Enhanced strength in Pt–25Au–25Cu–25Ni medium-entropy alloy by a combination of cold working and aging

Abstract

Precious metals and alloys are widely used in the aerospace industry and microelectronic devices due to their excellent chemical stability and electrical properties. However, the expensive price limits their broad use. The multi-principal element approach shows the ability to reduce the cost and retain desirable properties. Therefore, a precious metal medium entropy alloy, Pt–25Au–25Cu–25Ni, was designed and prepared, and the effect of annealing temperature on the microstructure and mechanical and electric properties of Pt–25Au–25Cu–25Ni alloy was studied. The alloy is a face-centered cubic phase after annealing at temperatures above 850 °C. The decomposition along the grain boundaries occurs after annealing at temperatures 400–750 °C. After annealing at low temperatures, the cold-deformed alloy shows a significant age-strengthening effect, whereas the solution-treated alloy does not. The hardness of the solution-treated alloy stabilized around 225 HV. But aging of cold-deformed samples at 400 °C for 1 h showed the maximum ultimate tensile strength and hardness of 1497 MPa and 454 HV, 179 MPa and 56 HV increased compared with the cold-deformed alloy. The TEM results show that the nanosized L12 ordered phase formed during aging at low temperatures, and acts as an aging strengthening phase. And the cold deformation promotes the L12 phase formation during aging. Meanwhile, the electric resistivity of cold-deformed samples after aging at low temperatures decreases in a large stage. The lowest value appeared as 53.36 μΩ cm.