ZrB2–SiC spiral fibers prepared by combining liquid rope effect with non-solvent-induced phase separation method: A promising toughening material for ultra-high temperature ceramics

Spiral fibers were considered to be an ideal toughening phase of ultra-high torsional release effect. In this work, ZrB2 (Z)–20 vol% SiC (S) spiral fiber (ZSsf) with controllable structure was prepared by a combination approach of liquid rope effect and non-solvent-induced phase separation. Dominantly depended on the kinematic viscosity (η), dropping height (H), and flow rate (Q), the geometric parameters of ZSsf involving filament diameter (d) and coil diameter (D) were followed the relationship of d ≈ 0.516×10−3Q1/2H−1/4 and D ≈ 0.25×10–3(Q/H)1/3, respectively, within the optimized η of 10–15 Pa·s. Three different microstructures of ZSsf were achieved by adjusting the polymer/solvent/non-solvent system assisted with phase diagram calculation, including dense, hollow, and hierarchical pore structures. The ZrB2–SiC with 1 wt% ZSsf composites prepared by hot isostatic pressing (HIP) exhibited a ~30% increase in fracture toughness (KIC, 4.41 MPa·m1/2) compared with the ZrB2–SiC composite, where the microscopic fracture toughness of the ZSsf was ~80% higher than that of the matrix. The fibers with a ~10 nm in-situ-synthesized graphite phase amongst grain boundaries of ZrB2 and SiC changed the fracture mode, and promoted the crack deflection and pull-out adjacent the interface of matrix and the fiber.