Yield strength anomaly and microstructural evolution of solution-treated Ni-Fe-based superalloy deformed by high-temperature tension

In this study, the as-cast Ni-Fe-based superalloy GH4650T (HT650T) subjected to only two steps solution heat treatment shows good mechanical property at high temperature, and the yield strength increases abnormally with the increase of temperature. Correspondingly, the reasons for yield strength anomaly are explored in terms of precipitation behavior of strengthening phases, dislocation movement and evolution trend of grain boundary species. The experimental results indicated that the solution-treated GH4650T alloy can still maintain good mechanical property at high temperature, which is attributed to M 23 C 6 carbides with fine particle morphology distributed along grain boundaries. In addition, the yield strength anomaly observed in solution-treated GH4650T alloy during high-temperature tension is primarily attributed to continuous dynamic recrystallization. Dislocations interact each other through planar slips, forming string-like low angle grain boundaries (LAGBs) network inside the grain, the LAGBs network evolves to form sub-grains, and further plastic deformation prompts LAGBs in the sub-grains to transform into high-angle grain boundaries (HAGBs). The strong obstruction of HAGBs on dislocation movement eventually leads to the pile-ups of high-density dislocations at HAGBs, which eventually results in the increase of yield strength anomaly of GH4650T alloy.