Columbia,  permission.  ACKNOWLEDGEMENT  The" author i s g r a t e f u l f o r f i n a n c i a l a i d i n the form of a research a s s i s t a n t s h i p provided by the Defence Research Board of Canada. Funds f o r the present work were nrovided by the Defence Research Board of Canada under Research Grant DRB 7510-18. The author g r a t e f u l l y acknowledges the assistance o f Dr. V. G r i f f i t h s , under whose d i r e c t i o n t h i s i n v e s t i g a t i o n was performed, and the t e c h n i c a l advice and assistance given by Mr. R, Butters and Mr. R. R i c h t e r .  TABLE OF CONTENTS  Page I.  II.  INTRODUCTION  ......  o  .  .  o  o  .  o  «  o  o  .  9  O  .  0  .  o  «  «  *  I  o  A.  Object of t h e I n v e s t i g a t i o n . . .  1  B.  The Zirconium-Niobium  3  A l l o y System  14  PROCEDURE AND RESULTS . A*  A l l O y Melt 6 1*3.3.1 S  o  «  o  9  0  «  4  >  f  t  o  o  o  o  o  o  «  «  «  e  »  ©  #  16  ,'B.. P r e l i m i n a r y Work C.  III.  Isothermal. Transformation Study AllOyS  2.  Transformations i n Vycor Capsules  3.  Resistance Measurements  .  o  .  e  a  o  .  o  23  . . . . . . . . . . . . .  1.  .  1A-  .  .  .  .  .  .  .  .  .  .  .  .  23  .  .  25 30  ...  49  DISCUSSION OF RESULTS AND CONCLUSIONS  IV. APPENDICES 1.  Resistance Data  2.  Related Phase Diagrams  «.«... .  o  .  .  ...... .  o  .  .  .  .  . . . . . . . . .  .  .  .  .  .  o  o  53 55  3 . ASTM d-Spacings f o r Related Zirconium Compounds . . . . . 5 9 V. REFERENCES » » • • » « » » • • • • • » • * • » • • • • • • • • • • • 60  LIST OF ILLUSTRATIONS  Figure 1.  Page A comparison of the neutron cross s e c t i o n of zirconium w i t h that . „ „ of other elements  .....  .  .....  2  2.  The zirconium-niobium phase diagram ( a f t e r Rogers and Atkins) . . . .  3.  Room temperature r e s i s t i v i t i e s of zirconium-niobium a l l o y s i n two conditions  .  .  o  o  .  .  .  .  »  .  .  .  •  .  . o  . . .  o  .  o  .  o  7  o  4.  Change i n r e s i s t a n c e of a 17.5/5 Nb a l l o y on slow heating  5.  V a r i a t i o n i n l a t t i c e parameter w i t h composition f o r a l l o y s quenched from 1100°C  7  . . . . . .  8  '  8  6.  M i c r o s t r u c t u r e of a zirconium - 15% Nb a l l o y quenched from 800°C. . .  10  7.  M i c r o s t r u c t u r e of a zirconium - 12% Nb a l l o y quenched from 1250°C . .  10  8.  The zirconium-niobium a l l o y system ( a f t e r Bychkov et a l ) .  12  9.  Hardness vs composition of zirconium-niobium a l l o y s f o r d i f f e r e n t 12  thermal treatments 10.  T-T-T  curve f o r a zirconium - 14.6% Nb a l l o y ( a f t e r Domagala). . . . .  13  11.  Diagram of the l e v i t a t i o n melting apparatus of Polonis et a l  12.  Vickers hardness vs weight percent Nb f o r as-cast Zr-Nb a l l o y s  13.  Pure zirconium, as-cast  20  14.  Zirconium - 4.16% niobium, as-cast  20  15.  Zirconium - 4.62% niobium, as-cast  20  16.  Zirconium - 14.2% niobium, as-cast  20  17.  Zirconium - 13% niobium, as-cast  18.  Zirconium - 19.6% niobium, as-cast  19.  Zirconium - 4.6% niobium - heat t r e a t e d  20.  Zirconium - 19.6% niobium - heat t r e a t e d  21.  T y p i c a l ingot produced by the l e v i t a t i o n method.  ....  17 19  ...  ,.. • . . . . . . . . .  21  . . . . . . . . . . . . . . . . .  21  .  21 21  . . . . . . . . . .  24  ILLUSTRATIONS (continued)  Page  22. Microstructures of a Z r - 17.4% Nb a l l o y i s o t h e r m a l l y transformed at 630°C 23.  26  Microstructures of a Zr - 17.455 Nb a l l o y i s o t h e r m a l l y transformed 27  at 354°C 24.  Microstructures of a Zr - 17.4% Nb a l l o y i s o t h e r m a l l y transformed at 630°C  25.  28  Change i n Vickers hardness f o r the 17.4% Nb a l l o y i s o t h e r m a l l y transformed a t the temperatures shown  26.  •  29  T-T-T curve f o r a zirconium - 17.4% niobium a l l o y based on hardness * . . » . • • • . • * • .  32  27.  Diagram o f furnace and vacuum chamber assembly . . . . . . . . . . .  33  28.  General view of apparatus  34  29.  View of main vacuum furnace elements  30.  Diagram of r e s i s t a n c e measuring c i r c u i t  31.  Vacuum furnace assembly showing p o s i t i o n of furnace and connections.  36  32.  Close-up o f l i d showing the method of a t t a c h i n g the specimen . . . .  38  33.  The change of the r a t i o o f r e s i s t a n c e t o i n i t i a l r e s i s t a n c e  39  34.  Change of r e s i s t a n c e on heating the n e a r - e q u i l i b r i u m s t r u c t u r e o f  changes  . . . . . . . .  . .  34 . . . . . . .  ....  40  a Zr - 16.4% Nb a l l o y 35.  Some t y p i c a l r e s i s t a n c e - time curves obtained on a Zr - 16.4% a l l o y  36.  Tentative T-T-T curve f o r a Z r - 16.4% Nb a l l o y , based on r e s i s t a n c e data  37.  . . . . . * • • • •  42  43  Hardness change i n a Zr - 16.4% Nb a l l o y , i s o t h e r m a l l y transformed at 515°C  38.  35  43  Microstructures o f the 16,4% Nb a l l o y i s o t h e r m a l l y transformed a t 515°C  45  39.  Needles i n a Zr - 16.4% Nb a l l o y water quenched a f t e r 48 h r s . a t 800°C 46  40.  Back r e f l e c t i o n Laue p i c t u r e s of the Zr - 16.4% Nb a l l o y  47  LIST OF TABLES  Page 1.  Some Physical and Mechanical Properties of Zirconium and Niobium. . .  2.  The Mechanical Properties of Zirconium-Niobium Alloys at Room-  3  4  Temperature 3.  Y i e l d Strengths of Zirconium-Niobium Alloys at 649°C  4.  Analysis of the Alloy Materials of Domagala et a l  14  5.  Analysis of Foote C r y s t a l Bar Zirconium  15  6.  Spectrographic Analysis of Niobium  15  7.  Decrease i n Gas Content of Niobium on Vacuum Sintering  15  8.  Data Pertinent to the C o i l Design  17  9.  Composition and As-cast Vickers Hardness o f Zr-Nb Alloys Prepared  . . . . . . . . .  by Levitation Melting 10.  r  18  D-spacings (Angstroms) from X-ray Measurements f o r Alloys Made with Sponge Zr  . .  11.  Dimensions of C o i l Used to Prepare  12.  Weight Data f o r Alloys of C r y s t a l Bar Zirconium Base  17„  D-spacings (Angstroms) f o r the 1 7 . 4 % Niobium A l l o y Isothermally  Alloys of C r y s t a l Bar Zirconium  Transformed at 5 1 4 ° C 14.  5  23  31  D-spacings (Angstroms) f o r a 1 6 . 4 % Niobium a l l o y Isothermally Transformed at 5 1 5 ° C  44  ISOTHERMAL TRANSFORMATIONS IN EUTECTOLD .ZIRCONIUM-NIOBIUM ALLOYS  INTRODUCTION  A.  Object of the I n v e s t i g a t i o n For use w i t h i n t h e f i s s i o n zone of nuclear reactors which have t o  work at high temperatures-, the u s u a l engineering m a t e r i a l s are unsuitable, e i t h e r because they absorb too many neutrons or react with the f u e l .  Thus  a t t e n t i o n has been d i r e c t e d t o metals formerly regarded as r a r e , and great advances have been made i n the development o f such m a t e r i a l s f o r engineering use. Of t h e metals w i t h r e l a t i v e l y high melting p o i n t s , zirconium has the lowest absorption c r o s s - s e c t i o n f o r thermal neutrons  (see F i g . l ) .  It  was therefore considered t o be a p o t e n t i a l l y important s t r u c t u r a l or canning m a t e r i a l f o r reactors operating at medium and high temperatures.  However,  since the creep strength of zirconium at elevated temperatures was found to be poor, extensive studies of the a l l o y i n g behaviour of zirconium have been undertaken.  These s t u d i e s , which are described i n a recent volume,^  c o n s t i t u t e d a search f o r a l l o y s having high-temperature  strength coupled  w i t h the r e t e n t i o n of t h e a t t r a c t i v e nuclear and chemical p r o n e r t i e s of pure zirconium. I t was therefore the object of the present work to add t o the data on zirconium a l l o y s by studying isothermal transformations i n zirconium-niobium a l l o y s of eutectoid composition and thereby determining the r e l a t e d TimeTemperature-Transformation (T-T-T) diagram.  -  Table I Thermal-Neutron Cross Section (Barns) of Commonly Available Elements With Melting Points of Metallic Elements In Low and Intermediate Cross Section Group* Low Cross Section ( <I.O Barn) • . Melting Element cr. Point ( C) 0.0002 Oxygen Carbon 0.0045 Beryllium 0.009 1280 Fluorine 0.01 Bismuth 0.032 Magnesium 0.05'» 6SI Silicon 0.13 Phosphorus 0.19 Zirconium 0.18 1845 Lead 0.17 327 Aluminum 0.22 660 Hydrogen 0.33 Calcium 0.43 '850 Sodium 0.49 98 Sulphur 0.49 Tin 0.6S Z32 C  iii  Intermediate Cross Section (1.0 to 10.0 Barn?)-Melting am Point ( C) Element I.I Zinc 419 Columbium I.I 2415 Barium 1.2 704 Strontium 1.2 770 Nitrogen 1.8 Potassium 2.0 ' 64 Germanium 2.3 Iron 2.4 1539 Molybdenum 2.4 262S Gallium 2.7 30 Chromium 2.9 1890 Thallium 3.3 300 Copper 3.6 10S3 Nickel 4.5 14S5 Tellurium 4.5 Vanadium 4.7 1710 Antimony 6.4 630 Titanium 5.6 1725 C  .  