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, epsilon < 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 epsilon = 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.