Laser-assisted synthesis of Cu-Al-Ni shape memory alloys: effect of inert gas pressure and Ni content

Abstract

The paper explores applicability of laser-assisted synthesis for producing high density Cu–Al–Ni alloys with shape memory characteristics, that could be further developed towards a method of additive manufacturing of large size Cu-based shape memory alloys (SMA). The manufacturing approach consists in laser melting of elemental powder mixture in a controlled atmosphere of varying relative pressure of protective argon gas, producing alloys of 14.2 wt.% Al and Ni content varying between 2 and 4 wt.%. All the fabricated alloys are found to have attained martensitic microstructures capable of SMA specific phase transformations in the temperature range from 85 to 192 °C. Both gas pressure and content of Ni are found to affect the specific transformation temperatures, transformation enthalpies, and mechanical properties. In particular, increasing gas pressure suppresses the austenite to martensite transformation reducing microhardness, and also has an indirect effect through microstructure, mainly the size of crystalline domains and porosity associated with release of adsorbed gases. In conclusion, the selective laser melting (SLM) employed in this work is shown capable of producing high density Cu–Al–Ni SMA (porosity ~2%).