Effect of TIG surface melting on structure and wear properties of air plasma-sprayed WC–Co coatings

• Quality of re-melted layer improved by homogenizing of microstructure and eliminating of porosities.
• Surface-melted WC–Co coatings increased hardness and wear resistance.
• Substrate material mixed with WC–Co coating composition during surface melting process.
• Re-melting of the sprayed layer resulted in metallurgical bonding to substrate

In this study, mild steel substrates were coated with WC–Co by air plasma-sprayed (APS) method. The coated specimens were then subjected to surface melting by tungsten inert gas (TIG) method. Microstructure, phase changes, microhardness and wear properties of as-sprayed and surface-melted specimens were investigated. Surface melting resulted in formation of thick layers containing tungsten-rich dendrites together with W6Co6C and Fe6Co6C carbides. The hardness of the melted layer reached to the values as high as 1250 Vickers, while the hardness of the sprayed layer was maximum 900 Vickers. As a result, as-sprayed WC–Co-coated specimens showed relatively higher wear rate in comparison with those of surface-melted specimens.