A novel compact preparation process has been developed to produce a Cu-20Ni-20Mn alloy. This process involves heating-cooling combined mould (HCCM) continuous casting, a solution treatment at 800 °C, rolling at room temperature and a final ageing step at 450 °C. This process eliminates two hot deformation processes, namely, hot forging and hot rolling, greatly improving production efficiency and reducing production costs compared with the traditional preparation process. The alloy fabricated by this process was found to have excellent mechanical properties. Additionally, the formation of precipitated phases during the ageing step is accelerated by this new process. The hardness of the samples reaches 476 HV after ageing for 10 h. Stable, ordered precipitates of Ni3Mn(L12 phase) are observed in the rolled specimen, and the orientation relationship between the copper matrix and ordered Ni3Mn phase (L12 phase) is [200]Cu//[010]Ni3Mn and [011]Cu//[011]Ni3Mn. Precipitation strengthening is the main reason for the increase of strength of the sample during the ageing process. The mechanical properties and ageing precipitation process of the alloy are affected by the rolling process. The precipitation rate of the rolled sample is greatly increased during the ageing process, leading to a larger amount of precipitates.
A Cu-Ni-Si alloy containing (Ni + Si) ≥ 5 wt.%, with the addition of Cr, is fabricated by HCCM continuous casting and two steps of aging treatment. The evolution of the microstructures and precipitations, as well as the effect of Cr atoms, is studied in this paper. An excellent combination of mechanical property (hardness HV 250–270) and electrical conductivity (46–47 %IACS) is obtained by the first step aging at 500 °C for 0.25 h and the second step aging at 450 °C for 1 h. The cold rolling and aging process are directly conducted on the solution treated specimens fabricated by HCCM continuous casting process without hot deformation, since the excellent homogeneity of matrix is obtained by solution treatment with δ-Ni2Si precipitates dissolved. It is found that the formation of discontinuous precipitation is suppressed by the formation of Cr3Si cores of 5–10 nm before the formation δ-Ni2Si. Then, the nucleation and growth of δ-Ni2Si precipitates occurs around the boundaries of these Cr3Si cores, leading to an enhanced nucleation rate. This study provides a promising direction for the design and optimization of Cu-Ni-Si alloys based on the further understanding of the effect of the addition of Cr.
Revealing the recrystallization behavior and mechanism of this new alloy is of great significance to subsequent research. In this study, the Ni-36.6W-15Co ternary medium heavy alloy was solution-treated at 1100–1200 °C for different lengths of time. The grain size change, microstructure and texture evolution as well as twin development during recrystallization annealing were analyzed using SEM, EBSD and TEM techniques. The study found that complete recrystallization occurs at 1150 °C/60 min. In addition, it takes a longer amount of time for complete recrystallization to occur at 1100 °C. The value of the activation energy Q1 of the studied alloys is 701 kJ/mol and the recrystallization process is relatively slow. By comparing the changes of microstructure and texture with superalloys, it is found that the recrystallization mechanism of the studied alloy is different from that of the superalloy. The development of annealing twins has a great influence on the recrystallization behavior and mechanism. The results show that the twin mechanism is considered as the dominant recrystallization mechanism of the studied alloy, although the formation and development of sub-grains appear in the early stage of recrystallization.
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