Properties of hard alloy materials

Hard alloy is a powder metallurgy product made by sintering high hardness refractory metal carbides (WC, TiC) in micrometer sized powders with cobalt (Co) or nickel (Ni), molybdenum (Mo) as binders in a vacuum furnace or hydrogen reduction furnace.
Carbides, nitrides, borides, etc. of the IV B, V B, and VI B group metals are collectively referred to as hard alloys due to their particularly high hardness and melting point. Below, we will focus on carbides to illustrate the structure, characteristics, and applications of hard gold.
In metal type carbides formed by IVB, VB, and VIB group metals and carbon, due to the small radius of carbon atoms, they can fill the gaps in the metal lattice and retain the original lattice form of the metal, forming interstitial solid solutions. Under appropriate conditions, this type of solid solution can continue to dissolve its constituent elements until it reaches saturation. 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 comply with the valence rules. When the dissolved carbon content exceeds a certain limit (such as Ti: C=1:1 in titanium carbide), the lattice pattern will change, causing the original metal lattice to transform into another form of metal lattice. At this time, the interstitial solid solution is called a interstitial compound.
The melting points of metal type carbides, especially the IVB, VB, and VIB group metal carbides, are above 3273K, with hafnium carbide and tantalum carbide being 4160K and 4150K respectively, which are currently the highest melting points among known substances. Most carbides have a high hardness, with a microhardness greater than 1800kg · mm2 (microhardness is one of the hardness representation methods, commonly used in hard alloys and hard compounds, with a microhardness of 1800kg · mm2 equivalent to Mohs diamond hardness 9). Many carbides are not easily decomposed at high temperatures and have stronger antioxidant capacity than their constituent metals. Titanium carbide has the best thermal stability among all carbides and is a very important metal type 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.
In addition to carbon atoms, nitrogen and boron atoms can also enter the gaps in the metal lattice, forming interstitial solid solutions. They have properties similar to interstitial carbides, such as conductivity, thermal conductivity, high melting point, high hardness, and high brittleness.
The matrix of hard alloy consists of two parts: one is the hardening phase; The other part is bonded metal.
Hardened phases are carbides of transition metals in the periodic table of elements, such as tungsten carbide, titanium carbide, and tantalum carbide. Their hardness is very high, and their melting points are all above 2000 ℃, some even exceeding 4000 ℃. In addition, the nitrides, borides, and silicides of transition metals also have similar characteristics and can serve as hardening phases in hard alloys. The presence of hardened phases determines that alloys have extremely high hardness and wear resistance.
The requirements for the particle size of tungsten carbide WC in hard alloys vary depending on the different uses of hard alloys. Hard alloy cutting tools: For example, precision machining alloys such as foot cutting machine blades and V-CUT knives use ultrafine, sub fine, and fine particle WC, coarse machining alloys use medium particle WC, and alloys for gravity cutting and heavy cutting use medium particle WC