Hot-pressed boron carbide is one of the hardest materials available in commercial shapes, and gives outstanding resistance to abrasive wear.
It can be polished to a mirror finish and has good resistance to acids. It is refractory and chemically inert, but less resistant to oxidation than silicon carbide.
Boron Carbide tends to contain second-phase graphite and it is this property which has a major influence on the strength of the material.
The composition ranges from B4C at 78.25 wt% boron to at least B6.5C at 85.4 wt% boron.
Commercial boron carbide is produced by reacting and fusing boric oxide and carbon, in an electric arc furnace.
Boron carbide does not melt congruently, therefore the liquid in contact with the boron carbide, does not have the same composition as the solid. This means that the liquid must be solidified at a rate so that the liquid and solid don"t reach an equilibrium.
The material which is in a molten state becomes increasingly rich in carbon, therefore when the liquid solidifies its composition is one of boron carbide and graphite.
Hot pressing (including hot isostatic pressing) is a way of producing covalent ceramic materials such as boron carbide, which are fully dense and in pure single-phase form.
Hot pressing limits the size and complexity of shapes which can be produced, to shape these diamond grinding is used.
