MODELING THE FLOW-STRESS ANOMALY IN GAMMA-TIAL .1. EXPERIMENTAL-OBSERVATIONS OF DISLOCATION MECHANISMS

Mechanical tests on a polycrystalline gamma-Ti47Al51Mn2 alloy between - 150 and 1000 degrees C and subsequent microstructure analysis clearl y distinguish between three temperature domains which correspond to di fferent deformation mechanisms. At low temperatures, the motion of sup erdislocations dragging faulted dipoles is rate controlling. At interm ediate temperatures where a stress anomaly is observed, screw simple d islocations are observed with cusps, the density of which increases wi th increasing temperature. A description of the simple dislocation mot ion based on these observations is developed. The glide of a screw sim ple dislocation in two planes through a Peierls mechanism is believed to be the intrinsic source for the formation of pinning points. It is proposed that these pinning points can be erased by lateral motion of superkinks: an unzipping process. A model for this pinning-unzipping m echanism will be fully developed in part II. At high temperatures, the climb of simple dislocations appears to control the deformation.