High Cross Section (>I0 Barns)-  Element Manganese Tungsten Tantalum Chlorine Cobalt Silver Lithium Gold Hafnium Mercury Iridium Boron Cadmium Samarium Gadolinium  <r« 13 19 21 32 35 60 07 94 115 380 440 750 2,400 6,500 44.0011  Table II Thermal-Neutron Cross Sections and Melting Points of Metallic Elements W i t h .Melting Points Above S0O°C  Metal Beryllium Magnesium Zirconium Aluminum  Lou  I .  t Sectiun Mfltluii Point (~C) I2K0 o.oin O.OS't 6S1 0. 18 1815 0.22 660  •  Intermediate Crosi SixtionMetal Melting Point ( C Columbium 1.1 241S Iron 2.4 1539 Molybdenum 2.4 2625 Chromium 2.9 1890 Copper 3.6 1083 Nickel 4.5 1455 Vanadium 4.7 1710 Titanium 5.6 1725 J  Table III Selected Refractory Metals and Low Cross Section ( < 1.0 Barn) Metal ff« Zirconium 0.18  Figure 1 .  Alloys  Intermediate Cross Sections (<10 Bams. >1.0 B a r n ) -  r-  Metal Iron Molybdenum Stainless steels Nickel-base alloys (Hastelloys, Monels. Inconels, Nichrome) Titanium  2.4 2.4 ~ 1  A comparison of the neutron cross section of zirconium with that of other elements (after M i l l e r ) . 2  2  -  B, The Zirconium-Niobium A l l o y System Zirconium and niobium are both members of the second t r a n s i t i o n group of elements having atomic numbers of 40 and 41 r e s p e c t i v e l y , l i s t s some of t h e i r p h y s i c a l and mechanical Drooerties. two a l l o t r o p i c m o d i f i c a t i o n s j  Table 1  Zirconium e x i s t s i n  alpha, which i s close-packed-hexagonal and i s  stable below 862°C, and beta, which i s body-centred-cubic and i s stable between 862°C and the melting point of 1852°C. Niobium i s body-centred-cubic at a l l temperatures below i t s m e l t i n g point of 2415°C. The a d d i t i o n of a l l o y i n g elements t o zirconium a f f e c t s i t s a l l o t r o p i c transformation temperature.  Some elements r a i s e t h i s temperature w h i l e  others lower i t j that i s , c e r t a i n elements s t a b i l i z e the alpha phase w h i l e others s t a b i l i z e the beta phase.  Pfeil  and Smoluchowski"'" have discussed  3  e x t e n s i v e l y the t h e o r e t i c a l aspects of the a l l o y i n g behaviour of zirconium. Mcintosh  has reviewed t h e a l l o y systems of niobium.  Of the elements of  i n t e r e s t t o t h i s work, oxygen, nitrogen, and hafnium s t a b i l i z e the alpha phasej niobium and tantalum s t a b i l i z e the beta. be a beta s t a b i l i z e r .  I t i s a l s o f e l t that hydrogen tends t o  The r e l a t e d r>hase diagrams f o r these elements i n zirconium  may be found i n the Appendix. Table 1 Some P h y s i c a l and Mechanical Properties o f Zirconium and Niobium.  Atomic Number Atomic Weight Crystal Structure  a cph  Zirconium  Niobium  40  41 92.91  91.92  a = 3.232A c - 5.147A  bcc a = 3.300A  c/a = 1.593  0 bcc a = 3.61A (~900°C) A l l o t r o p i c Transformation Melting Point R e s i s t i v i t y R.T/*<-ohm-cm Hardness R.T. 0  826 °C 1852°C 40 ~ 7 0 VPN  2415°C 15.22 ~ 40 VPN  The e a r l i e s t work on the zirconium-niobium system appears to have been done by Anderson and co-workers at the U.S. Bureau of Mines.->  Three  alloys were prepared containing 0 , 6 , 5 . 1 , and 1 2 . 9 % * niobium r e s p e c t i v e l y . The 0 . 6 % a l l o y , which was composed mainly of the Widmanstatten  structure, as  seen i n pure zirconium under similar conditions, contained also a l i t t l e of a second phase.  Pfeil^  1  believed t h i s second phase to be retained beta.  In the  5 . 1 % a l l o y , the needles are described as 'fine needles', and small spheroids of a second phase randomly dispersed are mentioned i n the d e s c r i p t i o n of the 'asswaged microstructure*.  The 1 2 . 9 % a l l o y was composed of very large grains  f i l l e d with f i n e l y f o l i a t e d f e r n - l i k e patterns.  The microstructures of the zirconium-niobium a l l o y s prepared by  7 Litton  are not reported, but the mechanical properties at room temperature were  appreciably d i f f e r e n t from those obtained on the a l l o y s of Anderson et al,(see Table 2 ) .  TMs may be due to the difference i n heat treatment.  were annealed at 7 2 5 ° C .  Litton's alloys  Neither the time of annealing, nor the rate  of cooling to room temperature i s stated.  The Bureau of Mines alloys were  annealed 2 0 - 3 0 minutes at 8 5 0 ° C a f t e r swaging and then air-cooled. Table 2 . The Mechanical Properties of Zirconium-Niobium Alloys at Room Temperature.  Author  Anderson et a l Litton Anderson Litton Litton Anderson Litton Litton Litton ... '.„, ... _  Wt.% Niobium 0.6 2.5 5.1 7.5 12.5 12.9 17.5 22.5  27.5  Y i e l d Strength (psi) 0 . 0 5 % offset  Ultimate Strength psi  0.2% o f f s e t 54,600  63,300 79.800 . 93,700 81,500 78,700 67,500 57,800  -  ;  4  Weight percentages are used throughout unless otherwise seated.  83,700 87,500 104,700 107,000 102,000 150,300 91,200 72,500 74,300  The decrease i n the y i e l d s t r e n g t h of L i t t o n s a l l o y s containing above 7 . 5 % niobium, may mean that under t h e c o n d i t i o n of the experiments, the a l l o y s contained an i n c r e a s i n g amount of the beta phase.  The y i e l d strengths at  649°C  of the Bureau o f Mines a l l o y s are shown i n Table 3 . Table 3 . Y i e l d Strengths of Zirconium-Niobium A l l o y s at  Composition Wt. % Nb.  649°C.  Y i e l d Strength ( p s i ) 0 . 2 % offset  0 . 6  9 , 3 2 0  5 . 1  7 , 9 1 0 1 0 , 0 2 0  1 2 . 9  These values are r e a d i l y e x p l i c a b l e on t h e hypothesis that niobium depresses the a-p transformation of zirconium. The a l l o y containing 5.1% niobium would appear t o contain an appreciable amount of beta phase at  649°C.  8 Simcoe and Mudge  observed an increased s t r e n g t h i n both 0.5 and 1.0%  niobium a l l o y s made w i t h hafnium-containing zirconium and a l s o stated that l e s s than 0.5% niobium i s soluble i n zirconium a t 800°C. o According to Keeler the strength of zirconium i s increased by additions of niobium to a content o f at l e a s t 3 % . Keeler"^ a l s o observed a maximum i n hardness at about 10 atomic percent niobium and commented on the b r i t t l e n e s s o f a l l o y s of t h i s composition. In 1 9 5 2 , Hodge-*"'- i n v e s t i g a t e d the zirconium-niobium system UP t o about 25% niobium.  His data on melting points were not s u f f i c i e n t l y numerous to  d i s t i n g u i s h w i t h c e r t a i n t y between the a l t e r n a t i v e s o f a narrow e u t e c t i c h o r i z o n t a l and a wide f l a t minimum i n the s o l i d u s curve.  Hodge t e n t a t i v e l y  suggested that transformations i n the s o l i d s t a t e appeared t o i n d i c a t e that the  -  6  -  eutectoid i n the zirconium-rich alloys lay at about 625°C and 1 0 % niobium and that the s o l u b i l i t y of niobium i n zirconium at 625°C was near 6 % . 12  In 1 9 5 5 , Rogers and Atkins Figure 2 .  published the Phase diagram shown i n  Complete mutual s o l i d s o l u b i l i t y exists f o r an i n t e r v a l below the  solidus l i n e , a continuous curve with a f l a t minimum near 2 2 % niobium and 1740°C.  The liquidus was not determined, but the narrow range of melting at  about 2 0 % niobium was noted.  On cooling, the s o l i d solution breaks UP, except  at the niobium-rich side, from two causes:  zirconium-rich alloys transform  under the influence of the B —• a transformation i n pure zirconium; . alloys of intermediate composition decompose into two s o l i d solutions below 1000°C.  The  combined e f f e c t i s the formation of a eutectoid at a temperature of 6 l 0 ° C and a composition of 1 7 . 5 % niobium.  The eutectoid horizontal extends from 6 . 5 to  8 7 . 0 % niobium. Some age-hardening effects were observed i n the zirconium-rich alloys but the position of the solvus l i n e s remained uncertain.  The analysis  given f o r the material used showed that the impurity content of the zirconium was low.  This material was low-hafnium (less than 0 . 0 5 % ) grade zirconium which  had been produced by the iodide and fabricated to plates. the p r i n c i p a l impurities  process, melted under a protective atmosphere  The niobium analysis was known only approximately, being tantalum ( 0 . 5 % ) and carbon ( 0 . 2 5 % ) plus a few  hundredths of one percent each of i r o n , s i l i c o n , and titanium. Certain of t h e i r r e s u l t s are reproduced as Figures 3 , 4> and 5 since these data affected the course of the present investigation.  