As a typical transition metal boride, tungsten diboride (WB2) is a new type of superhard material with high melting point, high hardness (hardness greater than or equal to 40GPa), high conductivity and excellent wear resistance, which is widely used in high-temperature structural materials, refractory materials, electrode materials and other fields.
WB2 crystal structure diagram, Cao Xiaozhou/Journal of Inorganic Materials
From the perspective of production technology, the production methods of WB2 powder include chemical vapor deposition, element synthesis, floating zone melting, molten salt electrolysis and self-propagating combustion synthesis. However, WB2 powder can be prepared by pressureless sintering. The production steps of WB2 ceramics are as follows: after the boron powder and tungsten powder are evenly mixed in proportion, the blank is pressed and formed in the steel mold under the pressure of 100MPa, then the blank is placed in the graphite crucible, then placed in the vacuum carbon tube furnace for heating, heat preservation and cooling, and then ground into WB2 powder after cooling, and the WB2 powder is pressed and formed in the steel mold, Finally, the final product can be obtained by pressureless sintering in the vacuum sintering furnace at a heating rate of 10 ℃/min to the target temperature for 2h.
WB2 Powder Micromorphology, Cao Xiaozhou/Journal of Inorganic Materials
The results show that with the increase of sintering temperature, the pores in WB2 ceramics will be less and less, and the degree of densification will be higher and higher, and the bending strength and hardness will be enhanced accordingly. With the increase of sintering temperature, the apparent porosity of WB2 ceramics becomes smaller and smaller, while the relative density becomes larger and larger. This is because the high temperature sintering process mainly depends on the mutual diffusion between atoms at high temperature. The sintering temperature increases, the diffusion intensifies, and the indirect contact surface of powder particles increases. The volume diffusion and mass transfer process of the material itself is more complete. The positions between particles are rearranged, and the connection between particles changes from weak van der Waals force to strong crystal contact, So that the porosity is reduced and the relative density is increased.