Internal Diameter Coating Production by Pulsed-Gas Dynamic Spraying

In this work, pure metal and cermet coatings have been produced using the Pulsed-Gas Dynamic Spraying (P-GDS) process on internal diameter geometries using different types of feedstock powders and substrates.
In the P-GDS process, the powder feedstock particles are accelerated to high impact velocities and intermediate temperatures (usually below melting temperature), in a non-reacting gas, thus enabling the production of dense coatings that exhibit the chemical and microstructural composition of the feedstock particles. The particle impact temperature achieved through this process lead to a low required critical velocity for the particles to plastically deform and form a coating. The P-GDS technique uses compression waves (CW) that are produced at a constant frequency and injected into a quiescent inert gas in a spray gun, which contains the powder feedstock material to be sprayed. Due to their nature, the CW coalesce to form shock waves and generate behind their passage in the gun a high-speed intermediate temperature flow. This induced flow accelerates and heats the powder feedstock material towards a substrate where they deform and bond (mechanical and/or metallurgic bonding) upon impact. The cycle is repeated, starting with the powder injection in the gun, when the pressure inside the gun reaches the ambient atmospheric pressure.
The effect of the processing conditions on the coating microstructure and process efficiency is investigated using different analysis techniques (OM, SEM, XRD, and microhardness measurements). A detailed comparison of powders and coatings microstructures, phase compositions, and hardness are presented and discussed in detail.