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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 in th© Department of MINING AND METALLURGY We accept this thesis as conforming to the standard required from candidates for the degree of MASTER OF APPLIED SCIENCE. Members of the Department of Mining and Metallurgy THE UNIVERSITY OF BRITISH COLUMBIA November, 1957-ABSTRACT Isothermal transformations i n eutectoid zirconium-niobium alloys have been studied by resistometric 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 resistometric method gave data which were not i n agreement with data obtained by room-temperature measurements. A T-T-T curve established by room-temperature hardness and metallography was found to be s i m i l a r to one obtained by a previous i n v e s t i -gator. The lack of agreement between measurements made at high temperature and those made at room temperature suggests that a s t r u c t u r a l change i s occurring i n these alloys during the quench from the transformation tempera-ture. For t h i s reason, room temperature metallography i s unsatisfactory f o r following transformations i n these a l l o y s . The analysis of micro-structure i s complicated by the presence of a needle-like •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 that the resistometric technique i s a sensitive method fo r observing transformations i n zirconium-niobium a l l o y s . In presenting t h i s thesis In p a r t i a l fulfilment of the requirements fo r an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by his representative. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of ML^^.^ <^~<J tod/,^j^ The University of B r i t i s h Columbia, Vancouver 5\ Canada. Date 7 M 7 ACKNOWLEDGEMENT The" author i s grateful f o r f i n a n c i a l aid i n the form of a research assistantship provided by the Defence Research Board of Canada. Funds for 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 of Dr. V. G r i f f i t h s , under whose di r e c t i o n t h i s investigation was performed, and the te c h n i c a l advice and assistance given by Mr. R, Butters and Mr. R. Richter. TABLE OF CONTENTS Page I. INTRODUCTION . . . . . . o . . o o . o « o o . 9 . O 0 . o « « * o I A. Object of the Investigation . . . 1 B. The Zirconium-Niobium Alloy System 3 I I . PROCEDURE AND RESULTS . 1 4 A * AllOy Melt 6 1*3.3.1 S o « o 9 0 « 4 > f t o o o o o o « « « e » © # 1A-,'B.. Preliminary Work 1 6 C. Isothermal. Transformation Study . . . . . . . . . . . . . 2 3 1 . AllOyS . . o . e a o . o . . . . . . . . . . . . . 2 3 2 . Transformations i n Vycor Capsules . 2 5 3 . Resistance Measurements . . . 3 0 I I I . DISCUSSION OF RESULTS AND CONCLUSIONS 4 9 IV. APPENDICES 1 . Resistance Data « . « . . . . . . . . . . . . . . . . . 5 3 2 . Related Phase Diagrams . o . . . o . . . . . . . . . . o o 5 5 3 . ASTM d-Spacings f o r Related Zirconium Compounds . . . . . 5 9 V. REFERENCES » » • • » « » » • • • • • » • * • » • • • • • • • • • • • 6 0 LIST OF ILLUSTRATIONS Figure Page 1. A comparison of the neutron cross section of zirconium with that . „ „ of other elements . . . . . . . . . . . 2 2 . The zirconium-niobium phase diagram (after Rogers and Atkins) . . . . 7 3. Room temperature r e s i s t i v i t i e s of zirconium-niobium alloys i n two conditions . . o o . . . . » . . . • . . o . . . o . o . o o 7 4. Change i n resistance of a 17.5/5 Nb a l l o y on slow heating . . . . . . 8 5. Variation i n l a t t i c e parameter with composition f o r alloys quenched from 1100°C ' 8 6. Microstructure of a zirconium - 15% Nb a l l o y quenched from 800°C. . . 10 7. Microstructure 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 (after Bychkov et a l ) . 12 9. Hardness vs composition of zirconium-niobium alloys f o r di f f e r e n t thermal treatments 12 10. T-T-T curve f o r a zirconium - 14.6% Nb a l l o y (after Domagala). . . . . 13 11. Diagram of the l e v i t a t i o n melting apparatus of Polonis et a l . . . . 17 12. Vickers hardness vs weight percent Nb f o r as-cast Zr-Nb alloys . . . 19 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 ,.. • . . . . . . . . . 21 18. Zirconium - 19.6% niobium, as-cast . . . . . . . . . . . . . . . . . 21 19. Zirconium - 4.6% niobium - heat treated . 21 2 0 . Zirconium - 19.6% niobium - heat treated 21 21. Typical ingot produced by the l e v i t a t i o n method. . . . . . . . . . . 24 ILLUSTRATIONS (continued) Page 22. Microstructures of a Zr - 17.4% Nb a l l o y isothermally transformed at 630°C 26 23. Microstructures of a Zr - 17.455 Nb a l l o y isothermally transformed at 354°C 27 24. Microstructures of a Zr - 17.4% Nb a l l o y isothermally transformed at 630°C 28 25. Change i n Vickers hardness f o r the 17.4% Nb a l l o y isothermally transformed at the temperatures shown • 29 26. T-T-T curve f o r a zirconium - 17.4% niobium a l l o y based on hardness changes . . . . . . . . * . . » . • • • . • * • . 32 27. Diagram of furnace and vacuum chamber assembly . . . . . . . . . . . 33 28. General view of apparatus 34 29. View of main vacuum furnace elements . . 34 30. Diagram of resistance measuring c i r c u i t . . . . . . . 35 31. Vacuum furnace assembly showing p o s i t i o n of furnace and connections. 36 32. Close-up of l i d showing the method of attaching the specimen . . . . 38 33. The change of the r a t i o of resistance to i n i t i a l resistance . . . . 39 34. Change of resistance on heating the near-equilibrium structure of a Zr - 16.4% Nb a l l o y 40 35. Some t y p i c a l resistance - time curves obtained on a Zr - 16.4% a l l o y 42 36. Tentative T-T-T curve f o r a Zr - 16.4% Nb a l l o y , based on resistance data . . . . . * • • • • 43 37. Hardness change i n a Zr - 16.4% Nb a l l o y , isothermally transformed at 515°C 43 38. Microstructures of the 16,4% Nb a l l o y isothermally transformed at 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 hrs.at 800°C 46 40. Back r e f l e c t i o n Laue pictures 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. . . 3 2 . The Mechanical Properties of Zirconium-Niobium Alloys at Room-Temperature 4 3 . Yield Strengths of Zirconium-Niobium Alloys at 649°C . . . . . . . . . 5 4. Analysis of the Alloy Materials of Domagala et a l 14 5 . Analysis of Foote Crystal Bar Zirconium 15 6 . Spectrographic Analysis of Niobium 15 7. Decrease in Gas Content of Niobium on Vacuum Sintering 15 8. Data Pertinent to the Coil Design 17 9. Composition and As-cast Vickers Hardness of Zr-Nb Alloys Prepared by Levitation Melting r 18 10. D-spacings (Angstroms) from X-ray Measurements for Alloys Made with Sponge Zr . . 11. Dimensions of Coil Used to Prepare Alloys of Crystal Bar Zirconium 1 2 . Weight Data for Alloys of Crystal Bar Zirconium Base 23 17„ D-spacings (Angstroms) for the 1 7 . 4 % Niobium Alloy Isothermally Transformed at 5 1 4 ° C 3 1 1 4 . D-spacings (Angstroms) for a 1 6 . 