Physical and mechanical properties of single crystals of Co-Al-W based alloys with L1_2 single-phase and L1_2/fcc two-phase microstructures

摘要

The values of all the three independent single-crystal elastic constants and polycrystalline elastic constants of CO_3(Al,W) experimentally determined by resonance ultrasound spectroscopy at liquid helium temperature are 15-25% larger than those of Ni_3(Al,Ta) but are considerably smaller than those previously calculated. Because of the large value of E_(111)/E_(100) and c_(ij) of Co_3(Al,W), two-phase microstructures with cuboidal L1_2 precipitates well aligned parallel to <100> and well faceted parallel to {100} are expected to form very easily in Co-base alloys, as confirmed indeed by experiment. Values of yield stress obtained for [001]-oriented Ll_2/fcc two-phase single crystals moderately decrease with the increase in temperature up to 800°C and then decrease rapidly with temperature above 800°C without any anomaly in yield stress.