Hajime Suto

The microstructure and mechanical properties of yttria-stabilized zirconia prepared by arc-melting

The microstructure of ZrO2-Y2O3 alloys prepared by arc-melting was examined mainly by electron microscopy. It was found that the microstructure changed markedly with yttria content between 0 and 8·7 mol%. Pure zirconia was a single monoclinic phase, while ZrO2-8·7 mol% Y2O3 alloy was single cubic phase as expected from ZrO2-Y2O3 phase diagram. Tetragonal phase was found in alloys with 1 to 6 mol% Y2O3 together with monoclinic or cubic phase. The tetragonal phase found in present alloys normally had a lenticular shape with a length 1 to 5μm and a width 0.1 to 0.3μm, which is much larger than that formed by annealing. The phase with a herring-bone appearance was found in alloys with Y2O3 between 2 and 3 mol%, which was recognized to be a metastable rhombohedral phase. The structure of the present alloys is likely to be formed by martensitic or bainitic transformation during fairly rapid cooling from the melt temperature. The change in hardness and toughness with yttria content of the alloys is discussed on the basis of microstructural observations.

The intermediate compound in the In2O3-SnO2 system

The In2O3-SnO2 binary system between 1473 and 1873 K has been investigated by TEM observations in detail. The intermediate compound has been detected above 1573 K in the composition range from 47.9 to 59.3 mol% SnO2, that crystal structure is long range ordered cubic system similar to In2O3 phase. On the other hand, below 1473 K, the intermediate compound is decomposed into In2O3 and SnO2 phases, according to the eutectoid reaction.

The modulated structure formed by isothermal ageing in ZrO2-5.2 mol % Y2O3 alloy

The modulated structure produced by isothermal ageing of ZrO2-5.2 mol % Y2O3 alloy was examined mainly by electron microscopy. It was found that the modulated structure was formed at ageing temperatures between 1400 and 1600° C, but not at 1700° C. The structure is developed by spinodal decomposition, which produces compositional fluctuation in the elastically soft 〈111〉 direction in cubic zirconia. The hardness increase caused by the development of modulated structure during ageing is larger than the hardening by precipitation of tetragonal phase in the cubic matrix.

The metastable two-phase region in the zirconia-rich part of the ZrO2-Y2O3 system

ZrO2-Y2O3 alloys with yttria contents between 2.0 and 6.3 mol% were prepared by arcmelting. The microstructure of the alloys after isothermal ageing was examined by electron microscopy. It was found that a modulated structure was formed in alloys aged at appropriate temperatures. The modulated structure resembles the structure of spinodally decomposed metallic alloys and ceramics. The range in which the modulated structure is developed is inside the cubic-tetragonal two-phase region of the ZrO2-Y2O3 system. The modulated structure is associated with metastable phase decomposition.

The cubic-to-β martensitic transformation in ZrO2―Sc2O3

The nature of the cubic-to-β (c-β) transformation and the microstructure of theβ-phase were examined in ZrO2-10.5 and 12.5 mol % Sc2O3 alloys. The c -β transformation is induced during cooling from the high-temperature cubic phase region by martensitic transformation. The microstructure of theβ-phase usually has a herring-bone appearance, which is made of a unique array of four orientation variants. Two types of interfaces are formed in the structure; long straight interfaces and short interfaces. The former and the latter interfaces are nearly parallel to the {011}β and {012}β type planes, respectively, which correspond to the {001}c and {011}c planes in the parent cubic phase. The {011}β and {012}β type interfaces are fully coherent, low-energy interfaces. The herring-bone structure is likely to be a favourable one for minimizing the strain energy and interfacial energy associated with the c -β transformation, which is a characteristic microstructure developed by martensitic transformation.

Crystal structure and scratch testing of κ-Al2O3 on WC-Co substrates with a TiC interlayer

Abstract The crystal structure of κ-Al2O3, determined by electron and X-ray diffractions, was an orthorhombic structure with lattice constants of a = 0.477 nm, b = 0.83 nm and c = 0.894 nm. The Vickers hardness of κ-Al2O3 was about 1800. The adhesion strength between coatings and substrate was estimated from the critical load of the scratch test with a pyramidal indenter as being about 80 kgf mm−2 for the κ-Al2O2/( WC-Co alloy) system with a chemically vapour-deposited TiC interlayer and 1 kgf mm−2 for that system without a TiC interlayer.

Pack Cementation Treatment of Titanium Using Tetracalcium Phosphate Powder for Biomedical Applications

The surface modification of commercially pure titanium (CP Ti) by pack cementation treatment at 973 K using tetracalcium phosphate (Ca4(PO4)2O, TTCP) slurry was investigated. An HAp phase and a CaTiO3 phase were observed on the reaction layer of the CP Ti substrate after pack cementation treatment at 973 K for 86.4 ks. TTCP powder decomposed to HAp and CaO, and CaO reacted with TiO2 to form CaTiO3. The reaction layer on the CP Ti substrate consisted of inner and outer layers and the particles were in the outer reaction layer. The pores observed on the reaction layer were formed by the detachment of particles from the outer layer. The bonding strength of the reaction layer was 68.1 MPa. Apatite completely covered the surface of the pack-cementation-treated CP Ti after immersion in Kokubo solution for 21.6 ks; such rapid apatite formation suggests that pack cementation treatment improves the biocompatibility of titanium.