4 % Niobium alloy Isothermally Transformed at 5 1 5 ° C 4 4 ISOTHERMAL TRANSFORMATIONS IN EUTECTOLD .ZIRCONIUM-NIOBIUM ALLOYS INTRODUCTION A. Object of the Investigation For use within the f i s s i o n zone of nuclear reactors which have to work at high temperatures-, the usual engineering materials are unsuitable, either because they absorb too many neutrons or react with the f u e l . Thus attention has been directed to metals formerly regarded as rare, and great advances have been made i n the development of such materials f o r engineering use. Of the metals with r e l a t i v e l y high melting points, zirconium has the lowest absorption cross-section f o r thermal neutrons (see F i g . l ) . I t 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 material for 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 studies, which are described i n a recent volume,^ constituted a search f o r alloys having high-temperature strength coupled with the retention of the attractive nuclear and chemical pronerties of pure zirconium. I t was therefore the object of the present work to add to the data on zirconium alloys by studying isothermal transformations i n zirconium-niobium a l l o y s of eutectoid composition and thereby determining the related Time-Temperature-Transformation (T-T-T) diagram. - 2 -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 Intermediate Cross Section High Cross Section ( <I.O Barn) • . (1.0 to 10.0 Barn?)-- . (>I0 Barns)-Melting Melting Point (CC) Element cr. Point (CC) Element am Element <r« Oxygen 0.0002 Zinc I.I 419 Manganese 13 Carbon 0.0045 Columbium I.I 2415 Tungsten 19 Beryllium 0.009 1280 Barium 1.2 704 Tantalum 21 Fluorine 0.01 Strontium 1.2 770 Chlorine 32 Bismuth 0.032 iii Nitrogen 1.8 Cobalt 35 Magnesium 0.05'» 6SI Potassium 2.0 ' 64 Silver 60 Silicon 0.13 Germanium 2.3 Lithium 07 Phosphorus 0.19 Iron 2.4 1539 Gold 94 Zirconium 0.18 1845 Molybdenum 2.4 262S Hafnium 115 Lead 0.17 327 Gallium 2.7 30 Mercury 380 Aluminum 0.22 660 Chromium 2.9 1890 Iridium 440 Hydrogen 0.33 Thallium 3.3 300 Boron 750 Calcium 0.43 '850 Copper 3.6 10S3 Cadmium 2,400 Sodium 0.49 98 Nickel 4.5 14S5 Samarium 6,500 Sulphur 0.49 Tellurium 4.5 Gadolinium 44.0011 Tin 0.6S Z32 Vanadium Antimony Titanium 4.7 6.4 5.6 1710 630 1725 Table II Thermal-Neutron Cross Sections and Melting Points of Metallic Elements With .Melting Points Above S0O°C Lou I . t Sectiun • Intermediate Crosi Sixtion-Metal Mfltluii Point (~C) Metal Melting Point ( J C Beryllium o . o i n I2K0 Columbium 1.1 241S Magnesium O.OS't 6S1 Iron 2.4 1539 Zirconium 0. 18 1815 Molybdenum 2.4 2625 Aluminum 0.22 660 Chromium 2.9 1890 Copper 3.6 1083 Nickel 4.5 1455 Vanadium 4.7 1710 Titanium 5.6 1725 Table III Selected Refractory Metals and Alloys Low Cross Section ( < 1.0 Barn) Metal ff« Zirconium 0.18 Intermediate Cross Sections r- (<10 Bams. >1.0 B a r n ) -Metal Iron Molybdenum Stainless steels Nickel-base alloys (Hastelloys, Monels. Inconels, Nichrome) Titanium 2.4 2.4 ~ 1 Figure 1 . A comparison of the neutron cross section of zirconium with that of other elements (after M i l l e r 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 respectively, Table 1 l i s t s some of their physical and mechanical Drooerties. Zirconium exists i n two a l l o t r o p i c modificationsj 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 melting point of 2415°C. The addition of a l l o y i n g elements to zirconium affects i t s a l l o -t r o p i c transformation temperature. Some elements raise t h i s temperature while others lower i t j that i s , certain elements s t a b i l i z e the alpha phase while others s t a b i l i z e the beta phase. P f e i l 3 and Smoluchowski"'" have discussed extensively 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 the a l l o y systems of niobium. Of the elements of interest to 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. I t i s also f e l t that hydrogen tends to be a beta s t a b i l i z e r . The related r>hase diagrams f o r these elements i n zirconium may be found i n the Appendix. Table 1 Some Physical and Mechanical Properties o f Zirconium and Niobium. Atomic Number Atomic Weight Crystal Structure 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.T0/*<-ohm-cm Hardness R.T. Zirconium 40 91.92 a cph a = 3.232A c - 5.147A c/a = 1.593 0 bcc a = 3.61A (~900°C) 826 °C 1852°C 40 ~70 VPN Niobium 41 92.91 bcc a = 3.300A 2415°C 15.22 ~ 40 VPN The earliest 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 respectively. The 0 . 6 % alloy, which was composed mainly of the Widmanstatten structure, as seen in pure zirconium under similar conditions, contained also a l i t t l e of a second phase. Pfeil^ 1 believed this second phase to be retained beta. In the 5 . 1 % alloy, the needles are described as 'fine needles', and small spheroids of a second phase randomly dispersed are mentioned in the description of the 'as-swaged microstructure*. The 1 2 . 9 % alloy was composed of very large grains f i l l e d with finely foliated fern-like patterns. The microstructures of the zirconium-niobium alloys prepared by 7 Litton are not reported, but the mechanical properties at room temperature were appreciably different from those obtained on the alloys of Anderson et al,(see Table 2 ) . TMs may be due to the difference in heat treatment. Litton's alloys were annealed at 7 2 5 ° C . 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 after swaging and then air-cooled. Table 2 . The Mechanical Properties of Zirconium-Niobium Alloys at Room Temperature. Author Wt.% Niobium Yield Strength (psi) Ultimate Strength psi 0 . 0 5 % offset 0.2% offset Anderson et a l 0 . 6 5 4 , 6 0 0 8 3 , 7 0 0 Litton 2 . 5 6 3 , 3 0 0 8 7 , 5 0 0 Anderson 5 . 1 7 9 . 8 0 0 . 1 0 4 , 7 0 0 Litton 7 . 5 9 3 , 7 0 0 1 0 7 , 0 0 0 Litton 1 2 . 5 8 1 , 5 0 0 1 0 2 , 0 0 0 Anderson 1 2 . 9 - 1 5 0 , 3 0 0 Litton 1 7 . 5 7 8 , 7 0 0 9 1 , 2 0 0 Litton 2 2 . 5 6 7 , 5 0 0 7 2 , 5 0 0 Litton ... ';.„, ... _ 27 . 5 5 7 , 8 0 0 7 4 , 3 0 0 4 Weight percentages are used throughout unless otherwise seated. The decrease i n the y i e l d strength of Littons alloys containing above 7 . 5 % niobium, may mean that under the condition of the experiments, the alloys contained an increasing amount of the beta phase. The y i e l d strengths at 6 4 9°C of the Bureau of Mines alloys are shown i n Table 3 . Table 3 . Y i e l d Strengths of Zirconium-Niobium Alloys at 6 4 9 ° C . Composition Y i e l d Strength (psi) Wt. % Nb. 0 . 2 % offset 0 . 6 9 , 3 2 0 5 . 1 7 , 9 1 0 1 2 . 9 1 0 , 0 2 0 These values are r e a d i l y explicable on the hypothesis that niobium depresses the a-p transformation of zirconium. The a l l o y containing 5.1% niobium would appear to contain an appreciable amount of beta phase at 6 4 9 ° C . 8 Simcoe and Mudge observed an increased strength i n both 0.5 and 1.0% niobium alloys made with hafnium-containing zirconium and also stated that less than 0.5% niobium i s soluble i n zirconium at 800°C. o According to Keeler the strength of zirconium i s increased by additions of niobium to a content of at least 3 % . Keeler"^ also observed a maximum i n hardness at about 10 atomic percent niobium and commented on the br i t t l e n e s s of alloys of t h i s composition. In 1 9 5 2 , Hodge-*"'- investigated the zirconium-niobium system UP to about 25% niobium. His data on melting points were not s u f f i c i e n t l y numerous to distinguish with certainty between the alternatives of a narrow eutectic horizontal and a wide f l a t minimum i n the solidus curve. Hodge t e n t a t i v e l y suggested that transformations i n the s o l i d state appeared to indicate that the - 6 -eutectoid i n the zirconium-rich alloys lay at about 625°C and 10% niobium and that the solubility of niobium in zirconium at 625°C was near 6%. 