Cold gas dynamic spraying of metal matrix composite coatings with subsequent friction stir processing

The present study forms an initial investigation in to the development of an innovative process to apply wear resistant surface layers to a chosen substrate material. Tungsten carbide – cobalt chromium, chromium carbide – nickel chromium and aluminium oxide coatings were cold spray deposited on to AA5083 grade aluminium and subsequently friction stir processed. In order to improve the deposition efficiency of the cold spray process, coatings were co-deposited with powdered AA5083. Friction stir processing (FSP) has been used in combination with the cold spray deposited coating to produce an engineered surface layer containing evenly dispersed reinforcing particles that reflects the constituent phases of the feedstock powder. Microstructural characterisation was performed on the test specimens making use of micro-hardness testing, light optical and scanning electron microscopy with electron dispersive spectroscopy to establish the elemental composition of the processed layer. The resulting data was contrasted with as-deposited coatings (no FSP) to highlight the variation in microstructure between the two conditions.
The results demonstrate that FSP has improved the dispersal of reinforcing particles within the metal matrix composite layer with the average interparticle spacing decreasing by up to 68%. The micro-hardness of friction stir processed material shows an increase of approximately 540% over the unaltered substrate and 118% increase over the as-deposited MMC layer, in the case of the tungsten carbide reinforced coating.