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UBC Theses and Dissertations
Removal of inclusions from cast superalloy revert Haruna, Yasushi
Abstract
It is known that the recycling of superalloy scrap causes the mechanical properties and the casting performance of reverted alloys to deteriorate. This is due to contamination of the alloy by inclusions. The contaminants affect the microstructure of the casting in terms of modification of MC carbide morphology and an increase in the amount of microporosity. Removal of such contaminants from the reverted superalloys is mandatory especially for the production of critical cast parts. The removal of TiN and HfO₂ has been investigated in this work. The computation of the precipitation conditions for TiN in IN100 and HfO₂ in Mar-M247 has been carried out using available thermochemical data, taking into account the segregation taking place during freezing. The formation reactions are: TiN(₈) T and Hf0₂(₈) (s) Hf + 2O, where Ti, N, Hf and 0 are dissolved in the liquid superalloy. The solubility product for TiN precipitation in IN100 is calculated as log K’tin = —2.62 at the liquidus temperature. The saturation solubility of nitrogen is lowered due to Ti segregation during freezing. The saturation solubility of oxygen for Hf0₂ precipitation in Mar-M247 is estimated as less than 1 ppm at the liquidus temperature, and that Hf0₂ particles mostly form by the reaction with the oxide crucible during remelting. The formation and the removal mechanisms of these inclusions are examined using DS and EB remelting techniques. It is concluded that the main factor for MC carbide morphology change in IN100 is the solidification conditions not the alloy’s nitrogen content. The total nitrogen content in the liquid determines the number of TiN particles that are found as nuclei in blocky carbides. In Mar-M247, it is confirmed that HfO₂ is formed by the reaction withA1₂O₃ crucible during multiple remelting. It is demonstrated that EB remelting is valid for TiN and HfO₂ particle removal. These inclusions are removed by a separation mechanism due to the interfacial tension forces between the particles and the liquid surface and not by a buoyancy mechanism. The saturation solubility of nitrogen for TiN precipitation in IN100 is determined to be approximately 6 ppm at the liquidus temperature which represents an aim-point for refining in recycling the alloys. Finally, the practical EBCHR conditions for removal of those inclusions are also discussed.
Item Metadata
| Title |
Removal of inclusions from cast superalloy revert
|
| Creator | |
| Publisher |
University of British Columbia
|
| Date Issued |
1994
|
| Description |
It is known that the recycling of superalloy scrap causes the mechanical properties
and the casting performance of reverted alloys to deteriorate. This is due to contamination
of the alloy by inclusions. The contaminants affect the microstructure of the casting in
terms of modification of MC carbide morphology and an increase in the amount of
microporosity. Removal of such contaminants from the reverted superalloys is mandatory
especially for the production of critical cast parts.
The removal of TiN and HfO₂ has been investigated in this work. The computation
of the precipitation conditions for TiN in IN100 and HfO₂ in Mar-M247 has been carried out
using available thermochemical data, taking into account the segregation taking place during
freezing. The formation reactions are:
TiN(₈) T
and
Hf0₂(₈) (s) Hf + 2O,
where Ti, N, Hf and 0 are dissolved in the liquid superalloy. The solubility product for
TiN precipitation in IN100 is calculated as log K’tin = —2.62 at the liquidus temperature.
The saturation solubility of nitrogen is lowered due to Ti segregation during freezing. The
saturation solubility of oxygen for Hf0₂ precipitation in Mar-M247 is estimated as less than 1
ppm at the liquidus temperature, and that Hf0₂ particles mostly form by the reaction with the
oxide crucible during remelting.
The formation and the removal mechanisms of these inclusions are examined using
DS and EB remelting techniques. It is concluded that the main factor for MC carbide
morphology change in IN100 is the solidification conditions not the alloy’s nitrogen content. The total nitrogen content in the liquid determines the number of TiN particles that are found
as nuclei in blocky carbides. In Mar-M247, it is confirmed that HfO₂ is formed by the
reaction withA1₂O₃ crucible during multiple remelting.
It is demonstrated that EB remelting is valid for TiN and HfO₂ particle removal.
These inclusions are removed by a separation mechanism due to the interfacial tension forces
between the particles and the liquid surface and not by a buoyancy mechanism. The
saturation solubility of nitrogen for TiN precipitation in IN100 is determined to be
approximately 6 ppm at the liquidus temperature which represents an aim-point for refining in
recycling the alloys. Finally, the practical EBCHR conditions for removal of those
inclusions are also discussed.
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| Extent |
4779284 bytes
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| Genre | |
| Type | |
| File Format |
application/pdf
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| Language |
eng
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| Date Available |
2009-03-02
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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 |
10.14288/1.0078488
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| URI | |
| Degree | |
| Program | |
| Affiliation | |
| Degree Grantor |
University of British Columbia
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| Graduation Date |
1994-11
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| Campus | |
| Scholarly Level |
Graduate
|
| Aggregated Source Repository |
DSpace
|
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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.