Processing and properties of zirconium diboride-based composites

Abstract

Two zirconium diboride-base composites were produced and characterised. The chosen starting compositions were: 55 wt.% ZrB 2 +41 wt.%TiB 2 +4 wt.% Ni and 83 wt.% ZrB 2 +13 wt.% B 4 C+4 wt.% Ni. The microstructure and properties of these composites were compared to those of a monolithic ZrB 2 +4 wt.% Ni material. In all cases, metallic Ni as the sintering aid promoted the formation of the liquid phase which improved mass transfer mechanisms during sintering. From the powder mixture ZrB 2 +TiB 2 , two solid solutions of Zr–Ti–B were obtained. In the case of the other mixture, B 4 C particles were dispersed in the ZrB 2 matrix. The composite materials have better mechanical properties than those of the monolithic ZrB 2 ceramic; in particular the fracture toughness and the flexural strength were almost doubled at room temperature. Long term oxidation tests indicated that the ZrB 2 -based composites, particularly the composite containing B 4 C as the second phase, were more resistant to oxidation than the monolithic ZrB 2 due to the formation of surface oxide products which were protective against the complete degradation by oxidation observed for the ZrB 2 matrix material.