Figure 3 shows  the comparison of room temperature r e s i s t i v i t i e s f o r a l l o y s quenched to room temperature after 2 0 hours at 900°C (curve A) and f o r a l l o y s annealed at temperatures below the eutectoid i n order to obtain the equilibrium structure (curve B).  For compositions between 4 and 13% niobium t h i s annealing consisted  of 1 2 0 hours at 590°C plus 1 6 0 hours at 575°C whereas compositions between  i  '  .  1  - 7  C,  1  i '  ,  1  !•  !  1 A o  B  !  ft  P 3  UJ Q>-— lit hr  F Cb  hr '•'Cb  3  600  a  / i  400  <i  •» •  \'  f\ I  r — *  '  1  r  i i  +  J  200  I 10  0  20  30  40  50  60  70  80  90  IOC;  COLUMBIUM, P E R CENT  Figure 2.  The zirconium-niobium phase diagram ( a f t e r Rogers and A t k i n s ) 1  0  40 60 80 . 1 0 0 WT.% NIOBIUM Figure 3: Room Temperature R e s i s t i v i t i e s o f Zirconium-Niobium A l l o y s i n Two Conditions; A, Quenched from 900°C, B, E q u i l i b r i u m S t r u c t u r e , ( a f t e r Rogers and Atkins )  20  - 8 -  F i g u r e 4 . Change i n r e s i s t a n c e o f 17.5% n i o b i u m a l l o y on slowheating. Break i n d i c a t e s t h e t r a n s f o r m a t i o n o f t h e l o w - t e m p e r a t u r e e q u i l i b r i u m s t r u c t u r e at t h e e u t e c t o i d t e m p e r a t u r e . ( A f t e r Rogers and A t k i n s - * - ) . 2  3.20! 0  I  1  J  1——I  20 40 60 80 100% Nb F i g u r e 5» V a r i a t i o n i n l a t t i c e parameter w i t h c o m p o s i t i o n f o r a l l o y s quenched f r o m 1100°C. A l l are b o d y - c e n t e r e d cubic structures. No p o i n t s o c c u r f o r c o m p o s i t i o n s below 15% s i n c e some t r a n s f o r m a t i o n o c c u r r e d a t t h e r a t e s o f c o o l i n g employed. ( A f t e r Rogers and A t k i n s ^ - ) . 2  - 9 15 and 90% niobium were held f o r 240 hours at 590°C plus 160 hours at 575°C. Figure 4 shows the plot of simultaneous measurements of resistance and temperature on a wire specimen of an a l l o y of eutectoid composition as i t was to slow heating.  The  subjected  sharp decrease i n the resistance at 6l0°C represents  crossing of the eutectoid h o r i z o n t a l .  the  Figure 5 gives the v a r i a t i o n of l a t t i c e  parameter with composition for a l l o y s between 15 and 100% niobium which had been quenched from 1100°C„  A l l such a l l o y s were i n a single phase condition and  possessed a body-centered-cubic structure.  No points were plotted f o r compositions  less than 15% niobium since the zirconium-rich a l l o y s were seen to undergo some transformation  at the rates of cooling attained.  The rate of cooling  was  s u f f i c i e n t l y e f f e c t i v e to r e t a i n the high temperature condition i n a l l but the low-niobium a l l o y s because the transformation i n g l y sluggish as the niobium content was  i n the s o l i d state became increas-  increased beyond 5%.  Alloys rapidly  cooled from 900°C were a l l single phase except those between 44 and 77% I t was  niobium.  also suspected that some p r e c i p i t a t i o n of a from the B-zirconium occurred  during rapid cooling.  In 1956,  No microstructures were presented i n the above report.  Domagala and Mcpherson"^ described t h e i r i n v e s t i g a t i o n of the  zirconium-niobium system. zirconium and  3  From experiments on a l l o y s prepared from iodide  'high p u r i t y ' niobium powder, they obtained data which did not agree  with c e r t a i n aspects of the work of Rogers and Atkins.  They described a  15%  niobium a l l o y quenched a f t e r 136 hours at 800 C as a two-phase a + 3 structure 9  (see Figure 6).  From t h i s and other considerations, they believed that the  eutectoid h o r i z o n t a l i n t h i s system was composition was  at a temperature of 800°G, the eutectoid  at 17% niobium, and a continuous series of s o l i d solutions  existed only above 1180°C.  Rogers and Atkins' r e p l y to t h i s c r i t i c i s m was cooled from 700°C and 800°C showed strong lines of two  that t h e i r a l l o y s  body-centered-cubic phases.  F i g u r e 6.  M i c r o s t r u c t u r e of a z i r c o n i u m 15% Nb a l l o y quenched from 800°C. C o n s i d e r e d t o be two phase a + 3 s t r u c t u r e by Domagala and M c P h e r s o n . 1 3  Figure  7.  M i c r o s t r u c t u r e of a zirconium 12% Nb a l l o y quenched f r o m 1250°C. ( A f t e r Rogers and A t k i n s ) . 1 3  -  A few weak l i n e s were a l s o p r e s e n t i n t h e X - r a y p a t t e r n s and t h e s e were t o be r e p r e s e n t a t i v e  -  11  believed  o f a w h i c h had formed as the a l l o y passed t h r o u g h t h e They p r e s e n t e d a p h o t o m i c r o g r a p h o f a 12% n i o b i u m  transformation temperature.  a l l o y w h i c h was quenched from 1 2 5 0 ° C (see F i g u r e 7 ) . was s t a t e d t o be c h a r a c t e r i s t i c of a l l o y s quenched from an e x t e n s i v e  This n e e d l e - l i k e  structure  c o n t a i n i n g f r o m 8 t o 15% n i o b i u m  range o f t e m p e r a t u r e s .  I t was b e l i e v e d t h a t  the  network came i n t o e x i s t e n c e when t h e a l l o y went t h r o u g h t h e t r a n s f o r m a t i o n range and t h a t i t was p r o b a b l y r e l a t e d t o t h e h i g h e l e c t r i c a l r e s i s t a n c e  and c o n s i d e r -  a b l e b r i t t l e n e s s o f r a p i d l y - c o o l e d a l l o y s i n t h i s range o f c o m p o s i t i o n . and A t k i n s d i d not b e l i e v e t h a t t h i s was a two-phase In 1957, shown i n F i g u r e 8 .  Bychkov e t a l " ^ p u b l i s h e d the  Rogers  structure.  z i r c o n i u m - n i o b i u m phase d i a g r a m  T h i s d i a g r a m i s s i m i l a r i n , f o r m t o t h a t o f Rogers and A t k i n s  but the e u t e c t o i d h o r i z o n t a l here i s a t 5 5 0 ° C and the e u t e c t o i d c o m p o s i t i o n i s a t 12% n i o b i u m .  A l s o t h e minimum i n t h e s o l i d u s curve o c c u r s at 1 6 0 0 ° C  t h a n a t 1 7 4 0 ° C as found by Rogers and A t k i n s .  rather  Bychkov et a l used i o d i d e  z i r c o n i u m c o n t a i n i n g 1 . 5 % h a f n i u m and n i o b i u m c o n t a i n i n g 1 . 0 %  nrocess  tantalum.  The methods used by t h e two groups t o f a b r i c a t e t h e i r a l l o y s b y h o t - r o l l i n g and f o r g i n g were e s s e n t i a l l y t h e same.  The hardness measurements on t h e a l l o y s  of  Bychkov are i n c l u d e d as F i g u r e 9 .  A f t e r the experimental part of the present  i n v e s t i g a t i o n was  completed,  a r e p o r t was r e c e i v e d o f t h e work performed at Armour by a group headed by 15  Domagala  .  F i g u r e 10 shows t h e T-T-T curve w h i c h t h i s group o b t a i n e d f o r a  zirconium-14o6% niobium a l l o y .  Data were o b t a i n e d by m e a s u r i n g r e s i s t i v i t y and  hardness of quenched specimens at room t e m p e r a t u r e .  T h e i r a l l o y s were  prepared  from sponge z i r c o n i u m and n i o b i u m s h e e t by a r c - m e l t i n g i n a w a t e r - c o o l e d h e a r t h under an argon atmosphere. d i a m e t e r r o d s and c e n t r e l e s s  copper  The i n g o t s o b t a i n e d were h o t - f o r g e d t o 3 / 8 ' '  ground t o 3 / 1 6 "  diameter.  Three t o f o u r i n c h l e n g t h s  - 12  2500 HOC ^ "00 ° .1800 1/700 § 1500  f  >-•  A20  ,| ItOO BOO 700 500  —  _5l <o°c  Zrl0Z03O*0SOS0P0809O!W Bee. %Hb  Figure.8.  The zirconium^niobium a l l o y system ( a f t e r Bychkov et a l ^ ) . 1  20  60 80 100 Wt.% Nb 40  Figure 9« Hardness-vs comppsition of Zr-Nb a l l o y s f o r d i f f e r e n t thermal treatments'; 1. As-cast. 2. Furnace cooled from 650°C. < 3. Quenched from 750°C. ( a f t e r Bychkov et  al 0. - " lz  - 13 -  o  800  CO  CD CO  U  HO <D Q CO in  CO  §  "TO  F i g u r e 10.  IDTT  TOOTT  Time-Minutes T - T - T curve f o r a Z r - - 1 4 . 6 % Nb a l l o y ( a f t e r  o f t h i s m a t e r i a l were used f o r r e s i s t i v i t y measurements.  1U,U00  Domagala ^), 1  The heat t r e a t m e n t s  c o n s i s t e d o f f i r s t h e a t i n g t h e specimen t o 1000°C i n a g l o b a r f u r n a c e , i n w h i c h a dynamic h e l i u m atmosphere was m a i n t a i n e d .  A f t e r 8 t o 10 m i n u t e s a t  1000°C,  t h e specimen was quenched i n t o a n o t h e r r e s i s t a n c e f u r n a c e and i s o t h e r m a l l y t r a n s f o r m e d , i n a h e l i u m atmosphere, f o r a s p e c i f i c l e n g t h o f t i m e , a f t e r w h i c h i t was quenched t o room t e m p e r a t u r e by p l u n g i n g i t i n t o w a t e r .  