2 INDEPENDENT STRAIN-HARDENING MECHANISMS IN SINGLE-CRYSTAL GAMMA-TI-56AL COMPOUND

The strain hardening of gamma-Ti-56Al by superdislocations (b=[101]) o ccurs by two independent mechanisms in two different temperature range s: from room temperature to approximately 623 K; and from 623 to 1073 K. The activation energy for the low temperature mechanism was found t o be 0.014 eV, compared to 0.2-0.22 eV for the high temperature mechan ism. The transition from the low temperature mechanism to the high tem perature mechanism occurs near 623 K where a burst of double jogs is b elieved to occur through a thermally activated process. Many extended double jogs 15-20 nm wide were observed in the alloy deformed at 673 K . The beginning of the extended jog formation near 673 K in Ti-56Al is coincident with the near-zero value of the strain rate sensitivity pa rameter near 673 K in Ti-54Al.