A quantitative assessment of the three-dimensional microstructure of a γ-γ′ alloy

We present the first quantitative analysis of the three-dimensional microstructure of a gamma-gamma' alloy that does not make any a priori assumptions about the gamma'-particle morphologies. The gamma'-particle size distribution is derived using the particle volumes to provide a measure of the particle sizes that is independent of particle morphology and is found to be somewhat broader and to have a lower maximum peak height than the theoretical prediction in the absence of elastic stress. Non-equiaxed gamma' particles are found to be approximately equally likely to have rod-like, plate-like or mixed-character morphologies. In contrast with theoretical predictions, smaller particles tend to be more non-equiaxed than larger particles. The latter two findings are a result of the attractive interparticle configurational forces induced by stress at the corners of neighbouring particles. By analysing the distribution of particle side lengths, it is concluded that the average thickness of the sheets of gamma'-particles is between 0.4 and 0.6 mum.