Microstructure Investigation of WC-Based Coatings Prepared by HVOF onto AZ31 Substrate

In this paper, three commercial cermet powders, WC-Co-Cr, WC-Co and WC-Cr(3)C(2)-Ni, were sprayed by the High Velocity Oxy Fuel (HVOF) method onto magnesium alloy AZ31 substrate. The coatings were investigated in terms of their microstructure, phase analysis and residual stress. The manufactured coatings were analyzed extensively using optical microscopy (OM), X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM). Based on microstructure studies, it was noted that the coatings show satisfactory homogeneity. XRD analysis shows that in WC-Co, WC-Co-Cr and WC-Cr(3)C(2)-Ni coatings, main peaks are related to WC. Weaker peaks such as W(2)C, Co(0.9)W(0.1), Co and W for WC-Co and W(2)C, Cr(3)C(2) and Cr(7)C(3) for WC-Cr(3)C(2)-Ni also occur. In all cermet coatings, linear stress showed compressive nature. In WC-Co and WC-Cr(3)C(2)-Ni, residual stress had a similar value, while in WC-Co-Cr, linear stress was lower. It was also proved that spraying onto magnesium substrate causes shear stress in the WC phase, most likely due to the low elastic modulus of magnesium alloy substrate.