Study on the microstructure and properties of additively manufactured NiTi coating

By employing the first-principles calculations along with SEM, XRD, 3D laser confocal microscopy, and nanoindentation techniques, the structure and properties of additively manufactured NiTi coatings under different atmospheres were investigated. Using an inert atmosphere spraying system, NiTi alloy wires were used instead of NiTi powder to prepare the coatings, reducing the oxygen content from 6.8 wt% in atmospheric NiTi coatings to 2.3 wt% in inert atmosphere NiTi coatings. The NiTi coatings prepared under an inert atmosphere exhibited significantly fewer cracks, defects, and precipitates, with porosity reduced to 0.85+0.11vol%, resulting in a denser coating structure. Cavitation tests revealed that after 120 minutes of cavitation, the cavitation resistance of NiTi coatings prepared in an inert atmosphere (weight loss: 41.2+4.1 mg) was significantly superior to that of coatings prepared in an atmospheric environment (weight loss: 63.7+4.2 mg). The first-principles calculations indicated that the NiTi3 and Ni3Ti phases formed during the spraying process are more stable than other precipitated phases. The NiTi and Ni3Ti phases exhibit lower anisotropy, while the NiTi3 phase shows significant anisotropy. The minor precipitation of NiTi3 and Ni3Ti phases contributes to enhancing the toughness and hardness of the coatings, thereby improving their cavitation resistance potential. The NiTi and NiTi3 phases exhibit certain metallic properties, which can improve electrical conductivity. The Ni3Ti has weaker metallic properties and electrical conductivity, demonstrating superior corrosion resistance.