Reactive Synthesis of B4C–CrB2, B4C–TiB2, AND B4C–TiCrB2 Heterophase Ceramics by Spark Plasma Sintering

Abstract

The reactive synthesis of heterophase refractory ultrahard B₄C-based composites by spark plasma sintering (SPS) was examined. To produce heterophase B₄C + TiB₂ + CrB₂ ceramics, the chemical reaction between boron carbide and chromium oxide and between boron carbide and titanium carbide resulting in boron carbide–chromium diboride and boron carbide–titanium diboride composites was previously studied. The reactive sintering of B₄C + Cr₂O₃ + C and B₄C + TiC mixtures using boron carbide powders obtained from the Zaporizhzhya Abrasive Plant and Donetsk Chemical Reagent Plant (Ukraine) was compared. The boron carbide powders differed in the ratio of B₁₃C₂ and B₄C phases and particle sizes. The reactively synthesized TiB₂, CrB₂, and CrTiB₂ boride phases positively influenced the SPS consolidation and properties of the boron carbide composites. The B₄C–CrB₂ and B₄C–TiB₂ ceramics subjected to Vickers hardness testing under a load of 98 N showed HV levels of 23–29 GPa and 26–28 GPa. The ceramics demonstrated brittle fracture according to the Half-penny model, with a fracture toughness of 3 MPa∙m^1/2 for B₄C–CrB₂ and 4.4 MPa∙m^1/2 for B₄C–TiB₂. The 90 vol.% B₄C–5.5 vol.% TiCrB₂–4.5 vol.% C ceramics with ~33 GPa hardness and ~ 4 MPa∙m^1/2 fracture toughness were produced by reactive SPS from a mixture of B₄C (Zaporizhzhya Abrasive Plant), 6.6 wt.% TiC, and 11 wt.% Cr₂O₃. The high strength of TiCrB₂ ceramics was attributed to the stress–strain state, where the matrix phase of boron carbide was subjected to compressive stresses. The high hardness and fracture toughness allow the B₄C–TiCrB₂ composite to be classified as an ultrahard ceramic material.