The rapid microstructural evolution of gas atomised Ni superalloy powder compacts was studied using a Gleeble 3500 thermomechanical simulator, finite element based numerical model and electron microscopies. The study found that the microstructural changes are governed by the characteristic temperatures of the alloy. At a temperature below the gamma prime solvus, the powders maintained the dendritic structures. Above the gamma prime solvus temperature but in the solid-state, grain spheroidisation and coarsening were rapid although the fine-scale microstructure was largely retained. Once the incipient melting temperature of the powder was exceeded, microstructural change was rapid, and at higher temperatures still, into the solid+liquid state, the powder compact partially melted and then re-solidified with no trace of the original structure, despite the fast timescales. The study reveals the relationship between short, severe thermal excursions and microstructural evolution in powder processed components, and gives guidance on the upper limit of temperature and time for powder-based processes if desirable fine-scale features of powders are to be preserved
