B4C-SiC composites with tuneable mechanical properties: Role of Al2O3 - Y2O3 sintering additives

While outstanding properties of boron carbide (B ₄C)-silicon carbide (SiC) composites make them potential candidates for ballistic and wear resistance applications, the applicability is rather limited due to processing challenges to obtain high density and superior mechanical properties. In the present work, B ₄C-10 wt% SiC composites are spark plasma sintered without additives and with 6 wt% (Al ₂O ₃ -Y ₂O ₃) additives at 1600 °C, 1700 °C and 1800 °C. When sintered at 1600 °C, the relative density increased from 94% for the composites without additives to ∼99% with Al ₂O ₃-Y ₂O ₃ additives. The formation of liquid phase comprising Al-Y-Si-O improved density and mechanical properties of the composites. TEM analysis of the composite sintered with (2 wt% Al ₂O ₃ - 4 wt% Y ₂O ₃) additives at 1800 °C confirmed clean grain boundaries between B ₄C, SiC and liquid phase precipitates. When sintered at 1700° C, the indentation fracture toughness increased from 4.3 MPa.m ^0.5 for the composite without additive to 6.0 MPa.m ^0.5 for the composite with 6 wt% Al ₂O ₃ additive due to increased instances of crack splitting, bridging and deflection.