HIGH-TEMPERATURE (111) SLIP BEHAVIOR OF A DIRECTIONALLY SOLIDIFIED NI3AL ALLOY

The deformation behavior of {111} slip in a directionally solidified (DS) Ni3Al-Zr-B alloy has been investigated in tension in the temperature range of 773-1373K. At 0.2% strain, deformation rate was found to be exponential with yield stress above the peak temperature (1023K). However, at a larger strain of 3.8% strain, deformation rate on flow stress obeyed a power law relation above the peak temperature, with the stress exponent n=4.89 in the temperature range of 1073-1173K, suggesting a deformation mechanism of edge dislocation climb, and n=2.70 in the temperature range of 1273-1373K, suggesting a deformation mechanism of viscous screw dislocation glide. The dislocation structure developed with increasing stress and strain, the dislocation density, rho, was related to the applied stress, sigma, as rho proportional to sigma(1.7), and no steady state dislocation density was achieved up to 3.8% strain. With increasing temperature, the activation volume decreased below the peak temperature, and stayed constant at a low level above the peak temperature, reflecting two different processes of thermal activation or unpinning of the Kear-Wilsdorf locks.