EFFECT OF GRAIN SIZE ON MECHANICAL PROPERTIES OF 3Y-TZP CERAMICS

The dependence of mechanical properties of 3Y-TZP ceramics on their grain sizes in the range from 0.19 mu m to 2.15 mu m has been investigated. Vickers indentation tests were used to determine hardness and fracture toughness. The hardness decreased with increasing grain size. The fracture toughness was almost constant for ceramics with the grain size tip to 0.40 mu m and then grew with increasing grain size up to 7.8 MPam(0.5) for ceramics with grain size of 1.8 mu m. Above this grain size a spontaneous transformation from tetragonal to monoclinic phase occurred. Ceramic samples with grain sizes of 0.30 mu m and 0.78 mu m yielded similar bending strength, 1020 and 1011 MPa, respectively. The microstructural coarsening required for achieving larger grain size resulted in a higher scatter of strength values, which was demonstrated by a lower Weibull modulus (13.0 vs. 7.54). The mechanical properties of nanocrystalline 3Y-zirconia ceramics coarsened to the grain size range from 0.085 to 0.70 mu m were also investigated and compared. Differences in mechanical behaviour of investigated ceramics were observed and their possible causes discussed.