Role of Grain Size on the Brittle-to-Ductile Transition of the Strongly Ordered Alloy Ni sub 3 Al: Report on Progress During Year-2

摘要

Experiments have been performed to characterize the structure and the mechanical properties of polycrystalline Ni sub 3 Al prepared by consolidating rapidly solidified powders. Results show that powders, as solidified, are fine grained (0.1 to 1.5 mu m) and relatively structure free, but are only partially ordered. As consolidated, the material is again relatively structure free, but now the grains are larger (approximately 15 mu m) and recrystallized. Particles are inhomogeneously distributed, and appear to impede grain growth. There is no evidence to suggest grain boundary segregation of elements other than sulfur. Grain refinement imparts marked hardening at low temperatures, but owing to the occurrence of boundary sliding imparts weakening at intermediate temperatures. Refinement also increases hardness, but has no significant effect on the rate of work hardening nor on the tensile elongation at low temperatures. At intermediate temperatures, grain refinement leads to enhanced ductility, owing to grain boundary sliding. Intergranular fracture is accompanied by localized plastic flow in excess of that which occurs throughout the bulk of the grain. 19 figures. (ERA citation 08:023952)