Diamond-reinforced composites prepared by cold spray are emerging materials simultaneously featuring outstanding thermal conductivity and wear resistance. Their mechanical and fatigue properties relevant to perspective engineering applications were investigated using miniature bending specimens. Cold sprayed specimens with two different mass concentrations of diamond 20% and 50% in two metallic matrices (Al – lighter than diamond, Cu – heavier than diamond) were compared with the respective pure metal deposits. These pure metal coatings showed rather limited ductility. The diamond addition slightly improved ductility and fracture toughness of the Cu-based composites, having a small effect also on the fatigue crack growth resistance. In case of the Al composites, the ductility as well as fatigue crack growth resistance and fracture toughness have improved significantly. The static and fatigue failure mechanisms were fractographically analyzed and related to the microstructure of the coatings, observing that particle decohesion is the primary failure mechanism for both static and fatigue fracture.

Diamond-reinforced copper matrix composites (DCMC) have great potential for heat sink applications due to their excellent thermal properties. In this investigation, thick DCMC coatings were fabricated via cold spraying using copper-clad diamond powder or its mixture with copper powder. With pure clad diamond powder, the diamond in the original feedstock was almost completely retained in the coating, which contained more than 40 wt% diamond. With mechanically mixed clad diamond and Cu powder, the diamond fraction in the coating was even larger than that of the original feedstock. It was found that the added Cu powder acts as a buffer, effectively preventing the fracture of diamond in the coating.

This work shows that with computer-controlled detonation spraying, the phase composition of coatings can be changed relative to that of the feedstock powders. New phases can appear in substantial quantities due to chemical reactions of reduction, oxidation, and nitridation as well as interfacial interactions between phases in composite powders. The key advantage of computer control is that it precisely regulates the quantity and stoichiometry of explosive gas mixtures. It has thereby been found that TiO 2 experiences partial reduction to titanium suboxides and that chemical reactions with nitrogen are also possible. It has also been found that when nitrogen is present, titanium aluminides, Ti 3 Al and TiAl, are likely to form nitrides in the sprayed coatings. Interfacial reactions between the phases of a composite have been studied, and in the case of the Ti 3 SiC 2 -Cu system, it has been found that deintercalation of Si can be prevented by maintaining relatively cold spraying conditions. At higher temperatures, coatings of an unusual phase composition form in which carbon-deficient TiCx inclusions are distributed in the Cu matrix as modified by the dissolution of silicon. The formation of new phases affects coating microstructure development and results in new microstructural features.

This study assesses the effectiveness of nickel-coated diamond powder for producing metal-diamond composite coatings by cold spraying. The results of the investigation show that diamond fracturing was mitigated by the protective nickel coating. In general, the softer the metal matrix and the finer the diamond, the less fracturing that occurs and the greater the diamond fraction in the composite layer. It is also shown, however, that deposition efficiency and diamond fraction must be improved especially for diamond sizes of 50 μm and above.

Molybdenum disulfide (MoS 2 ) films are widely used to improve friction performance, but they are difficult to fabricate using conventional thermal spray processes due to thermal decomposition of the feedstock powder. In this study, Cu-MoS 2 composite coatings are fabricated by cold spraying using mechanically milled powders containing different concentrations of MoS 2 . Investigators found that increasing the concentration of MoS 2 in the powder improved some coating properties while degrading others. Through testing it was determined that the ideal concentration of MoS 2 is 5wt%. Increasing the milling time of the powder mixture also provided benefits in terms of hardness and wear resistance.