Fabrication of continuously and symmetrically graded Si 3 N 4 -based ceramics under uniformly thermal field

Functionally graded materials (FGMs) have attracted more and more attention due to their graded changes on composition or microstructure to satisfy some conflicting properties in one component. However, the interfacial stress induced by the composition difference across an interface would degrade the reliability of components and hinder its advancement. Herein, a general process to fabricate continuously and symmetrically graded Si 3 N 4 -based ceramics is designed to address the problem above. By the combination of gaseous gradient diffusion and in-situ gas reaction, the graded ceramics with hard surface and tough core are first prepared under uniformly thermal field. The edge area of graded ceramics exhibits fine microstructure, high hardness (19.82GPa), and low fracture toughness (4.73 MPa·m 1/2 ), while the interior exhibits a distinct difference with coarse grains, low hardness (18.31GPa) and high fracture toughness (6.12 MPa·m 1/2 ). The thickness of continuously graded microstructure is effectively controlled and regulated by optimizing sintering regimes.