Effects of Al Addition and Annealing on Microstructure and Properties of Ni-Ti Coatings Synthesized on SUS 316L Stainless Steel Substrates Using Mechanical Alloying Method

Ni-Ti coatings with different Al contents were synthesized on SUS 316L stainless steel substrates by the mechanical alloying method. The effects of Al addition and annealing treatment on the microstructures, microhardness, wear and corrosion resistances of the coatings were investigated. The results showed that the as-synthesized coatings possessed composite structures of Ti particles as reinforcements and Ni-Al lamellas as matrix. Their thicknesses increased with the increase in the Al addition from 0 to 15 wt.%. Intermetallic phases were hardly detected in the coatings with Al content below 15 wt.%. The coating with 10 wt.% Al exhibited optimal microstructure, mechanical properties and favorable corrosion resistance. The subsequent annealing treatment promoted both diffusion in the coating and interdiffusion between the coating and the substrate, which was conductive to the alloying of the coating and the enhancement at the interface. The microhardness increased from about 520 HV_0.1 to about 680 HV_0.1 and both the friction coefficients and the wear weight loss decreased about 20% after annealing. The corrosion resistance of the coating decreased after annealing. The corrosion potential decreased slightly, but the corrosion current density was doubled. The as-synthesized Ni-Ti coatings had the potential to protect the substrate from being severely worn or corroded.