Microstructure and properties of a novel Cu20Ni 20Mn-xGa alloy with high strength, high elasticity and high plasticity

Abstract

The Cu20Ni20Mn alloy possesses both high strength and excellent elastic modulus, which has the potential to work in some extreme environments. In our study, by adding Ga into the Cu-Ni-Mn alloy, a new kind of Cu20Ni20Mn-xGa (x = 0, 1, 5 wt%) alloys were produced. After undergoing different thermal-mechanical treatments, these alloys were comprehensively investigated particularly for their mechanical properties and microstructures. While at the peak aging condition, the ultimate tensile strength and total elongation of the Cu20Ni20Mn-1Ga alloy are 1476 MPa and 7.9% respectively, both are higher than that of the Ga-free case (1391 MPa and 3.9%). The Ga added in small amount facilitates the nucleation of NiMn nanoprecipitates inside the grain instead of on the grain boundary, which provides enormous precipitation strengthening and greatly enhances the alloy. However, with addition of excessive Ga (e. g. 5 wt%), discontinuous Ni2MnGa precipitates are observed at grain boundaries, which greatly reduce the ductility of the alloy. Based on our research, we believe that adding appropriate amount of Ga is beneficial for the mechanical properties of the Cu-Ni-Mn alloys, which will become a potential strengthening method for Cu alloys in the future.