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[en] In the commercial field, greater reproduceability of ceramic materials was achieved by systematic process control of the steps in manufacture. By improvement of the microstructure design, the strength and toughness against tearing of the materials were increased. The articles give a survey of theoretical and experimental results in manufacture and of the composition of ceramics with reinforced structure. Preferred materials are zirconium-, aluminium- and yttrium oxide, silicon oxide and -nitride and titanium- and silicon carbide. (DG)

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[en] This book presents the papers given at a conference which focused on the growing interest in processing which the technological applications of ZrO₂ have fostered. Topics considered at the conference included phase transformations, mechanical properties, microstructure, applications, and processing

[en] Transformation-toughened (i.e. ZrO/sub 2/-toughened) ceramics represent a new class of high performance ceramics with spectacular strength properties at low and intermediate temperatures. However, at temperatures above about 700⁰C, most of these tough oxide-base ceramics can no longer be used as load-bearing engineering parts because of characteristic deficiencies. The aim of the present paper is to provide and discuss microstructural design strategies which may enable ZrO/sub 2/-toughened ceramics to be applied at higher temperatures. From the various strategies suggested, three appear to show good prospects, namely (a) the prevention of glassy intergranular films, (b) the addition of hard high modulus particles and (c) whikser or fibre reinforcement. Experimental approaches are presented from some ZrO/sub 2/-toughened ceramics, elg. tetragonal ZrO/sub 2/ polycrystals and ZrO/sub 2/-toughened cordierite, spinel and mullite

[en] This book presents a review of current understanding of zirconia-based ceramics. The 76 papers comprise six sections including phase transformations and phase stability, mechanical aspects of transformation toughening, microstructural aspects of transformation toughening, structural and other applications, electrolytic properties and applications, and processing

[en] The fracture toughness of Al₂O₃ is considerably increased by the incorporation of fine monoclinic ZrO₂ particles. Hot-pressed composites containing 15 vol% ZrO₂ yield K/sub 1c/ values of approximately equal to 10 MN/m/sup ³/₂/, twice that of the Al₂O₃ matrix. It is hypothesized that this increase results from a high density of small matrix microcracks absorbing energy by slow propagation. The microcracks are formed by the expansion of ZrO₂ during the tetragonal → monoclinic transformation. Since extremely high tensile stresses develop in the matrix, very small ZrO₂ particles can act as crack formers, thus limiting the critical flaw size to small values

[en] Mechanical properties of Si₃N₄--ZrO₂ composits were studied. Part of the added ZrO₂ was stabilized in the cubic lattice form at room temperature. Hot pressing and annealing pure ZrO₂ in an N₂ atmosphere caused the cubic phase to form. Cubic ZrO₂ is not caused by O deficiency. N partially stabilized ZrO₂ exhibits considerable fracture toughness but air annealing at 600⁰C leads to rapid oxidation and disintegration

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[en] Bansal and Heuer [Am. Ceram. Soc., 58: 235-38(1975)] have concluded that the useful mechanical properties of PSZ, i.e. good fracture toughness and thermal shock resistance, can be attributed to a fine dispersion of monoclinic precipitates in the cubic grains. These coherent precipitates are thought to impede crack propagation, according to a model proposed by Lange, [Philos. Mag., 22: 983-92(1970)] which is based on the concept that a crack front possesses a line energy; i.e. the fracture energy of a composite dispersion increases when the crack front, pinned by the dispersions, bows out between the pinning positions. It is felt that this model cannot be applied to PSZ nor can the precipitates contribute significantly to the relatively high fracture energy of PSZ compared with other energy-dissipation processes. Data and information are presented showing that it is unjustified to consider this material as an example of evidence that the small precipitates in the grains contribute to the good properties of PSZ