PREPARATION OF TIB2 SINTERED COMPACTS BY HOT-PRESSING

A sintered compact of titanium diboride (TiB2) was prepared by hot pressing of the synthesized TiB2 powder, which was obtained by a solid-state reaction between TiN and amorphous boron. Densification of the sintered compact occurred at 20 MPa and 1800° C for 5 to 60 min with the aid of a reaction sintering, including the TiB2 formation reaction between excess 20 at % amorphous boron in the as-synthesized powder (TiB2 + 0.2B) and intentionally added 10 at % titanium metal. A homogeneous sintered compact of a single phase of TiB2, which was prepared by hot pressing for 30 min from the starting powder composition [(TiB2 + 0.2B) + 0.1 Ti], had a fine-grained microstructure composed of TiB2 grains with diameters of 2 to 3 μm. The bulk density was 4.47 g cm-3, i.e. 98% of the theoretical density. The microhardness, transverse rupture strength and fracture toughness of the TiB2 sintered compact were 2850 kg mm-2, 48 kg mm-2 and 2.4 MN m-3/2, respectively. The thermal expansion coefficient increased with increasing temperature up to 400° C and had a constant value of 8.8 x 10-6 deg-1 above 500° C. © 1990 Chapman and Hall Ltd.