Phase transformations and strengthening during ageing of CuNi10Al3 alloy

Microstructure and mechanical properties of precipitation hardened Cu–10.5 wt.% Ni–3.15 wt.% Al (CuNi10Al3) after thermal and thermomechanical treatments were investigated. The highest strengthening in this alloy (yield strength larger than 1GPa) has been obtained after thermomechanical treatment (supersaturation, 50% cold reduction, ageing at 773 K). Some alternative procedures to obtain high strength are also proposed. The microstructure shows discontinuous precipitates at grain boundaries. Transmission electron microscopy and X-ray diffraction helped to establish that the main strengthening phase in this alloy is γ′ (Ni3Al with ordered L12 structure) which precipitates discontinuously and continuously. The β phase (NiAl-B2 structure) also forms during each of the described treatments.