Production of titanium-containing metal-ceramic composites based on boron carbide in the nanocrystalline state

摘要

The results of the study of the production technology, phase composition, structure and physico-mechanical properties of metal-ceramic materials based on boron carbide and their components are presented. Boron carbide was obtained by direct synthesis from chemical elements using amorphous boron and carbon black. By mechanical dispersion, solid reagents were converted into an ultrafine state. Using a chemical method, nanoscale (70-80nm) boron carbide was synthesised from suspension solutions of amorphous boron and liquid hydrocarbons. Boron carbide-based metal-ceramic composite powder B4C-(Co-Ni-Ti) was obtained by mechanical dispersion of the constituent components. Based on results of studying of the temperature-dependence of wetting angle of boron carbide with Co-Ni-Ti metallic alloy, the compacting modes of metal-ceramic composite powders by plasma-spark sintering and hot pressing have been developed. The influence of the component content of the binder metal (alloy) on some physico-mechanical properties (linear expansion coefficient, hardness, and bending strength) of hardmetal-ceramic materials based on boron carbide was studied. It was found that the optimum content of the metal component in the composite is approximate to 25wt-%. In the temperature range 300-600 degrees C, the materials obtained are characterised by stable dimensional factors, since in this temperature range the thermal conductivity coefficient does not depend much on temperature. At room temperature, their bending strength is about 1GPa. A new method of chemical synthesis of nanocrystalline ceramic compositions of boron carbide and titanium diboride using suspension solutions for the preparation of powders and their spark plasma sintering was also developed to obtain a compacted material of composition B4C+30wt-%TiB2, which has a high hardness of 95 HRA (with maximum microhardness 45.6GPa) and sufficient strength (with a bending strength of 834MPa).