Deformation of polycrystalline Ni₃Al at high strain rates and elevated temperatures

The mechanical response of Ni₃Al to deformation at high temperatures has long been known to exhibit a flow stress/temperature anomaly. The variations in the yield and flow stress/temperature in Ni₃Al have been widely studied at quasi-static strain rates, ε dot < 1 s^-1. In this study polycrystalline Ni₃Al with 0.095 at.% boron was deformed over a wide range of strain rates (0.001-8000 s^-1) and temperatures (77-1273 K). Dynamic strain rate tests were conducted over the entire temperature range using a split Hopkinson bar. At 300 K the yield stress remains constant with increasing strain rate. The anomalous yield behavior is observed at ε dot = 3000 s^-1. The yield stress was found to be strain rate sensitive at temperatures >823 K. In all cases the work hardening exhibited a rate sensitivity, increasing with increasing strain rate and decreasing with increasing temperature. In Ni₃Al deformed at all rates and at temperatures below 473 K the microstructure observed with TEM was mostly {111} <110> dislocations with coarse planar slip bands forming at the highest strain rates. As the temperature increased more {100} <110> dislocations were observed but the overall density of the dislocations decreased.