EFFECT OF ALLOY COMPOSITION ON PRECIPITAT ION BEHAVIOR IN CU-NI-SI ALLOYS

An influence of the alloy content of nickel and silicon on the precipi tation kinetics and precipitation hardening mechanism in Cu-Ni-Si allo ys 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 atomi c content of nickel is twice that of silicon. During isothermal aging two kinds of precipitates, Ni2Si and Ni2Si, were observed. Ni2Si presi pitates are plate-like in shape and have an orthorhombic type crystal structure. The orientation relationship between Ni2Si and matrix is, ( 110)Cu//(001)Ni2Si, [001]Cu//[010]Ni2Si. The Ni3Si precipitates are sp herical and have a L1(z)-type crystal structure coherent with the matr ix. From analysis of the hardening mechanism, it suggested that harden ability in the Cu-Ni-Si alloys during precipitation is mostly contribu ted to misfit-strain hardening of Ni2Si.