Optimization Of Heat Treatment Parameters For Enhanced Mechanical Performance Of The G27 Nickel-based Superalloy

Sammanfattning

G27 is a recently developed, γ’-strengthened Ni-based superalloy designed for high-temperature applications requiring high mechanical properties. This study investigated the influence of heat treatment parameters on its microstructural evolution, precipitation behaviour, and hardness, to optimise processing conditions. A systematic three-step heat treatment was designed, consisting of two solutionising steps followed by an ageing treatment to promote controlled γ’ precipitation. The influence of temperature and holding time at each stage was evaluated through microstructural characterization and hardness measurements. Additionally, a simplified heat-treatment route consisting of direct ageing after a single solutionising step was investigated and compared with the full three-step treatment. The precipitation kinetics were compared with simulations obtained by JMatPro 16 and Thermo-Calc thermodynamic software to provide further insight into the precipitation behaviour during heat treatment. The results demonstrated that enhanced hardness can be achieved through controlled γ’ precipitation. Hardness values of approximately 485 HV0.5 were obtained using both the full three-step heat treatment and the direct-ageing route, indicating that comparable strengthening can be achieved through a simplified processing pathway. In addition, grain size was found to depend strongly on the applied temperature–time conditions, highlighting the sensitivity of microstructural evolution to the thermal history. These findings demonstrate the significant influence of heat-treatment parameters on both precipitation behaviour and microstructural development. Overall, the findings confirm that controlled thermal processing enables tailoring of the microstructure and enhancement of mechanical properties in G27 alloy. The combination of high hardness, controllable grain size, and effective γ′ precipitation highlights the alloy's potential for aerospace applications and provides guidance for the optimization of future processing routes.