The ends of  rods were t h e n ground p r i o r t o t h e measurement o f room-temperature  the  resistivity.  A s l i c e was t a k e n o f f t h e specimen f o r h a r d n e s s measurements and m e t a l i o g r a p h i c o b s e r v a t i o n ! t h e specimen was t h e n heated a g a i n t o 1000°C and t h e c y c l e  The a n a l y s i s o f t h e i r m a t e r i a l s i s g i v e n i n Table 4 . used p r o b a b l y c o n t a i n e d about 2.0% h a f n i u m .  repeated,  The z i r c o n i u m  -  Table 4 .  1 4  -  •  A n a l y s i s o f t h e A l l o y M a t e r i a l s o f Domagala e t a l ^  Impurity  Sponge Z i r c o n i u m As r e c e i v e d  Oxygen Nitrogen Hydrogen Carbon Fe Mg CI  Imnurity  0 . 0 2 %  vxm.  6 5  Wt. %  Ta C Ti Si Fe  0 . 1 2 4 %  . 0 2 %  ppm.  0 . 0 2 3 % . 0 4 2 %  0 . 5 0 . 1 0 . 0 4 0 . 0 2 0 . 0 1  . 0 2 3 % . 0 3 7 %  II.  A.  A r c - m e l t e d and forged bar-stock  0 . 1 3 1 %  49  Niobium  PROCEDURE AND RESULTS  Alloy Materials. The z i r c o n i u m used i n t h i s i n v e s t i g a t i o n was a v a i l a b l e i n two g r a d e s ;  namely, l o w - h a f n i u m r e a c t o r grade sponge i n t h e f o r m o f 5 / 8 ' " d i a m e t e r r o d and i o d i d e c r y s t a l b a r as produced by t h e F o o t e M i n e r a l Company.  The a n a l y s i s o f  t h e F o o t e c r y s t a l b a r i s g i v e n i n T a b l e 5 but no a n a l y s i s f o r t h e r e a c t o r sponge was r e c e i v e d .  grade  I t i s most c e r t a i n t h a t t h i s l a t t e r m a t e r i a l was f a b r i c a t e d  from a r c - m e l t e d sponge.  I t s i m p u r i t y c o n t e n t w o u l d be t h e r e f o r e  o f t h e c r y s t a l b a r except w i t h r e g a r d t o h a f n i u m and gas c o n t e n t . c o n t e n t o f r e a c t o r grade sponge i s about 0.01%.  s i m i l a r to that The hafnium  A l t h o u g h a gas a n a l y s i s was  not g i v e n i t may be estimated"*" t h a t t h e oxygen and n i t r o g e n c o n t e n t o f t h e sponge i s about 0 . 1 2 and 0.005% r e s p e c t i v e l y and t h a t t h e oxygen c o n t e n t o f t h e c r y s t a l b a r i s about 0 , 0 1 % . The n i o b i u m used i n t h i s work was o b t a i n e d as 4 . 7 mm d i a m e t e r r o d f r o m J o h n s o n , M a t t h e y and Company.  T h e i r a n a l y s i s i s given i n Table 6 .  Although  no gas a n a l y s i s i s g i v e n , the gas c o n t e n t may be e s t i m a t e d f r o m t h e d a t a o f T a b l e 7 i f , as was p r o b a b l y t h e c a s e , t h i s m a t e r i a l was p r e p a r e d by the vacuum s i n t e r i n g of niobium powder^. Table. 5 . A n a l y s i s o f Foote C r y s t a l Bar Z i r c o n i u m  I m p u r i t y Element  Weight P e r c e n t  Si Al Mn Mg Fe Cr Sn Ti Ni Ca Cu Mo Hf  0 . 0 0 5 0 . 0 0 4 0 . 0 0 1 0 . 0 0 2 0 . 0 0 2 0 . 0 0 1  nil 0 . 0 0 4  trace 0 . 0 0 5 0 . 0 0 0 5  approx.  nil 2„17  Table 6 Spectrographs I m p u r i t y Element  A n a l y s i s of Niobium Weight  Ta Ni Fe ti  Percent  0 „ 5 0 . 0 0 0 7 .  0 . 0 0 4 0 . 0 1 2  Table 7 Decrease i n Gas Content o f N i o b i u m on Vacuum S i n t e r i n g Raw Powder Oxygen Nitrogen Hydrogen  0 . 9  w t . 1o  A f t e r Vacuum S i n t e r i n g 0 . 0 2  0 . 1  0 . 0 1  0 . 2 7  0 . 0 0 1  wt. %  - 16 B.  P r e l i m i n a r y Work The f i r s t problem w h i c h r e q u i r e d s o l u t i o n was the p r e p a r a t i o n o f  alloyso  The pronounced tendency f o r z i r c o n i u m (and n i o b i u m ) , t o t a k e UP l a r g e  amounts o f oxygen, n i t r o g e n , and hydrogen i n s o l i d s o l u t i o n r e q u i r e d t h a t m e l t i n g be performed i n vacuum o r an i n e r t atmosphere.  The a c c e p t e d method f o r  p r e p a r i n g a l l o y s of r e a c t i v e metals i n v o l v e s a r c - m e l t i n g i n a w a t e r - c o o l e d copper h e a r t h .  Such f a c i l i t i e s were not a v a i l a b l e .  However, the  levitation  17 m e l t i n g a p p a r a t u s o f P o l o n i s et a l  w i t h w h i c h t h e above a u t h o r s had  f u l l y p r e p a r e d t i t a n i u m - b a s e a l l o y s was a v a i l a b l e . been  amply d e s c r i b e d ^ and t h e r e f o r e 1  i n c l u d e d here  (see F i g u r e 1 1 ) .  success-  This melting technique  o n l y a diagram o f the apparatus w i l l  I t was found t h a t whereas  has be  s o l i d zirconium could  be l e v i t a t e d w i t h t h e c o i l of P o l o n i s , t h e l i q u i d m e t a l c o u l d n o t , even w i t h a l a r g e r source o f h i g h f r e q u e n c y power as d e l i v e r e d by a L e p e l v a l v e  oscillator  r rated at  2 3 » 5  KVA.  A c o i l d e s i g n was e v e n t u a l l y f o u n d w h i c h was s u c c e s s f u l  t h i s r e g a r d (see T a b l e 8) and s i x a l l o y s were p r e p a r e d .  These a l l o y s  in  represent  t h o s e w h i c h were t h e r e s u l t o f optimum o p e r a t i o n , t h a t i s , i n t h e s e cases t h e m e t a l l e v i t a t e d w e l l , no a r c i n g o c c u r r e d between c o i l and specimen, t h e m e t a l was h e l d i n l e v i t a t i o n f o r about 3 0 s e c o n d s , between t h e m e t a l and c o i l d u r i n g c a s t i n g .  and no c o n t a c t  occurred  . I t may be s t a t e d t h a t the improved  c o i l d e s i g n was o n l y 5 0 % s u c c e s s f u l - o n l y 8 out o f 16 charges t o t h e y i e l d e d i n g o t s w h i c h were c o n s i d e r e d t o be  apparatus  satisfactory.  These a l l o y s were made f r o m t h e r e a c t o r - g r a d e n i o b i u m d e s c r i b e d above.  z i r c o n i u m and t h e  Homogeneous i n g o t s were o b t a i n e d by i n s e r t i n g t h e  niobium i n a hole d r i l l e d i n the z i r c o n i u m specimen.  The c o m p o s i t i o n s were  c a l c u l a t e d s i m p l y from t h e r e l a t i v e w e i g h t s o f t h e components charged t o a p p a r a t u s s i n c e w e i g h i n g b e f o r e and a f t e r m e l t i n g showed a l o s s of l e s s one p a r t i n  2 0 0 0 .  liquid  the than  Tree machining brass e/)d plate 'fm i 5 m . Vie in thick • V in. diom.  'Lucite 'cylinder - v in. 0.0. \ • - Vs in. thick 7 in. long. (  rubber  (set in groove  O  ring  in brass  gasket pJate)  Ve \.n..diom steel rods Induct/on coil Vs tn. GO. copper tubing 0 03H wall  \  Copper mould-  //2'/«in.  Tubing to pipe  inf  0. D. 3Ai in |  connector  \ f in diom. rubber  lon-er * 5/-i6Xn,  Power  leads -.  '•Wooden  T To pressure and vacuum  Figure 11.  gouge. pump  Argon  Qringgasket  brass p/ote Sin... sin. thick platform  inlet Scale Vu i n = 1 i n .  Diagram of t h e l e v i t a t i o n melting apparatus of Polonis et a l 7 . 1  Table 8 Data P e r t i n e n t t o t h e C o i l Design which was SuccessfullyUsed t o Prepare Zr-Nb A l l o y s by L e v i t a t i o n M e l t i n g Turn No. 1  (top) (Reverse t u r n )  2 3 4 5. 6 7 9  Note: T"  1.618 1.610 1.450 1.322 1.144 1.000 0.859  0.780  8  10  C o i l Diameter 0,D. inches  (bottom)  0.755 0.721  C o i l i s made from 1/8*» O.D. Conner tubing - wound on s u i t a b l e c o n i c a l mandrell. O v e r a l l height o f c o i l i s .1.500 inches.  -  18  M e l t i n g was done under argon w h i c h had been p u r i f i e d by p a s s i n g o v e r P2O5 beads and t h r o u g h a c a l c i u m t r a i n w h i c h was h e l d a t  -  it  Just p r i o r  550°C.  t o m e l t i n g t h i s argon was g e t t e r e d w i t h a hot z i r c o n i u m f i l a m e n t i n t h e f o r m o f o005  8 8  diameter w i r e .  The a l l o y s prepared are l i s t e d i n Table 9 t o g e t h e r w i t h t h e i r as Vickers  Hardness.  Figure 1 2 .  cast  A p l o t o f as c a s t hardness vs c o m p o s i t i o n i s g i v e n i n  M i c r o hardness v a l u e s were o b t a i n e d w i t h a Bergsman M i c r o h a r d n e s s  T e s t e r mounted on a L e i t z M e t a l l o g r a p h .  A l o a d o f 1 0 0 grams was u s e d .  Table 9 . C o m p o s i t i o n and As C a s t V i c k e r s Hardness o f Z r - N b A l l o y s P r e p a r e d by L e v i t a t i o n M e l t i n g  % Mb  Wto  As Cast Hardness VPN  0  179  0  175  4o  16  311  4.62  334  5.94  317  13.0  281  14.2 19  • 0 6 3  216  |  Heat t r e a t m e n t s were c a r r i e d out on some o f t h e a l l o y s by s e a l i n g p o r t i o n s o f them i n e v a c u a t e d Vycor c a p s u l e s .  The specimens were wrapped i n  molybdenum c o i l and z i r c o n i u m t u r n i n g s were packed i n t o b o t h ends o f  the  capsule.  alloys  are  R e p r e s e n t a t i v e m i c r o s t r u c t u r e s o f a s - c a s t and h e a t - t r e a t e d  shown i n F i g u r e s 1 3 t h r o u g h 2 0 „ Powder p a t t e r n s were a l s o t a k e n o f a s - c a s t f i l i n g s and h e a t - t r e a t e d  powder.  