Physical and mechanical properties of single crystals of Co-Al-W based alloys with L1₂ single-phase and L1₂fcc two-phase microstructures

Single-crystal elastic constants of Co₃(Al,W) with the cubic L1₂ structure have been experimentally measured by resonance ultrasound spectroscopy at liquid helium temperature. The values of all the three independent single-crystal elastic constants and polycrystalline elastic constants of Co₃(Al,W) experimentally determined are 15-25% larger than those of Ni₃(Al,Ta) but are considerably smaller than those previously reported. Two-phase microstructures with cuboidal L1₂ precipitates being well aligned parallel to <100> and well faceted parallel to (100) are expected to form very easily in Co-base superalloys because of the large value of E₁₁₁|E₁₀₀ and C_ij of Co₃(Al,W). This is indeed confirmed by experiment. Values of yield stress obtained for both [001] and [123] orientations of L1 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. Slip on (111) is observed to occur for both orientations in the whole temperature range investigated.