A mechanistic study for the fracture mode and ductility variation in a powder metallurgy superalloy hot-isostatic-pressed at sub- and super-solvus temperatures

Abstract

The mechanisms responsible for tensile fracture mode and ductility variation in a powder metallurgy superalloy hot-isostatic-pressed (HIPed) at near γ′-solvus temperatures have been studied. The presence of deformed structure, decoration of precipitates along the prior particle boundaries and the duplex grain structure were identified as the microstructural features responsible for the inter-particle dominant fracture and low ductility of the sub-solvus HIPed material. They led to strain localization near the prior particle boundaries and crack initiation along them, which were decorated with precipitates and provided easy propagation paths for cracks. Whilst the increased grain size, increased grain size uniformity as well as unpinning of the prior particles boundaries precipitates, were identified as the factors contributing to the high ductility of the super-solvus HIPed material, which featured a more transgranular dominant fracture. The results presented also provide new insights in improving the processing of this type of materials.