Low-temperature consolidation of high-strength TiB2 ceramic composites via grain-boundary engineering using Ni-W alloy

The concept of the consolidation of titanium diboride at relatively low temperature via formation of the solid solution was used in this research. A specially designed Ni-W alloy prepared by mechanical alloying method was used as the solid solution formation additive. The low amount of Ni-W alloy and TiB2 powder were mixed together and consequently consolidated in the temperature interval from 1300 degrees C to 1400 degrees C. The development of the microstructure and resulting mechanical behaviour of these composites were analysed in detail. The grain size of TiB2 below 3 micrometres was obtained for all processing temperatures. The highest processing temperature of 1400 degrees C resulted in the flexural strength on the level of 875 MPa and the elastic modulus being nearly 500 GPa. The fracture toughness was about 5 MPa m(0.5). Formation of the solid solution was confirmed by XRD and TEM analysis. Due to the targeted change in chemical composition on grain boundaries and TiB2 lattice distortions by addition of transition metals with higher ionic radii a hypothesis about the preferential formation of solid solution layer on the surface of TiB2 grains taking into account their orientation was formulated.