Harnessing phase transition to achieve multiphase BN‑reinforced silica glass with high strength and toughness

Amorphous glass lacks long-range ordered microstructure, suppressing interface-dependent toughening mechanisms and thus exhibiting inherently low fracture toughness. Herein, a phase-transformation-driven strategy is proposed for in-situ constructing multiphase reinforcing phases, and a series of multiphase boron nitride (BN)-reinforced fused silica composites are prepared under varied sintering temperatures. Microstructure characterization demonstrates that the reinforcing phase consists primarily of cubic BN (cBN), turbostratic BN (tBN), and hexagonal BN (hBN), with tunable phase compositions. Excellent interfacial bonding and the synergistic effect of distinct reinforcing phases significantly enhance the overall properties of fused silica composites. Specifically, the cBN-tBN-hBN synergy endows the composites with a maximum microhardness of 7.9 GPa and compressive strength of 1576 MPa; layered tBN and hBN boost flexural strength, fracture toughness, uniaxial compressive strain and thermal conductivity to maxima of 218 MPa, 2.4 MPa·m^1/2, 2.8%, and 7.9 W·m^{− 1}·K^{− 1}, respectively. These values represent substantial improvements over pristine fused silica, reaching the highest performance levels reported to date for fused silica and its composites. This study clarifies the correlation between distinct BN reinforcing phases and the overall performance of fused silica composites, and provides a viable technical route for strengthening and toughening amorphous glasses.