Effect of Alloy Composition on Precipitation Behavior in Cu-Ni-Si Alloys

Abstract

An influence of the alloy content of nickel and silicon on the precipitation kinetics and precipitation hardening mechanism in Cu-Ni-Si alloys has been studied.The degree and the rate of precipitation and the hardness change in the precipitation process increase with increasing an alloying elements. The degree and the rate of precipitation and the hardness changes show a maximum value in the condition that the atomic content of nickel is twice that of silicon.During isothermal aging two kinds of precipitates, Ni2Si and Ni3Si, were observed. Ni2Si presipitates are plate-like in shape and have an orthorhombic type crystal structure. The orientation relationship between Ni2Si and matrix is, (110)Cu\varparallel(001)Ni2Si, [001]Cu\varparallel[010]Ni2Si. The Ni3Si precipitates are spherical and have a L12-type crystal structure coherent with the matrix.From analysis of the hardening mechanism, it suggested that hardenability in the Cu-Ni-Si alloys during precipitation is mostly contributed to misfit-strain hardening of Ni2Si.