Effect of Solution Cooling Rate on Microstructure and Hardness of X-750 Superalloy ‎

X-750 Superalloy is a precipitation hardened nickel-chromium alloy that maintains its corrosion and oxidation resistance up to 704 °C. Although with increasing temperatures up to 704 °C most of the effects of hard deposition are eliminated, the heat treatment components have a good strength up to 982 °C. For this reason, it is important to apply heat treatment to stabilize the precipitation phases in the X-750 superalloy. The purpose of this study was to investigate the effect of cooling rate on the microstructure and changes in the morphology and size of the particles size of γ' in the X-750 superalloy as well as the relationship between microstructure and hardness. For this purpose, during two-step heat treatment of solution and aging treatment to obtain optimum γ' particle size, different cooling rates after solution treatment were taken and visual analyzes were performed on the obtained microstructures. The results showed that nucleation of secondary γ' particles occurred after cooling rate after solution but their growth was dependent on the aging temperature. The formation of secondary γ' is also dependent on the cooling environment after dissolution and with increasing cooling rate, the amount of secondary γ' depositional particles decreases. Also, with increasing cooling rate after solution treatment, the average size of initial γ' particles decreased from 126.5 to 30 nm and their percentage increased from 59 to 66.91. The highest hardness belongs to the 2-AC heat treatment cycle, which has the highest amount of γ' particles.