Theoretical concepts for the liquid phase sintering of a new low temperature tungsten heavy alloy. Ph.D. Thesis
The kinetics and processing conditions of liquid phase sintering have been addressed in the development of a novel heavy alloy, W-Ni-Mn. Solubility criteria were considered in the selection of manganese as an alloying element to the W-Ni system. The addition of manganese resulted in a depressed melting point of the matrix and consequently sintering in this system was achieved at temperatures 300 deg C lower than in the conventional heavy alloys. Concurrent with solubility criteria, the rearrangement stage in liquid phase sintering was treated. During rearrangement, it was found that two factors need to be considered when estimating the time scales involved, (1) the shrinkage due to capillary forces and (2) heat transfer through a particulate compact. When capillary and viscous drag forces are accounted for, the time scales in rearrangement were found to be in the microseconds range for metal systems. On the other hand, heat transfer was found to be the time limiting factor for metallic specimens with time scales in the range of seconds. Coarsening in liquid phase sintered systems was also considered. A coalescence function was introduced to the continuity equation for the grain size distribution. Coalescence resulted in a broadening of the grain size distribution. At high volume fractions of the solid phase, the grain size distribution was skewed to the right as compared to the symmetrical behavior observed at low solid volume fractions. While these observations agree with previous experimental measurements on liquid phase sintered microstructures and the experimental measurements in the W-Ni-Mn system, this treatment shows that the overall effect of coalescence on the grain size distribution functions is minimal. This is due to the fact that coarsening kinetics in coalescence follows the same time dependency as in diffusion. The addition of manganese to the W-Ni system resulted in smaller grain sizes than that observed in the W-Ni system.
- Research Organization:
- Pennsylvania State Univ., University Park, PA (United States). Davey Lab.
- OSTI ID:
- 237323
- Report Number(s):
- N-96-23122; NIPS-96-07629; TRN: 9623122
- Resource Relation:
- Other Information: TH: Ph.D. Thesis; PBD: Jan 1993
- Country of Publication:
- United States
- Language:
- English
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