12 In 1 9 5 5 , Rogers and Atkins published the Phase diagram shown in Figure 2 . Complete mutual solid s o l u b i l i t y exists for an interval below the solidus line, 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 solid solution breaks UP, except at the niobium-rich side, from two causes: zirconium-rich alloys transform under the influence of the B —• a transformation in pure zirconium; . alloys of intermediate composition decompose into two solid solutions below 1000°C. The combined effect 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 lines remained uncertain. The analysis given for 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 process, melted under a protective atmosphere and fabricated to plates. The niobium analysis was known only approximately, the principal impurities being tantalum ( 0 . 5 % ) and carbon ( 0 . 2 5 % ) plus a few hundredths of one percent each of iron, s i l i c o n , and titanium. Certain of their results 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 for alloys quenched to room temperature after 2 0 hours at 900°C (curve A) and f o r alloys annealed at temperatures below the eutectoid in order to obtain the equilibrium structure (curve B). For compositions between 4 and 13% niobium this annealing consisted of 1 2 0 hours at 590°C plus 1 6 0 hours at 575°C whereas compositions between o 3 UJ Q-6 0 0 4 0 0 2 0 0 i ' . 1 C, 1 i ' , 1 !• ! 1 A B ! ft P F hr hr >-— lit Cb / i 3 < i '•'Cb •» f \ \ ' a + • ' I r — * r i i 1 J - 7 I 0 10 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 IOC; C O L U M B I U M , P E R C E N T Figure 2. The zirconium-niobium phase diagram (after Rogers and A t k i n s 1 ) 0 20 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 of Zirconium-Niobium Alloys i n Two Conditions; A, Quenched from 900°C, B, Equilibrium Structure, (after Rogers and Atkins ) - 8 -F i g u r e 4 . Change i n r e s i s t a n c e of 17.5% n i o b i u m a l l o y on slow-h e a t i n g . Break i n d i c a t e s the t r a n s f o r m a t i o n o f the low-temperature 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 temperature . ( A f t e r Rogers and Atkins-*- 2 ) . 3.20! I 1 J 1——I 0 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 from 1100°C. A l l are b o d y - c e n t e r e d -c u b i c s t r u c t u r e s . No p o i n t s o c c u r f o r composi t ions 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 for 240 hours at 590°C plus 160 hours at 575°C. Figure 4 shows the plot of simultaneous measurements of resistance and tempera-ture on a wire specimen of an alloy of eutectoid composition as i t was subjected to slow heating. The sharp decrease in the resistance at 6l0°C represents the crossing of the eutectoid horizontal. Figure 5 gives the variation of l a t t i c e parameter with composition for alloys between 15 and 100% niobium which had been quenched from 1100°C„ A l l such alloys were in a single phase condition and possessed a body-centered-cubic structure. No points were plotted for compositions less than 15% niobium since the zirconium-rich alloys were seen to undergo some transformation at the rates of cooling attained. The rate of cooling was sufficiently effective to retain the high temperature condition i n a l l but the low-niobium alloys because the transformation i n the solid state became increas-ingly sluggish as the niobium content was increased beyond 5%. Alloys rapidly cooled from 900°C were a l l single phase except those between 44 and 77% niobium. It was also suspected that some precipitation of a from the B-zirconium occurred during rapid cooling. No microstructures were presented in the above report. In 1956, Domagala and Mcpherson"^3 described their investigation of the zirconium-niobium system. From experiments on alloys prepared from iodide zirconium and 'high purity' niobium powder, they obtained data which did not agree with certain aspects of the work of Rogers and Atkins. They described a 15% niobium alloy quenched after 136 hours at 8009C as a two-phase a + 3 structure (see Figure 6). From this and other considerations, they believed that the eutectoid horizontal in this system was at a temperature of 800°G, the eutectoid composition was at 17% niobium, and a continuous series of solid solutions existed only above 1180°C. Rogers and Atkins' reply to this criticism was that their alloys cooled from 700°C and 800°C showed strong lines of two 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. Cons idered 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 . F i g u r e 7. M i c r o s t r u c t u r e o f a z i r c o n i u m -12% Nb a l l o y quenched from 1250°C. ( A f t e r Rogers and A t k i n s 1 3 ) . - 11 -A few weak l i n e s were a l s o present i n t h e X - r a y p a t t e r n s and these were b e l i e v e d to be r e p r e s e n t a t i v e of a which had formed as the a l l o y passed through t h e 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 . They presented a photomicrograph of a 12% n i o b i u m a l l o y which was quenched from 1 2 5 0 ° C (see F i g u r e 7 ) . T h i s n e e d l e - l i k e s t r u c t u r e 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 c o n t a i n i n g from 8 t o 15% n i o b i u m quenched from an e x t e n s i v e 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 of 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 of c o m p o s i t i o n . Rogers 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 s t r u c t u r e . I n 1 9 5 7 , Bychkov e t a l " ^ p u b l i s h e d the z i r c o n i u m - n i o b i u m phase diagram shown i n F i g u r e 8 . T h i s diagram i s s i m i l a r i n , f o r m t o t h a t of 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 at 12% n i o b i u m . A l s o the minimum i n the s o l i d u s curve occurs at 1 6 0 0 ° C r a t h e r t h a n at 1 7 4 0 ° C as found by Rogers and A t k i n s . Bychkov et a l used i o d i d e nrocess z i r c o n i u m c o n t a i n i n g 1 . 5 % hafnium and n i o b i u m c o n t a i n i n g 1 . 0 % t a n t a l u m . 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 by 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 the same. The hardness measurements on the a l l o y s o f Bychkov are i n c l u d e d as F i g u r e 9 . A f t e r t h e e x p e r i m e n t a l p a r t o f 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 the T-T-T curve which t h i s group o b t a i n e d f o r a z i r c o n i u m - 1 4 o 6 % n iobium a l l o y . Data were o b t a i n e d by measuring 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 sheet 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 copper h e a r t h under an argon atmosphere. 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 ' ' diameter rods and c e n t r e l e s s ground t o 3 / 1 6 " d i a m e t e r . 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 (after Bychkov et a l 1 ^ ) . 20 40 60 80 100 Wt.% Nb Figure 9« Hardness-vs comppsition of Zr-Nb al 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. (after Bychkov et al l z0. - " - 13 -o CO CD CO U HO <D Q CO in CO § 800 "TO IDTT Time-Minutes TOOTT 1U,U00 F i g u r e 10. T-T-T curve f o r a Z r --14.6% Nb a l l o y ( a f t e r Domagala 1 ^), 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. 