Influence of Annealing on the Microstructure and Mechanical Properties of Ni-W/Boron Composite Coatings

Ni-W/boron composite coatings are deposited from an ammonia citrate bath with a boron particle suspension. The effect of the boron incorporation into the Ni-W alloy coating and subsequent heat treatment of the deposits on the microstructure and properties of the Ni-W/boron coatings have been investigated. The boron particles can be uniformly dispersed in the Ni-W alloy, which can lead to an enhancement in the wear performance and hardness of the coatings. The XRD results show that a new Ni4W phase can be formed, especially at heat treatment temperatures beyond 400 °C. The grain size of the deposits is smaller than 10 nm with heat treatment temperatures lower than 600 °C and increases with the heat treatment temperature increasing. The higher temperature will significantly cause the grain coarsening (25.8 nm at 700 °C). Furthermore, the hardness and wear resistance increase with the formation of the Ni4W phase and the inverse Hall–Petch relationship at the lower heat treatment temperatures (<600 °C). While the grain coarsening causes the hardness of the deposits to decrease at the temperature of 700 °C.