Performance and application characteristics of tungsten carbide

       The tungsten-carbon binary system can form two crystalline carbides, namely WC and W2C. Among them, WC is the main raw material for the manufacture of cemented carbide, and it is also an important raw material powder for the preparation of high wear-resistant coatings in the field of thermal spraying.



WC has high hardness, especially its high temperature hardness. WC can be well wetted by metal melts such as C0, Ni, Fe, etc., and cobalt melts have the best wettability. When the temperature is increased to above the melting point of the metal, the boundary can be dissolved in these metal melts, and when the temperature is lowered, the excellent properties of WC0 can be precipitated, so that it can use metals such as drill or nickel as the binder phase material. After high-temperature sintering or coating treatment, a wear-resistant coating with good wear resistance is formed.



The main disadvantage of WC is its poor resistance to high temperature oxidation. It is severely oxidized in the air at 500°C to 800°C, and is easily decomposed into W2C and carbon under strong heat in the experimental atmosphere, which is the so-called "carbon loss". This can pre-protect the WC particles by using heat-resistant and oxidation-resistant metal as the coating layer or binder phase; it can also form a composite carbide with TaC, TiC, etc., to improve the heat-resistant and oxidation-resistant performance of WC. WC is still stable when heated to 2850°C in Ar atmosphere, and is not affected in high temperature nitrogen.



The melting point and hardness of W2C are higher than that of WC. It can form a W2C-10 WC eutectic mixture with WC. The melting point is lower and it is easy to cast. It is the so-called "cast tungsten carbide" or "fusible tungsten carbide", and its average carbon content is 3.8% ~ 20% (mass), of which W2C content is 78% ~ 80% <mass>, and WC content is 20% ~ 22% (mass). This kind of cast tungsten carbide is the hardest and most wear-resistant with lower cost A material.



WC powder can also be bonded with cobalt-based, nickel-based and iron-based self-fluxing alloy powder, nickel-aluminum self-adhesive composite powder, and is widely used to prepare high wear-resistant coatings, especially wear-resistant particle wear, hard surface wear and Areas such as erosion and wear of mud and sand.



Tungsten carbide powder is mainly used as the raw material powder for thermal spraying wear-resistant coatings. Vacuum plasma spraying and protective atmosphere plasma spraying wear-resistant coatings can be used, but the adhesion of the coatings is not good.