Effects of sub-solvus ageing on the tensile and creep properties of a new cast nickel-based superalloy

• Published in: Journal of materials science & technology Vol. 212; pp. 289 - 302
• Main Authors: Zhao, Peng-Fei, Hou, Kun-Lei, Wang, Min, Ou, Mei-Qiong, Yang, Ya-qian, Ma, Ying-Che
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 20.03.2025
• Subjects: Deformation mechanism; Heat treatment; Mechanical property; Nickel-base superalloy; Precipitation strengthening; Nickel-base superalloy; Heat treatment; Precipitation strengthening; Mechanical property; Deformation mechanism
• ISSN: 1005-0302; 1941-1162
• DOI: 10.1016/j.jmst.2024.06.014

•Large-sized γ1' particles obtained from sub-solvus aging heat treatment enhance the plasticity of alloy K4800.•An excessive content of large-sized γ1' phase leads to a shorter creep life for the K4800 alloy.•The mechanical properties of cast alloy K4800 are controlled by sub-solvus aging heat treatment. For nickel-based superalloys with medium volume-fraction γʹ phase (20 %–40 %), dual or multi-stage aging treatments are usually conducted to generate a microstructure containing the multimodal distribution of γʹ for a balance of strength and plasticity. In the present study, the microstructure and high-temperature properties of a novel cast nickel-based superalloy K4800 were investigated after being subjected to three heat treatments (HT) procedures, namely HT1: 1180 °C/4 h + 1090 °C/2 h + 800 °C/16 h, HT2: 1180 °C/4 h + 1060 °C/2 h + 800 °C/16 h and HT3: 1180 °C/4 h + 800 °C/16 h. It was found that the sub-solvus aging treatments at 1090 and 1060 °C precipitated sub-micron-sized (∼300 nm) primary γʹ phase which enhanced the ductility during 800 °C tensile (the total elongation of T1, T2, and T3 samples were 6.75 %, 7.3 %, and 3.25 %, respectively) without evidently impairing the strength. After careful microstructure observation and deformation mechanism analysis, the enhancement of elongation was rationalized that the precipitation of the sub-micron-sized primary γʹ phase decreased the volume-fraction and size of the nanometer-sized γʹ phase which was precipitated at 800 °C, and simultaneously, promoted the dislocation movement by suppressing the non-planar slip. However, an excessive amount of the sub-micron-sized primary γʹ phase led to a faster ripening process of the nanometer-sized γʹ during creep, which decreased the creep life at 800 °C/430 MPa (T1: 125 h, T2: 199 h, and T3: 198 h). Based on this, we monitored the number density of nanometer-sized γʹ phase coexisting with different amounts of large γʹ during creep. An area fraction less than 7 % of the sub-micron-sized γʹ phase was considered to have little detrimental effect on the creep life of K4800 alloy, which corresponded to a sub-solvus temperature range about 1080–1090 °C. [Display omitted]