Mechanical property strengthening by post-heat treatments in NiTiCu shape memory alloys fabricated by twin-wire arc additive manufacturing

To address the challenges of wide transformation hysteresis as well as the poor properties of NiTibasedalloys fabricated by twin-wire arc additive manufacturing, post-heat treatments wereemployed in as-deposited NiTiCu alloys. After aging at 450°C, 550°C, and 650°C, the alloysexhibited significant reduction in the precipitate sizes, narrow transformation hysteresis, uniformdistribution of microhardness, and substantial improvement in mechanical properties. With theincrease of the aging temperature, the matrix grain size and the precipitate size coarsened, whichwas detrimental to the resultant mechanical properties. The alloys aged at 450°C exhibited thenarrowest transformation hysteresis of 11.7°C and optimal mechanical properties (tensile strengthof 539 MPa and fracture strain of 6.9%). The enhancement of mechanical properties can beattributed to the smaller matrix grain size and precipitate size and the higher proportion of highanglegrain boundaries in this material condition. This work provides practical significance for thetwin-wire arc additive manufacturing and performance optimisation of NiTi-based ternary alloys.