As a third-generation wide-bandgap semiconductor material, silicon carbide (SiC) plays a critical role in high-temperature, high-frequency, and high-power devices. The physical vapor transport (PVT) method is the dominant technique for growing high-quality SiC single crystals. However, its closed high-temperature environment imposes strict requirements on the corrosion resistance and thermal field uniformity of graphite crucibles. Tantalum carbide (TaC) coatings, known for their high melting point, excellent thermal conductivity, and outstanding corrosion resistance, have become a key material for extending crucible life and improving crystal quality.
Graphite crucibles are prone to oxidation and corrosion in high-temperature environments exceeding 2200 °C, leading to a short service life. Corrosion by-products such as CO₂ and SiO₂ can contaminate the crystals, forming carbon or silicon inclusions that induce defects like micropipes and dislocations, significantly degrading crystal quality. To address this challenge, researchers identified TaC as a highly promising coating material due to its high melting point (~3880 °C), strong thermal conductivity (22 W/m·K), and corrosion resistance.
Before 2010, TaC coatings were not widely used in SiC crystal growth due to challenges in fabrication processes and cracking caused by the mismatch in thermal expansion coefficients between TaC and the graphite substrate. With intensive research into coating preparation methods-particularly after 2010-researchers successfully deposited high-quality TaC coatings on graphite surfaces using chemical vapor deposition (CVD) and molten salt reaction methods. Since 2020, TaC coatings have entered industrial application. Thanks to their ability to significantly suppress graphite oxidation in the PVT environment, TaC coatings extend crucible life to more than three times that of uncoated graphite crucibles. Experiments show that after 500 hours of continuous use at 2200 °C, TaC-coated graphite crucibles exhibit only micron-scale corrosion pits on the surface, whereas uncoated graphite is severely carbonized.
The main methods for preparing TaC coatings include in-situ reaction, slurry sintering, plasma spraying, and chemical vapor deposition.
In-situ reaction method: Uses metallic tantalum powder and carbon materials as raw materials; through solid-state reaction, tantalum and carbon directly combine on the carbon material surface to form a TaC coating.
Slurry sintering method: Coating powders are mixed uniformly with solvents and additives to form a stable suspension slurry, which is evenly applied to the substrate surface, dried, and then sintered at high temperature to produce a TaC coating. This method yields dense, crack-free TaC coatings with grain sizes of 10–50 μm and coating thickness around 100 μm. The grain growth exhibits no preferred orientation, avoiding the formation of penetrating cracks.
Plasma spraying method: Coating material is melted at high temperature, atomized into fine droplets or high-temperature particles by a high-velocity jet, and sprayed onto a pretreated substrate surface to form a coating.
Chemical vapor deposition (CVD): The core mechanism involves multiple physicochemical steps-precursor pyrolysis, gas-phase diffusion, interfacial reactions, and surface deposition-inside a high-temperature reaction chamber, ultimately forming a dense functional coating on the substrate surface.