The influence of HVAF powder feedstock characteristics on the sliding wear behaviour of WC–NiCr coatings

In this paper, the HVAF technique was used to deposit coatings with mechanically milled nano and micron blended WC–NiCr powders. The mechanically milled nano powder was produced using the high-energy ball milling process. Due to low particle heating and high particle velocity in the HVAF process, the fine and dense microstructure of the mechanically milled powder remains almost unchanged after spraying. The sliding wear resistance of the two coatings was evaluated by ball-on-disc tests. It was found that the sliding wear resistance of the coating produced using mechanically milled powders was greatly improved compared with the coating produced using micron blended powder. The sliding wear resistance of the coating produced using mechanically milled powder was about two hundred times than that of the coating produced using blended powder. The coefficient of friction for the coating produced using mechanically milled powder increased steadily from 0.22 to 0.51, while for the coating produced using blended powder it attained a steady value of 0.58. Both the coating produced using mechanically milled powder and blended powder were characterized in terms of their microstructure by X-ray diffraction, and scanning electron microscopy in the as-sprayed state as well as after sliding wear. The sliding wear mechanism was also discussed.