A 1 1 . 5 4 cm powder camera was u s e d w i t h f i l t e r e d copper Ka r a d i a t i o n .  The X - r a y d a t a a r e shown i n T a b l e 1 0 t o g e t h e r w i t h t h e NBS p u b l i s h e d v a l u e s ' ' 1  for a-zirconium  0  - 19 -  -oL  —  g  ^  Wt. Figure  12.  15  % Nb.  V i c k e r s Hardness vs w t . % Nb f o r a s - c a s t Z r - N b alloyso  20  - 20 -  F i g u r e 1 3 . Pure Z r - a s - c a s t Widmanstatten a . E t c h HN0 + HF i n l a c t i c a c i d X300.  F i g u r e 14. Z r - 4.16% Nb - a s cast. Transformed 3. E t c h as above. X300.  3  F i g u r e 1 5 . Z r - 4.62% Nb a s - c a s t  Retained B . ^ r * ^ ^ ^ ^ 5  E t c h as above. X 3 0 0 .  F i g u r e 16. Z r - 14.2% Nb a s - c a s t .  Retained 8.  E t c h as a b o v e .  X300.  - 21 -  F i g u r e 17,  Z r - 13% Nb a s - c a s t . Retained 3 + needles. E t c h HN0 + HF i n g l y c e r i n e X300. 3  F i g u r e 19. Z r - 4.6% N b .  850°C -* 12 h r . 620°C  —* f u r n a c e c o o l e d . P r e d o m i n a n t l y a. E t c h as above. X300.  F i g u r e 1 8 . Z r - 19.6% Nb a s - c a s t . Retained 3 needles. E t c h as above. X300 +  Figure 20.  Z r - 19.6% Nb 850°C — 12 hr.620°C —*• f u r n a c e c o o l e d . Eutectoid. E t c h as above. X300.  - 22 -  T a b l e 10 D-Spacings  (Angstroms) f r o m X - r a y Measurements  f o r A l l o y s Made from Sponge Z i r c o n i u m NBS Hf-free a-Zr 2.798 2 . 5 7 3 2.459  1.894 1.616 1.463  As-Cast Hf-free Zr 2.793  2.561 2 o452 1.883 1.609 1.456  1.399  1.356  1.368 1.350 1.287 1,229 1.169 1.084 1.059 1.036 1.006 0.978  0.978  0.966  0 . 9 6 4  0.900 0.877 0.857 0.829 0.82Q  As-Cast Z r - 1 9 , 6 # Nb  1.681 1.601 1.356  1.163  1.164  1.226  1.766  1.757  1.539 1.433  1.436  1.456 1.427  1.245  I . 2 4 5  1.390  1.117  1.111  1.313  0.930 0.898 0.876  1 . 3 6 3  1.343 1.284 1.236  1.035 1.004  2.759 2.563 2.459 2.350 2.215 1.891 1.743 1.608  2.490  1.879 1 . 7 7 2  Z r - 1 9 . 6 % Nb 3 h.800°C - * l6h.620°O^Fce.cooled  2.494  2.437 2.012  1.281  1.080  As-Cast Zr-13#Nb  2.771 2 . 5 3 7  1.447  0.947 0 . 9 3 3  As-Cast Z r - 6 % Nb  1.002  1.108 1.081 1.055  0.945  0 . 9 4 2  1.034  1.005  0.989 0.975 O.966 0 . 9 4 4  0.935 0.899 0.887 0.875 0.829 0.818 0.809  C.  Isothermal Transformation Study 1.  Alloys I t was d e c i d e d t o f o l l o w i s o t h e r m a l t r a n s f o r m a t i o n s i n z i r c o n i u m -  n i o b i u m a l l o y s o f c o m p o s i t i o n s n e a r t o t h e e u t e c t o i d v a l u e as g i v e n by Rogers and A t k i n s .  F o r ' t h e base m a t e r i a l , t h e i o d i d e c r y s t a l b a r was chosen because  o f i t s assumed low oxygen c o n t e n t .  S i n c e oxygen has such a tremendous  on t h e p h y s i c a l p r o p e r t i e s o f z i r c o n i u m  effect  i t was f e l t t h a t t h e advantages g a i n e d  by u s i n g low-oxygen z i r c o n i u m would g r e a t l y o u t w e i g h any d e l e t e r i o u s e f f e c t s t o the l a r g e r hafnium content of the c r y s t a l b a r .  Hafnium forms  due  continuous  s o l i d s o l u t i o n s w i t h z i r c o n i u m i n b o t h t h e a and 3 p h a s e s . Three a l l o y charges were s u c c e s s f u l l y m e l t e d and c a s t by t h e l e v i t a t i o n method u s i n g the c o i l . o f d i m e n s i o n s g i v e n i n T a b l e 11.  Unlike  the  procedure used p r e v i o u s l y and by P o l o n i s , where t h e specimen was s i m p l y p l a c e d i n t h e - c o i l , m e l t i n g was a c c o m p l i s h e d by s u p p o r t i n g t h e charge i n t h e t o p t h i r d  u o f t h e c o i l on a 0.005 d i a m e t e r z i r c o n i u m w i r e w h i c h was a t t a c h e d t o a g l a s s , hook i n t h e t o p p l a t e o f t h e . a p p a r a t u s .  P u r i f i e d argon was used as b e f o r e a t a  p o s i t i v e p r e s s u r e o f 5 p s i g and was g e t t e r e d w i t h a hot z i r c o n i u m f i l a m e n t p r i o r to the melting of the charge. Figure 21. Table  One o f t h e i n g o t s produced i s p i c t u r e d i n  The d a t a p e r t a i n i n g t o t h e t h r e e s a t i s f a c t o r y i n g o t s i s g i v e n i n  12. Table  12  Weight Data f o r A l l o y s o f C r y s t a l B a r Z r B a s e . Alloy  Wt. Z r i n gms.  Wt. Nb i n gms.  T o t a l Wt. i n - gms.  Ingot Wt. i n gms.  Z-17 • Z-18  5.1415 5.1750 5.3885  1.0100 1.0915 1.0305  6.1515 6.2665 6.4190  6.1605  Z-20  6.2735 6.4245  Wt. i n c r e a s e i n gms. 0.0090 0.0070 0.0055  Wt. % Nb 16.39 17.40 1 6 . 0 4  - 24 -  Figure 21.  T y p i c a l ingot produced by the l e v i t a t i o n method.  Table 1 1 Dimensions of C o i l Used t o Prepare A l l o y s of Crystal-Bar Zirconium Base. Turn 1  O.D.'»  (bottom)  0 . 7 3 8  2  0 . 4 9 4  0 . 7 3 8  0.808 0.871  3 4 5  0 . 8 8 8  6  0 . 9 4 2  7  1 . 0 1 5  8  1.119  9  1.211  10  1.375  11  12 (top - reverse turn) Height o f c o i l =  I.D."  1 7 7 0 • »  1 . 5 6 3  1 . 3 2 6  1.632  C o i l made of 1 / 8 * ' Conner  tubing.  The i n c r e a s e  i n w e i g h t was assumed t o be due t o t h e a d d i t i o n o f  z i r c o n i u m w i r e w h i c h was wrapped around t h e charge  (a l e n g t h o f 3 i n c h e s o f  w i r e - r e p r e s e n t i n g t h e amount b e l i e v e d added, weighs 0.0065 gm).  This  a d d i t i o n a l w e i g h t o f z i r c o n i u m was i n c l u d e d i n t h e c a l c u l a t i o n o f t h e a l l o y composition. The f a b r i c a t i o n o f t h e s e a l l o y s t o w i r e s was t h e n a t t e m p t e d .  The  f i r s t a l l o y t r i e d (16.4% Nb) was w i r e drawn f r o m a d i a m e t e r o f 0 . 1 8 5 * ' 0 . 0 4 0 " diameter. lubricant.  No i n t e r m e d i a t e a n n e a l i n g was r e q u i r e d .  However, i t was n o t i c e d t h a t t h e w i r e s u r f a c e  down t o  Soap was used as a showed copper  smears  due t o t h e w i r e d i e s h a v i n g been p r e v i o u s l y used t o draw a c o n s i d e r a b l e  length  o f copper w i r e .  The second a l l o y c o u l d o n l y be drawn t o 0 . 1 1 0 " d i a m e t e r ,  t h i r d t o 0 . 1 7 5 " d i a m e t e r before s e v e r e c r a c k i n g o c c u r r e d .  I t was  the  therefore  o b v i o u s t h a t t h e o r i g i n a l copper c o a t i n g i n t h e w i r e d i e s had p r e v e n t e d g a l l i n g o f the f i r s t a l l o y and had t h e r e b y f a c i l i t a t e d t h e d r a w i n g o f t h i s a l l o y t o w i r e .  I t was d e c i d e d a t t h i s stage t o f o l l o w two c o u r s e s ;  t o use s l i c e s  t h e 17.4% Nb a l l o y , h e a t - t r e a t them i n evacuated v y c o r c a p s u l e s , t o  of  gather  i s o t h e r m a l t r a n s f o r m a t i o n d a t a , and a p a r t f r o m t h i s t o d e s i g n and c o n s t r u c t a p p a r a t u s w h e r e i n t h e w i r e s o f t h e 16.4% Nb a l l o y c o u l d be h e a t e d and t h e i r r e s i s t a n c e measured w i t h t i m e a t d i f f e r e n t i s o t h e r m a l t r a n s f o r m a t i o n t e m p e r a t u r e s .  2.  Transformations i n Vycor Capsules. S l i c e s o f t h e 17.4% Nb a l l o y w i r e ( . 1 1 0 " d i a m e t e r and . 0 5 " t h i c k )  were wrapped i n molybdenum f o i l and i n d i v i d u a l l y s e a l e d i n .evacuated capsules.  Z i r c o n i u m c h i p s were a l s o s e a l e d i n w i t h the specimen t o g e t t e r t h e  atmosphere when a t t e m p e r a t u r e . 1"  Vycor  Each specimen was h e l d at 900°C f o r 1 hour i n a  tube f u r n a c e and t h e n q u i c k l y t r a n s f e r r e d t o a n o t h e r f u r n a c e w h i c h was h e l d  a t a lower t e m p e r a t u r e .  Each specimen was h e l d a t t h i s t e m p e r a t u r e f o r a  s p e c i f i c t i m e and t h e n r a p i d l y c o o l e d t o room temperature by p l u n g i n g t h e  capsule  (a)  1 h r . 900°C -rt 15 min.630°C -> WQ. 3 + needles.  (c)  1 h r . 9 0 0 ° C - - 2 1/2 h r , 630°C -+ WQ. P r e c i p i t a t i o n o f a + eutectoid. Figure 2 2 .  (b)  (d)  1 h r . 900°C — 1 h r . 630°C — WQ Anomalous s t r u c t u r e - no n e e d l e s .  1 h r . 900°C — 8 h r s . 6 3 0 ° C -* WQ Eutectoid + a.  M i c r o s t r u c t u r e s o f a Z r - 17.4% Nb a l l o y i s o t h e r m a l l y t r a n s f o r m e d a t 6 3 0 ° C . E t c h HN0 + HF i n g l y c e r i n e . X30O. 3  Figure 2 3 .  Microstructures of a Zr - 17.4% Nb a l l o y isothermally transformed at 354°C. Etch HN0 + HF i n glycerine. X 3 0 0 3  (a)  1 hr.900°C — 3 0 m i n . 6 3 0 ° C — WQ.  3 + needles.  (b)  1 h r . 