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 CO, Ni, Fe and other metal melts, especially cobalt melt has the best wettability. When the temperature is raised to above the melting point of the metal, the interface can be dissolved in these metal melts, and when the temperature is lowered, the excellent properties of WC0 can be precipitated, making it possible to use metals such as diamond or nickel as the bonding 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 that it has poor resistance to high temperature oxidation. It is severely oxidized in the air at 500 ° C ~ 800 ° C, and is easily decomposed into W2C and carbon by strong heat in the experimental atmosphere, which is the so-called "carbon loss". This can pre-protect WC particles by using heat-resistant and anti-oxidative metal as a coating layer or binder phase; it can also form composite carbides with TaC, TiC, etc., to improve the heat-resistant and anti-oxidative properties of WC. WC is still stable when heated to 2850 °C in Ar atmosphere, and it 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+WC eutectic mixture with WC. The melting point is lowered and it is easy to cast. It is the so-called "cast tungsten carbide" or "fusible tungsten carbide". 3.8% ~ 20% (mass), of which W2C is 78% ~ 80% <mass>, and WC is 20% ~ 22% (mass). This 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-bonding composite powder, and is widely used in the preparation of high wear-resistant coatings, especially wear-resistant particle wear, hard surface wear and mud sand erosion wear and other fields.



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