V. I. Barbashov, M. M. Bilousov
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Straining fetures of zirconia nanoceramics and single crystals immediately under hydrostatic pressure up to 1.2 GPa have been studied by means of static or kinetic microindentation at various intrusion rates of the diamond indentor from 10-5 to 10-3 mm/s. When studying straining kinetics under point loading, experimental curves load F vs indentor intrusion depth h were recorded automatically using computerized data processing.
Tests on microindentation under high hydrostatic pressure were conducted using original installation developed by the authors.
Cubic phase ZrO2 single crystals (fianite) as well as tetragonal phase ZrO2 single crystals were objects of studying. Polycrystalline ZrO2 specimens were sintered from nanosize powders (particle size about 30 nm) doped with 3-4 mol. % Y2O3 to stabilize the tetragonal phase.
It is shown by way of kinetic microindentation that the curves F (h) in partially stabilized tetragonal ZrO2 single and polycrystals have multistage appearance with different values of activation parameters. In standard tests (microhardness) it was established that fracture toughness factor KIc decreases with increasing hydrostatic pressure up to 0.4 GPa. In the pressure range 0.4 to 1.2 GPa growth of KIc was observed.
Analysis of the results obtained has shown that the multistage behavior of kinetic curves in the tetragonal phase specimtns is connected with phase transformation into more closely paced modification in some area under indentor. Fracture toughness experiments indicate in favour of the same mechanisms: softening at pressures up to 0.4 GPa is due to suppression of the tetragonal-to-monoclinic transformation in crack tip zone being the main mechanism of the transformation toughening.

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