Ti-Al alloy phase layer/Ti-Al carburizing composite coating was prepared on the surface of titanium alloy by the stepwise coating method of hot dip aluminization and then carburizing. The weight gain results of the composite coating showed that the titanium alloy coated with the composite coating had long-term stability (≥16 days) at 800oC. The microstructure, phase structure and composition of the composite coating were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).The composite coating is composed of an alloy phase layer and a carburized layer. The natural transition of four phases (Ti3Al/TiAl/TiAl2/TiAl3) in the alloy phase layer, significantly improves the interfacial bonding between the coating and the substrate, and slows down the propagation of microcracks through the coating.Al2O3, TiC and C in the carburizing layer improve the surface hardness of the coating, and TiAl2 and Al2O3 also have excellent oxidation resistance at high temperature.

Carburizing of stainless steels at low temperatures (below 500°C) develops a high content carbon layer, known for its high hardness. X-ray Diffraction investigation indicates that carburization treatment does not impact the structure of substrate; however, introduced carbon causes expansion in the carburized layer through the increase in d-spacing. Characterization of carbon concentration and hardness profiles indicate that carbon content gradually decreases while moving further into the substrate; and the origin of the increased hardness of the expanded layer arises from the super-saturated carbon content, following the solid solution strengthening theory. An area that is not well understood is in regard to the carburized layer’s relation to the substrate and the significance in their differences. Using two grades of stainless steel, AISI 316L and PH 17-4, it was observed that the carburized layer is not a separate layer, but a higher carbon content version of the substrate,

This paper presents a new method of preparing a coating on the Ti65 titanium alloy by a two-step procedure comprising hot-dipped aluminum and solid carburization. The effects of the carburization in the presence of NaCl deposit at 810oC have been systematically studied. In this article, the microstructure, morphology, phase composition of the coating, and the corrosion products were investigated by SEM, EDS, and X-ray diffraction. Results indicated that the corrosion resistance of hot dip aluminum/carburizing composite coating was not significantly enhanced by hot dip aluminum coating. This can be attributed to the formation of TiC and Ti3AlC after carburization, which promoted the formation of loose and unprotected TiO2 in the coating during molten salt corrosion. In addition, the oxidation of the carbon atom into CO2 /CO leaded to a high concentration of vacancy in the coating, creating channels for NaCl to penetrate the coating and accelerated the corrosion rate.

The fusion of surface-modified steel with tungsten carbide (WC) and NiCrBSi powder through laser metal deposition has emerged as a formidable strategy for fortifying components against wear and corrosion in extreme operating environments. Meticulous selection of WC content, innovative pre-alloying techniques, and precise control of laser metal deposition profoundly influence the mechanical properties and microstructural evolution of WC-NiCrBSi coatings applied to surface-enriched commercial alloy steel (805M2, 832M13, and 827M40). These tailored coatings exhibit exceptional resilience, ideal for harsh industrial settings in Oil and gas drilling, petrochemical, and Mining sectors. Advanced materials testing techniques, including scanning electron microscopy, light optical microscopies, and microhardness testing, unveil the innate hardness attributes, with findings highlighting the unassailable fortitude of the Mixed matrix layer's side face. The amalgamation of these testing methodologies with laser metal deposition promises an unparalleled path to extend the operational lifespan of critical components in challenging working conditions. The research horizon for WC-NiCrBSi coatings remains broad, with the potential to enhance durability, operational efficiency, and cost-effectiveness across diverse applications.