7 – Current status and future prospects of warm spray technology☆

A modification of high-velocity oxy-fuel (HVOF) thermal spray process named as warm spray (WS) has been developed. By injecting room-temperature inert gas into the combustion gas jet of HVOF, the temperature of the propellant gas can be controlled in a range approximately from 2300 to 1000 K so that many powder materials can be deposited in thermally softened state at high impact velocity. In this chapter, the characteristics of WS process were analyzed using gas dynamic simulation of the flow field and heating/acceleration of powder particles in comparison with HVOF, cold spray (CS), and high-velocity air-fuel spray. Transmission electron microscopy of WS and CS titanium splats revealed marked differences in the microstructures stemming from the different impact temperatures. Mechanical properties of several metallic coatings formed under different WS and CS conditions were compared. The characteristics of WC-Co coatings made by WS were demonstrated for wear-resistant applications.