The use of cold gas dynamic spraying to produce tungsten carbide based coatings has increased over the past decade. Powders may be accelerated to high speeds to produce thick, dense coatings, comparable to some coatings produced using high temperature deposition methods. In the absence of high temperatures, during cold spray, severe plastic deformation of the powder particles are required to ensure good adhesion to the substrate.
This is readily achieved when ductile metals such as Ni, Cu, Co and Al are deposited. However WC – which is a hard, brittle material – does not undergo plastic deformation and must therefore be co-deposited with a ductile binder to produce WC-based coatings.
Majority of the published cold spray research undertaken uses high pressure systems, while there is limited research available on the use of low pressure cold spray systems to produce hard coatings. While it has been shown that material properties are generally better when using high pressure systems, there are several advantages or benefits to using low pressure systems. The use of low pressure cold spraying is deemed to be economical and versatile, and has been deemed safe and easy to automate. It may also be employed as a portable system to conduct on-site repairs, similar to the use of portable welding machines. The low temperatures and pressures used also ensure that the system is energy efficient, which in certain parts of the world are critical. In the current paper a summary of the research undertaken in our research group to produce WC-Ni coatings using low pressure cold gas dynamic spraying is given.
This article appeared in the Sept/Oct issue of Metal Powder Report.