Mechanical and Tribological Properties of Ni-B and Ni-B-W Coatings Prepared by Electroless Plating

Abstract

Ni-B binary coating and Ni-B-W ternary coating were successfully prepared on titanium alloy (TC4) substrates by electroless plating to improve the hardness and wear resistance, followed by annealing treatment for better mechanical properties and tribological properties. The morphology, composition, microstructure, mechanical properties, and tribological behaviors of the coatings were characterized. Both as-plated coatings were amorphous, while the composition and morphology of the Ni-B-W coating differed from those of the Ni-B coating. Additionally, the Ni-B-W coating had better mechanical and tribological properties with a more considerable hardness (13.5 GPa), a minor friction coefficient (0.42), and a lower wear rate (0.10 × 10−7 cm3/(N·m)). After annealing, both coatings were crystalline. In parallel to the as-plated coating, the annealed coatings showed larger hardness values because of the formation of hard phases. Moreover, the crystalline grain of the coatings grew as the annealing temperature rose from 350 °C to 650 °C. Accordingly, the coatings showed a minor hardness value, a major friction coefficient, and severe wear under the same conditions. Above all, the Ni-B-W coating annealed at 350 °C showed the best performance, with an average grain size of 26.3 nm, hardness of 15.9 GPa, friction coefficient of 0.34, and wear rate of 0.09 × 10−7 cm3/(N·m).