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The influence of tin particles on the nucleation of spurious grains during single crystal casting of superalloys Wang, Tao
Abstract
Spurious grains are defects that arise in single crystal turbine blades of superalloys. Because they can act as favorable locations for crack initiation and in-service failure, they often lead to blades being rejected. Although spurious grains in single crystal castings may nucleate by many mechanisms, strong but indirect evidence exists that the presence of nitride and oxide inclusions can reduce the amount of undercooling necessary for grain nucleation and hence increase the formation of spurious grains. In this project, this hypothesis, in regard to nitride inclusions, was tested directly by experiments. In the experiments, the nucleation of spurious grains was "turned on" by providing nitride inclusions at the liquidus temperature, in alloys where the oxide content is constant and known. Solidification front undercooling was varied by changing the solidification velocity in order to estimate the critical undercooling for nucleation. A thermal model of the single crystal casting process was developed to analyze the thermal history of the casting process. Equiaxed grains and columnar to equiaxed transitions (CET) were observed in alloys with a nitrogen content much higher than the saturation solubility, in those cases where the solidification front undercooling was in excess of the critical undercooling. Experiments were done on samples with a simple shape. Dendrite tip undercoolings were estimated by using the well-known KGT model using the pseudo binary approximation. The influence of nitrogen content on the nucleation kinetics was quantitatively studied based on theories given in the literature.
Item Metadata
Title |
The influence of tin particles on the nucleation of spurious grains during single crystal casting of superalloys
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2003
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Description |
Spurious grains are defects that arise in single crystal turbine blades of superalloys.
Because they can act as favorable locations for crack initiation and in-service failure, they
often lead to blades being rejected. Although spurious grains in single crystal castings may
nucleate by many mechanisms, strong but indirect evidence exists that the presence of nitride
and oxide inclusions can reduce the amount of undercooling necessary for grain nucleation
and hence increase the formation of spurious grains. In this project, this hypothesis, in regard
to nitride inclusions, was tested directly by experiments. In the experiments, the nucleation of
spurious grains was "turned on" by providing nitride inclusions at the liquidus temperature, in
alloys where the oxide content is constant and known. Solidification front undercooling was
varied by changing the solidification velocity in order to estimate the critical undercooling for
nucleation. A thermal model of the single crystal casting process was developed to analyze
the thermal history of the casting process. Equiaxed grains and columnar to equiaxed
transitions (CET) were observed in alloys with a nitrogen content much higher than the
saturation solubility, in those cases where the solidification front undercooling was in excess
of the critical undercooling. Experiments were done on samples with a simple shape. Dendrite
tip undercoolings were estimated by using the well-known KGT model using the pseudo
binary approximation. The influence of nitrogen content on the nucleation kinetics was
quantitatively studied based on theories given in the literature.
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Extent |
6454253 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-11-13
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0078625
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2003-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.