900°C -* 1 1 / 2 hr.630°C -•WQ, 3 + needles + spheroids.  F i g u r e 2 4 . M i c r o s t r u c t u r e s o f a Z r - 1 7 . 4 % Nb a l l o y i s o t h e r m a l l y t r a n s f o r m e d at 630°C. E t c h HN0 + HF i n g l y c e r i n e . X1600 3  -  i n t o cold water.  29  The capsule was not broken, to increase the cooling r a t e ,  because o f the s m a l l size of the specimen.  Other w o r k e r s ^  1  obtained more r a p i d  c o o l i n g by smashing the capsule on quenching i n t o water but they were d e a l i n g * i t h specimens 3/8" i n diameter by 2»' long and could subsequently grind away any surface contamination. The specimens were mounted i n l u c i t e , p o l i s h e d and etched, and examined m e t a l l o g r a p h i c a l l y .  Some of the structures observed are p i c t u r e d i n  Figures 22 through 2i+. Microhardness measurements were taken  on each specimen w i t h a  Bergsman Microhardness Tester mounted on a L e i t z Metallograph.  These r e s u l t s  are p l o t t e d i n Figure 2 5 .  280,—  0  ft.  V  1  Figure 2 5  ,  !  1  10 100 Time-Minutes  i  r  1000  1  10,000  Change i n Vickers hardness f o r the 17.U% Nb a l l o y i s o t h e r m a l l y transformed at the temperature shown.  -  X-ray patterns were obtained, using a powder camera and f i l t e r e d copper Ka r a d i a t i o n , of as-cast and heat-treated powder of the zirconium -17.4% niobium a l l o y .  Data so obtained i s presented i n Table 13.  From the hardness data a T-T-T curve was p l o t t e d (see Figure 26,) which, 15 i t may be seen, i s s i m i l a r to that obtained by Domagala  f o r a zirconium -14.6%  niobium a l l o y (see Figure 10). 3.  Resistance Measurements. The apparatus sketched i n Figure 27 and p i c t u r e d i n Figures 28, 2 9 ,  and.31 was constructed t o f a c i l i t a t e the measurement of specimen r e s i s t a n c e by the use of the c i r c u i t of Rogers and Atkins shown i n Figure 30. I n i t i a l l y , a zirconium element was used f o r the s e l f - g e t t e r i n g vacuum furnace winding.  However, the poor creep strength of zirconium lowered the  furnace e f f i c i e n c y .  A tantalum winding was found to be more s a t i s f a c t o r y i n that  i t s l i f e was much longer than the zirconium winding and i t s s e l f - r e g u l a t i n g property ensured b e t t e r furnace c o n t r o l at temperature. The furnace was c o n t r o l l e d by a Honeywell C i r c u l a r Scale C o n t r o l l e r u s i n g a Pt-Pt-lORh thermocouple and was operated on a 220 v c i r c u i t .  Temperatures  were c o n t r o l l e d t o ±0.5°C. The vacuum system consisted of a mechanical pump, an o i l d i f f u s i o n pump, and a l i q u i d a i r t r a p . at  Pressures of 5 x 10~5 mm Hg or b e t t e r were achieved  temperature. In the potentiometric c i r c u i t a standard 0.1000 ohm r e s i s t o r was used.  The p o t e n t i a l s were measured w i t h a Pye P r e c i s i o n Potentiometer i n conjunction w i t h a Pye Scalamp Galvanometer. used £0.04%.  The accuracy of the potentiometer on the range  With reference t o the c i r c u i t diagram, i f connections are made as  -  Table D-spacings  (Angstroms)  t r a n s f o r m e d a t 514°C.  As-Cast  comparison.  900°C — WQ .  2.671 2.495  2.496  900°C -+ 1 h r , 514° C WQ 2.776 2.655 2.544 2.463 2.328  2.324 1.902  1.894 1.766  1.763  1.879 1.751  1.638 1.616 1.463  1.442  1.399  1.403  1.396  1.368 1.350 1.287  1.377  1.371 1.342  1.248  1.249  1.243  1.121  1.117 1.064  1.112 1.084 1.061  1.016  1.039 1.020  1.036 1.017  0.943  0.945  0.942  0.899 0.893 0.883 0.833 0.791  0.903 0.878  1.466  1.229  1.169 1.084 1.059 1.036 1.006 0.978 0.966 0.947 0.933 0.900 0.877 0.857 0.829 0.820  900°C — 5 h r . 514°C — WQ 2.762 2.651 2.547 2.453 2.354 2.319 1.885 1.881 1.743 1.664 1.639  1.613 1.467 1.434  0  1.441  isothermally  V a l u e s f o r t h e a s - c a s t a l l o y and f o r  2.798 2.573 2.459  13  f o r the 17.4% Nb a l l o y  a a - Z r (NBS) are i n c l u d e d f o r a - Z r (NBS)  3 1  0.964  0.832 0.788  1.613 1.458 1.428 1.397 1.388 1.362 1.346 1.281 1.233  1.168 1.106 1.079 1.066 1.053 1.034 1.005 0.977 0.964 0.934 0.933 0.898 0.876 0.829 0.817 0.809  -  800 700  600  500  400 1  Figure 26.  lb too^" Time - minutes. 1  m  m  m m b  T-T-T curve f o r a Zr - 1 7 . 4 % Nb a l l o y based on hardness changes.  - 33 -  4.00' ,<  3.00 f t 7  * — r  JUL c  o  2.00"  6.00"  1.625"  4.15'  C)  o  -1.52'  Figure 27.  Diagram o f Furnace and Vacuum,Chamber Assembly. 1. Brass can 4. Specimen 7. Measuring 2. Brass l i d 5. Lava block thermocouples. 3. Radiation s h i e l d s 6. Furnace c o n t r o l 8. S e l f - g e t t e r i n g thermocouple. furnace.  - 34 -  Figure 28.  G e n e r a l v i e w o f a p p a r a t u s showing f u r n a c e c o n t r o l e l e m e n t s , vacuum s y s t e m , t r a n s f o r m a t i o n chamber, p o t e n t i o m e t r i c m e a s u r i n g equipment. P r e s s u r e measuring a p p a r a t u s i s not shown.  F i g u r e 2 9 . View o f main vacuum f u r n a c e elements, B u t t e r ' s s e l f g e t t e r i n g furnace, water cooled c a n , l i d showing t h e t h e r m o c o u p l e s .  - 35 -  I Specimen  -0  Specimen Temperature  -O -O  Specimen P o t e n t i a l  -0  0 nn v  0-100 V ohm '\  0.1000 ohm  -  Standard P o t e n t i a l  o  40 ohm 0-100 ma  12 v o l t  Figure 30.  Diagram of .resistance.measuring- c i r c u i t , (a) Pt, (b) Pt-lORh.  - 36 -  Figure 31*  Vacuum f u r n a c e assembly showing p o s i t i o n o f f u r n a c e and c o n n e c t i o n s - w i t h l i d and upper r a d i a t i o n s h i e l d s removed.  as shown and a s t e a d y c u r r e n t i s m a i n t a i n e d i n t h e c i r c u i t , t h e r e s i s t a n c e s  of  the specimen and s t a n d a r d a r e i n t h e same r a t i o as the v o l t a g e drops a c r o s s t h e m . A w i r e specimen of t h e 16.4% Nb a l l o y , 4 cm. l o n g , w h i c h had been a n n e a l e d f o r 48 h o u r s , i n an e v a c u a t e d V y c o r c a p s u l e , a t 800°C, was a t t a c h e d t o t h e P t - P t 10 Rh c o u p l e s v i a a «Lava« Z i r c o n i u m washers  b l o c k c o n n e c t o r as shown i n F i g u r e 3 2 .  ( 0 . 0 1 0 * • t h i c k ) were so p l a c e d t h a t one washer r e s t e d on t h e  Lava b l o c k , t h e thermocouple on the w a s h e r , one end of t h e a l l o y w i r e on t h e t h e r m o c o u p l e , and a n o t h e r z i r c o n i u m washer between t h e a l l o y and t h e n u t .  All  were h e l d f i r m l y i n c o n t a c t by t i g h t e n i n g t h e nut on the s t e e l b o l t . The specimen was p l a c e d i n the a p p a r a t u s , c o n n e c t i o n s made, and t h e system pumped down. The f i r s t specimen was h e a t e d t o 800°C and a f t e r  8-10  minutes a t t h i s t e m p e r a t u r e , i t was quenched t o 455°C by s i m p l y c u t t i n g t h e f u r n a c e power.  The specimen reached 455°C i n l e s s t h a n 60 s e c o n d s .  I t was h e l d  at t h i s t e m p e r a t u r e and s i m u l t a n e o u s measurements o f p o t e n t i a l and t e m p e r a t u r e were t a k e n .  A f t e r s e v e r a l hours at 455°C i t was c o o l e d t o room t e m p e r a t u r e and  i t s r e s i s t a n c e measured.  The change o f t h e r a t i o o f r e s i s t a n c e a t t i m e t t o t h e  i n i t i a l r e s i s t a n c e at 455°C i s shown i n F i g u r e 33 t o g e t h e r w i t h t h a t f o r a n o t h e r specimen o f the 16.4% Nb a l l o y w h i c h s t a r t e d i n t h e same quenched c o n d i t i o n b u t w h i c h was t r a n s f o r m e d at  507°C.  The f i r s t specimen was h e a t e d a g a i n s l o w l y t o 800°C and t h e p l o t o f r e s i s t a n c e v e r s u s t e m p e r a t u r e o b t a i n e d i s shown i n F i g u r e 3 4 .  I t was h e l d at  800°C and t h e n quenched t o a l o w e r t e m p e r a t u r e , h e l d f o r s e v e r a l hours and t h e change o f r e s i s t a n c e n o t e d .  I t was t h e r e a f t e r c y c l e d t o 800°C and t r a n s f o r m e d  at l o w e r t e m p e r a t u r e s s e v e r a l t i m e s . T h i s p r o c e d u r e was r e p e a t e d f o r t h e second specimen.  A l s o , the measurements on t h e second specimen i n c l u d e d f e e d i n g t h e  p o t e n t i a l i n t o a Honeywell S t r i p Chart Recorder.  The r e s i s t a n c e changes c o u l d  - 38 -  Figure 3 2 .  Close-up showing method of attaching specimen to thermocouples v i a a small refractory block. Zr washers not shown.  - 39 -  F i g u r e 33*  The change o f the r a t i o o f r e s i s t a n c e t o i n i t i a l f o r i s o t h e r m a l l y transformed specimens.  