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 which 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 minutes a t 1000°C, the specimen was quenched i n t o another r e s i s t a n c e furnace 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 which i t was quenched t o room temperature by p l u n g i n g i t i n t o w a t e r . The ends of t h e rods were t h e n ground p r i o r t o t h e measurement of room-temperature r e s i s t i v i t y . A s l i c e was t a k e n o f f the specimen f o r hardness 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 ! the specimen was t h e n heated a g a i n t o 1000°C and the c y c l e r e p e a t e d , 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 . The z i r c o n i u m used p r o b a b l y c o n t a i n e d about 2.0% hafnium. - 1 4 -Table 4 . • A n a l y s i s of the A l l o y M a t e r i a l s o f Domagala et a l ^ I m p u r i t y Sponge Z i r c o n i u m Niobium As r e c e i v e d A r c - m e l t e d and I m n u r i t y Wt. % f o r g e d b a r - s t o c k Oxygen 0 . 1 3 1 % 0 . 1 2 4 % Ta 0 . 5 N i t r o g e n . 0 2 % 0 . 0 2 % C 0 . 1 Hydrogen 4 9 vxm. 6 5 ppm. T i 0 . 0 4 Carbon 0 . 0 2 3 % S i 0 . 0 2 Fe . 0 4 2 % Fe 0 . 0 1 Mg . 0 2 3 % C I . 0 3 7 % I I . PROCEDURE AND RESULTS A . A l l o y M a t e r i a l s . 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 grades; namely, low-hafnium r e a c t o r grade sponge i n the form o f 5 / 8 ' " diameter r o d and i o d i d e c r y s t a l bar as produced by the Foote M i n e r a l Company. The a n a l y s i s o f t h e Foote c r y s t a l b a r i s g iven i n Table 5 but no a n a l y s i s f o r t h e r e a c t o r grade sponge was r e c e i v e d . 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 content would be t h e r e f o r e s i m i l a r to t h a t o f t h e c r y s t a l bar except w i t h r e g a r d t o hafnium and gas c o n t e n t . The hafnium content o f r e a c t o r grade sponge i s about 0.01%. A l though 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 the oxygen and n i t r o g e n content o f t h e sponge i s about 0.12 and 0.005% r e s p e c t i v e l y and t h a t the oxygen content o f the c r y s t a l bar i s about 0,01%. 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 diameter rod from Johnson, Matthey and Company. T h e i r a n a l y s i s i s g i v e n i n Table 6 . Although no gas a n a l y s i s i s g i v e n , the gas content may be es t imated f rom t h e data o f Table 7 i f , as was p r o b a b l y t h e case , t h i s m a t e r i a l was prepared by the vacuum s i n t e r i n g o f n i o b i u m p o w d e r ^ . Table. 5 . A n a l y s i s of 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 Percent S i 0 . 0 0 5 A l 0 . 0 0 4 Mn 0 . 0 0 1 Mg 0 . 0 0 2 Fe 0 . 0 0 2 Cr 0 . 0 0 1 Sn n i l T i 0 . 0 0 4 N i t r a c e Ca 0 . 0 0 5 Cu 0 . 0 0 0 5 Mo n i l Hf approx . 2 „ 1 7 Table 6 S p e c t r o g r a p h s A n a l y s i s of Niobium I m p u r i t y Element Weight Percent Ta 0 „ 5 N i 0 . 0 0 0 7 Fe . 0 . 0 0 4 t i 0 . 0 1 2 Table 7 Decrease i n Gas Content o f Niobium on Vacuum S i n t e r i n g -Raw Powder A f t e r Vacuum S i n t e r i n g Oxygen 0 . 9 w t . 1o 0 . 0 2 w t . % N i t r o g e n 0 . 1 0 . 0 1 Hydrogen 0 . 2 7 0 . 0 0 1 - 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 a l l o y s o The pronounced tendency f o r z i r c o n i u m (and n iobium), t o take 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 accepted method f o r p r e p a r i n g a l l o y s o f 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 l e v i t a t i o n 17 m e l t i n g apparatus o f P o l o n i s et a l w i t h which t h e above authors had s u c c e s s -f u l l y prepared 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 . T h i s m e l t i n g technique has been amply d e s c r i b e d 1 ^ and t h e r e f o r e o n l y a diagram o f the apparatus w i l l be i n c l u d e d here (see F i g u r e 11) . I t was found t h a t whereas s o l i d z i r c o n i u m c o u l d 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 , the 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 requency power as d e l i v e r e d by a L e p e l v a l v e o s c i l l a t o r r r a t e d a t 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 found which was s u c c e s s f u l i n t h i s r e g a r d (see Table 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 r e p r e s e n t those which were the 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 these 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, the l i q u i d 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 seconds, and no contact o c c u r r e d between the m e t a l and c o i l d u r i n g c a s t i n g . . 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 the apparatus 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 s a t i s f a c t o r y . These a l l o y s were made from the r e a c t o r - g r a d e z i r c o n i u m and the n i o b i u m d e s c r i b e d above. 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 the n i o b i u m i n a h o l e d r i l l e d i n the z i r c o n i u m specimen. The composi t ions were c a l c u l a t e d s i m p l y from the r e l a t i v e weights of the components charged t o t h e apparatus s i n c e w e i g h i n g before and a f t e r m e l t i n g showed a l o s s of l e s s t h a n one p a r t i n 2 0 0 0 . ( 'Lucite 'cylinder - v in. 0.0. \ • - Vs in. thick 7 in. long. Induct/on coil Vs tn. GO. copper tubing 0 03H inf wall \ Copper mould- 0. D.  3Ai in | //2'/«in. Tubing to pipe connector \ Power leads -. T To pressure gouge. and vacuum pump Argon inlet Tree machining brass e/)d plate 'fm i 5 m . Vie in thick • V in. diom. rubber O ring gasket (set in groove in brass pJate) Ve \.n..diom steel rods f in diom. rubber Qringgasket lon-er brass p/ote Sin... sin. * 5/-i6Xn, thick '•Wooden platform Scale Vu in= 1 i n . Figure 11. Diagram of the l e v i t a t i o n melting apparatus of Polonis et a l 1 7 . Table 8 Data Pertinent to the C o i l Design which was Successfully- Used to Prepare Zr-Nb Alloys by Levitation Melting Turn No. C o i l Diameter 0,D. inches 1 (top) (Reverse turn) 1.618 2 1.610 3 1.450 4 1.322 5 . 1.144 6 1.000 7 0.859 8 0.780 9 0.755 10 (bottom) 0.721 Note: C o i l i s made from 1/8*» O.D. Conner tubing - wound on T" suitable conical mandrell. Overall height of c o i l i s .1.500 inches. - 1 8 -M e l t i n g was done under argon which had been p u r i f i e d by p a s s i n g i t over P2O5 beads and t h r o u g h a c a l c i u m t r a i n which was h e l d a t 5 5 0 ° C . J u s t p r i o r to 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 the form o f o 0 0 5 8 8 d iameter 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 cas t V i c k e r s Hardness . A p l o t o f as cas t hardness vs c o m p o s i t i o n i s g i v e n i n F i g u r e 1 2 . M i c r o hardness v a l u e s were obta ined 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 of 1 0 0 grams was u s e d . Table 9 . Composi t ion and As Cast V i c k e r s Hardness o f Zr-Nb A l l o y s  Prepared by L e v i t a t i o n M e l t i n g W t o % Mb As Cast Hardness VPN 0 1 7 9 0 1 7 5 4 o 1 6 3 1 1 4 . 