ZrB 2–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

Abstract

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 (ZS_sf) 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 (<i>η</i>), dropping height (<i>H</i>), and flow rate (<i>Q</i>), the geometric parameters of ZS_sf involving filament diameter (<i>d</i>) and coil diameter (<i>D</i>) were followed the relationship of <i>d ≈</i> 0.516×10⁻³<i>Q</i>^1/2<i>H</i>^−1/4 and <i>D ≈</i> 0.25×10^–3(<i>Q</i>/<i>H</i>)^1/3, respectively, within the optimized <i>η</i> of 10–15 Pa·s. Three different microstructures of ZS_sf 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% ZS_sf composites prepared by hot isostatic pressing (HIP) exhibited a ~30% increase in fracture toughness (<i>K</i>_IC, 4.41 MPa·m^1/2) compared with the ZrB₂–SiC composite, where the microscopic fracture toughness of the ZS_sf was ~80% higher than that of the matrix. The fibers with a ~10 nm <i>in-situ-</i>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.