Utilization of Composite Powders to Apply Ceramic Coatings in Cold Spray

Several thermal spray technologies, such as plasma spray and high velocity oxy-fuel (HVOF) have been utilized in order to apply hydroxyapatite (HA) coatings onto titanium and titanium alloys for biomedical applications. A dilemma arises when using thermal spray techniques to apply ceramics coatings such as HA. These materials require significant processing temperatures in order to provide sufficient particle melting to achieve an appropriate coating thickness. This melting often leads to changes in physical and chemical properties of the HA resulting in unknown variations in the coating's biocompatibility. A process such as Cold Gas Dynamic Spray can be utilized to provide coatings of HA, as melting of the feedstock particles is not required. Cold Spray offers an innovative deposition process for both ceramics and metals. This line of sight, solid-state process utilizes a supersonic gas stream to accelerate particles beyond a critical velocity. These unheated particles, upon impact with a substrate will plastically deform to create a coating. To date, difficulties have arisen to acquire adequate coating thickness when spraying ceramics due to their brittle nature. The goal of the paper is to show the early developments of using cold spray to apply functionally graded coatings with significant thicknesses of composite titanium and HA.