Difference between ta-C DLC coating and TaC tantalum carbide coating

ta-C is pure carbon film, a type of DLC diamond-like coating. And TaC/TAC is tantalum carbide, a type of metal carbide. The two are completely different materials.

01 What is DLC ta-C coating #

DLC(DIAMOND-LIKE CARBON) Diamond-like carbon coating, a synthetic material with SP3 (diamond structure) and SP2 (graphite structure) or hybridized with elements such as hydrogen, silicon, fluorine, and metals. dLC is a generic term for carbon film materials, whose anisotropic properties depend on the ratio of the structural bonds and the type of ligand-bonded elements. ta-C films are an amorphous sp3 bonded DLC structure around 70%, without hydrogen.

For mechanical contact type self-lubricating applications, the conventional DLC solution is a hydrogenated amorphous (a-C:H) carbon film, with significant performance differences under different operating condition constraints (temperature, load, oxidizing atmosphere, etc.).

ta-CIt is an amorphous tetrahedral carbon film, which can be used in more severe working conditions while retaining the unique properties of DLC. Such as lifting:

• Improved wear resistance
• Increased resistance to friction chemical wear
• Wider pressure/temperature range

However, higher stresses result in thinner ta-C coatings; depositing film thicknesses requires polishing to reduce surface roughness.

02 Tantalum Carbide Coating #

Most search engines can not distinguish ta-C and TaC. tantalum carbide (TaC) has high hardness (Mohs hardness of 9-10 at room temperature, high melting point (about 3880 ℃), high Young's modulus (283-550GPa), strong electrical conductivity (conductivity of 25 ℃ at 32.7-117.4μΩ-cm), high-temperature superconductivity (10.5K), resistance to chemical corrosion candles and thermal shock ability, and high catalytic activity for ammonia decomposition and hydrogen separation. It has high catalytic activity for ammonia decomposition and hydrogen separation. The main uses are cemented carbide, capacitors, electronic devices, high-temperature components, chemical equipment and armor-piercing bullets. It is also used as TaC protective coating on the surface of carbon-based materials, which can effectively enhance their oxidation resistance, corrosion resistance, wear resistance and mechanical properties.

Hafnium-tantalum carbide alloy refers to the compound tetratantalum-hafnium pentacarbonate, which has the highest melting point of any known compound.

Preparation of tantalum carbide #

Preparation of tantalum carbide: solid-phase, liquid-phase and gas-phase methods, such as sintering, CVD, gel (sol-gel). Slurry sintering method is difficult to prepare composite coatings, coating thermal shock resistance is poor; CVD method prepared by the coating composition can be controlled, the highest density, but the deposition efficiency is low.

The coefficient of thermal expansion of TaC (6.6 × 10^-6K^-1) has certain differences with carbon based materials such as graphite, carbon fiber, C/C composites, resulting in single-phase TaC coatings that are prone to cracking and peeling. In order to further improve the performance of TaC coatings, researchers have developed coating systems such as composite coating system, solution-strengthened coating system, and gradient coating system.

03 High temperature resistance is not equal to oxidation resistance #

Many materials, such as tantalum carbide, have extremely high melting points, but oxidize rapidly in air. Although tantalum and tantalum alloys have excellent high-temperature mechanical properties, but its high-temperature antioxidant performance is poor, tantalum metal will be accelerated oxidation above 500 ℃ to generate Ta2O5. Tantalum and tantalum alloys of high-temperature antioxidant protection there are two main methods: ① high-temperature antioxidant protection of the surface coating ② high-temperature antioxidant protection of alloying.

Although the alloying method can enhance the antioxidant properties of tantalum and tantalum alloys, it will have a greater impact on the other properties of the matrix, especially on the high temperature mechanical properties of the matrix.

Surface coating can simultaneously have the advantages of low oxygen permeability, good chemical and physical compatibility and stability, low volatility, good matching of the coefficient of thermal expansion and bonding ability, high-temperature self-healing ability, and can not affect the original good mechanical properties of the tantalum alloy substrate, etc. It is the best solution to the problem of high-temperature mechanical properties and antioxidant properties of tantalum alloys.

• Many precious metals such as Ir, PL, Rh, HI, etc. have high melting point characteristics of which the melting point of metal Ir up to 2410 ℃ because of its high temperature oxygen permeability coefficient and oxygen diffusion coefficient is low, so it has excellent high temperature antioxidant performance, but the vapor pressure of its oxides is higher in order to avoid the metal Ir directly exposed to high temperature atmospheric environment needs to be added to the outer layer of the metal Ir other components of the coating.
• High-temperature oxidation-resistant ceramic silicide coatings such as MoSi, SiN; and SiC are of interest because of their good thermal stability (oxygen diffusion coefficient of 10-"g/(cm's) at 1200°C) and 10-1g/(cm's) at 2200°C).
• Composite coating is a high-temperature resistant ceramic coating and high-temperature resistant glass or high-temperature oxide (outer layer) used in combination with a high-temperature resistant antioxidant coating, which can not only work in high-temperature environments, but also has the ability of the coating of the micro-crack self-healing ability. Such as: CVD-MoSi barrier layer, Ir-Si diffusion layer, SrZrO; (Al0;) corrosion-resistant layer.

Other details: https://zhuanlan.zhihu.com/p/446428135