Surface Modification of Ti-6Al-4V Alloy by Depositing MMC Coating with Variant of Matrix Phases through TIG Cladding Method

Abstract

Ti-6Al-4V alloy has numerous applications in the field of aircraft, chemical, marine, and biomedical industries because of its remarkable properties, like, high strength-to-weight ratio, elevated melting temperature, excellent corrosion resistance, and biocompatibility. Nevertheless, its poor wear resistance, restrains its scope of application, when it is working under a wear and friction environment. Depositing a hard and wear resistance coating through Tungsten Inert Gas (TIG) cladding route was found as a suitable approach to enhance the wear resistance of Ti-6Al-4V alloy. TiC as a reinforcement ceramic, widely used in composite coating, and proficiently improve the hardness and wear resistance of a metallic component, even at elevated temperature. Present research emphasized on the development of TiC reinforced hard and wear resistance composite coatings on Ti-6Al-4V alloy, by using a variety of matrix phases through TIG cladding route. Primarily, TiC-Co coating was fabricated on a Ti-6Al-4V alloy plate using TiC/Co powder blend. Co as a matrix phase with TiC reinforcement enhanced the interfacial bonding and accelerated the anti-oxidation and abrasive wear resistance of the composite coating. The effect of processing current, and stand-off-distance (SOD) during TIG cladding on the quality and performance of the coating was also analyzed. It was revealed that the TiC-Co composite coating developed with higher SOD (6 mm) and lower current (120 A) exhibited higher hardness and wear resistance against different counter rotating discs. Further, to increase the microstructural uniformity of the composite coating nano-Y2O3 was added to the precursor powder, and accordingly TiC-Co-Y2O3 cladding was developed on the Ti-6Al 4V alloy by the TIG cladding method. With the addition of nano-Y2O3, the melting efficiency of the precursor augmented, which completely melted the TiC particles and transformed them into elongated dendrites during solidification. The addition of nano-Y2O3 effectively refined the grain structure of the clad material, and improved the micro-hardness, fracture toughness, and ductility of the coating. Almost, a four times reduction in the wear value was recorded for TiC-Co-2%Y2O3 coating as compared to TiC-Co coating. In the succeeding work, TiC reinforced composite coating with NiCoCrFeTi high entropy alloy (HEA) as matrix phase was developed on Ti-6Al-4V alloy. The microstructural analysis of the coating revealed that, along with dendritic TiC, the presence of HEA matrix, augmented the wear resistance of the coating enormously, and shows almost 7.5 times lower wear value as compared to the uncoated Ti-6Al-4V alloy. Through EBSD, XRD, and thermodynamic analysis, the formation of BCC/FCC phases shows the possibility of solid solution/intermetallic in the coating. Additionally, large area TiC-NiCoCrFeTi HEA composite coating was also fabricated through side-by-side deposition of the consecutive clad tracks. A least discrepancy in the thickness and hardness of the coating was witnessed for using 50% overlapping to produce the large area cladding. The corrosion test performed on the TiC-NiCoCrFeTi HEA coating showed its adequate corrosion resistance in 3.5% NaCl solution.