Abstract
Different microstructure features were obtained under various heat treatment conditions, which provided insight into the factors controlling the critical strength in a polycrystalline Ni-Co-base disk superalloy (TMW-4M3 alloy) with two-phase structure. The contribution of each microstructure feature, namely, the grain size, annealing twin boundary, and distribution of γ' precipitates, to the total strength was analyzed quantitatively by measuring the Vickers hardness over a range of nano- to micro-size. The grain boundary strengthening decreased with increasing solution heat treatment temperature, while the secondary and tertiary γ' precipitation hardening increased. Therefore, there is an optimum combination of microstructure features for achieving the highest tensile strength in such superalloys.
