Effect of Two-Step Sintering on the Mechanical and Electrical Properties of 5YSZ and 8YSZ Ceramics

Yttria-stabilized zirconia (YSZ) has been widely used in structural and functional ceramics because of its excellent physicochemical properties. In this paper, the density, average gain size, phase structure, and mechanical and electrical properties of conventionally sintered (CS) and two-step sintered (TSS) 5YSZ and 8YSZ are investigated in detail. As the grain size of YSZ ceramics became smaller, dense YSZ materials with a submicron grain size and low sintering temperature were optimized in terms of their mechanical and electrical properties. 5YSZ and 8YSZ in the TSS process significantly improved the plasticity, toughness, and electrical conductivity of the samples and significantly suppressed the rapid grain growth. The experimental results showed that the hardness of the samples was mainly affected by the volume density, that the maximum fracture toughness of 5YSZ increased from 3.514 MPa·m^1/2 to 4.034 MPa·m^1/2 in the TSS process, an increase of 14.8%, and that the maximum fracture toughness of 8YSZ increased from 1.491 MPa·m^1/2 to 2.126 MPa·m^1/2, an increase of 42.58%. The maximum total conductivity of the 5YSZ and 8YSZ samples under 680 °C increased from 3.52 × 10^-3 S/cm and 6.09 × 10^-3 S/cm to 4.52 × 10^-3 S/cm and 7.87 × 10^-3 S/cm, an increase of 28.41% and 29.22%, respectively.