EXPERIMENTAL-EVIDENCE OF TEMPERATURE PATH INDEPENDENCE IN THE POLYCRYSTALLINE ALLOY NI3AL

The results from a series of elevated temperature prestrain experiment s on a hypostoichiometric polycrstalline Ni3Al are presented. Experime nts were conducted to examine the deformation characteristic of ''ther mal reversibility'' or temperature path history independence (TPHI). T emperature path history independence was experimentally observed from prestraining experiments (also known as Cottrell-Stokes experiments) i n which the specimen was deformed at different temperatures; the resul ts were compared to those obtained from tests conducted at constant te mperature. The purpose of such experiments was to macroscopically eval uate the effects of intrinsic dislocation mobility and dislocation sub structure on deformation. These experiments provide a framework in whi ch to evaluate fundamental characteristics of thermally activated defo rmation processes. The results for polycrystalline Ni3Al alloys indica te that the mechanisms responsible for thermal strengthening is indepe ndent of prior deformation history. This observation implies that the mechanism of anomalous strengthening in such alloys is fully reversibl e and independent of the development of a dislocation ''substructure'' .