Thick Cu-hBN Coatings Using Pulsed Gas Dynamic Spray Process: Coating Formation Analysis and Characterization.

Abradable coatings are mostly sprayed using melting-associated thermal spray methods, which come with some drawbacks limiting their usage. While the manufacturing of these coatings using cold spray (CS) can potentially offer considerable advantages, there has been limited successes in depositing such coatings using this techniqe. In this study, the deposition mechanisms of Cu-hBN mixtures used as an abradable material model were studied using the pulsed gas dynamic spray process (PGDS). Coating microstructure analysis using electron channeling contrast imaging method, Raman spectroscopy, microhardness and fracture surface analyses were performed. Three sets of coatings were sprayed with 0, 9.8 and 18.6 vol.% hBN and balanced Cu powder mixtures. Averages of approximately 9 and 16 vol.% hBN phase was retained in the deposited coatings with a fine distribution of hBN at particle boundaries while deposition of these powder mixtures was unsuccessful using CS (using similar spray parameters and slightly lower pressure). It has been found that the higher temperature of particles in the PGDS as well as the "powder packets" structure typical of PGDS is due to the pulsatile nature facilitate coating deposition while an increase in the hBN phase significantly decreases the process DE. Vortex-like structures were observed in the coatings with high hBN phase content and attributed to the nature of the solid lubricant phase and decreased DE. It was shown that the hBN phase was trapped either at the inter-branching space of the dendritic feedstock powder Cu particles (demonstrating the importance of the feedstock powder selection) or at inter-particle boundaries due to the shock-induced acceleration of packets of particles, revealing the role of the process physics in the deposition of this material. [ABSTRACT FROM AUTHOR]