Tribo-Corrosion behavior of TiC coated AISI 4340 steel in Jatropha Curcas biodiesel

Abstract

There is an increasing demand for hard coatings which possesses a combination of different functional properties such as high wear and corrosion resistance. In this work Fe-TiC composite coating was synthesized by preplacement of 1 mg/mm2 of TiC particulate and melting it using a conventional TIG torch arc heat source. Four melt tracks were glazed on the surface of the AISI 4340 steel at energy input varied between 1176 J/mm to 1680 J/mm in argon gas environment. A hemispherical composite layer with a thickness of 1 mm was successfully obtained. The melt tracks at 1176 J/mm have microstructure that consists of semi-melted TiC particulate. While melt tracks processed at higher energy inputs showed formation of TiC dendritic structure. The composite coating processed at 1344 J/mm developed maximum hardness of 1000 Hv. The coating hardness was found to be strongly dependent on the density of TiC dendrites that segregates at the top of the melt pool. The tribological behaviour of surface modified AISI 4340 steel was performed using CSM pin-on-disc tribometer at room temperature under both dry sliding and jatropha curcas biodiesel lubricated conditions. The electrochemical corrosion test of AISI 4340 steel was conducted using a computer controlled Autolab potentiostat under jatropha curcas biodiesel electrolyte. The room temperature tribological properties of the composite coated AISI 4340 steel has a maximum wear volume of 0.165 mm3 while AISI 4340 steel has a maximum wear volume of 3.67 mm3. The composite coated steel exhibited 20 times lower volume loss compared to alloy steel due to complex geometry of the solidified TiC dendrites that strongly bonded to the Fe-based alloy. The micrograph of the worn surfaces of coated steel showed smoother wear scar while low alloy steel substrate underwent sever plastic deformation and abrasive wear. Incorporation of TiC adversely increases the friction coefficient of TiC composite coated steel compared to alloy steel due to the formation of oxide layer. The composite coating exhibits approximately twice lower wear volume of 0.035 mm3 in comparing to alloy steel with wear volume of 0.062 mm3 at 10N load and 400 sliding speed. The composite coated steel showed compatible friction coefficient compared to low alloy steel under lubricated condition with an average coefficient of friction of 0.07 to 0.11. The micrograph of the worn surface showed pitting and corrosive type of wear for steel substrate while the composite coating showed smoother wear scars with mild oxidation products located near to the TiC interface with the matrix. The electrochemical behaviour in presence of jatropha biodiesel based on the polarization curves showed that incorporation of TiC into the steel surface reduced the corrosion current density because of the fair electrical conductivity of TiC to the electric current in biodiesel electrolyte. Conclusively, Fe-TiC composite coating successfully improved the Tribo-corrosion resistance of the AISI 4340 steel in the presence of biodiesel.