Effects of pressureless two-step sintering on the densification and properties of tetragonal zirconia

• Main Authors: Chee, H. C. Alexander, Singh, R. S. K., Lee, K. Y. Sara
• Format: Article
• Published: Korean Assoc Crystal Growth, Inc
• Subjects: TA Engineering (General). Civil engineering (General)
• Online Access: http://eprints.um.edu.my/26953/

The effects of pressureless two-step sintering (TSS) on the densification and mechanical properties of tetragonal zirconia polycrystals were investigated and compared with that obtained by conventional single-step sintering (SSS). The TSS profile involved firing at a high temperature, T-1 of 1450 degrees C followed by cooling to a lower temperature, T-2 of 1250 degrees C and soaking for various holding time ranging from 2 h to 10 h. The results showed that the tetragonal phase stability was not disrupted by TSS. A high relative density, above 96%, was obtained for the TSS samples regardless of holding time when compared to SSS which exhibited about 99% of theoretical density when sintered at 1450 degrees C. Nonetheless, the beneficial effects of TSS in enhancing the Vickers hardness and fracture toughness of tetragonal zirconia when compared to SSS, without incurring grain growth have been revealed. The single-step sintering yielded large tetragonal grains, about 0.56 mu m, if compared TSS which exhibited a refine microstructure having grain sizes ranging from 0.27 mu m (for 2 h holding time) to 0.35 mu m (for 10 h holding time). This feature of TSS which allows for the inhibition of grain boundary migration and the activation of grain boundary diffusion at lower dwelling temperature during sintering were responsible for the enhancement of the mechanical properties of tetragonal zirconia.