Anisotropic mechanical properties and hardening mechanisms in ZrO2–Y2O3 solid solution crystals

Abstract. The anisotropy of the mechanical properties of single crystal ZrO2 — 2.8 mol.% Y2O3 solid solutions has been studied. The crystals have been grown by skull melting technique. The microhardness and fracture toughness have been tested for different crystallographic planes by indentation with different indenter diagonal orientations. The study shows that the microhardness of the material depends on the crystallographic orientation but slightly whereas the fracture toughness varies for different planes. The maximum fracture toughness has been observed in the crystal specimen cut laterally to the <100> orientation. We have studied the anisotropy of the microhardness in the material for different indenter diagonal orientations. The maximum fracture toughness has been obtained for the {100} plane and the <100> indenter diagonal orientation. The phase composition inside and outside the indents on the {100}, {110} and {111} surfaces for 20, 3 and 1 N loads has been studied in local areas using Raman spectroscopy. The degree of the tetragonal−monoclinic transition has been evaluated for different crystallographic planes and different indenter diagonal orientations. The tetragonal−monoclinic transition proves to be anisotropic, and this affects the transformation hardening mechanism. The maximum amount of the monoclinic phase is present in the vicinity of the indent in the {100} plane for the <100> indenter diagonal orientation. The highest fraction toughness has also been observed in the {100} plane for the <100> indenter diagonal orientation. Probably, the abovementioned indenter diagonal orientation provides for the maximum stress concentration along the coherent conjugation planes between the tetragonal and the monoclinic phases during the tetragonal−monoclinic transition, i.e. (100)t||(100)m and [001]t||[010]m.

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