Characterization of (Zr,Ti)B2-SiC composites obtained by hot press sintering of ZrB2-SiC-TiO2 powder mixtures

Abstract

The ability to enhance mechanical and oxidation properties for severe environmental applications has led to substantial academic interest in multiphase ultra-high temperature ceramics (UHTC). The purpose of this work is to study the in-situ solid solution formation of (Zr,Ti)B₂ from ZrB₂ and TiO₂ in a ZrB₂-SiC composite using hot pressing reaction sintering. For this, a mixture of 10, 20, and 30 % vol% SiC with ZrB₂ was mixed with 2.0 wt% TiO₂. Hot pressing sintering was performed with a load of 20 MPa at a final temperature of 1850 °C/30 min in an argon atmosphere. The microstructures, crystalline phases, densities, mechanical properties, and oxidation resistance of the composites were examined and compared with ZrB₂-SiC samples lacking TiO₂. In samples where TiO₂ was added, the matrix grain size slightly decreased, the fracture mode was mainly intergranular, and the SiC grain morphology changed the aspect ratio to be more equiaxed. The solid solution (Zr,Ti)B₂ was produced, and it was demonstrated by EDS elemental map images and the XRD analysis that Ti atoms incorporate into the ZrB₂ crystalline structure. The development of solid solutions showed no impact on relative densities or Vickers hardness. However, the solid solution formation favored an improvement in fracture toughness, probably owing to the smaller matrix grain size and intergranular fracture mode. Samples exhibiting (Zr,Ti)B₂ formation presented lower oxidation resistance than undoped samples in the same oxidizing condition.