PRECIPITATION IN A Cu-20%Ni-8%Sn ALLOY AND THE PHASE DIAGRAM OF THE Cu-Ni RICH Cu-Ni-Sn SYSTEM.

Abstract

The precipitation sequence k and equilibrium phase diagram at 823 K were investigated by optical and electron microscopic observations, X-ray analysis, and hardness measurements. The equilibrium precipitate phase was delta phase ( beta -Cu//3Ti type). The precipitation sequence is: (1) alpha -supersatulated solid solution, (2) formation of the modulated structure and (3) growth of equilibrium alpha and delta phases. The ordered phases at 723 K and 673 K were DO//2//2 and L1//2 type, respectively. The phase boundaries among ( alpha plus gamma (DO//3)), ( alpha plus gamma plus delta ), ( alpha plus delta ), ( alpha plus delta plus theta (DO)//1//9)) and ( alpha plus theta ) regions were determined.