Tribological Behaviors of Electroless Nickel-Boron Coating on Titanium Alloy Surface

Titanium alloys are excellent structural materials in engineering fields, but their poor tribological properties limit their further applications. Electroless plating is an effective method to enhance the tribological performance of alloys, but it is difficult to efficiently apply to titanium alloys, due to titanium alloy's strong chemical activity. In this work, the electroless Nickel-Boron(Ni-B) coating was successfully deposited on the surface of titanium alloy(Ti-6AL-4V) via a new pre-treatment process. Then, linearly reciprocating sliding wear tests were performed to evaluate the tribological behaviors of titanium alloy and its electroless Ni-B coatings. It was found that the Ni-B coatings can decrease the wear rate of the titanium alloy from 19.89×10-3 mm3 to 0.41×10-3 mm3, which attributes to the much higher hardness of Ni-B coatings. After heat treatment, the hardness of Ni-B coating further increases corresponding to coating crystallization and hard phase formation. However, heat treatment does not improve the tribological performance of Ni-B coating, due to the fact that higher brittleness and more severe oxidative wear exacerbate the damage of heattreated coatings. Furthermore, the Ni-B coatings heat-treated both in air and nitrogen almost present the same tribological performance. The finding of this work on electroless coating would further extend the practical applications of titanium alloys in the engineering fields.