6 2 3 3 4 5 . 9 4 3 1 7 1 3 . 0 2 8 1 1 4 . 2 • 1 9 0 6 3 2 1 6 | Heat t reatments were c a r r i e d out on some o f the a l l o y s by s e a l i n g p o r t i o n s of them i n evacuated 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 both ends o f the c a p s u l e . 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 a l l o y s are 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 of 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 used 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 are shown i n Table 1 0 t o g e t h e r w i t h the NBS p u b l i s h e d v a l u e s 1 ' ' f o r a - z i r c o n i u m 0 - 19 -- o L — g ^ 15 20 Wt. % Nb. Figure 12 . V i c k e r s Hardness vs w t . % Nb f o r a s - c a s t Zr-Nb a l l o y s o - 20 -F i g u r e 13. Pure Z r - a s - c a s t F i g u r e 14. Z r - 4.16% Nb - a s -Widmanstatten a . c a s t . E t c h HN0 3 + HF i n Transformed 3. l a c t i c a c i d X300. E t c h as above. X300. F i g u r e 15. Zr - 4 .62% Nb a s - c a s t F i g u r e 16. Z r - 14.2% Nb a s - c a s t . Retained B . ^ r * ^ 5 ^ ^ ^ R e t a i n e d 8. E t c h as above. X300. E t c h as above. X300. - 21 -F i g u r e 17, Z r - 13% Nb a s - c a s t . F i g u r e 18 . Zr - 19.6% Nb a s - c a s t . R e t a i n e d 3 + n e e d l e s . R e t a i n e d 3 + n e e d l e s . E t c h HN0 3 + HF i n E t c h as above. X300 g l y c e r i n e X300. F i g u r e 19. Zr - 4.6% Nb. 850°C -* 12 h r . 620°C —* furnace 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 2 0 . Zr - 19.6% Nb 850°C — 12 hr.620°C —*• furnace c o o l e d . E u t e c t o i d . E t c h as above. X300. - 22 -Table 10 D-Spacings (Angstroms) f rom 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 As-Cast As-Cast As-Cast As-Cast Zr-19.6% Nb 3 h.800°C H f - f r e e H f - f r e e Z r Zr-6% Nb Zr-13#Nb Z r - 1 9 , 6 # Nb -* l6h.620°O^Fce.cooled a - Z r 2.798 2 . 7 9 3 2 . 7 7 1 2.759 2 . 5 7 3 2.561 2 . 5 3 7 2.494 2.490 2.563 2 . 4 5 9 2 o 4 5 2 2.437 2.459 1.894 1.883 2.012 2.350 1.616 1.609 1 . 8 7 9 2.215 1 . 4 6 3 1.456 1 . 7 7 2 1 . 7 6 6 1.757 1.891 1 . 3 9 9 1.681 1.743 1.368 1 . 3 5 6 1.601 1.539 1.608 1.350 1 . 4 4 7 1.433 1.436 1 . 4 5 6 1.287 1.281 1.356 1 . 3 1 3 1 . 4 2 7 1,229 1 . 2 2 6 1 . 2 4 5 I . 2 4 5 1.390 1.169 1.163 1 . 1 6 4 1.117 1 . 1 1 1 1 . 3 6 3 1.084 1 . 0 8 0 1 . 3 4 3 1.059 1 . 2 8 4 1.036 1 . 0 3 5 1 . 2 3 6 1.006 1 . 0 0 4 1.002 1.108 0.978 0.978 1.081 0 . 9 6 6 0 . 9 6 4 1 . 0 5 5 0 . 9 4 7 0.945 0 . 9 4 2 1.034 0 . 9 3 3 0 .930 1 . 0 0 5 0.900 0.898 0.989 0.877 0.876 0.975 0.857 O . 9 6 6 0.829 0 . 9 4 4 0.82Q 0.935 0.899 0.887 0.875 0.829 0.818 0.809 C. I s o t h e r m a l T r a n s f o r m a t i o n Study 1. A l l o y s I t was decided 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 of composi t ions near to the 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 bar was chosen because o f i t s assumed low oxygen c o n t e n t . S ince oxygen has such a tremendous e f f e c t on the p h y s i c a l p r o p e r t i e s of z i r c o n i u m i t was f e l t t h a t the advantages ga ined 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 outweigh any d e l e t e r i o u s e f f e c t s due t o the l a r g e r hafnium content o f t h e c r y s t a l b a r . Hafnium forms 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 both t h e a and 3 phases. Three a l l o y charges were s u c c e s s f u l l y melted and cast by the l e v i t a t i o n method u s i n g the c o i l . o f d imensions g i v e n i n Table 11. U n l i k e 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 accomplished by s u p p o r t i n g the charge i n the t o p t h i r d u o f the c o i l on a 0.005 diameter 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 before at a p o s i t i v e pressure 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 t h e m e l t i n g o f t h e c h a r g e . One o f the i n g o t s produced i s p i c t u r e d i n F i g u r e 2 1 . The d a t a p e r t a i n i n g t o the 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 Table 12. Table 12 Weight Data f o r A l l o y s o f C r y s t a l Bar Z r Base . A l l o y Wt. Z r Wt. Nb T o t a l Wt. Ingot Wt. Wt. i n c r e a s e Wt. % i n gms. i n gms. i n - gms. i n gms. i n gms. Nb Z-17 • 5.1415 1.0100 6.1515 6.1605 0.0090 16.39 Z-18 5.1750 1.0915 6.2665 6 . 2 7 3 5 0.0070 1 7 . 4 0 Z - 2 0 5.3885 1.0305 6.4190 6 . 4 2 4 5 0.0055 1 6 . 0 4 - 24 -Figure 21. Typical 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 to Prepare Alloys of Crystal-Bar Zirconium Base. Turn O.D.'» I.D." 1 (bottom) 2 3 4 5 6 7 8 9 1 0 1 1 12 (top - reverse turn) 0 . 7 3 8 0 . 4 9 4 0 . 7 3 8 0.808 0.871 0 . 8 8 8 0 . 9 4 2 1 . 0 1 5 1.119 1 . 2 1 1 1 . 3 7 5 1 . 5 6 3 1 . 3 2 6 1 . 6 3 2 Height of c o i l = 1 7 7 0 • » 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 the a d d i t i o n of z i r c o n i u m w i r e w h i c h was wrapped around the charge (a l e n g t h of 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). T h i s a d d i t i o n a l weight o f z i r c o n i u m was i n c l u d e d i n the c a l c u l a t i o n o f t h e a l l o y -c o m p o s i t i o n . The f a b r i c a t i o n of these a l l o y s t o w i r e s was t h e n at tempted. 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 from a d iameter o f 0 . 1 8 5 * ' down t o 0 . 0 4 0 " d i a m e t e r . 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 . Soap was used as a l u b r i c a n t . 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 showed copper smears due t o t h e w i r e d i e s having 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 l e n g t h 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 e t h i r d t o 0 . 1 7 5 " diameter before severe c r a c k i n g o c c u r r e d . I t was t h e r e f o r e obvious 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 the w i r e d i e s had prevented g a l l i n g of 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 drawing 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 at t h i s stage t o f o l l o w two courses ; t o use s l i c e s o f the 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 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 from t h i s t o d e s i g n and c o n s t r u c t apparatus wherein t h e w i r e s of t h e 16.4% Nb a l l o y c o u l d be heated 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 at 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 . T r a n s f o r m a t i o n s i n Vycor C a p s u l e s . 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 iameter 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 Vycor c a p s u l e s . Z i r c o n i u m chips 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 at t e m p e r a t u r e . Each specimen was h e l d at 900°C f o r 1 hour i n a 1 " tube furnace 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 another f u r n a c e which was h e l d a t a lower temperature . Each specimen was h e l d at t h i s temperature f o r a s p e c i f i c t ime 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 c a p s u l e (a) 1 h r . 900°C -rt 15 min.630°C -> WQ. 3 + n e e d l e s . (b) 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 . (c) 1 h r . 