THE PLASTIC-FLOW OF BINARY NI3AL SINGLE-CRYSTALS

Flow stress measurements were performed on single crystals of binary Ni-rich Ni3Al as a function of temperature, orientation, and sense of the applied uniaxial stress. Data were collected over temperatures ranging from liquid nitrogen to 1300 K. In agreement with previous studies on other L1(2)-type Ni3Al based alloys, the yield strength of binary Ni3Al presented a positive temperature dependence up to about 1100 K. The critical resolved shear stress (CRSS) for the {111}<110> slip was found to be orientation dependent, mostly over the positive temperature range (400-1100 K). A tension/compression asymmetry, whose sense and magnitude are orientation dependent, appeared over the same range of temperatures. An orientation dependence was also found for the CRSS for {010}<110> slip at high temperatures where the yield strength of Ni3Al decreases with temperature. In this temperature regime, unlike for the Ni3Al + X alloys, a flow stress asymmetry is found, the sense and magnitude of which are orientation-independent. The magnitude of the peak temperature is orientation-independent as determined from the tensile tests, but it varies randomly with orientation for the compressive tests.