Fracture Behaviors and Ferroelastic Deformation in W/Cr Co-Doped Bi sub(4)Ti sub(3)O sub(12) Ceramics

In this paper, the influence of Cr sub(2)O sub(3) additive (y = 0~0.4 wt%) on fracture behaviors, ferroelastic deformation, and mechanical strengths of Bi sub(4)Ti sub(2.95)W sub( 0.05)O sub(12.05) (BTW) Aurivillius ceramics was investigated. For these W/Cr co-doped Bi sub(4)Ti sub(3)O sub(12) ceramics (BTW-yC), SEM analysis on their fractured surfaces demonstrate that the transgranular fracture is the main fracture mechanism, however, the intergranular fracture also exists in the sample at y = 0.3. Impedance analyses based electrical resonance show that their Poisson's ratio and Young's modulus vary with y in a similar trend, while the frequency constant and elastic compliance exhibit a contrary varying trend with y. On the other hand, under the Vickers indentation, the crack propagation in BTW-yC ceramics takes the form of the long-straight extension, small-angle deflection, and short-distance branching at y = 0, 0.2, and 0.4, respectively. In the uniaxial compression tests, the stress-strain behavior of ceramics consist of three stages, i.e., linear elastic deformation, ferroelastic domain switching, and microcrack propagation. The ferroelastic domain switching tends to form the resistance for the microcrack propagation. Furthermore, uniaxial bending tests prove that the fracture strength is dependent on the grain size and fracture toughness, Overall, the sample at y = 0.1 gains a better mechanical strength among BTW-yC ceramics.