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High Temperature Materials

Dense and cellular zirconia produced by gel casting with agar: Preparation and high temperature characterization

A modified gel-casting process was developed to produce both dense and highly porous (40% volume) yttria tetragonal zirconia polycrystal (Y-TZP) using agar, a natural polysaccharide, as gelling agent. A fugitive phase, made of commercial polyethylene spheres, was added to the ceramic suspension before gelling to produce cellular ceramic structures. The characterization of the microstructural features of both dense and cellular ceramics was carried out by FEG SEM analysis of cross-sections produced by focused ion beam.

Oxidation Protective Glass-Ceramic Coating for SiC Fibre Reinforced Glass Matrix Composites

A protective coating for SiC fiber reinforced borosilicate glass-matrix composites based on zinc borosilicate (ZBS) glass-ceramic was developed. The coating was deposited on the composite surfaces by a simple and cost-effective method, based on slurry dipping followed by a densification and crystallisation stage carried out at optimised temperature and holding time. The coatings were shown to be able to withstand temperatures of up to 700 °C without softening and without exhibiting microcracking.

New generation of brake callipers to improve competitiveness and energy savings in very high performance cars

This paper concerns with the optimisation of the innovative rheocasting process to produce a new generation of brake callipers, characterised by very high reliability and strength. The attained very promising properties favoured their use on a very high performance car and the presented technique can be further extended for other important challenging applications. The prototype components are produced using T6 heat treated A357 alloy. Results on the samples machined directly from the produced callipers are in detail described and analysed.

Optimized Slurries for Spray Drying: Different Approaches to Obtain Homogeneous and Deformable Alumina-Zirconia Granules

Spray drying is widely used for producing granulated feed materials for compaction process, which is the current industrial method for manufacturing alumina-zirconia femoral heads. The optimization of the granules compaction behavior requires the control of the slurry rheology. Moreover, for a dual-phase ceramic suspension, the even phase distribution has to be kept through the atomization step. Here we present two approaches addressing the key issues involved in the atomization of a composite system.

Microstructure and mechanical properties of alumina-5vol.%zirconia nanocomposites prepared by powder coating and powder mixing routes

Zirconia toughened alumina (ZTA) nanocomposites are attractive structural materials which combine the high hardness and Young's modulus of the alumina matrix with an additional toughening effect by the zirconia dispersion. In this study two approaches to prepare ZTA are compared. For the first approach, an ultrafine alumina powder was coated with 5 vol% zirconia by a wet chemical method. For the second one, the reference material was prepared by intensively mixing and milling the same alumina with nanoscale zirconia powder.

Processing of alumina-zirconia composites by surface modification route with enhanced hardness and wear resistance

Zirconia toughened alumina (ZTA) materials are frequently used in mechanical engineering and biomedical applications due to their enhanced toughness, strength and wear resistance compared to monolithic alumina. In this study, a submicron size alumina powder was modified via wet chemical route: the alumina particles surface was coated with zirconium chloride, to yield 10 vol% zirconia by subsequent thermal treatment. From this powder, several ZTA materials were produced by slip casting, sintered at different temperatures from 1475 to 1575 °C.