9 0 0 ° C - - 2 1 / 2 h r , 630° C (d) 1 h r . 900°C — 8 h r s . 6 3 0 ° C -* WQ -+ WQ. P r e c i p i t a t i o n o f a + E u t e c t o i d + a . e u t e c t o i d . F i g u r e 2 2 . M i c r o s t r u c t u r e s o f a Zr - 17.4% Nb a l l o y i s o t h e r m a l l y t ransformed at 6 3 0 ° C . E t c h HN0 3 + HF i n g l y c e r i n e . X30O. Figure 23. Microstructures of a Zr - 17.4% Nb alloy isothermally transformed at 354°C. Etch HN03 + HF i n glycerine. X 3 0 0 (a) 1 hr.900°C — 3 0 m i n . 6 3 0 ° C — WQ. 3 + n e e d l e s . (b) 1 h r . 900°C -* 1 1 / 2 hr.630°C -•WQ, 3 + needles + s p h e r o i d s . 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 Zr - 1 7 . 4 % Nb a l l o y i s o t h e r m a l l y t ransformed at 630°C. E t c h HN0 3 + HF i n g l y c e r i n e . X1600 - 2 9 -into cold water. The capsule was not broken, to increase the cooling rate, because of the small size of the specimen. Other workers^ 1 obtained more rapid cooling by smashing the capsule on quenching into water but they were dealing * 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 , polished and etched, and examined metallographically. Some of the structures observed are pictured i n Figures 22 through 2i+. -Microhardness measurements were taken on each specimen with a Bergsman Microhardness Tester mounted on a Leitz Metallograph. These results are plotted i n Figure 2 5 . 280,— ft. , ! 1 i r 1 0 V 1 10 100 1000 10,000 Time-Minutes Figure 2 5 Change i n Vickers hardness f o r the 17.U% Nb a l l o y isothermally transformed at the tempera-ture shown. X-ray patterns were obtained, using a powder camera and f i l t e r e d copper Ka rad 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 plotted (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 pictured i n Figures 28, 2 9 , and.31 was constructed to f a c i l i t a t e the measurement of specimen resistance 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 for the self-gettering 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 satisfactory i n that i t s l i f e was much longer than the zirconium winding and i t s self-regulating property ensured better furnace control at temperature. The furnace was controlled by a Honeywell Circular Scale Controller using a Pt-Pt-lORh thermocouple and was operated on a 220 v c i r c u i t . Temperatures were controlled to ±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 trap. Pressures of 5 x 10~5 mm Hg or better were achieved at 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 potentials were measured with a Pye Precision Potentiometer i n conjunction with a Pye Scalamp Galvanometer. The accuracy of the potentiometer on the range used £0.04%. With reference t o the c i r c u i t diagram, i f connections are made as - 3 1 -Table 13 D-spacings (Angstroms) f o r the 17.4% Nb a l l o y i s o t h e r m a l l y t ransformed at 514°C. Values f o r t h e a s - c a s t a l l o y and f o r a a - Z r (NBS) are i n c l u d e d f o r comparison. a - Z r (NBS) As-Cast 900°C — WQ . 900°C -+ 1 h r , 514° C WQ 900°C — 5 h r . 514°C — WQ 2.798 2.776 2.762 2.671 2.655 2.651 2.573 2.544 2.547 2.459 2.495 2.496 2.463 2.453 2.328 2.354 2.324 2.319 1.894 1.902 1.885 1.879 1.881 1.766 1.763 1 . 7 5 1 1.743 1.664 1.638 1 . 6 3 9 1.616 0 1.613 1.613 1.463 1 . 4 6 6 1.467 1.458 1.441 1 . 4 4 2 1.434 1.428 1.399 1.403 1 . 3 9 6 1.397 1.388 1.368 1.377 1.371 1.362 1.350 1.342 1.346 1.287 1.281 1 . 2 2 9 1.248 1 . 2 4 9 1 . 2 4 3 1 . 2 3 3 1.169 1.168 1.121 1.117 1.112 1.106 1.084 1.084 1.079 1.064 1.061 1.066 1.059 1.053 1.036 1.039 1.036 1.034 1.006 1.016 1.020 1.017 1.005 0.978 0.977 0.966 0.964 0.964 0.947 0.943 0.945 0 . 9 4 2 0.934 0.933 0.933 0.900 0.899 0.903 0.898 0.877 0.893 0.878 0.876 0.857 0.883 0.829 0.829 0.833 0.832 0.817 0.820 0 .791 0.788 0.809 800 7 0 0 6 0 0 5 0 0 4 0 0 1 1 lb Time - minutes. t o o ^ " m m m m b Figure 26. T-T-T curve for a Zr - 1 7 . 4 % Nb alloy based on hardness changes. - 33 -4.00' ,< 3.00 f t 7 JUL * — r c 2.00" 6.00" o 4.15' 1.625" C) o -1.52' Figure 27. Diagram of Furnace and Vacuum,Chamber Assembly. 1. Brass can 4. Specimen 7. Measuring 2. Brass l i d 5. Lava block thermocouples. 3. Radiation shields 6. Furnace control 8. Self-gettering thermocouple. furnace. - 34 -F i g u r e 2 8 . G e n e r a l v iew o f apparatus showing furnace c o n t r o l e lements , vacuum system, 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 measuring equipment. P r e s s u r e measuring apparatus i s not shown. F i g u r e 2 9 . View o f main vacuum furnace e lements , B u t t e r ' s s e l f -g e t t e r i n g f u r n a c e , water c o o l e d can, l i d showing t h e thermocouples . - 35 -I Specimen 0-100 V ohm '\ 40 ohm -0 Specimen Temperature -O -O Specimen Potential - 0 0 nn 0.1000 ohm Standard Potential v - o 12 volt 0-100 ma Figure 30. Diagram of .resistance.measuring- circ u i t , (a) Pt, (b) Pt-lORh. - 36 -Figure 31* Vacuum furnace assembly showing p o s i t i o n of furnace 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 steady 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 , the r e s i s t a n c e s o f the specimen and s t a n d a r d are i n t h e same r a t i o as the v o l t a g e drops across them. A w i r e specimen of the 16.4% Nb a l l o y , 4 cm. l o n g , w h i c h had been annealed f o r 48 h o u r s , i n an evacuated Vycor c a p s u l e , a t 800°C, was a t t a c h e d t o the P t - P t 10 Rh couples v i a a «Lava« b l o c k connector as shown i n F i g u r e 32 . Z i r c o n i u m washers (0 .010*• 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 the Lava b l o c k , the thermocouple on the washer, one end of t h e a l l o y w i r e on t h e thermocouple, and another 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 . A l l were h e l d f i r m l y i n contact by t i g h t e n i n g the 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 , connect ions made, and the system pumped down. The f i r s t specimen was heated t o 800°C and a f t e r 8-10 minutes at 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 the furnace power. The specimen reached 455°C i n l e s s t h a n 60 seconds. I t was h e l d at t h i s temperature and s imultaneous measurements o f p o t e n t i a l and temperature 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 cooled t o room temperature and i t s r e s i s t a n c e measured. The change o f the r a t i o o f r e s i s t a n c e at t ime 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 another 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 the same quenched c o n d i t i o n but which was t ransformed at 507°C. The f i r s t specimen was heated a g a i n s l o w l y t o 800°C and the p l o t o f r e s i s t a n c e versus temperature o b t a i n e d i s shown i n F i g u r e 34 . I t was h e l d at 800°C and t h e n quenched t o a lower 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 the 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 lower temperatures s e v e r a l t i m e s . T h i s procedure was repeated f o r the 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 the p o t e n t i a l i n t o a Honeywel l S t r i p Chart R e c o r d e r . The r e s i s t a n c e changes could - 38 -Figure 3 2 . Close-up showing method of attaching specimen to thermocouples via 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 of 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 f o r i s o t h e r m a l l y t r a n s f o r m e d specimens. - 4 0 Figure 3 4 . Change of resistance on heating the near-equilibrium structure of a Zr - 1 6 . 