Cold spraying is a promising process for fabricating functional coatings. Because of the solid-state particle deposition, the electrical and chemical properties of the coatings are similar to those of the bulk materials. Mechanical properties, on the other hand, differ from those of bulk materials due to severe plastic deformation of the particles. Residual stress may thus be an important variable to track during cold spraying although the formation mechanism is not entirely clear. In this study, the residual stress of metallic (copper) and ceramic (titania) coatings is measured during the cold spray process. The results are presented and discussed.

Aluminum nitride (AlN) ceramics is characterized with its high thermal conductivity and chemical stability. However, it was impossible to fabricate AlN coatings by conventional thermal spray processes directly from AlN feedstock powder due to thermal decomposition of AlN during spraying. In the last decade we were apple to fabricate the AlN coatings through the reactive plasma spraying process (RPS) in the atmospheric ambient. This study describes the way to fabricate high thermal conductivity plasma sprayed AlN coatings. The thermal conductivity of the AlN coatings was investigated by laser flash method. The as sprayed coating had very low thermal conductivity (2.43 W/m.K), compared to the AlN value. It is attributed to presences of high oxide content (Al 5 O 6 N, γ-Al 2 O 3 and α-Al 2 O 3 phases), low density (2.32 g/cm 3 ) and high porosity in the plasma sprayed coating (about 22%). Besides that, although the N 2 gas flow improved the nitride content, the thermal conductivity decreased gradually. It is related to the further increase of the coating porosity and decreasing its density with the N 2 gas. The influence of the process parameters on the thermal conductivity was investigated and to fabricate high thermal conductivity AlN coating adjusting the oxide content, the coating porosity and microstructure are the main factors. Very high thermal conductivity (about 95 W/m.K) atmospheric plasma sprayed AlN coating was fabricated. The coating consists of mainly AlN phase (more than 95% AlN), very small amount of oxide phases, low porosity (about 3%) with a sintered microstructure (nicked-shape sintered particles).

Cold spraying is a promising candidate for the metallization of carbon fiber reinforced polymer (CFRP) composites, but it requires the use of a protective interlayer deposited by either flame or plasma spray. This study evaluates the effect of different surface treatments on interlayer adhesion strength. CFRP samples were treated mechanically, chemically, and thermally and then a copper layer was deposited by atmospheric plasma spraying. Adhesion strength was measured by pullout testing and the results are compared with surface roughness measurements, SEM fracture surface images, FIB bisections of single Cu splats, and XPS analysis of the chemical affinity between the polymer and copper.