Verification of the ability of Cu to dissolve in BCC δ in a δ-γ Solid Solution above 1200 °C and boosting δ nano-hardness in Cu-containing PHSS

• Published in: Scripta materialia 2022-04, Vol.211, p.114505, Article 114505
• Main Authors: Gan, Neng-Hao, Sun, Yi-Hsuan, Tsao, Tzu-Ching, Li, Chia-Lin, Liu, Jia-Heng, Yen, Hung-Wei, Hsueh, Chun-Hway, Yang, Jer-Ren, Wang, Shing-Hoa, Yeh, Jien-Wei, Chang, Horng-Yi, Hou, Wen-Hsing
• Format: Article
• Language: English
• Subjects: Dual phases; Nanoindentation; Precipitation; Stainless steels; Transmission electron microscopy (TEM)
• ISSN: 1359-6462; 1872-8456
• DOI: 10.1016/j.scriptamat.2022.114505

Because Cu is an austenite γ stabilizer, it is thought that Cu only dissolves in the FCC γ phase but not in the BCC δ when Cu-containing PHSS are treated in a dual δ-γ solid solution at high temperature. However, the nano precipitation of Cu in the allotriomorphic δ found upon quenching from 1295°C. To study this unexpected phenomenon, thermodynamic calculations were performed. The predicted solubilities of Cu in the γ and δ at 1295°C were 3.52 and 1.99 wt%. Consequently, quenching the solid solution from 1295 to 25°C results in the ultra-supersaturation of Cu in the δ. The vacancy concentration in the δ solution was estimated to change from 1024 vac./m3 at 1295°C to105 vac./m3 at 25°C; quenching yields excess vacancies. Thus, Cu-rich nanoparticles precipitate in the δ matrix through the interdiffusion of the ultra-supersaturated Cu and excess vacancies. [Display omitted]