Development and characterization of hard coating layer on CP-Ti using Fe-C-Si powder mixture

Abstract

The growing demand for increasing the wear resistance and hardness of metallic materials has inspired the development of several processes for protective coatings. Tungsten inert gas (TIG) surface modification is one of the most promising processes for this purpose. It enables the formation of a uniform coating by melting the preplaced powder to form the desired composition on the substrate material. In this study, Fe, C and Si (Fe-C-Si) ternary powders were synthesized by preplacement of 1 mg/mm2 on commercial purity titanium (CP-Ti) substrate using conventional TIG torch arc heat source to form an hard intermetallic compounds. Three different preplaced powder mixtures (PPM) with nominal compositions of 97Fe2C1Si (PPM1), 94Fe4C2Si (PPM2) and 91Fe6C3Si (PPM3) were separately melted on CP-Ti substrate at energy inputs from 945 J/mm to 1350 J/mm in an argon gas environment. The characterization of surface modified CP-Ti was performed using SEM, EDX and XRD analyzer whereas hardness property was measured using MVK-H2 microhardness tester. The tribological behaviour of the surface modified CP-Ti was performed using CSM ball on plate tribometer at room temperature under dry sliding conditions. Results showed that addition of 1 mg/mm2 of Fe-C-Si powder melting at different energy inputs created a hemispherical melt pool layer with a good metallurgical bonding with the substrate. In general, resolidified melt layers produced different variety of dendrite microstructure whereby the dendrites concentration is more near the surface area compared to the deeper melt depth. The modified surface with PPM2 exhibited maximum hardness of ~ 800 HV 0.5 kgf compared to PPM1 with the hardness value of ~ 530 HV0.5 kgf followed by hardness value of 470 HV 0.5 kgf for PPM3. The hardness developed on the modified surface was found to be strongly dependent on the population of TiC dendrites that segregate at the top of the melt pool layer. The surface modified with different PPM composition showed a significant improvement in the wear resistance. The surface modified with PPM2 is more effective with lowest wear rate of 1.2×〖10〗^(-4 ) mm^3/Nm compared to CP-Ti which showed highest wear rate of 5.9×〖10〗^(-4) mm^3/Nm. The surface profilometry study showed that CP-Ti processed with PPM2 depicted the lowest wear crater depth of 4.4 μm compared to 65 μm depth for the CP-Ti substrate. Incorporation of Fe-C-Si powder mixture showed a distinctly different friction characteristic under sliding against alumina ball at room temperature, which exhibited a decrease in friction coefficient as compared to untreated CP-Ti substrate. Therefore, TIG melting process can be employed for surface modification of CP-Ti along with other materials in order to improve the hardness and wear resistance properties.