Temperature Dependence of the Yield Stress of Ni₃Fe Single Crystals

Abstract

Compression tests have been made on well characterized Ni₃Fe single crystals over the temperature range 77 to 830 K in order to obtain systematic yield stress data comparable with well established data on Cu₃Au single crystals. Below room temperature the fully ordered Ni₃Fe has a lower yield stress than the disordered Ni₃Fe, as has been generally observed in various ordered alloys. It is demonstrated that strength peaks in ordered Ni₃Fe appear both at an intermediate temperature below T_c and just below T_c. The strengthening mechanism in the former is compatible with the Brown mechanism, and that in the latter is due to disordering as is the case with Cu₃Au. In contrast, the increase in flow stress with increasing temperature of ordered Cu₃Au at lower temperatures reported in literature is attributable to the thermally activated cross slip from {111} to {100} planes. Based on the phase stability concept, the differences in strength behavior between Ni₃Fe and Cu₃Au can be interpreted in terms of the differeces in APB morphology, i.e., the anisotropy of APB energy.