IMSE
Institute of Materials Science and EngineeringPublications list
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.
Titanium particle-reinforced glass ceramic matrix composites were prepared by sintering under an Ar atmosphere titanium particles (Tip) and the glass powders 45ZnO-15PbO-40B2O3 (mol%) (ZPB) for the ZPBT composites and 48.8SiO2-48.8CaO-2.4B2O3 (SCB) for the SCBT composites. Each composite was characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and differential thermal analysis. In order to modify the interfacial strength of the composites, glass matrices with different amounts of TiO2 (TZPB and TSCB, 7 and 2.1 mol% TiO2, respectively) were prepared.
Research groups: PetroMat
The influence of isothermal treatment at 400°C on the microstructure of a magnesium alloy/graphite composite was studied. The composite was characterized by Auger electron spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction. Due to thermal treatment, the reaction zone containing carbides grows.
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.
Research groups: PetroMat
Research groups: CeraMat
An investigation of the thermolysis of 3% yttria doped zirconia samples has been undertaken using the method of Controlled transformation Rate Thermal Analysis (CRTA) under a residual pressure of 4.5 x 10 4 mbar. Investigation of the water washed samples reveals a simple water loss. Thermolysis of the ethanol washed samples however, reveal a series of mechanisms without ethanol production. Several ethene related species are evolved during the course of the reaction indicating the catalytic nature of zirconia.
Research groups: PetroMat
Purpose: The main goal of this study is to develop and obtain some competitive products, with high added value. In particular, the attention will be focused on the possibility to obtain a new class of Cobalt based alloy by Ti addition. Design/methodology/approach: Modification of the composition by Ti addition can increase the corrosion resistance, processing and at the same time can improve the alloy biocompatibility. Findings: Addition of these elements has a positive effect on the alloy hardness.
In the present work, TiO2 films deposited on polyethylene terephthalate substrates by dip coating technique were subsequently treated by DC glow discharge plasma as a function of discharge potential. Hydrophilicity of these TiO2 film surfaces was analyzed by contact angle measurements. Atomic force microscopy (AFM) revealed changes in surface morphology of the plasma treated TiO2 films. Modifications in structural and chemical composition of the TiO2 films were detected by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).
Premature failure of dies is a critical problem of manufacturers in hot-working processes, e.g. metal die casting, hot extrusion and/or thixoextrusion of aluminium/magnesium or steel. Typically, die material has to be resistant to heat cycling or corrosion environment, to plastic deformation and wear, especially when exposed to high temperature during continuous working cycle. The resistance of dies could be increased by the modification of their surfaces, i.e. by the application of an adequate coating. An improvement of the resistance of H11 steel substrate will be presented and discussed.
Research groups: PetroMat
In the present work, a new humidity sensor based on nanostructured hematite deposited by a wet chemical route on a low-cost natural inorganic phylosilicate (sepiolite) powder was obtained. The nanometric character of these particles has been evaluated by X-ray diffraction, thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) and transmission electron microscopy.
Research groups: CeraMat
Ceramic nanocomposites, containing at least one phase in the nanometric dimension, have received special interest in recent years. They have, in fact, demonstrated increased performance, reliability and lifetime with respect to monolithic ceramics.
Ageing behaviour at 180 °C of 6061 aluminium alloy-SiCw composites, drawn from bars obtained in various extruded ratios, and 6061 aluminium alloy used as matrix, have been compared. These materials were dissolved in a salt bath at 529 and 557 °C for 2 h, quenched in ice-water, and aged at 180 °C in an oil bath for increasing periods. Ageing kinetics were studied with Brinell hardness measurements and differential scanning calorimetry (DSC).
Research groups: AddiMat
Two experimental aluminium alloys (belonging to 2000 and 7000 series respectively) were welded using the laser beam welding (LBW) technique and an Al–Si alloy as filler. Different combinations of pre- and post-welding thermal treatments were proposed. The change of strength during aging treatments was investigated by microhardness measurements carried out on the weld and on the regions of the alloys not affected by the LBW process. The microstructure of the welded specimens was studied by scanning electron microscopy and energy dispersive X-ray spectroscopy.
Samples of titanium with a commercial purity grade 4 and of alloys Ti-6Al-4V and Ti-4Al-2Sn-4Mo were surface hardened by laser alloying with boron. This treatment was carried out by contemporaneously laser melting of the titanium alloy surface and powders containing boron which were injected on the surface of the specimens. The alloying powders were deposited on the metal surface either before or during laser treatment. Boronizing powders with different chemical compositions (B, B4C, TiB2, MoB, MoB2 and W2B5) were used to prepare surface coatings.
Research groups: PetroMat
In aeronautic field there is always a continuous research, implementation and application of more and more advanced technologies. This leads to the adoption of lasers in the aluminium sheets cutting to create plane external structures as an alternative at the more consolidate mechanical cutting techniques such as the use of punching machines.
