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Reactive plasma sprayed coatings were prepared on carbon steel substrates with Ti and B4C as starting materials. Two kinds of gases (Ar and N2) were used as feeding gases for powders, respectively. 10 wt.% Cr was added in the powders as binder to increase the bond strength of the coating. The phases, microstructure, micro-hardness and corrosion polarization behavior in 3.5 wt.% NaCl solution of the two coatings were studied. The results show that TiN-TiB2 coatings were prepared under both conditions. The two coatings have typically laminated structure. However, the coating prepared with Ar as feeding gas has higher porosity and some unmelted Cr particles. It also contains certain content of titanium oxides. The microhardness of coating prepared with Ar as feeding gas is lower due to its higher porosity, unmelted Cr particles and some amounts of TiO2. The corrosion resistance of TiN-TiB2 coating prepared with Ar as feeding gas in 3.5 wt.% NaCl solution is worse than that of the coating prepared with N2 as feeding gas. Yet the corrosion resistance of reactive plasma sprayed TiN-TiB2 coating is improved greatly compared with that of carbon steel. The thermodynamic analysis of reactive plasma spraying process is also discussed. [ABSTRACT FROM AUTHOR]

Abstract: Wear resistance of reactive plasma sprayed TiB2–TiC0.3N0.7 based composite coatings and the as-sprayed coating with laser surface treatment was investigated using plate-on-plate tests. Wear tests were performed at different normal loads and sliding speeds under dry sliding conditions in air. The surface morphologies of counterparts against as-sprayed and laser remelted coatings were investigated. The microstructure and chemical composition of wear debris and coatings were studied using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively. The results show that the wear resistance of the laser remelted coating is improved significantly due to their increased microhardness and reduced flaws. The primary wear mechanism of the remelted coating is oxidation wear and its minor wear mechanisms are grain abrasion and fatigue failure during the course of wear test. In contrast, the primary wear mechanism of the as-sprayed coating is grain abrasion at the low sliding speed (370rpm) and fatigue failure at the high sliding speed (549rpm). The oxidation wear mechanism is a minor contributor for the as-sprayed coating. [ABSTRACT FROM AUTHOR]

The coatings were deposited by reactive plasma spraying (RPS) in air and low-pressure plasma spraying (LPPS) based on the reaction between Ti and B4C powder, respectively. The thermal spray powder of Ti and B4C added with powder Cr (metallic binder) in air is compared with that without powder Cr addition in the low pressure. (Prior to deposition, the powder was screened and separated for RPS whereas spray drying, sintering and sieving were done for LPPS.) The phase composition and the microstructure of coatings were studied by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The anti-corrosion property of coatings was also investigated. It is found that the coating prepared by RPS, which is more densification, is composed of TiN, TiB2, and a small phase fraction of titanium oxides. The composition of the coating deposited by reactive LPPS is TiB2, Ti(C, N), Ti4N3− x and impurity phase of Ti5Si3. There is no appearance of titanium oxides in low pressure. The coatings have the typical lamellar structure and adhere to the bond coating well. The mean Vickers microhardness value of the coating deposited by RPS is higher than that of the coating deposited by LPPS. Furthermore, the corrosion resistance of the coating deposited by RPS is superior to that of the coating prepared by LPPS in near neutral 3.5 wt% NaCl electrolyte. [ABSTRACT FROM AUTHOR]