Enhanced microstructural and mechanical gradients on silicon nitride ceramics

Continuous in situ functionally graded silicon nitride materials with outstanding gradients in their morphological and mechanical characteristics are developed using the spark plasma sintering technique with an asymmetric setting of punches and die, and placing an electrical insulator barrier between the top punch and the ceramic powder compact. Temperature gradients well above 150 °C are created across the specimen inducing significant variations through the specimen thickness (3.5 mm) in phase transformation (78%) and grain size (240%). Hardness and toughness gradients of 2.0 GPa mm−1 and 1.2 MPa m1/2 mm−1, respectively, are attained.