Evaluation of nanoscaled precipitates in a Cu-Ni-Si-Cr alloy during aging

The concurrent existence of three kinds of nano-scaled precipitates, ordered face-centered cubic beta-Ni3Si, orthorhombic delta-Ni2Si and ordered face-centered cubic (Ni, Cr, Si)-rich phase, was found in a Cu-Ni-Si-Cr alloy during aging at 500 degrees C by high resolution transmission electron microscopy and scanning transmission electron microscopy. It is the first time to report the precipitation of ordered fcc (Ni, Cr, Si)-rich phase in Cu-Ni-Si system alloys during aging. The morphology of beta-Ni3Si precipitates changed from spheroid to ellipsoid with prolonged aging time. The delta-Ni2Si precipitates had its six variants lying on the {01 1}(Cu) habit planes and maintained disc-like during the whole aging process. The orientation relationships with copper matrix were as follows: (001)(Cu)//(001)(delta), [110](Cu)//[010](delta) for delta-Ni2Si, and cube-on-cube ones for beta-Ni3Si and (Ni, Cr, Si)-rich phase. The precipitation of (Ni, Cr, Si)-rich phase is responsible for high strength at overaging conditions as 500 degrees C (C) 2014 Elsevier B.V. All rights reserved.