In this work, ZrB2-20 vol.% MoSi2 (denoted as ZM) composite coatings were fabricated by atmospheric plasma spray (APS) and vacuum plasma spray (VPS) techniques, respectively. Phase composition and microstructure of the composite coatings were characterized. Their oxidation behaviors and microstructure changes at 1500 °C were comparatively investigated. The results showed that VPS-ZM coating was composed of hexagonal ZrB2, tetragonal and hexagonal MoSi2, while certain amount of ZrO2 existed in APS-ZM coating. The oxide content, surface roughness and porosity of VPS-ZM coating were apparently lower than those of APS-ZM coating. The mass gain of APS-ZM coating was maximum at the beginning (1500 °C, 0 h) and then decreased with the oxidation time extending, while the mass of VPS-ZM coating gradually increased with increasing the oxidation time. The possible reasons for the different oxidation behaviors of the two kinds of coatings were analyzed.

•ZrB2–MoSi2 composite coatings were fabricated by low pressure plasma spray (LPPS) technique.•The effect of MoSi2 content on the oxidation behaviors at 1200 °C and 1500 °C was focused.•Corrosion processes and products were characterized and analyzed.•Improved oxidation resistance was observed with increasing MoSi2 content.In this work, ZrB2-based composite coatings with different contents of MoSi2 were fabricated by low pressure plasma spray (LPPS) technique. The oxidation behavior and microstructure evolution of the ZrB2–MoSi2 composite coatings were characterized at 1200 °C and 1500 °C. The results showed that the ZrB2–MoSi2 coatings exhibited lamellar microstrucuture with uniform MoSi2 distribution in the ZrB2 matrix. Silica, m-ZrO2, zircon and small amount of MoB were formed after the oxidation at 1200 °C. While only silica, m-ZrO2 and zircon were formed at 1500 °C. The increase of MoSi2 is helpful to improve the oxidation resistance of the composite coatings. The thickness of the total oxidized layer of ZrB2–40 vol.% MoSi2 coating was about 17–22 μm after 6 h oxidation at 1200 °C and 264–270 μm after 6 h oxidation at 1500 °C.

•TaSi2 coating fabricated by vacuum plasma spray technique was reported.•The microstructure of TaSi2 coating was characterized in detail.•The thermal stability was evaluated by TG-DTA and oxidation tests.•TaSi2 coating had exellent thermal stability at 500 °C up to 50h. Obvious oxidation was observed after oxidation at 800 °C for 1h.This work was aimed at reporting a new method for fabrication of TaSi2 coating. In this research, vacuum plasma spray (VPS) process was applied to fabricate TaSi2 coating. The chemical composition and microstructure of the coating was characterized by SEM, XRD, TEM and EDS. Its thermal stability was evaluated by TG-DTA and oxidation tests at 500 °C–1000 °C. The results showed that the TaSi2 coating was composed of hexagonal TaSi2 phase and presented dense lamellar microstructure combining defects, such as pores, interfaces and oxygen impurity. There was a sharp weight increase in TG curve at range of 800 °C–1000 °C with an exothermic phenomenon. The coating exhibited excellent thermal stability at 500 °C up to 50 h in atmospheric environment. Obvious oxidation was observed at 800 °C. The TaSi2 coating was completely oxidized and fragmented into pieces after oxidation at 900 °C for 1 h. The oxidation mechanism was also discussed.

Plasma spray is one of the suitable technologies to deposit carbide coatings with high melting point, such as ZrC. However, in the spray processes performed under atmosphere, oxidation of the carbide powder is inevitable. To investigate the influence of the oxidation behavior of feedstock on microstructure and ablation resistance of the deposited coating, ZrC coatings were prepared by atmospheric and vacuum plasma spray (APS and VPS) technologies, respectively. SiC-coated graphite was applied as the substrate. The obtained results showed that the oxidation of ZrC powder in APS process resulted in the formation of ZrO and Zr2O phases. Pores and cracks were more likely to be formed in the as-sprayed APS-ZrC coating. The VPS-ZrC coating without oxides possessed denser microstructure, higher thermal diffusivity, and lower coefficients of thermal expansion as compared with the APS-ZrC coating. A dense ZrO2 layer would be formed on the surface of the VPS-ZrC-coated sample during the ablation process and the substrate can be protected sufficiently after being ablated in high temperature plasma jet. However, the ZrO2 layer, formed by oxidation of the APS-ZrC coating having loose structure, was easy to be washed away by the shearing action of the plasma jet.

