Hierarchical nanoporous-based design strategy towards ductile ceramics with excellent strain hardening capability

Overcoming the inherent brittleness of ceramics is a longstanding, unsolved challenge in materials science and engineering. Here, we demonstrate a new effective strategy to achieve a brittle-ductile transition in ceramics by introducing a hierarchical spinodal structure. Combining phase field method and molecular dynamics (MD) method, we first constructed nanoporous SiC samples with 1-level and hierarchical 2-level structures separately using a phase field method whose rationality is well validated, featuring spinodal topologies. Then, the mechanical response of the nanoporous ceramics under compression is investigated by all-atom MD simulations to discover the underlying nanoscale deformation mechanisms. The results revealed that the 1-level nanoporous SiC samples exhibited conventional brittleness due to stress-concentration-induced cracking; in stark contrast, the hierarchical 2-level samples displayed a ductile, strain-hardening, metal-like behavior, which is attributed to the presence of dispersed nuclei of defects like stacking faults, which effectively dispersed stress and prevented stress-concentration-induced failure. The strength of the hierarchical nanoporous ceramics follows Shi's law rather than classical Gibson-Ashby law. Our study not only elucidates the two distinct deformation mechanisms but also introduces a highly effective hierarchical nanoporous strategy for the design of ductile ceramics with excellent strain hardening capability, addressing the enduring challenge of brittleness in ceramics.