CALPHAD-aided designing complex brass alloys and revealing the evolution mechanism of δ-Ni2Si reinforcing phase

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2025-02, Vol.923, p.147759, Article 147759
• Main Authors: Shan, Xingrun, Peng, Bo, Li, Guoliang, Dong, Bowen, Wang, Xianlong, Liu, Shichao, Jie, Jinchuan, Li, Tingju
• Format: Article
• Language: English
• Subjects: Calculation of phase diagrams (CALPHAD); Microstructure evolution; Ni2Si phase; Solidification; α-Cu
• ISSN: 0921-5093
• DOI: 10.1016/j.msea.2024.147759

Nickle silicides are usually introduced in Cu alloys as hard reinforcing phase to give materials excellent comprehensive properties. In this study, Cu-20Zn-7xNi-2xSi alloys with the specific fraction of δ-Ni2Si reinforcement and adjustable performance were designed with guidance of phase diagram calculation. The non-isothermal eutectic reaction is ascertained according to the two freedoms of temperature and composition derived from the Gibbs phase rule. The increasing contents of Ni and Si widen the solidification interval of δ-Ni2Si, while that of the α-Cu is almost invariable. The large formation temperature interval leads to the solidification of δ-Ni2Si being divided into four stages: the primary phase about 100 μm formed in the liquid phase, the divorced eutectic phase due to the non-equilibrium solidification, the eutectic phase formed by partial solute enrichment, and the nanoscale phase that precipitates from the α-Cu matrix. Furthermore, the increasing volume fraction of δ-Ni2Si phase results in a significant enhancement in the strength and hardness of the alloys accompanied by a reasonable sacrifice (24 %) of plasticity. Combined with EBSD analysis, it is found that the superior mechanical properties are primarily attributed to the secondary phase strengthening established by the synergistic action of δ-Ni2Si particles and phase boundaries (PBs). However, the excessive size of δ-Ni2Si induces strain localization and results in premature fracture caused by local stress concentration at PBs. This study provides a novel insight for the composition design of complex brass alloys with adjustable mechanical performance by controlling the fraction of reinforcement phase.