Determination of residual stress on TIG-treated surface via nanoindentation technique in Co-Cr-Mo-C alloy

The present study was undertaken to determine the amount of residual stress on the surface subjected to Tungsten Inert Gas (TIG) welding process in different protective gas environments (Ar-xN(2), x = 20, 30 and 40 volume percent). It was shown that the increase of volume fraction of N-2 gas in the welding environment led to more residual stress mainly due to the higher heat input. Nanoindentation technique was employed to obtain the variations of residual stress when Ar-40N(2) protective gas was in use. Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) method were used for microstructural study and phase identification. It was shown that applying higher heat input followed by quenching induced fully martensitic structure with very little amount of retained austenite. In addition, the magnitude of the residual stress in the TIG-treated area was measured to be approximate to 381 MPa using nanoindentation technique which was higher than the base metal. The type of residual stress was compressive which could be helpful for enhancing the surface properties and wear resistance of the alloy as a hip implant.