Effect of microstructural instability on the tensile properties of Inconel 617 alloy at advanced ultra-supercritical temperatures

The present investigation highlights the tensile deformation behavior of the Inconel 617 alloy in the temperature range of 650–800 °C, considering the operational temperature range of advanced ultra-supercritical boiler tubes. The results of tension tests conducted at 27, 650, 700, 750 and 800 °C at a constant strain rate of 10 –3 /s have revealed anomalous increase in yield strength of the alloy with increasing test temperature from 650 to 750 °C as well as type C and type B serrations within the uniform strain region of the stress–strain curves obtained at 700 and 750 °C, respectively, owing to dynamic strain aging. Transmission electron microscopy of the tension-tested samples has revealed significant evolution of the γ′ precipitate along with (Cr,Mo) 23 C 6 after tension test at 750 °C and the presence of only (Cr,Mo) 23 C 6 after tension test at 800 °C. The increase in the volume fraction of γ′ precipitate with the increase in tension test temperature from 700 to 750 °C has been found to be responsible for the anomalous increase in yield strength. The difference between the volume fractions of γ′ precipitate in the samples after tension tests at 700 and 750 °C has been considered to cause the difference in the type of serrations. Contrarily, the absence of γ′ precipitate in the microstructure during tensile deformation at 800 °C has caused a significant decrease in the yield strength of the alloy.