Detonation spraying of Ti-Cu mixtures in different atmospheres: Carbon, nitrogen and oxygen uptake by the powders

The phase composition and microstructure of coatings formed by detonation spraying of Ti-Cu powder mixtures using C2H2 + kO(2) explosive charges with k varying from 0.7 to 2.0 were studied. The Ti-Cu system was selected to demonstrate the possibilities of forming metal matrix composites (MMCs) with in-situ synthesized ceramic particles during the coating deposition. The formation of composite microstructures needs to be considered when obtaining carbon-containing MMCs by detonation spraying using acetylene-oxygen mixtures at k < 1. The focus of the present study is the phase formation, microstructure development and hardness variation of the coatings caused by carbon, oxygen and nitrogen uptake by the Ti-Cu mixtures during spraying. Carbon released in the form of graphene nanoplatelets as a result of incomplete combustion of acetylene at k = 0.7 reacted with titanium, and, in the presence of nitrogen (a carrier gas), the TiCxNy phase formed in the coatings. Copper was found to play a protective role, reducing the conversion degree of titanium into the ceramic phases. Deposits containing 21 - 44 wt.% of ceramic components formed when an explosive charge equal to 50% of the gun barrel volume was used, the nature and concentration of the ceramic phases depending on k. At k = 2.0 and an explosive charge of 50%, a composite coating reinforced with Ti2O3, TiO and TiN (comprising 41 wt.% in total) was obtained. This composite showed a microhardness of 480 HV, which was due to a high content of ceramic phases synthesized in situ during spraying.