Microstructural Characterization and Mechanical Behaviour of Steel Surface Modified with In Situ Grown Tantalum Carbide Through TIG Arcing

Surface properties of bearing steel and other small automotive parts are generally modified in an effort to enhance its hardness and wear characteristics. In the current study, tantalum and graphite powders are added to surface of steel during tungsten inert gas (TIG) arcing to create in situ tantalum carbide to improve reinforcement to the modified surface in addition to the hard martensite matrix. Numerical simulation using COMSOL software was performed to estimate the thermal profile and validated by the experimental observation. The microstructural characteristics of the matrix were examined using optical, scanning and transmission electron microscope (OM, SEM and TEM). High resolution transmission electron microscope (HRTEM) along with electron energy loss spectrum (EELS) mode was employed to understand the type of carbide particles formed. It was found that the top modified surface contains TaC particles which enhances the hardness. The extent upto which different zones like fusion and heat affected zone, base metal, etc formed after the arcing was established both by microscopic examination and micro-hardness mapping. Modified surfaces show a notable increase in hardness from 100 to 150 percent relative to the base material. The weight loss during wear testing for different modified surfaces was significantly reduced by two to four times when compared to the substrate, indicating the presence of an effective wear resistance mechanism in the modified surfaces.