Mechanistic Understanding of Powder Compaction in Metals.
Annual technical rept. 1 Apr 84-15 Feb 86,
CORNELL UNIV ITHACA NY DEPT OF MATERIALS SCIENCE AND ENGINEERING
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In this, the first annual report, results from hot-pressing experiments on NixAl1-x powders are described. The stoichiometry of the alloy is varied in the range 0.64x0.52. The change in composition allows us to change the diffusion coefficient by nearly two orders of magnitude. The principal mechanisms of powder compaction are plastic flow by dislocations and diffusional transport. The relative contribution of these two mechanisms can, therefore, be separated by varying the composition. Also, the dislocation mechanism is expected to dominate when densification is carried out at high stresses. Dislocation activity is also expected to influence microstructure evolution by dynamic recrystallization. The results described in this report demonstrate that the diffusional and dislocation mechanisms can indeed be separated by changing the stress and the composition. At high stresses, we have found evidence of precipitation of new grains at interfaces. Current and future work is being directed toward understanding the role of shear strain in densification and in microstructure evolution during powder compaction. Author
- Metallurgy and Metallography