1993

The corrosion resistance and electrochemical behavior of sintered AISI 304L and AISI 316L samples is evaluated in sulfate and chloride containing solutions. It is shown that the sintering atmosphere strongly influences the microstructure of austenitic stainless steels. Samples sintered in nitrogen-based atmosphere show better mechanical properties but lower corrosion resistance than samples sintered in vacuum because of the precipitation of chromium carbides.

(High resolution) TEM and FTIR spectroscopy of in-situ CO adsorption at 300and ∼ 78 K have been used to characterize particle morphology and surface Lewis acidity of three preparations of tetragonal ZrO2 stabilized with Y2O3. Depending on preparation, the starting materials are in the form of individual coin-shaped platelets, or of huge aggregates of small particles. In either case, few low-index crystal planes are most frequently exposed, and the particle edges are irregular.

Today, cordierite plays a very important role in the reduction of noxious substances emitted from internal combustion engines. Honeycomb structures with parallel channels offer a good solution as supports for catalysts at an acceptable counterpressure. Porous ceramic materials permit an efficient mechanical filtration of carbonaceous particles contained in the exhaust gases of diesel engines, which are forced to flow through the walls.

This paper compares Al2O3-ZrO2 composites obtained from the same powder precursors dried by two different methods: spray drying and alcohol extraction via sol-gel route. The composite with 15% ZrO2 obtained by sintering microsphere powders produced via a sol-gel method exhibited better mechanical properties.

Ceramic (cordierite) honeycomb structures are employed in the automotive industry for trapping and incineration of particulate material from the exhaust gases of diesel-powered cars. The most diffuse pollutants present in the particulates are sodium, lead, iron, calcium, zinc and vanadium: they can react with cordierite during regeneration of the filter.

The characterization of TiB2/C-coated SiC fibres and their interface region in a Ti-6Al-4V based composite has been performed by using scanning electron microscopy (SEM), energy-dispersion X-rays (EDX) and Auger electron spectroscopy (AES). The features of the as-received fibre and the reactivity between fibre and matrix occurring during preparation of the composite have been studied in this paper.

Examples of interfaces in metal matrix composites (MMC) are presented in this paper; in particular, Al alloys reinforced with B4C or SiC particles; pure Al reinforced with melt-spun intermetallic ribbons (Ni3Al); Mg alloys reinforced with C long fibers; Ti alloys reinforced with double coated (C/TiB2) SiC fibers. Kinetic studies of artificial aging on Al 6061/SiCp and Al 6061/SiCw composites are also presented. Several analytical techniques have been used for these studies: a good knowledge of the interfaces in MMC is fundamental for the design of these materials.