4 % Nb alloy. be seen more c l e a r l y i n ,this case but the accurate determination of temperature was s a c r i f i c e d . Some representative curves f o r isothermal change of resistance with time are shown i n Figure 35. Complete resistance data i s given i n Appendix 1. A tentative T-T-T curve, f o r the 16.4% Nb a l l o y , based on resistance data i s shown i n Figure 36. In conjunction with the resistance 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 previously. These specimens were examined metallographically, 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 ra 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 with the wire axis perpendicular t o the x-ray beam. F i l t e r e d cobalt Ka radiation was employed. X-ray data from the 'powder' patterns are presented i n Table 14, the change of hardness i s plotted 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. - 4 2 -3.6, Time - minutes Figure 35. Some typical resistance-time curves obtained on a Zr - 16.4% alloy. Figure 36. Tentative T-T-T curve for a'Zr - 16.4% Nb alloy, based on resistance data. 240r 0 v I 10 100 1000 10000 Time - minutes Figure 37. Hardness change in a Zr - 16.4% Nb alloy isothermally transformed at 515°C. T a b l e 14 D-apacings (Angstroms) f o r a Zr-16 .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 515°C. Values f o r the 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 comparison. ' NBS As-Cast 850°C — WQ 850°C — 1 h r . 850°C ^ 2 1 / 2 h r . 850°C — 4 h r . a - Z r 515°C -» WQ 515°C —• WQ 515°C ^ W Q 2.798 2.911 2 . 5 7 3 2.459 2.486 2 . 4 6 5 2.003 • 2 . 0 4 2 1.894 1.757 1 . 7 5 2 1.734 1.871 1.616 1.835 1.463 1.438 1.433 1 . 4 2 9 1.713 . IL.399 1 . 5 7 2 1.368 1.498 1.350 1.418 1.287 1 . 2 2 9 I . 2 4 6 1 . 2 4 3 1 . 2 4 1 L.169 1.113 1.114 1.111 1.107 - 1 . 0 8 4 1.080 1.076 1.059 1 . 0 6 6 1.036 1.016 1.016 1.017 1.037 1.011 1.006 1.002 1 .001 0.978 0.966 0.957 0.947 0.943 0 . 9 4 2 0.941 0.949 0.933 0.939 0 . 9 4 0 0.900 0.883 0.896 0.896 0.896 6 . 8 7 7 0.882 0.880 0.874 0.857 0.829 0 .831 0.832 0.832 0.830 0.829 0 .820 0.790 0.790 0.789 0.788 - 4 5 (a) WQ from 850°C. f> + needles (b) 850°C — lhr .520°C -* WQ. 3 + a + n e e d l e s . (c) 8 5 0 ° C — 2 1 / 2 h r . 5 2 0 ° C - * WQ. a + e u t e c t o i d (d) 850°C —• 4 hrs.520°C —• WQ, E u t e c t o i d . F i g u r e 38 M i c r o s t r u c t u r e s o f specimens of the 1 6 . 4 % Nb a l l o y annealed 4 8 hours at 8 5 0 ° C , quenched t o 5 2 0 ° C and h e l d at t h i s tempera-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 3 -HF i n g l y c e r i n e . X 3 0 0 . Figure 3 9 . Needles i n a Zr - 16.4% Nb alloy water quenched after 48 hours at 800°C. Etch HN03 + HF i n glycerine. X2200 (a) WQ from 800°C. (b) 800°C — 1 hr. 515°C — WQ. Figure 40, Back reflection Laue pictures of a Zr -16.4% Nb alloy wire isothermally transformed at 515°C. Filtered Co Ka radiation -perpendicular to wire axis. (cont'd.) - 48 -(c) 800°C — 2 1/2 hr. 515°C — WQ Figure 40 (cont'd.) (d) 8O0°C — 4 hrs.515°C — WQ. I I I . 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 interpretation of some of the results of the present investigation. The room temperature measurements, such as hardness, on specimens heat-treated i n Vycor capsules gave data with 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 simi l a r t o the one obtained by Domagala for a 14.6% Nb a l l o y except that i t i s displaced to longer times. This displacement can be considered to be due to 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 of heat treatment employed. The methods used by Domagala would l i k e l y result i n gas contamina-t i o n of the specimen. I t . i s therefore believed that the higher niobium content of the present a l l o y i n addition to i t s lower gas impurity content s t a b i l i z e d the beta phase to lower temperatures and longer times and thereby accounts f o r the present T-T-T curve being displaced to the ri g h t of Domagala's on the time scale. 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 Atkins. However, Domagala mentions that t h i s structure was not always evident on metallographic observation. He also states that the structure could be the res u l t of etching. The introduction of hydrogen during the p i c k l i n g of 20 Titanium-base alloys has been observed to form hydrides whxch are very s i m i l a r to the black needles seen i n quenched zirconium alloys which have been chemically polished and etched. X-ray methods would not be too r e l i a b l e i n establishing a hydride phase because of the low scattering power of the hydrogen atom. The extra lines which appeared on the powder patterns taken of several - 50 -specimens could not be indexed as hexagonal or tetragonal. It was observed, however, that these lines 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 for ZrN (see Appendix 3). The possibility 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 lines and the lines noted by the ASTM for the simpler ZrN and ZrH compounds. The rings obtained on the back reflection Laue pattern of a specimen of 16.4% Nb quenched from 800°C were calculated to be high angle lines of a-zirconium. Although the calculated d-spacings for the extra lines on the powder patterns closely match those for ZrN, i t is not believed that sufficient nitrogen could have been absorbed during the wire-drawing operation or during the subsequent heat treatment to result in the formation of a nitride. Another possibility is 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 this structure therefore represents the result of a martensitic process i s most probable but the poss i b i l i t y that the needle structure is produced by etching should not be discarded. The results from resistance measurements were disappointing in that, although they showed a high sensitivity in observing transformation and indicated a trend to longer times with lower temperatures for the i n i t i a t i o n of transformation, successive quenches to the same isothermal transformation - 51 -temperature did not y i e l d the same data. However, i t was noted that above 500°C the data showed that i n i t i a t i o n of transformation was occurring at approximately the times given by the curve based on room temperature hardness measurements. Around 500°C there was a region of uncertainty as t o when transformation was occurring. Below 500°C the resistance measurements indicated a trend to longer times with decreasing temperature i n contrast to the room temperature hardness measurements. Records of the change i n specimen p o t e n t i a l with time as obtained from a strip-chart recorder showed a sharp peak occurring at about 500°C on quenching the specimen from 800°C. This peak occurred within the -60 seconds required to reach the desired transformation temperature. An experiment with a copper wire specimen showed no peak on quenching. It i s possible that some a or a * phase i s being formed as the specimen crosses the 3/?