Preparation Of The Electroless Ni-B Coating On Titanium Alloy And Study On Its Tribological Behavior

With the excellent physical/chemical properties,such as high strength-to-weight ratio and good corrosion resistance,etc.,titanium alloys have widely applications and play an important role in fields of biomedicine,aerospace and equipment manufacturing.But the actual application range of titanium alloy is still limited by its tribological properties.In order to improve the surface properties of titanium alloys,a variety of surface treatment technologies have been proposed.Among them,electroless plating has become one of the preferred solutions due to its good coating uniformity and deep plating ability.In this study,we propose two activation methods: hydrogenating treatment and double zincating deposition.Through the scratch test,the binding force between the electroless Ni-B coating and the titanium alloy substrate was evaluated.The stable preparation of electroless Ni-B coating on titanium alloy was realized by optimizing activation process.Then,the coated samples were heat-treated in air and nitrogen atmospheres.Subsequently,the tribological behaviors of the titanium alloy and the electroless Ni-B coatings were studied by a multi-function tribometer.The findings suggest: 1.As the electroless Ni-B coating increase the surface hardness of the titanium alloy substrate,the coating significantly enhances the tribological properties of the titanium alloy and reduces the wear volume by about 96.4 %.2.Due to the crystallization of the electroless plating coating after heat treatment,the precipitation of hard nickel-boron phase,and the accumulated thermal stress aggravate of brittleness of the coating.This makes it easier for micro-cracks to initiate during wear and extend along the grain boundary,causing the coating material to lift or peel off.Moreover,the more severe oxidative wear of the heat-treated coating than the as-plated coating leads to the formation of more oxides such as nickel oxide,which intensifies the wear volume of the heat-treated coating.Therefore,the wear resistance of the electroless Ni-B coating after heat treatment is lower than that before heat treatment.In addition,we also heated the coated samples in different atmospheres.The study found that the heat-treated coatings in the two atmospheres have no obvious difference in wear form,oxidative wear,etc.,so there is no significant difference in the wear volume under the same wear conditions.The slight difference in the wear volume of the two heat-treated coatings may be mainly related to the difference in hardness.