Effect of Grain Size on the Strength of Ll₂ Intermetallic Compounds

Abstract

Temperature dependence of strength in Ni₃Al and Ni₃Si with various grain sizes, 4 to 275 μm, are investigated through compression tests. The finer the grain size is, the positive temperature dependence of strength appears to be weaker. Thus HALL-PETCH parameter, k_y, for both alloys is evaluated at various test temperatures and is found to decrease above 200 K for Ni₃Si and 600 K for Ni₃Al. The apparent decrease in magnitude of the positive temperature dependence of strength in these alloys is then interpreted as stress relaxation which is found to become pronounced at higher test temperatures for finer grain sizes and for lower strain rates. It is concluded that grain boundary sliding is responsible for the stress relaxation and the activation energy for this thermally activated process is deduced to be 23 kJ/mol.