Solidification characteristics and precipitation behavior of the Cu–Cr–Nb alloys

Cu–Cr–Nb alloys have been application to thrust chamber of rocket engines due to its high strength and excellent conductivity. Moreover, the size and distribution of Cr2Nb phase in Cu–Cr–Nb alloys are closely related to these characteristics. To control the fine dispersion distribution of intermetallic compound Cr2Nb, the solidification characteristics and precipitation behavior of as-cast Cu–Cr–Nb alloy at three compositions (Cu–8Cr–4Nb, Cu–4Cr–2Nb, and Cu–2Cr–1Nb) were systematically investigated. Consequently, the as-cast microstructure of Cu–Cr–Nb alloys mainly consists of an α-Cu matrix, primary Cr2Nb intermetallic compounds with the C15 structure, and Cu–Cr eutectic structure. Furthermore, the reduction of Cr and Nb optimizes the precipitation characteristics of the Cu–Cr–Nb alloys, facilitating the morphological transition from rod-like to granular with smaller size. The precipitation of the intermetallic compound Cr2Nb is delayed, while the overall solidification process time is shortened with the decrease of Cr and Nb content. Due to the reduced nucleation and precipitation of Cr2Nb phase, the growth of precipitation is limited. Cr2Nb in Cu–8Cr–4Nb is irregular block up to 200 μm in size, and Cr2Nb in Cu–2Cr–1Nb is significantly reduced in size by 85% at a slow-cooling condition. Such strategy of the content reduction is of great significance to control the diffuse precipitation of Cr2Nb phase, optimizing the mechanical properties.