1989 Volume 75 Issue 6 Pages 964-971
Creep-rupture strengths and microstructures of two single crystal superalloys, NASAIR100 and CMSX-3, heat-treated at various conditions were investigated. As aging temperature was raised, γ' particles coarsened and its morphology changed as follows; irregular cube→regullar cube→rounded cube→plate. Optimum creep-rupture strength at 1040°C and 760°C was obtained in the specimens in which the initial γ' morphology was regularly cuboidal. The reason was related to the degree of perfection of "rafted" structure during 1040°C creep and to the change in the deformation mechanism from cutting to by-passing model during 760°C creep. The morphological change of γ' particles is strongly influenced by the lattice mismatch between γ and γ' phases, thus the optimum heat-treatment condition varies with alloys. For an alloy with larger absolute value of lattice mismatch, heat-treatment at lower temperature is desirable and for an alloy with smaller one, heat-treatment at higher temperature is available.