Mechanical behavior and dynamic strain ageing in Haynes®282 superalloy subjected to accelerated ageing

Abstract

The microstructure, hardness, impact toughness, and tensile properties of Haynes®282 alloy subjected to accelerated ageing at three temperature and time combinations were studied. Microstructural examination revealed that ageing promotes grain growth, the precipitation and coarsening of various phases and carbides in the matrix and at grain boundaries. While the ageing temperature and time has a minimal effect on the hardness and strength, it significantly deteriorates the ductility and impact strength of the alloy. Elevated temperature tensile behavior reveals that this alloy shows serrated flow due to dynamic strain ageing, and the type of serrations depends on the ageing treatment. In the as-received condition, serrations change from type A to a mixture of type A and type B, and further to type C with increase in strain. Alternately, only type C serrations are present on the flow curves of all the aged alloys. Dislocation interactions with interstitial solutes and substitutional solutes are responsible for the type A and mixture of type A and type B serrations, and type C serrations, respectively. Prolonged ageing also changes the deformation mode from planar slip to wavy slip on the account of γ’ coarsening. Fractographic examination of tensile tested and impact tested specimens indicated that the fracture mechanism transitions from ductile fracture with dimple features to brittle inter-granular features with an increase in the ageing duration. It was inferred that continuous inter-connected carbide network formed during ageing was responsible for reduction in ductility and impact strength.