Papers by Author: Zdzislaw Librant

Abstract: Fracture toughness K_Ic and four-point bending strength σ_c at high temperature (up to 1500 °C) of Y₂O₃ ceramics of various grain size were measured. The ceramics were prepared by pressureless air sintering and next hot isostatic pressing of high purity (99.99%) Y₂O₃ powder. Relative density of about 99 % was achieved. Photos of microstructures revealed small pores distributed mainly inside grains. For smallest grain size (2 - 9 μm) ceramics K_Ic and σ_c are almost constant from 20 ° to 1200 °C and next they decrease. For biggest grain size (about 44 μm) they increase up to 800 °C and next they keep constant up to 1200 °C. The micrographs analyses of fracture surfaces indicated that transgranular mode of fracture at room temperature changes to almost intergranular at higher temperatures.

Abstract: The aim of the paper is theoretical modelling and experimental verification of the nonsymmetric thermal shock crack propagation in compound ceramic Al2O3 and ZrO2. The theoretical problem formulation concerns the thermal shock problem in a strip or bar made of nonhomogeneous material, which can exhibit local fluctuation of its mechanical and thermal properties. Such approach allows for: analysis of the real non-homogeneous ceramic materials and solution of the composition optimisation problem for composite material with respect to thermal shock sensitivity. In particular the presented approach enables estimation of the stress intensity factors during thermal shock for any continuous composition of the ceramic material.

Abstract: The superplastic flow in tetragonal zirconia polycrystals stabilised 3mol% Y2O3 (3YTZP) is strongly affected by the dopant cations, which segregate at the grain boundary. It is proposed that this flow is controlled by grain boundary diffusion of Zr4+ ions and therefore the dopant cations should change the grain boundary diffusion. In order to prove this thesis the measurements of grain boundary diffusion coefficients were made using Hf4+ ions as tracer. Zirconia samples were doped with 1mol% of Al2O3, SiO2, MgO, MgAl2O4, GeO2 and TiO2. The tracer was deposited on the surface of the zirconia specimens by placing several drops of hafnium nitrate and then drying at 373 K. In this way, thin films of HfO 2 were obtained. The samples were heated in the range 1553 – 1773 K for 1 to 24 h. The concentration versus depth profiles were measured using secondary ion mass spectrometry (SIMS). Calculated hence grain boundary diffusion coefficients were several times bigger for doped samples than for pure 3Y-TZP samples.

Abstract: The paper deals with the experimental method of the mechanical properties estimation at the beginning of deformation process (elastic behaviour) of the material as well as during the whole deformation stages. The idea of the method results from the observation of the loading and unloading process of the material and analysis of the strain stage.