resistance  -  Figure 3 4 .  40  Change of resistance on heating the near-equilibrium structure of a Zr - 1 6 . 4 % Nb a l l o y .  be seen more c l e a r l y i n ,this case but the accurate determination of was  temperature  sacrificed. Some representative curves f o r isothermal change of r e s i s t a n c e w i t h  time are shown i n Figure 35. A t e n t a t i v e T-T-T  Complete r e s i s t a n c e data i s given i n Appendix 1. curve, f o r the 16.4% Nb a l l o y , based on r e s i s t a n c e  data i s shown i n Figure 36. In conjunction w i t h the r e s i s t a n c e measurements,-a few pieces of the 16.4% Nb a l l o y wire were sealed i n Vycor capsules and transformed at 515°C as has been described p r e v i o u s l y . These specimens were examined m e t a l l o g r a p h i c a l l y , microhardness  taken, and "powder' x-ray patterns obtained by mounting the wire  specimens i n a powder camera.  F i l t e r e d copper Kct r a d i a t i o n was' used.  Also,  back r e f l e c t i o n Lauepictures were taken of these wire specimens w i t h the wire a x i s perpendicular t o the x-ray beam. F i l t e r e d cobalt Ka r a d i a t i o n was employed. X-ray data from the 'powder' patterns are presented i n Table 14,  the  change of hardness i s p l o t t e d i n Figure 37, microstructures are shown i n Figures 38 and 39, and the back r e f l e c t i o n patterns are reproduced i n Figure 40.  -  3.6,  Time - minutes Figure 35.  Some t y p i c a l resistance-time curves obtained on a Zr - 16.4% a l l o y .  42  -  Figure 36.  Tentative T-T-T curve for a'Zr - 16.4% Nb a l l o y , based on resistance data.  240r  0  v  I  10  100  1000  Time - minutes Figure 37.  Hardness change i n a Zr - 16.4% Nb a l l o y isothermally transformed at 515°C.  10000  Table  14  D - a p a c i n g s (Angstroms) f o r a Z r - 1 6 . 4 # Nb a l l o y i s o t h e r m a l l y transformed at 515°C.  V a l u e s f o r t h e a s - c a s t a l l o y and f o r  pure a - Z r (NBS) a r e i n c l u d e d f o r c o m p a r i s o n .  ' NBS a-Zr  As-Cast  850°C — WQ  850°C — 1 h r . 515°C -» WQ  850°C ^ 2 1 / 2 h r . 515°C —• WQ  2.798 2.573  2.911  2.459 1.894 1.616 1.463 IL.399 1.368 1.350 1.287  2.486 1.757  1 . 2 2 9  I . 2 4 6  1.243  1.241  L.169  1.113  1.114  1.111  1.438  1.752  2.003 1.734  1.433  1.429  2 . 4 6 5  •  2 . 0 4 2  1.871 1.835 1.713 . 1.572  1.498 1.418  1.080  -1.084  1.059 1.036 1.006 0.978 0.966 0.947 0.933 0.900 6.877 0.857 0.829 0.820  850°C — 4 h r . 515°C ^ W Q  1.107 1.076 1.066  1.016  1.016  1.017  0.943  0 . 9 4 2  0.941  0.883  0.896 0.882  0.939 0.896 0.880  0.896 0.874  0.832 0.790  0.832 0.790  0.830 0.789  0.829 0.788  0.831  1.037 1.002  1.011 1.001 0.957 0.949 0 . 9 4 0  -  (a)  WQ f r o m 850°C.  (c)  850°C — 2  1/2  a + eutectoid F i g u r e 38  f> + n e e d l e s  hr.520°C -*  WQ.  45  (b) 850°C — l h r . 5 2 0 ° C -* WQ. 3 + a + needles.  (d)  850°C —• 4 hrs.520°C —• WQ, Eutectoid.  M i c r o s t r u c t u r e s o f specimens of t h e 1 6 . 4 % Nb a l l o y annealed 48 hours a t 8 5 0 ° C , quenched t o 5 2 0 ° C and h e l d a t t h i s t e m p e r a t u r e f o r t h e i n d i c a t e d t i n e . E t c h HN0 -HF i n g l y c e r i n e . X 3 0 0 . 3  Figure 3 9 .  Needles i n a Zr - 16.4% Nb a l l o y water quenched a f t e r 48 hours at 800°C. Etch HN0 + HF i n glycerine. X2200 3  (a)  (b) Figure 40,  WQ from 800°C.  800°C — 1 hr. 515°C —  WQ.  Back r e f l e c t i o n Laue pictures of a Zr 16.4% Nb a l l o y wire isothermally transformed at 515°C. F i l t e r e d Co Ka r a d i a t i o n perpendicular to wire axis.  (cont'd.)  - 48 -  (c)  (d)  Figure 40 (cont'd.)  800°C — 2 1/2 hr. 515°C — WQ  8O0°C — 4 hrs.515°C —  WQ.  III.  DISCUSSION OF RESULTS AND CONCLUSIONS  The work of Domagala on a zirconium - 14.6% niobium a l l o y can be used as a guide i n the i n t e r p r e t a t i o n o f some of the r e s u l t s of the present investigation. The room temperature measurements, such as hardness, on specimens heat-treated i n Vycor capsules gave data w i t h which a T-T-T curve could be drawn f o r the 17.4% niobium a l l o y .  This curve i s s i m i l a r t o t h e one obtained  by Domagala f o r a 14.6% Nb a l l o y except that i t i s displaced t o longer times. This displacement can be considered t o be due t o the higher niobium content of the 17.4 weight percent a l l o y and the d i f f e r e n t technique o f heat treatment employed.  The methods used by Domagala would l i k e l y r e s u l t i n gas contamina-  t i o n of the specimen.  I t . i s t h e r e f o r e believed that t h e higher niobium  content of t h e present a l l o y i n a d d i t i o n to i t s lower gas impurity content s t a b i l i z e d the beta phase t o lower temperatures and longer times and thereby accounts f o r t h e present T-T-T curve being d i s p l a c e d t o the r i g h t of Domagala's on t h e time s c a l e . The needle structure observed i n p a r t i a l l y transformed specimens was also observed by Domagala and, of course, much e a r l i e r by Rogers and A t k i n s . However, Domagala mentions that t h i s s t r u c t u r e was not always evident on metallographic observation. He a l s o s t a t e s that t h e s t r u c t u r e could be the r e s u l t of etching.  The i n t r o d u c t i o n of hydrogen during the p i c k l i n g of  20 Titanium-base a l l o y s has been observed t o form hydrides  whxch are very  s i m i l a r t o the black needles seen i n quenched zirconium a l l o y s which have been chemically polished and etched.  X-ray methods would not be too r e l i a b l e i n  e s t a b l i s h i n g a hydride phase because of the low s c a t t e r i n g power of t h e hydrogen atom.  The extra l i n e s which appeared on t h e powder patterns taken of s e v e r a l  - 50 specimens could not be indexed as hexagonal or tetragonal.  I t was observed,  however, that these l i n e s could be indexed to represent either as simple  cubic  or face-centred-cubic structure and that the calculated d-spacings were quite similar to those quoted by the ASTM f o r ZrN (see Appendix 3 ) .  The p o s s i b i l i t y  that a complex Zr-Nb-H or Zr-Nb-N compound i s being formed should not be overlooked.  This could explain perhaps the lack of complete agreement between  the observed l i n e s and the l i n e s noted by the ASTM f o r the simpler ZrN and ZrH compounds. The r i n g s obtained on the back r e f l e c t i o n Laue pattern of a specimen of 16.4% Nb quenched from 800°C were calculated t o be high angle lines of a-zirconium. Although the calculated d-spacings f o r the extra l i n e s on the powder patterns c l o s e l y match those f o r ZrN, i t i s not believed that s u f f i c i e n t nitrogen could have been absorbed during the wire-drawing operation or during the subsequent heat treatment to r e s u l t i n the formation of a n i t r i d e .  Another  p o s s i b i l i t y i s that what we are seeing i s the. result of a shear transformation which produces an intermediate structure.  This structure subsequently  breaks  down into the equilibrium products on holding at temperature as might be interpreted from the microstructure i n Figure 24b.  That t h i s structure  therefore represents the r e s u l t of a martensitic process i s most probable but the p o s s i b i l i t y that the needle structure i s produced by etching should not be discarded.  The r e s u l t s from resistance measurements were disappointing i n that, although they showed a high s e n s i t i v i t y i n observing transformation and indicated a trend to longer times with lower temperatures f o r the i n i t i a t i o n of transformation, successive quenches to the same isothermal transformation  - 51 temperature d i d not y i e l d the same data.  However, i t was noted that above  500°C the data showed t h a t i n i t i a t i o n o f transformation was occurring at approximately the times given by the curve based on room temperature hardness measurements.  Around 500°C there was a region o f u n c e r t a i n t y as t o when  transformation was o c c u r r i n g .  Below 500°C the r e s i s t a n c e measurements i n d i c a t e d  a trend t o longer times w i t h decreasing temperature i n contrast t o the room temperature hardness measurements. Records of the change i n specimen p o t e n t i a l w i t h time as obtained from a s t r i p - c h a r t recorder showed a sharp peak o c c u r r i n g at about 500°C on quenching the specimen from 800°C.  This peak occurred w i t h i n the -60 seconds  required t o reach the d e s i r e d transformation temperature.  