Influence of ageing on high temperature tensile deformation of a Ni-based superalloy, HAYNES 282

The effect of ageing time and temperature on the deformation mechanism and corresponding tensile properties are investigated in a γ/γ′ Ni-based superalloy, HAYNES 282. Through a systematic variation in duration (24 h and 216 h) and temperature of ageing (650 °C and 760 °C), a significant variation in strengthening microstructural features was achieved in the resulting microstructures. While in one case (650 °C, 24 h ageing condition), a microstructure with no γ′ was observed, for the rest of the cases, γ′ precipitates of varied sizes were observed. In one specific case (760 °C, 216 h ageing condition), very fine (4–6 nm) MC carbides were observed along with γ′ precipitates; in which these tiny MC carbides became the deciding factor for strength over γ′ precipitates. While common knowledge of smaller γ′ precipitates giving higher strength could explain the higher strength at 760 °C, 24 h ageing condition as compared to 650 °C, 216 h ageing condition, the further increase in strength in case of 760 °C, 216 h ageing condition, even with much larger γ′ precipitates was something quite interesting and counterintuitive. This paper elucidates this puzzling observation. The variation of tensile properties of these wide varieties of microstructures will be described in this paper in light of the underlying deformation mechanisms. A change in deformation mechanism from planar slip (microstructure with no γ′) to twinning (microstructure with γ′) and Orowan-looping (microstructure with γ′ along with fine nano carbides) as a function of microstructure explains the difference in strength, ductility, and strain hardening phenomena among the varied ageing conditions. • High temperature tensile deformation was studied as a function of ageing condition. • Deformation micro-mechanism explained the variation in tensile response. • Deformation is primarily through mechanical twinning along with slip. • Dominant role of fine nano carbides, present in a particular ageing condition. • Microstructure with no γ′ precipitate primarily deformed by planar slip.