Microstructure and properties of Ni-Co-Mn-Al magnetic shape memory alloy prepared by direct laser deposition and heat treatment

Ni-Co-Mn-Al magnetic shape memory alloys (MSMAs) has significant application prospects in driving, sensing, and refrigeration, however, its brittleness and difficulty in processing restrict the rapid development of applications. In this paper, the Ni-Co-Mn-Al alloy was prepared by laser direct deposition (DLD) and subsequent heat treatment (HT). The formability, microstructure, and properties of the samples were studied. The results show that the Ni-Co-Mn-Al alloy samples without obvious defects but with good formability were successfully prepared under the optimized DLD parameters. The deposited sample structure was composed of L10 martensite and 24.1 vol% gamma[(Co,Ni)Mn] phase, and its compressive strength was 1785 MPa and the maximum compressive strain was 30.3%. Amounts of gamma phases in the DLD samples hindered the martensitic transformation (MT). However, after HT at 850 C for 16 h, the alloy sample structure was composed of L10 martensite and 3.5 vol% gamma(Mn-rich) phase. The reduction of the gamma phase promoted the MT so that the prepared Ni-Co-Mn-Al alloy be provided with characteristics of reversible MT. Meanwhile, the compressive strength of the sample reached 1295 MPa and the maximum compressive strain was 20.7%. The Ni-Co-Mn-Al alloy with representative phase transformation and good mechanical properties had been obtained.