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

Abstract

The concurrent existence of three kinds of nano-scaled precipitates, ordered face-centered cubic β-Ni3Si, orthorhombic δ-Ni2Si and ordered face-centered cubic (Ni, Cr, Si)-rich phase, was found in a Cu–Ni–Si–Cr alloy during aging at 500°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 β-Ni3Si precipitates changed from spheroid to ellipsoid with prolonged aging time. The δ-Ni2Si precipitates had its six variants lying on the {011}Cu habit planes and maintained disc-like during the whole aging process. The orientation relationships with copper matrix were as follows: (001)Cu//(001)δ, [110]Cu//[010]δ for δ-Ni2Si, and cube-on-cube ones for β-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°C.