Effects of process parameters on microstructure and properties of Ni–Ti coatings synthesized by mechanical alloying method

Absrtact: Mechanical alloying method was applied to synthesize Ni–Ti coatings on 316L stainless steel substrates. Effects of milling parameters on microstructures, microhardnesses, wear and corrosion resistances of the coatings were investigated. Formation mechanism of the coating was elucidated. The as-synthesized coatings possessed inner layers with composite lamellar structures and outer alloyed layers. The coating grew in certain milling time and then flaked with further milling, which was closely in relation to the particle ductility and the heat levels accumulated with the particle deformations and the ball frictions. The coating thickness and roughness were improved with the increase of rotational speed. The higher rotational speed promoted the plastic deformation, cold welding and hardening of the particles, which was conductive to the coating deposition in the initial milling process but advanced the peeling process in the shorter milling time. The coating microhardness was improved with its growth, which reached about 2 times of the substrate microhardeness. The wear resistance was improved because of the as-synthesized coatings, which were proportional to their surface microhardnesses. The corrosion resistances of the as-synthesized coatings increased with the suitable increase of milling time and then they decreased with further milling. The increase of the rotational speed favored the improvement of corrosion resistance. In general, the coating prepared at the rotational speed of 350 r/min for 13 h possessed both favorable microstructure and properties, which could protect the substrate from severely worn or corroded effectively.