In the metal carbides formed by IVB, VB, and VIB metals and carbon, due to the small radius of carbon atoms, they can fill in the gaps of the metal lattice and retain the original lattice form of the metal to form an interstitial solid solution. Under appropriate conditions, this type of solid solution can continue to dissolve its constituent elements until saturation is reached. Therefore, their composition can vary within a certain range (for example, the composition of titanium carbide varies between TiC0.5 and TiC), and the chemical formula does not conform to the valence rule. When the dissolved carbon content exceeds a certain limit (for example, Ti:C=1:1 in titanium carbide), the lattice type will change, and the original metal lattice will be transformed into another form of metal lattice. Interstitial solid solutions are called interstitial compounds.
The melting point of metal carbides, especially IVB, VB, and VIB metal carbides are all above 3273K, of which hafnium carbide and tantalum carbide are 4160K and 4150K, respectively, which are currently known substances. The highest melting point. The hardness of most carbides is very large, and their microhardness is greater than 1800kg·mm2 (microhardness is one of the hardness representation methods, mostly used for cemented carbides and hard compounds, and the microhardness of 1800kg·mm2 is equivalent to Mohs one. Diamond-hardness 9). Many carbides are not easily decomposed at high temperature, and their oxidation resistance is stronger than that of their constituent metals. Titanium carbide has the best thermal stability among all carbides and is a very important metal carbide. However, in an oxidizing atmosphere, all carbides are easily oxidized at high temperatures, which can be said to be a major weakness of carbides.