Aging characteristics and precipitate analysis of Cu–Ni–Mn–P alloy

A copper-rich Cu–Ni–Mn–P alloy was designed to have high strength along with good electrical conductivity. Mechanical properties and electrical conductivities of three different Cu–Ni–Mn–P alloys and of the Cu–0.89%Ni–0.22%P and Cu–1.11%Mn–0.28%P alloys were measured as a function of aging time at 723 K. The aging characteristics of the Cu–Ni–Mn–P alloys showed that the optimum combination of mechanical and electrical properties was obtained at a Ni:Mn:P molar ratio of about 1:1:1. The optimized Cu–Ni–Mn–P alloy showed better mechanical and electrical properties than the Cu–Ni–P and Cu–Mn–P alloys. The structure of precipitates in the optimized alloy was analyzed by transmission electron microscopy. The precipitates of the Cu–Ni–Mn–P alloy were identified to have a composition of MnNiP. The precipitate particle consists of the hexagonal MnNiP phase (C22 type) with the orthorhombic MnNiP platelets (C23 type). The { 1   0   1 ¯   0 } h planes and 〈0 0 0 1〉h directions of the hexagonal phase are parallel to the {0 0 1}o planes and 〈0 1 0〉o directions of the orthogonal platelets, respectively.