Abstract
To improve the oxidation resistance of carbon composites at high temperatures, hafnium carbide (HfC) and titanium carbide (TiC) ultra-high-temperature ceramic coatings were deposited using vacuum plasma spraying. Single-layer HfC and TiC coatings and multilayer HfC/TiC coatings were fabricated and compared. The microstructure and composition of the fabricated coatings were analyzed using field-emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The coating thicknesses of the HfC and TiC single-layer coatings were 165 µm and 140 µm, respectively, while the thicknesses of the HfC and TiC layers in the HfC/TiC multi-layer coating were 40 µm and 50 µm, respectively. No oxides were observed in any of the coating layers. The porosity was analyzed from cross-sectional images of the coating layers obtained using optical microscopy. Five random areas for each coating layer specimen were analyzed, and average porosity values of approximately 16.8% for the HfC coating and 22.5% for the TiC coating were determined. Furthermore, the mechanical properties of the coating layers were investigated by measuring the hardness of the cross section and surface roughness. The hardness values of the HfC and TiC coatings were 1650.7 HV and 753.6 HV, respectively. The hardness values of the HfC and TiC layers in the multilayer sample were 1563.5 HV and 1059.2 HV, respectively. The roughness values were 5.71 µm for the HfC coating, 4.30 µm for the TiC coating, and 3.32 µm for the HfC/TiC coating.
Highlights
Ultra-high-temperature ceramics (UHTC) are materials of interest for extreme environments, such as those experienced for aerospace applications
We developed single layers of Hafnium carbide (HfC) and titanium carbide (TiC) and HfC/TiC multilayer single layers of can
The powder sizes of HfC and TiC were 8.7 μm and substrate was confirmed for the HfC/TiC multilayer coating
Summary
Ultra-high-temperature ceramics (UHTC) are materials of interest for extreme environments, such as those experienced for aerospace applications. Hafnium carbide (HfC) and titanium carbide (TiC) have melting points of 3958 ◦ C and 3100 ◦ C, respectively, and can be used as materials in thermal protection systems. HfC has a low oxygen diffusion coefficient and excellent thermal stability; it is an excellent heat-resistant material because the melting point of HfO2 is very high (2758 ◦ C) [2,3,4]. TiC is resistant to thermal shock, has excellent wear resistance [5,6], and is suitable for plasma spray coating due to its relatively low melting point. The coating layer is formed by melting a precursor material, accelerating the melted droplets, and depositing them on a substrate using a high-temperature plasma. Plasma spray coating methods are generally divided into VPS and atmospheric plasma spraying (APS) processes
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