- + 3 transus and the tempering of t h i s phase, i f a*, i s masking changes due to the subsequent decomposition of the retained 3 phase, or else, 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, therefore, that the apparatus which has been designed and constructed offers a sensitive means whereby phase transformations i n alloys may be studied. However, certain modifications to the apparatus and technique are required. 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 alloys to the variables of p r i o r heat-treatment, degree of cold work, tempera-ture cycling, and high temperature soaking time requires that a specimen be used for only one cycle to the isothermal transformation temperature. Although the contact between the specimen and thermocouples was considered to be sat i s f a c t o r y , t h i s contact could perhaps be improved. This could be achieved most e f f i c i e n t l y by pressure-welding. The spot-welding of the specimen to the thermocouples i s not believed to be a sa t i s f a c t o r y s o l u t i o n to 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 requisite spot-welding apparatus which would keep gas contamination i n such a small specimen to a minimum It i s also apparent that s t r u c t u r a l changes on quenching as measured potentiometrically 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 also be used f o r following isothermal transformations above 500°C to resolve whether a martensite process i s involved. Rather than substantiate the resistance measurements with room-temperature observations of metallography, hardness, and c r y s t a l structure 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 better correlation. The needle-shaped specimen would present less surface area than powder and thereby minimize gas contamination. This work has therefore indicated the complexity of the phase trans-formations occurring i n zirconium-niobium alloys and has described the techniques by which these processes may be studied to eventually determine, by thermodynamic analysis, after the accumulation of considerable data, the mechanisms of the reactions involved. APPENDIX 1 Resistance Data: Temperatures from l e f t to right are i n the experimental sequence Resistance values are i n OHMS x 10~ 2. Time i s i n hours. F i r s t s P ) e c i m e n 450 °C 458°C 448° C 546°C 418°C . 515 °C 494° C 538°C 568°C t R t R t R t R t R t R t R t R t R 0.0 3.33 0.050 2.41 0.033 3.23 0.083 3.22 0.017 2.72 0.083 2.86 0.067 2.80 0.067 2.90 0.067 2.98 0.167 3.33 0.067 2.41 0.067 3.21 0.167 3.19 0.100 2,72 0.250 2.86 0.200 2.80 0.133 2.90 0.183 2.99 0.333 3.34 0.617 2,40 0.250 3.22 0.250 3.20 0.500 2.72 0.433 2.81 0.350 2.80 0.233 2.91 0.300 2.99 0.583 3.34 1.680 2.41 0.583 3.21 0.400 3.20 1.116 2.72- 0.517 2.76 0.533 2.72 0.317 2.92 0.380 3.00 0.830 3.32 -2.750 2.31 1.920 3.22 0.517 3.21 2.370 2.72 0.683 2.73 0.650 2.65 0.417 2.95 0.480 3.02 0.867 3.33 3.260 2.28 2.750 3.19 0.983 3.46 3.330 2.72 0.933 2.93 1.133 2.71 0.600 3.13 0.600 3.19 1.116 3.33 3.850 2.29 4.150 3.16 1.230 3.61 3.660 2.71 1.050 2.92 1.480 2.71 0.780 3.23 0.720 3.30 1.450 3.34 4.260 2.27 6.670 3.02 1.450 3.90 4.020 2.71 1.500 2.91 1.000 3.27 0.830 3.34 1.920 3.36 4.760 2.26 16.920 2.58 1.970 4.03 4.410 2.70 2.000 2.91 1.230 3.27 1.000 3.35 2.330 3.38 5.180 2.26 17.780 2.57 3.060 4.10 4.950 2.68 2.780 3.29 1.167 3.42 2.660 3.39 7.760 2.26 3.450 4.11 5.360 2.67 11.080 3.49 2.920 3.39 8,460 2.26 4.080 4.19 5.780' 2.66 12.450 3.42 3.000 3.40 8.860 2.25 4.230 4.18 6.250 2.66 11.750 3.45 9.380 2.25 4.600 4.21 6.450 2.65 L2.410 3.45 21.710 2.26 5.580 4.36 7.500 2.63 13.660 3.45 22.930 2.26 5.710 4.20 10.660 2.60 14.660 3.45 5.920 4.22 11.180 2.60 16.160 3.45 6.400 4.26 11.660 2.58 7.230 4.34 22.310 2.53 7.630 4.34 23.830 2.53 I I Appendix 1 (cont'd.) S e c 0 n d S p e c i p e n 507°C 542°C 476 °C 431°C 493°G t R - t R • t R t R t R 0.050 3.35 0.033 4.83 0.033 4.42 0.067 4.30 0 4.62 0.183 3.36 0.100 4.83 0.200 4.41 0.100 4.29 0.083 4.56 0.233 3.37 0.417 4.89 0.533 4.43 O.250 4.31 0.133 4.55 : 0.417 3.39 0.583 4.90 0.720 4.43 0.400 4.29 0.300 4.63 0.583 3.39 1.000 4.84 1.230 4.45 0.650 4.29 0.833 4.66 0.780 3.40 •1.500 4.81 1.500 4.47 0.830 4.29 0.933 4.55 0.933 3.41 2.370 4.77 2.750 4.23 1.680 4.28 1.000 4.54 1.000 3.42 . 3.450 4.76 3.000 4.21 2.000 4.28 1.500 4.47 1.450 3.45 4.080 4.75 3.660 4.19 2.330 4.28 1.680 4.45 1.680 3.47 4.600 4.72 4.950 4.14 2.780 4.28 2.000 3.48 4.950 4.71 5.500 4.13 3.45 4.27 2.330 3.49 5.920 4.69 5.920 4.12 4.26 4.28. 5.580 3.53 6.670 4.69 6.450 4.11 5.18 4.27 5.920 3.53 9.380 4.67 8.860 4.09 10.660 4.28 6.400 3.53 10.660 4.65 10.660 4.07 23.830 4.23 6.670 .3.54 7.760 3.54 17.780 3.57 21.710 3.57 APPENDIX I I Related Phase Diagrams. Nitrogen At. % 25 40 0 5 10 13 Nitrogen Wt. % 1. The zirconium-nitrogen system. Oxygen, Wt. % 2 5 15 25 Oxygen, At'.. % 2. The zirconium-oxygen system. 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 for related zirconium compounds. ZrN Zr0 2 ZrH (approx.) 5 - ZrH £- ZrH 2.64 2.93 2.75 2.76 2.76 2.28 2.52 2.38 2.39 2.49 1.61 1.81 1.69 1.69 2.22 1.38 1.79 1.44 ' 1.44 1.76 1.32 1.55 1.38 1.38 1.66 . 1.14 1.53 1.19 1.20 1.48 1.05 1.47 1.09 1.10 1.38 1.02 1.29 1.07 1.07 1.37 0.93 1.27 0.97 1.24 1.17 0.92 1.13 1.13 1.11 1.10 1.09 1.05 1.08 1.04 1.02 6.99 0.99 0.98 cubic tetragonal cubic cubic tetragonal a Q =4.56 a 0 = 5.07 a Q = 4.76 a Q - varies a 0 = 4.97 c c = 5.16 between c Q = 4.45 4.77 and 4.78 - 60 -REFERENCES 1. Lustman, B., and Kerze, F., editors, 'The Metallurgy of Zirconium', National Nuclear Energy Series, McGraw-Hill 1955. . 2. M i l l e r , E.C., from paper i n ASM Symposium, * Zirconium and Zirconium Alloys' 1953. 3. P f i e l , P.C.L., 'A Discussion of the Factors Affecting the Constitution of Zirconium All o y s ' , AERE M/R 960, June.27, 1952. 4. Mcintosh, A.B., Jour. Inst. Metals 1855, 85_, A p r i l 1957. 5. Anderson, C.T., Hayes, E.T., Roberson, A.H., and K r o l l , W.J., 'A Preliminary Survey of Zirconium Alloys', U.S. Bureau of 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 Alloying Behaviour of Zirconium', March 1950. 7. L i t t o n , F.B., Iron Age, 167, 1951, 95-99 and 112-114. 8. Simcoe, C.R., and Mudge J r . , W.L., AEC Report No. WAPD-38, November 21, 1951. 9. Keeler, J.H., AEC Report No. S0-2504, January 5, 1952. 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., Journ. Metals 1034, September 1955. 13. Domagala, R.F., and McPherson, D.J., Journ. Metals 620, May 1956. i 14. Bychkov, Yu F., Rozanov, A.N., and Skorov, D.M., Atomnaya Energiya 2, February 1957, 146-157. 15. Domagala, R.F., 'A Study of the Mechanisms of Heat Treatment of Zirconium-Base Alloys'. Armour Research Foundation Report for AEC, July 17, 1956. 16. 0 ' D r i s c o l l , W.G., and M i l l e r , G.L., Journ. Inst. Metals 1758, 85_, AprjLl 1957. 17. Polonis, D.H., Butters, R.G., and Parr, J.G., Research 2 No. 2, February 1954. IS. Polonis, D.H., Butters, R.G., and Parr, J.G., Research 2» July 1954. 19. National Bureau of Standards (U.S.) Circular 539 V o l . I I , June 1953, p. 11. 20. McKinsey, C.R., Stern, M. and Perkins, R.A., Trans. ASM Preprint No. 38, 5_0 1957. 21. Douglas, D.L., Marsh J r . L . L . , and Manning, G.K., Trans. ASM Vol. 50, Preprint No. 20, 1957_ 

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