Effect of W-Based Compounds on the Tribological Properties of ZrB₂-SiC Ceramic Composites

ZrB₂-SiC ceramics are a class of materials with potential employ in the aerospace sector, owing to their excellent thermo-physical properties and their high melting point. In this work, ZrB₂-SiC ceramic composites were synthesized using the spark plasma sintering (SPS) technology, with a particular focus on the incorporation of various W-based compounds: tungsten carbide (WC), tungsten boride (WB) and tungsten silicide (WSi₂). The impact of these W-based compound additives on the microstructural, mechanical and tribological properties of the ZrB₂-SiC ceramic composites were systematically studied. The results revealed that the addition of WB and WSi₂ facilitated the in-situ formation of a (Zr, W)B₂ solid solution phase. In the case of WC addition, a more complex scenario unfolded, where both (Zr, W)B₂ and (Zr, W)C solid solution phases were observed. These solid solution phases were instrumental in forming a unique core-shell structure, which significantly improved the material's density, grain size and mechanical properties. The WC-added ZrB₂-SiC ceramic exhibited the highest relative density and the lowest average grain size. Detailed examinations of the mechanical properties of these composites indicated a marked enhancement in attributes such as hardness, yield strength and fracture toughness. The comparison of hardness, yield strength and fracture toughness of ceramic composites was WC-added ZrB₂-SiC ceramic > WSi₂-added ZrB₂-SiC ceramic > WB-added ZrB₂-SiC ceramic > ZrB₂-SiC ceramic. This phenomenon was attributed to the core-shell structure that contributed to a refined grain size, higher density and greater uniformity in the microstructure. Compared with ZrB₂-SiC ceramic, trans-granular crack propagation and crack branching were found in the crack propagation path of W-based compound added ceramics. The tribological properties were assessed through rigorous wear and friction tests. The addition of WC and WB substantially improved the stability of friction coefficient and the composite's wear resistance. The comparison of wear resistance of ceramic composites was WC-added ZrB₂-SiC ceramic > WB-added ZrB₂-SiC ceramic > WSi₂-added ZrB₂-SiC ceramic ≈ ZrB₂-SiC ceramic. Compared to the ZrB₂-SiC ceramics, the wear rate in the WC-added composites was significantly reduced, by approximately 50%. This improvement of WC-added composites was largely due to the formation of a dense, protective layer of alumina and tungsten oxide on the friction surface, as well as the enhanced mechanical properties. The worn surface of WB-added ZrB₂-SiC ceramic exhibited a distinct multi-cracked alumina friction layer, accompanied by the accumulation of larger alumina particles. On the worn surface of WSi₂-added ZrB₂-SiC ceramic, the effective alumina friction layer was not formed, resulting in pronounced grain fracture and pull-out. This research not only demonstrated the potential of W-based compounds in enhancing the mechanical and tribological properties of ZrB₂-SiC ceramic composites, but also provided a detailed explanation of the relative mechanisms.