Quantitative microstructural characterisation of Ni-base superalloys

The Ni-base superalloy Waspaloy was investigated as candidate material for rotor and disc applications in steam turbines of the next generation. Quantitative metallography has been performed using various microscopic techniques. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) have been applied for a stereological evaluation of the particle size distribution, particle number density and volume fraction of the γ' precipitates. Waspaloy was investigated after heat treatment and after ageing at relevant application temperature of 700 deg. C. In cooling experiments, the influence of the cooling rate on the γ' formation and growth was studied. The existence of γ' nano-stals with a volume fraction <1.5% was observed