•W/Cu composite coatings were fabricated by air plasma spray (APS) and vacuum plasma spray (VPS) processes.•Microstructure, some physical properties and thermal characters are compared.•Both thermal conductivity and CTE of VPS-W/Cu coating are much higher than those of APS-W/Cu coatings.•Reasons for the differences in thermal properties of W/Cu coatings are discussed.Tungsten (W) coatings with different copper (Cu) contents (15 vol.% and 25 vol.%) were fabricated by atmospheric plasma spray (APS) and vacuum plasma spray (VPS) technologies, respectively. Phase composition and microstructure of the composite coatings were characterized. Physical properties, including porosity, oxygen content, microhardness and density of the coatings were examined. Thermal properties, including coefficient of thermal expansion (CTE) and thermal conductivity of the coatings were characterized. The results showed that the oxide content and porosity in the VPS-W/Cu coatings were apparently lower than those of the APS-W/Cu coatings. The CTE and thermal conductivity of the W–Cu composite coatings increased with the addition of Cu. The VPS-W/Cu coatings had apparently higher CTE and thermal conductivity compared with the APS-W/Cu coatings containing similar Cu content. The effects of the Cu incorporation in the composite coatings and the fabrication process on the coatings' properties were discussed.

In this study, molybdenum disilicide (MoSi2) coatings were fabricated by vacuum plasma spraying technology. Their morphology, composition, and microstructure characteristics were intensively investigated. The oxidation behavior of MoSi2 coatings was also explored. The results show that the MoSi2 coatings are compact with porosity less than 5%. Their microstructure exhibits typical lamellar character and is mainly composed of tetragonal and hexagonal MoSi2 phases. A small amount of tetragonal Mo5Si3 phase is randomly distributed in the MoSi2 matrix. A rapid weight gain is found between 300 and 800 °C. The MoSi2 coatings exhibit excellent oxidation-resistant properties at temperatures between 1300 and 1500 °C, which results from the continuous dense glassy SiO2 film formed on their surface. A thick layer composed of Mo5Si3 is found to be present under the SiO2 film for the MoSi2 coatings treated at 1700 °C, suggesting that the phenomenon of continuous oxidation took place.

Silicon coatings were fabricated by vacuum plasma spraying technology. The morphology, composition, and microstructure of the coatings were investigated by FESEM, XRD, WDX, and TEM. The physical, mechanical, and thermal properties of the coatings were characterized. The results showed that vacuum plasma sprayed silicon coatings were compact and consisted of well-molten silicon splats. The oxidation introduced by the spraying process was limited. Small ball-like particles of size less than 1 μm existed both on the surface and inside of the coatings. The silicon coatings were made up of silicon grains with irregular shapes and different sizes of 0.5-1 μm. The longitudinal microstructure of silicon coatings exhibited typical two-layer microstructure of equi-axed nanometer grains and overlying columnar grains. The open porosity, density, and surface roughness of silicon coatings were 3.2%, 2.24 g/cm3, and 3.47 μm, respectively. And the microhardness and bonding strength of silicon coating, respectively, were 7.0 GPa and 20.6 MPa.

In this study, tungsten coatings were fabricated onto copper alloy substrate without and with gradient Cu + W and Ti + W bond coatings via vacuum plasma spraying technology (denoted as WNON, WCu+W and WTi+W, respectively). The bonding strength and residual stresses of coatings were measured and thermal loading tests with high heat flux were performed. The obtained results showed that the WCu+W coating had the highest bonding strength among the three kinds of coatings. The value of residual stresses in the WCu+W coating was much lower than those in the WNON and WTi+W coatings. The existence of hydrogenated titanium and high residual stresses resulted in the low bonding strength of the WTi+W coatings. Microcracks were observed on the surface of the WTi+W and WNON coatings after the thermal loading experiments. However, the WCu+W coating kept intact and no microcracks were found on its surface. It indicated that the addition of the gradient layer of Cu + W improved the mechanical and thermal loading properties of tungsten coatings, and it had potential application used as bonding coatings for plasma sprayed tungsten coatings on copper alloy substrates in fusion reactors.Research highlights► Tungsten coatings were fabricated onto copper alloy substrate with gradient Cu + W and Ti + W bond coatings via vacuum plasma spraying technology. ► The bonding strength, residual stresses and thermal loading properties of the coatings were analyzed and compared. ► The gradient layer of Cu + W improved the mechanical and thermal loading properties of tungsten coatings, having a promising prospect as bonding coatings for plasma sprayed tungsten coatings on copper alloy substrates in fusion reactors.