Research groups: CeraMat
Lithium metazirconate is a candidate in fusion reactor designs as a tritium-breeding material. An amorphous powder was synthesized by gelling zirconium propylate and lithium acetate: after heat treatment at 900 °C, pure Li2ZrO3-l was obtained. Preliminary tests made on sintered pellets, obtained from this powder, demonstrated an appropriate tritium release at low temperature, when the sample porosity was about 20% and the mean pore radius 3 μm. The subject of this paper was to realize a good compromise between mechanical properties and the spread porosity, necessary for tritium diffusion.
Research groups: CeraMat
In this paper we report the most significant results of a wide project which aimed to build up a sensor for the CO-detection with improved selectivity through catalytic activation.
Presently, one of the most interesting approaches to the generation of H2 is based on sulphur-based cycles, that however require structural components able to work in a corrosive environment at high temperature. Silicon carbide (SiC) is one of the most promising materials for this application, and to increase its limited toughness multilayered structures can be envisaged, since crack deviation and delamination increase energy adsorption during fracture.
Research groups: PetroMat
An innovative gel-casting process was developed in order to obtain macro porous ceramics scaffolds of hydroxyapatite to be used in regenerative medicine for bone tissue reconstruction. Mechanical investigation was carried out on different formulations of dense hydroxyapatite samples in order to evaluate the effect of the gel casting process parameters on the density, the elastic modulus, the tensile and the compressive strength. The fracture critical stress intensity factor (KIC) was also evaluated by means of microhardness measurements.
Research groups: PetroMat
Purpose: The main goal of this paper was the examination of the role of W addition on properties of two sinterhardened alloys with two different carbon levels. Additionally the influence of sinter-hardening process has been evaluated. Microstructural characteristic and mechanical properties of Ni-Mo steels with increasing amount of tungsten (from 0 to 0.3% wt.) were taken under consideration. Design/methodology/approach: Powder mixes have been compacted at 700MPa and sintered in a vacuum furnace with argon backfilling at 1120°C for 60 minutes.
Research groups: CeraMat
Dense and cellular ceramics were produced from yttria partially stabilized zirconia powders by gel-casting, using agar as a gelling agent and polyethylene spheres (125–300 μm diameter) as volatile pore forming agent to create 50–65 vol.% spherical macropores, uniformly distributed in a microporous matrix.
The mechanical properties of both dense and porous samples were investigated at the microscale by nanoindentation testing.
Research groups: CeraMat
This paper deals with the uniaxial compression behavior of porous ceramics within a wide range of porosity, varying from 30 to 75 vol%. The load–displacement curves recorded on porous alumina samples showed a transition between a typical brittle behavior at porosity fractions below 60 vol% and a damageable, cellular-like behavior, at higher porosity fractions. This transition in fracture mode was confirmed by in situ compression tests in an X-ray tomograph.
Research groups: PetroMat
Mesoporous alumina has been synthesised by the solution combustion synthesis method. While often the synthesis of mesoporous materials with a relatively narrow pore distribution requires the use of a template, this technique allows a simple and rapid synthesis of pure alumina without the use of any templating agent: by regulating the synthesis conditions is possible to obtain from relatively low surface area α-alumina to high surface mesoporous γ-alumina. The porosity of the latter was assessed chiefly by density functional method and was found to be in the range 2.8–3.5 nm.
Research groups: PetroMat
Platinum catalysts supported on ordered mesoporous carbons (OMC) are described. The mesoporous carbon support, CMK3 type, was synthesised as an inverse replica of a SBA-15 silica template. The platinum catalysts (i.e. Pt 20 wt% and Pt 10 wt%, respectively), obtained through a conventional wet impregnation method, have been investigated to determine their structural characteristics and electrochemical behaviour.
Research groups: CeraMat
Research groups: CeraMat
This paper reports a systematic investigation on Mg-substituted hydroxyapatite (Ca10−xMgx(PO4)6(OH)2) nanopowders produced by precipitation of Ca(NO3)2·4H2O and Mg(NO3)2. The Mg content ranged between 0.6 and 2.4 wt%. Semicrystalline Mg-substituted hydroxyapatite powders made up of needle-like nanoparticles were obtained, the specific surface area ranged between 87 and 142 m2/g. Pure hydroxyapatite nanopowder decomposed around 1000 °C.
Low-load indentation experiments have been performed on electrophoretic-deposited films of SiC particles on a graphite substrate. Films with thicknesses between 60 and 300 μm prepared at two current intensities and subsequently dried under different humidities were indented with spherical indenters with nominal radii of 10, 50, and 150 μm. Force-displacement data were analyzed to determine contact pressure and elastic modulus versus depth results.
Research groups: CeraMat
Three-phase composites in the system Al2O3–YAG–ZrO2 (AYZ) were produced by doping the surface of commercial alumina nanopowders with inorganic precursors of the second phases. Materials with three different compositions were prepared, in which 5, 20 and 33 vol.% of each second phase were respectively present. Pure crystalline phases were obtained in the final composites, as assessed by X-ray diffraction. Green bodies were produced by slip casting and uniaxial pressing.