Recovery of metal matrix composite drilling tools using a WC-Ni/Cr TIG-hardfacing technology

The recovery of worn and damaged drilling tools in oil and petroleum industries, which no longer meet reliable technological use, could significantly reduce the drilling cost and, therefore, the emission of toxic materials. The present study demonstrates first time an innovative solution for this problem using a WC-Ni/Cr Tungsten Inert Gas (TIG) hardfacing technology by which a damaged WC-based metal matrix composite was coated. The microstructure analysis of the recovered sample revealed remarkable diffusion activity of Cr and Cu elements across composite/hardfacing interface. This inter-diffusion depleted WC particles on both sides which enhanced the metallic bonding of the interface, creating a durable and strong adhesion. A significant amount of WC particles was fragmented and dissolved into the NiCr metallic matrix, which resulted in the formation of Cr23C6, W2C carbides and Ni2W4C secondary carbide. There was found a more than 100 % increase in micro-hardness of the metallic matrix of the recovered sample compared to the as-infiltrated sample. The tribological tests of the as-infiltrated and the TIG hard-faced specimens conducted in dry, water and fuel oil environments revealed that the highest coefficient of friction (0.75) was recorded for the as-infiltrated sample under dry conditions with the highest wear loss (0.8 mg) while the TIG hard-faced coated one exhibited improved wear properties (0.09 and 0.15 mg, respectively). This was attributed to the change of wear mechanism from WC particle pullout to abrasive and oxidative wear through the formation of SiO2 and WO3 oxides films. Thus, the TIG hardfacing process shows new and promising technology to recover WC-based metal matrix composites, improving their lifetime, and at the same time, both their mechanical and tribological properties.