Microstructure and phase composition of ZHS32 superalloy after selective laser melting, vacuum heat treatment and hot isostatic pressing

Using transmission electron microscopy (TEM) method, the microstructure and phase composition of nickel based superalloy ZHS32 processed by selective laser melting (SLM) of a powder composition on a monocrystalline substrate and their evolution during heat treatment (HT) and hot isostatic pressing (HIP) by different regimes have been studied. Particular features of the microstructure formed during SLM, the distribution of chemical elements in cells and their boundaries have been explored. It has been established that the material after SLM has a unidirectional heterophase cell structure consisting of the matrix γ- solid solution, nanosized γʹ- phase particles and a fine carbide phase at the cell boundaries. The influence of the HT and HIP temperature on the morphology and sizes of γʹ- phase particles, the distribution of alloying elements between γʹ- and γ- phases, the evolution of chemical composition, the type, size and distribution of carbide precipitates in the volume and boundaries of the cells after SLM have been studied. It has been shown that the alloy contains fine (Ta, Nb)C carbides with sizes up to 150 nm and carbides with sizes up to 1 µm, and (W, Cr) based carbides of the same sizes as well. The HIP process led to a formation of stacking faults on the phase boundaries between the γ- matrix and carbides. HT and HIP of SLM processed alloy ZHS32 has been shown to allow for obtaining a microstructure and phase composition typical for the single crystal alloy.