An experiment w i t h  a copper wire specimen showed no peak on quenching. I t i s p o s s i b l e that some a or a * phase i s being formed as t h e specimen crosses the 3/?- 3 transus and the tempering of t h i s phase, i f a*, +  i s masking changes due t o the subsequent decomposition  of the retained 3 phase,  or e l s e , as has been mentioned above, an intermediate, phase i s being formed i n t h i s region of temperature and subsequently  decomposing.  I t may be concluded, t h e r e f o r e , that the apparatus which has been designed and constructed o f f e r s a s e n s i t i v e means whereby phase transformations i n a l l o y s may be studied. technique are required.  However, c e r t a i n modifications t o the apparatus and  The apparent s t r u c t u r a l s e n s i t i v i t y of zirconium  a l l o y s t o the v a r i a b l e s of p r i o r heat-treatment,  degree of cold work, tempera-  ture c y c l i n g , and high temperature soaking time requires that a specimen be used f o r only one cycle to t h e isothermal transformation temperature.  Although  the contact between the specimen and thermocouples was considered t o be s a t i s f a c t o r y , t h i s contact could perhaps be improved. most e f f i c i e n t l y by pressure-welding.  This could be achieved  The spot-welding of t h e specimen t o the  thermocouples i s not b e l i e v e d to be a s a t i s f a c t o r y s o l u t i o n t o the problem. Great d i f f i c u l t i e s would beinvolved i n the design and operation of the r e q u i s i t e spot-welding apparatus which would keep gas contamination i n such a small specimen to a minimum I t i s a l s o apparent that s t r u c t u r a l changes on quenching as measured p o t e n t i o m e t r i c a l l y must be followed by a high-speed recorder, and that f a c i l i t y must be provided f o r simultaneous temperature measurement.  The  s t r i p recorder should a l s o be used f o r f o l l o w i n g isothermal transformations above 500°C t o resolve whether a martensite process i s involved. Rather than substantiate the r e s i s t a n c e measurements w i t h roomtemperature  observations of metallography, hardness, and c r y s t a l s t r u c t u r e as  determined by x-ray methods, i t i s f e l t that x-ray measurements at high temperature, using a needle-shaped specimen, would give b e t t e r c o r r e l a t i o n . The needle-shaped specimen would present l e s s surface area than powder and thereby minimize gas contamination. This work has t h e r e f o r e i n d i c a t e d the complexity of the phase t r a n s formations occurring i n zirconium-niobium a l l o y s and has described the techniques by which these processes may be studied to e v e n t u a l l y determine, thermodynamic a n a l y s i s , a f t e r the accumulation of considerable data, the mechanisms of the reactions involved.  by  APPENDIX 1 Resistance Data:  Temperatures from l e f t t o r i g h t are i n the experimental sequence Resistance values are i n OHMS x 10~ . Time i s i n hours. 2  F 450 °C t 0.0 0.167 0.333 0.583 0.830 0.867 1.116 1.450 1.920 2.330 2.660 2.920 3.000 11.750 L2.410 13.660 14.660 16.160  458°C R  t  0.050 3.33 0.067 3.33 0.617 3.34 1.680 3.34 3.32 -2.750 3.260 3.33 3.850 3.33 4.260 3.34 3.36 4.760 3.38 5.180 7.760 3.39 8,460 3.39 3.40 8.860 9.380 3.45 3.45 21.710 3.45 22.930 3.45 3.45  R  t  448° C  R  2.41 0.033 3.23 2.41 0.067 3.21 2,40 0.250 3.22 2.41 0.583 3.21 1.920 3.22 2.31 2.28 2.750 3.19 2.29 4.150 3.16 6.670 3.02 2.27 2.26 16.920 2.58 2.26 17.780 2.57 2.26 2.26 2.25 2.25 2.26 2.26  t  i  546°C  0.083 0.167 0.250 0.400 0.517 0.983 1.230 1.450 1.970 3.060 3.450 4.080 4.230 4.600 5.580 5.710 5.920 6.400 7.230 7.630  r  s  t  s P) e c i  418°C . R  R  t  3.22 3.19 3.20 3.20 3.21 3.46 3.61 3.90 4.03 4.10 4.11 4.19 4.18 4.21 4.36 4.20 4.22 4.26 4.34 4.34  0.017 0.100 0.500 1.116 2.370 3.330 3.660 4.020 4.410 4.950 5.360 5.780' 6.250 6.450 7.500 10.660 11.180 11.660 22.310 23.830  2.72 2,72 2.72 2.722.72 2.72 2.71 2.71 2.70 2.68 2.67 2.66 2.66 2.65 2.63 2.60 2.60 2.58 2.53 2.53  t  515 °C  0.083 0.250 0.433 0.517 0.683 0.933 1.050 1.500 2.000  m e  n 494° C  R  t  2.86 2.86 2.81 2.76 2.73 2.93 2.92 2.91 2.91  0.067 0.200 0.350 0.533 0.650 1.133 1.480  538°C  R  t  2.80 2.80 2.80 2.72 2.65 2.71 2.71  0.067 0.133 0.233 0.317 0.417 0.600 0.780 1.000 1.230 2.780  568°C  R  t  2.90 2.90 2.91 2.92 2.95 3.13 3.23 3.27 3.27 3.29  0.067 0.183 0.300 0.380 0.480 0.600 0.720 0.830 1.000 1.167 11.080 12.450  R  2.98 2.99 2.99 3.00 3.02 3.19 3.30 3.34 3.35 3.42 3.49 3.42  I  I  Appendix 1 (cont'd.)  S e c t  507°C  0.050 0.183 0.233 0.417 0.583 0.780 0.933 1.000 1.450 1.680 2.000 2.330 5.580 5.920 6.400 6.670 7.760 17.780 21.710  R -  t  542°C  3.35 0.033 3.36 0.100 3.37 0.417 3.39 0.583 1.000 3.39 3.40 •1.500 3.41 2.370 3.42 . 3.450 4.080 3.45 4.600 3.47 4.950 3.48 5.920 3.49 6.670 3.53 9.380 3.53 3.53 10.660 .3.54 3.54 3.57 3.57  n d  0  R  S  p  476 °C •t R  4.83 0.033 0.200 4.83 4.89 0.533 4.90 0.720 4.84 1.230 4.81 1.500 2.750 4.77 4.76 3.000 3.660 4.75 4.950 4.72 5.500 4.71 5.920 4.69 6.450 4.69 8.860 4.67 4.65 10.660  e  c i p t  431°C  4.42 0.067 0.100 4.41 O.250 4.43 0.400 4.43 0.650 4.45 0.830 4.47 1.680 4.23 4.21 2.000 2.330 4.19 2.780 4.14 4.13 3.45 4.26 4.12 5.18 4.11 4.09 10.660 4.07 23.830  e R  4.30 4.29 4.31 4.29 4.29 4.29 4.28 4.28 4.28 4.28 4.27 4.28. 4.27 4.28 4.23  n t  493°G  R  4.62 0 0.083 4.56 0.133 4.55 : 0.300 4.63 0.833 4.66 0.933 4.55 1.000 4.54 1.500 4.47 1.680 4.45  APPENDIX  II  Related Phase Diagrams. Nitrogen At. % 25  0  5  40  10  Nitrogen Wt. % 1.  The zirconium-nitrogen system.  13  Oxygen, Wt. %  2  5  15  Oxygen, At'.. % 2.  The zirconium-oxygen system.  25  3 . The zirconium-hydrogen system.  Tantalum - Atomic %'  2800 -  Tantalum - Weight % 4.  The niobium-tantalum system.  0  20  40  60  80  100  Tanatalum - Atomic % 5.  The zirconium-tantalum system.  - 59 -  -APPENDIX 3 D-spacings (Angstroms) from ASTM card index f o r r e l a t e d zirconium compounds.  ZrN  Zr0  2.64 2.28 1.61 1.38  2  ZrH (approx.) 2.38 1.69 1.44  1.81 1.79 1.55 1.53 1.47 1.29  1.14 1.05 1.02  1.38 1.19 1.09  2.76 2.49  2.22  1.69 1.44  '  1.76  1.38 1.20 1.10 1.07  1.07 0.97 0.92  1.27 1.17 1.13 1.10 1.05 1.04  0.93  £- ZrH  2.76 2.39  2.75  2.93 2.52  1.32  5 - ZrH  1.66  1.37 1.24  1.13 1.11 1.09 1.08 1.02  6.99  0.99  0.98 cubic a  Q  =4.56  tetragonal a = 5.07 c = 5.16 0  c  .  1.48 1.38  a  Q  cubic = 4.76  cubic - varies between 4.77 and 4.78  a  Q  tetragonal a = 4.97 c = 4.45 0  Q  - 60 REFERENCES 1.  Lustman, B., and Kerze, F., e d i t o r s , 'The M e t a l l u r g y of Zirconium', N a t i o n a l Nuclear Energy S e r i e s , McGraw-Hill 1955.  . 2.  M i l l e r , E.C., from paper i n ASM Symposium, * Zirconium and Zirconium A l l o y s ' 1953.  3.  P f i e l , P.C.L., 'A Discussion of the Factors A f f e c t i n g the C o n s t i t u t i o n of Zirconium A l l o y s ' , AERE M/R 960, June.27, 1952.  4.  Mcintosh, A.B.,  5.  Anderson, C.T., Hayes, E.T., Roberson, A.H., and K r o l l , W.J., 'A P r e l i m i n a r y Survey of Zirconium A l l o y s ' , U.S. Bureau o f Mines Report No. 4658, March 1950.  6.  P f e i l , P.C.L., 'A C r i t i c a l Review of the A l l o y i n g Behaviour of Zirconium',  Jour. I n s t . Metals 1855, 85_, A p r i l 1957.  March 1950. 7.  L i t t o n , F.B., Iron Age, 167, 1951, 95-99 and 112-114.  8.  Simcoe, C.R.,  9.  Keeler, J.H., AEC Report No. S0-2504, January 5, 1952.  and Mudge J r . , W.L.,  AEC Report No. WAPD-38, November 21, 1951.  10.  Keeler, J.H., AEC Report No. SO-2505, A p r i l 5, 1952.  11.  Hodge, E.S., AEC Report No. TID-5061, January 31, 1952.  12.  Rogers, B.A., and Atkins, D.F.,  13.  Domagala, R.F., and McPherson, D.J., Journ. Metals 620, May  14.  Bychkov, Yu F., Rozanov, A.N., and Skorov, D.M., Atomnaya Energiya 2, February 1957, 146-157. Domagala, R.F., 'A Study of the Mechanisms of Heat Treatment of Zirconium-  Journ. Metals 1034, September 1955. 1956. i  15.  Base A l l o y s ' . Armour Research Foundation Report f o r AEC, J u l y 17, 1956. 16.  0 ' D r i s c o l l , W.G.,  17.  P o l o n i s , D.H.,  Butters, R.G.,  and Parr, J.G., Research 2 No. 2, February 1954.  IS.  P o l o n i s , D.H.,  Butters, R.G.,  and Parr, J.G., Research 2» J u l y 1954.  19.  N a t i o n a l Bureau o f Standards (U.S.) C i r c u l a r 539 V o l . I I , June 1953, p. 11.  20.  McKinsey, C.R., Stern, M. and Perkins, R.A., Trans. ASM P r e p r i n t No. 38, 5_0 1957. Douglas, D.L., Marsh J r . L . L . , and Manning, G.K., Trans. ASM V o l . 50, P r e p r i n t No. 20, 1957_  21.  and M i l l e r , G.L., Journ. I n s t . Metals 1758, 85_, AprjLl 1957.  

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