Cold-Sprayed WC-Ni-Cu MMC Coatings with Improved Hardness

Cold-gas dynamic spraying (“cold spraying”) at low pressure (150 psig) was used to fabricate WC-Ni-Cu metal matrix composite (MMC) coatings. Tungsten carbide (WC)-based powder was mechanically blended with nickel (Ni) and copper (Cu) powder at various compositions. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Vickers micro-hardness testing were conducted on the cold-sprayed coatings. Image analysis was used to determine the WC content in the coatings. XRD profiles showed that no decarburization or oxidation of the WC reinforcing particles occurred in any of the coatings. The WC content in the coatings increased as the WC content in the powder increased, but did not increase further beyond 96 wt.% WC in the powder blend. The results from Vickers micro-hardness testing confirmed that the coatings with the highest amount of WC had the highest hardness value. The coatings fabricated with a powder composition of 96 wt.% WC + 2 wt.% Ni + 2 wt.% Cu yielded a hardness of 385 ± 73 Hv_0.3/10 (n = 50). These results suggest that it is possible to use cold spraying at low pressure to fabricate WC-based MMC coatings with improved hardness.