Effect of heat treatment process parameters on the microstructure and properties of GH4720Li superalloy

Abstract The solution temperature and aging temperature of GH4720Li superalloy are the critical factors in determining its microstructure stability and mechanical properties. However, the matching of solution temperature, primary aging temperature, and second aging temperature greatly influences the final microstructure and mechanical properties, and the mechanism was rarely studied. In this paper, the effects of solution temperature, aging temperature, and other process parameters on the grain size, precipitated phase, and mechanical properties of GH4720Li superalloy were systematically studied by orthogonal experiment, and a set of optimal heat treatment process parameters were found. The results show that the sample was solution treated in the temperature range of 1060 °C ∼ 1120 °C. When the solution temperature was 1160 °C ∼ 1100 °C, although the primary γ ′ phase gradually dissolved, the secondary γ ′ phase gradually increased, and the primary γ ′ phase was pinned at the grain boundary to hinder the grain growth, and the hardness of the alloy gradually increases. When the solution temperature exceeded 1100 °C, the primary γ ′ phase dissolved in large quantities, the grains grew up rapidly, and the hardness of the alloy decreased. The sample was subjected to two-stage aging treatment in the temperature range of 650 °C ∼ 770 °C and 760 °C ∼ 880 °C. As the aging temperature increased, the primary γ ′ phase of the sample gradually grew, and the ability to pin the grain boundary weakened. The volume fraction of the secondary γ ′ phase of the sample gradually decreased and coarsened, resulting in grain growth and a gradual decrease in the hardness of the sample. When the samples were treated by 1100 °C/OC × 4 h + 650°C /AC × 8 h + 760 °C/AC × 8 h, the grain size of the sample was the smallest, the average grain size was 4.5 μm, the distribution of γ ′ phase was the most uniform, and the mechanical properties are the best, reaching 47 HRC.