Impact of Thermal Exposure on Microstructure and Incipient Melting in DS-CM247LC Superalloy

ABSTRACT The directionally solidified (DS) CM247LC superalloy is widely used in gas turbine applications because of its excellent mechanical properties at elevated temperatures, which are strongly influenced by its microstructure and γ′ precipitate distribution. This study investigates the effects of solution annealing (SA) and low-temperature aging (LTA) on the alloy’s microstructure and performance. A high SA temperature of 1,270°C, exceeding the eutectic temperature, was deliberately selected to induce incipient melting and replicate localized overheating conditions that may occur in industrial components such as turbine blades, nozzle guide vanes, and combustor liners. The microstructural analysis revealed that annealing at this elevated temperature led to localized melting, particularly in regions enriched with refractory elements such as Aluminum (Al), Hafnium (Hf), and Tungsten (W). This incipient melting hindered complete homogenization and disrupted the uniform dissolution of carbides, resulting in reduced γ′ phase formation within the γ matrix during subsequent cooling and LTA. These findings highlight that exceeding the eutectic temperature during heat treatment can adversely affect microstructure refinement and stability, ultimately influencing the microstructural characteristics and hardness response of DS-CM247LC in high-temperature applications.