Reactive spark plasma sintering of ultrahard wear-resistant boron carbide-SiC-TaB2 composites from B4C with TaSi2 aids

Abstract

The fabrication of new ceramic composites by reactive spark plasma sintering (SPS) from B₄C with 5–30 vol% TaSi₂ aids was investigated, next evaluating some of their mechanical-tribological properties. First, it was found that, because a transient Si melt is formed, TaSi₂ aids reduce significantly the SPS temperature of B₄C (down to 1800°C for 5 vol% TaSi₂ and 1550°C for 30 vol% TaSi₂, temperatures at which pure B₄C is unsinterable). Second, it was found that reactive SPS from B₄C+TaSi₂ results in novel B₁₂(C,Si,B)₃–SiC–TaB₂ composites, with less B₁₂(C,Si,B)₃ and more SiC+TaB₂ with increasing vol% TaSi₂ aids. These composites are all very hard (≥27.5 GPa), some even superhard (∼32–33 GPa), and tougher than monolithic B₄C. In particular, the composite reactively SPS-ed from B₄C with 20 vol% TaSi₂ shows the optimal balance between sinterability (SPS at 1650°C), hardness (∼32.1 GPa), and toughness (∼3.5 MPa·m^1/2). And third, it was found in friction pairs with diamond and ZrO₂ that the optimally SPS-ed composite is highly resistant to the unlubricated sliding wear, undergoing only mild to very mild abrasion with specific wear rates in the order of 10⁻⁶–10⁻⁸ mm³/(N⋅m). Finally, the performance of these novel composites was compared with that of monolithic B₄C and composites reactively SPS-ed from B₄C with other metal disilicides.