Ultrahigh strength Cu-15Ni-8Sn alloy: Rotary swaging induces twin strengthening and regulates γ (DO3) phase precipitation

How to achieve the ultra-high strength of Cu-15Ni-8Sn alloy through process optimization without microalloying is of great significance and challenging. In this paper, the effects of solid solution + rotary swaging + aging (SRA) on the hardness, strength, and elongation of the alloy are studied by applying rotary swaging with high strain rate and large cumulative deformation before aging. The evolution law of grain orientation arrangement, twin formation characteristics, microstructure in deformation zone, and gamma (DO3) precipitation were observed and analyzed. The results show that the large deformation accumulated by rotary swaging induces a large number of deformation bands, deformation twins, and stacking faults. Deformation bands and twin boundaries provide nucleation sites for the precipitation of primary gamma (DO3) phases. During aging, the stacking faults grow into nanotwins, and the gamma (DO3) phase further dissolves and precipitates in the crystal, avoiding the grain-boundary nucleation. The tensile strength and yield strength of the SRA-treated Cu-15Ni-8Sn alloy reached 1411 MPa and 1405 MPa, respectively, and the elongation was 4 %. Compared with the conventional solution + aging process (SA), the yield strength of the alloy treated by SRA is increased by 91 % under the premise of the same elongation. The yield strength increment contributed by dislocation strengthening and layered gamma (DO3) phase precipitation strengthening accounts for 92 % of the strengthening effect of Cu-15Ni-8Sn alloy prepared by SRA process. Based on the research results of this paper, it can provide support for improving the comprehensive performance of Cu-15Ni-8Sn alloy in harsh service scenarios.