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High Temperature Materials

Fabrication of titanium matrix composites by high pressure plasma spraying

Titanium matrix composites reinforced with continuous fibres are candidate materials for high performance structural components in aerospace applications. The present work has been focussed on the use of a fabrication methodology of composite monotapes alternative to the well known fibre-foil techniques. The same fabrication procedure was also selected to produce composite preforms suitable for secondary consolidation processes, as those based upon diffusion bonding methods, in order to obtain multilayered composites.

Co-continuous Al/Al2O3 composite produced by liquid displacement reaction: relationship between microstructure and mechanical behaviour

Co-continuous 63%Al2O3/37%Al(Si) composite, known as C4 composite, was produced by submersion of silica glass specimens in a molten metal bath. The effect of temperature and composition of the metal bath on the reactive penetration rate was investigated. An infiltration speed exceeding 2 mm/h, increasing with temperature, and suitable for practical applications, was observed above 1100 °C. Mechanical properties of C 4 specimens were measured, at room temperature, and related to composite microstructure.

Hetoroporous heterogeneous ceramics for reusable thermal protection systems

Reusable thermal protection systems of reentry vehicles are adopted for temperatures ranging between 1000 and 2000 °C, when gas velocity and density are relatively low; they exploit the low thermal conductivity of their constituent materials. This paper presents a new class of light structural thermal protection systems comprised of a load bearing structure made of a macroporous reticulated SiSiC, filled with compacted short alumina/mullite fibers. Their manufacturing process is very simple and does not require special devices or ambient conditions.

Thermal fatigue behaviour of a 2014/Al2O3-SiO2 (Saffil Fibre) composite processed by squeeze casting

Thermal fatigue behaviour of a 2014/Saffil composite has been investigated. This composite was produced by infiltration of preforms of Saffil fibers (Al2O3-SiO2 fibers) with a 2014 aluminium alloy (Al-4.7Cu-1.0Si-0.6Mg). The composite samples, containing 13 vol.% of fibers, were sectioned and their microstructure was investigated by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). Tensile tests, hardness and microhardness measurements were carried out. The fracture surfaces were examined by SEM.

High temperature behaviour of a Ti-6Al-4V/TiCp composite processed by BE-CIP-HIP method

The high temperature behaviour of a Ti-6Al-4V/TiCp composite (10% Vol. of TiC) was investigated. A composite produced by Dynamet Technology according to the blended-elemental-cold-hot isostatic pressing (BE-CHIP) method was used. The stress-strain properties of the material were tested at 25, 200, 400, 500, 600 and 800°C. Composite specimens were aged in air at 500 and 700°C or under vacuum at 500, 700 and 1050°C, for periods ranging between 100 and 500 hours.

Degradation at 1200°C of a SiC coated 2D-Nicalon/C/SiC composite processed by SICFILL® method

The thermal stability of a 2D-Nicalon/C/SiC composite was studied through the variation of both mechanical properties and microstructure occurring during heat treating. The composite was processed by infiltration of SiC preforms according to SICFILL® method. The material toughness was enhanced by a carbon interphase put between the fibers and the matrix. In order to improve the thermal stability a CVI layer was deposited on the carbon interphase and the specimen surfaces were CVD covered by an external SiC seal coating about 165 μm thick.

Suitability of aluminizing for protection of nichel superalloys turbine blades in oxidative and corrosive environments

Three kinds of turbine blades (made by casting Renè 77, Renè 80 and CMSX-4 nickel based alloys) were submitted to an above pack aluminizing treatment. The suitability of this surface coating for preventing high temperature oxidation and hot salt corrosion was investigated. Oxidation tests were performed in air at 1050°C for 500 and 1000 h; salt corrosion at 950°C was studied by using a NaCl+Na2SO4 mixture. The microstructure of aluminized blades before and after these tests was compared by X-ray diffraction, scanning electron microscopy and electron probe microanalysis.

Forging of 2124/SiCp composite: preliminary studies of the effects on microstructure and strength

Forging behaviour of 2124 aluminium alloy containing 26 vol.% of SiC particles (average size 3 μm) was investigated by means of room and elevated temperature tensile tests (range of temperature 20–350°C). The results obtained were utilized to define the forging parameters (deformation ratio 3.5:1, strain rate 0.14 s−1, sample temperature during the hot deformation process ranging from 440 to 340°C). Microstructure of as-fabricated and forged specimens was investigated.

High temperature oxidation of multilayered SiC processed by tape casting and sintering

The oxidation behaviour of a multilayer SiC ceramic was investigated at high temperatures. The ceramic samples were processed by tape casting of a slurry containing α-SiC powders, forming of green tubular components and sintering without pressure. The oxidation resistance of this ceramic material was investigated by temperature programmed oxidation (TPO): the gaseous oxidation products were analysed by mass spectrometry. Thermal gravimetric analyses (TGA) were also performed.