Influence of cobalt content and HVOF deposition process on the cavitation erosion resistance of WC-Co coatings

Cavitation is a wear process that occurs in aqueous environments in which water vapor bubbles on the metal surface of a component implode, leading to erosion. The phenomenon can cause significant damage to structural metal alloys, and many components are therefore covered with coatings to protect against this damage. Thermal spray coatings have long been used for this purpose. With the advent of the HVOF (high velocity oxy-fuel) spray process it became possible to produce denser, harder, tougher coatings, which can be used in applications where fracture toughness is more important. Among the materials most frequently used, tungsten carbide-cobalt (WC-Co) cermet coatings offer a combination of high hardness, toughness and adherence and consequent wear resistance. In this work, two WC cermets with different Co (binder) contents were used to investigate the influence of Co content on the fracture toughness and cavitation resistance of WC coatings deposited by the HVOF process using different fuels. The influence of the HVOF process (specifically the type of fuel used) on the residual stresses in these coatings and their microstructure and properties was also studied. An increase in Co content led to an increase in the fracture toughness and cavitation resistance of the coatings. The primary wear mechanism appears to involve carbide particles becoming detached from the Co matrix. The greater compressive residual stress when liquid fuel was used in the HVOF process resulted in improved properties, including fracture toughness, and a concomitant improvement in cavitation resistance.