Effects of temperature and strain rate on mechanical behavior and microstructure evolution of CuNiSiCr alloy

The mechanical behavior and microstructural evolution of an aged Cu–2.7Ni–1.34Si–0.6Cr (at. %) alloy were investigated across strain rates of 0.001–8000 s⁻¹ and temperatures of 25–500 °C. Under quasi-static loading, the alloy exhibited excellent strength–ductility balance at room temperature and 300 °C, but severe ductility loss occurred at 500 °C, indicating intermediate temperature embrittlement. High strain rates induced little strengthening due to the alloy's low strain-rate sensitivity, as confirmed by the strain-rate jump tests, but improved the ductility at 500 °C by suppressing the grain-boundary damage. Strengthening mechanism calculation agreed with the measured yield strengths, showing that precipitation (Orowan bypassing) and dislocation hardening dominated at all the temperatures. The softening arose mainly from the temperature-dependent shear modulus decrease. Ductilizing analysis revealed that deformation twins were prevalent at room temperature and 300 °C at all strain rates, and at 500 °C at strain rates beyond 1000 s⁻¹. The phenomenon was explained in terms of stacking-fault energy, grain size, and orientation, consistent with the calculated critical twinning stresses. These results promote understanding of the microstructure and mechanical response of copper alloys under extreme service conditions.