Anisotropy of the mechanical properties and features of the tetragonal to monoclinic transition in partially stabilized zirconia crystals

Abstract

We have studied the structure, phase composition and mechanical properties, e.g. microherdness and impact toughness of partially stabilized zirconia crystals in the 2–4 mol.% stabilizing yttria concentration range. We have shown that with increasing concentration of stabilizing yttria the microhardness increases while the impact fracture toughness varies nonmonotonically and reaches the maximum for the partially stabilized zirconia crystal with 3 mol.% Y2O3. The anisotropy of the microhardness and impact fracture toughness was studied for wafers perpendicular to the 〈100〉, 〈110〉 and 〈111〉 directions with different indenter diagonal orientations. We have shown that the microhardness of the partially stabilized zirconia crystals depends but slightly on crystallographic orientation whereas the impact fracture toughness differs between crystallographic faces of the crystals. The highest impact toughness was obtained for the {100} plane and the indenter diagonal aligned parallel to the 〈100〉 direction, while the lowest impact toughness was obtained for the {110} plane and the indenter diagonal aligned parallel to the 〈110〉 direction. Local Raman study of the monoclinic phase distribution in the vicinity of the indentation shows that the maximum quantity of the monoclinic phase forms along the 〈110〉 direction regardless of indenter diagonal orientation. We have shown that the strain anisotropy during the phase transition has variable effect on crack impedance. The effect of transformation hardening mechanism depends on crack plane orientation and transition induced stress.