Serrated tensile flow in inconel X750 sheets: Effect of heat treatment

The tensile behavior of gamma prime precipitation hardened nickel-chromium superalloy X-750 sheets was investigated in the as received (i.e. non-heat treated NHT) and heat treated (HT) states. The evolution of mechanical properties were studied as a function of strain rate (10−3, 10−4, and 10−5 s−1) and temperature (23-900 °C). The Portevin Le Chatelier (PLC) effect was observed in both HT and NHT X-750, with the occurrence of saw-tooth type serrations accompanying hardening until rupture at intermediate temperatures. Above 800-900 °C, the stress-strain curves showed a softening effect, with the occurrence of sinusoidal serrations indicative of Dynamic Recristallization. The temperature ranges of the PLC effect were determined for both NHT and HT X750 highlighting the effect of heat treatment. The strain rate was observed to shift the PLC temperature regime for both NHT and HT X-750. Type A, B, and C PLC serrations were observed for both HT and NHT, and serration amplitude increased with temperature and decreasing strain rate. The NHT X-750 was found to exhibit more instances of normal PLC effect whereas the HT material exhibited more cases of inverse PLC behavior. The normal PLC regime activation energies were calculated for both NHT and HT cases respectively, and the results suggest carbon as the responsible solute for serrations in this range.