Development of W–ZrC composite coating on graphite by a TIG-aided surface cladding process

Abstract

In this study, a W–ZrC composite coating was applied on graphite substrate by a novel TIG-aided cladding process. The obtained overlay was uniform exhibiting no crack and discontinuity. In-situ reaction between WC and ZrO2 powders promoted by the heat of the TIG source resulted in overlay formation. To investigate and compare the effect of TiC and Co addition on composite microstructure and functionality, TiC and Co powders were added to WC powder. The phase formation, microstructure, adhesion, microhardness and toughness of the coating were the targets of the examinations and characterizations. The cross-sectional image of the coatings indicated a desired metallurgical bonding at the clad/substrate interface. The examined microhardness and toughness values of the composite coating with pure WC were 1700 HV and 4.7 MPam, respectively. These values were 2500 HV and 4 MPam for the sample containing TiC and Co additives. Extensive formation of solid solution between carbide materials and liquid phase formation by W and Co in the composite coating containing TiC and Co led to enhancement of the mechanical performance of the latter. Meanwhile, the improved resistance of the graphite against the oxidation and ablation is expected in presence of the composite clad layer in contrast to the bare graphite sample.