Microstructural features of SHS-pressing ZrB2-B4C and TiB2-B4C composites

In the present paper dense ceramic composites TiB2-B4C and ZrB2-B4C have been produced by means of pressure-assisted self-propagating high temperature synthesis (SHS). The method includes combustion synthesis of refractory compounds and its consolidation under high mechanical pressure. An equilibrium SHS product formed during the exothermic interaction in the mixture of Ti, Zr, B and C powders contains TiB2 or ZrB2 as a dispersed phase, and B4C as a ceramic binder. The influence of content of the ceramic binder (B4C) on the formation of the microstructure of SHS composites was studied. It is shown at the B4C content of 20 wt.% in the TiB2-B4C composite and at 5 wt.% in the ZrB2-B4C composite were formed dense TiB2 and ZrB2 particles. At content B4C 40 wt.% in the TiB2-B4C-composite and 20 wt.% in the ZrB2-B4C-composite the particles of the dispersed phase were formed in hollow shells form. The size and thickness of the shells depend on the initial Ti and Zr particles size. It had been proposed formation mechanism of hollow shells, are including stages formation the TiB2 and ZrB2 layers on the metallic particles surface, melting of the internal unreacted part of the metallic particles, and spreading of the melt on the outer surface of the product layer. The experimental results showed the “chemical furnace” had provided thermal regime needed to efficient consolidation SHS composites to minimum residual porosity. Physical and mechanical characteristics of SHS composites were studied depending on content of ceramic binder. It is shown that the maximum microhardness of the TiB2-B4C and ZrB2-B4C composites are 39.1– 44.8 GPa, and 20.4 – 24.5 GPa, accordingly. The flexural strength of the TiB2-B4C-composites is 140 – 210 MPa.