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In order to improve the wear resistance of 1Cr18Ni9Ti stainless steel in NaCl and acid solution environment, the WC-10Co-4Cr coatings with two grain sizes were prepared by plasma spraying, and the corrosion resistance in 3.5%(mass fraction, the same below)NaCl and acid solution(pH=5.0) were investigated. The results show that the WC, W2C, W and η (CoxWxC) exist in these coatings. The corrosion potential of these coatings is higher than that of 1Cr18Ni9Ti substrate in 3.5% NaCl solution. In the acid solution (pH=5.0) at different temperatures, the potential difference for the nanometer WC-10Co-4Cr coatings has little change with the temperature. The corrosion mechanism of the coatings in NaCl and acid solution is shown as follows:the oxygen atoms adsorbed on the surface of WC-10Co-4Cr coating, can impel the Co and WC to form the galvanic couple in 3.5% NaCl solution. In the acid solution (pH=5.0), Co phase in the WC-10Co-4Cr coatings is dissolved to Co2+, and formed the galvanic corrosion with WC phase, so the isolated WC particles are formed on the coating surface.

There is a significant impact of ablation angle on the anti-ablation performance of C/C composites. A self-designed oxygen-kerosene ablation system was employed to study the ablation behavior and mechanism of C/C composites. Typical ablation angle of the experiment was 90°, 60°, 45° respectively, and particle concentration of the gas-solid two-phase ablation flow was 1.37%. The microstructure of post-test samples was observed with the scanning electron microscope(SEM), and the ablation rate of samples was also calculated. The result shows that when the ablation angle is 90°, 60°, 45°,the corresponding mass ablation rate for ablation experiment is 0.146,0.123,0.100g/s respectively. With the decrease of ablation angle, the mass ablation rate of samples is decreased gradually; while for the samples affected by particle erosion, the corresponding mass ablation rate is 0.452,0.455,0.432g/s and the line ablation rate is 1.863,1.323,0.843mm/s. The mass ablation rate is approximately unchanged and the line ablation rate is decreased. The smaller the ablation angle is, the more serious the thermalchemical ablation of gas, and thus increase the erosion area of axial fiber bundle under ablation condition and ablation gradient of radial fiber under ablation/erosion condition.

A self-designed oxygen-kerosene ablation system was employed to study the ablation mechanism and performance of the carbon-carbon composites. Particle concentrations of the gas-solid two-phase ablation flow were 0, 1.37%, 2.22%, and 2.64% respectively. The microstructure of post-test samples was analysed through the scanning electron microscope (SEM), and the ablation rate was calculated. The influence principle of particle concentrations on the ablation rate of the carbon-carbon composites was studied, and the mechanism of ablation was analysed. Experiment results show that with no particles involved the mass ablation rate is 0.159g/s and the linear ablation rate is 0.175mm/s, while with particles introduced, the minimum mass ablation rate and linear ablation rate are 0.432g/s and 0.843mm/s respectively, with the increase of particle concentrations, the ablation rate becomes accelerated. Particle erosion makes the ablation of sample seriously intensified, and the ablation gradient of radial fiber on erosion surface is increased with the increase of particle concentrations as well.

NiCr matrix WSe2-BaF2·CaF2-Y-hBN and WSe2-BaF2·CaF2-Y powders were prepared by mechanical granulation and crushing, and composite coatings were fabricated by atmospheric plasma spray technology. The microstructures and phase compositions of the powders, as well as the coatings, were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The friction coefficient and the wear behavior of the coatings from ambient temperature to 800°C were evaluated using a ball-on-disk tribometer. From the investigation of the worn surfaces, it was concluded that brittle fracture and delamination were the dominant wear mechanisms of the coatings at low temperature. At higher temperatures, a dense and protective oxide layer (BaCrO4and NiO) is generated on the worn surfaces of the coatings. Layered hexagonal BN particles reduce the direct contact and severe adhesion between friction pairs. Thus, the friction coefficient of the NiCr-WSe2-BaF2·CaF2-Y-hBN coating is stable at the evaluated temperatures relative to the non-hBN coating. These fluorides exhibit excellent properties in these coatings over a large temperature range. [ABSTRACT FROM PUBLISHER]