Materials Science Forum Vols. 514-516

Abstract: This paper is concerned with a notch sensibility study of a thermoplastic composite produced from a bi-directional woven E-glass fibres and polypropylene. Experimental tests were performed in three points bending using notched and unotched specimens of polypropylene glass fibres reinforced laminates to evaluate flexural properties and fatigue behaviour. Fatigue results were plotted as the stress range against the number of cycles to failure. The fatigue damage was measured in terms of the stiffness loss. The testes carried out using notched specimens present lower values of both static and fatigue strengths than the unnotched specimens tests.

Abstract: High temperature oxidation of TiC ceramic matrix Fe40Al and Ni3Al toughened composites (Fe40Al/TiC, Ni3Al/TiC) of different TiC contents, made by pressureless melt infiltration, was investigated. Oxidation experiments were conducted in air for up to 65 hours at 700-1100°C. Weight gains of the composites showed that Fe40Al/TiC is more oxidation resistant than Ni3Al/TiC ones. SEM/EDS and X-ray diffraction showed that the dense oxidation layers of the two types of composites are mainly composed of crystalline TiO2. The growth of the oxidation layer follows parabolic passive oxidation kinetics, the calculated values of the activation energy of the oxidation mechanism being 270-280kJ.mol-1 and 240-250kJ.mol-1 for Fe40Al/TiC and Ni3Al/TiC, respectively. Al2O3 and Ni-rich phases were also detected in the oxidation layer of Fe40Al/TiC and Ni3Al/TiC, respectively.

Abstract: Unsaturated polyester resins are extensively used in the automotive industry as matrix for polymer based composite materials, but have poor impact resistance. Toughness can be improved dispersing a softer phase in brittle polymers. Scrap tyres constitute a significant waste problem and are a low-cost source for rubber. The objective of this work is the mechanical characterization of matrix systems containing solid rubber particles obtained from scrap tyres. Several pre-treatments were tested based on contact time and temperature. The flexural and Charpy impact behaviour of the modified resins showed a decrease in performance. Dynamic mechanical tests did not result in clear evidence of phase mixing. Optical microscopy showed the presence of contaminant particles, which were considered the cause for the low performance. Among the modified resins, a positive shift in flexural behaviour occurred when pre-heating was used. It is thought the strategy may prove effective in enhancing resin toughness, if the waste rubber is purified prior to its utilization.

Abstract: In this work, the (Zr-Ti)(Fe-Cr)2 based compounds have been synthesized while charging-discharging hydrogen ability has been examined. Relatively low hydrogen pressure has been used for the hydrogenation of the samples. After following the discharging procedure, a high desorbed amount of hydrogen ~180 (ml of H2)/(gr of the alloy) has been measured on the first 15 min by using a volumetric device. The crystal structure has been analyzed by means of x-ray diffraction (XRD) while a Rietveld analysis has been performed on the x-ray diffraction patterns and the characteristic MgZn2 type of structure has found to be the dominant phase in both compounds. The scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX) have been used for microstructural studies and quantitative analysis, respectively. Magnetic measurements have been performed on the samples and a paramagnetic behaviour has found to be at room temperature.

Abstract: The failure of carbon fibre bundles of Tenax 5131 HTA with 6000 filaments is characterised using the European Standard EN 1007-5. It is shown that the addition of liquid paraffin to the bundle causes a global change of the load-displacement curve and the effects of the presence of a liquid lubricant are discussed.

Abstract: In this work a theoretical model describing the consolidation of glass fibrepolypropylene (GF/PP) towpregs into composites by compression moulding is studied. Such model relates the constant pressure applied by the press to the other processing operational (consolidation time and temperature) and material variables (fibre/polymer content and packing arrangement, matrix viscosity and powder and fibre dimensions). Compression tests were carried at different temperatures and constant press pressures on unidirectional GF/PP towpreg preforms. The experimentally determined displacement/time curves were compared to the model simulations assuming an isothermal consolidation and two different fibre/polymer packing arrangements, one triangular and the other hexagonal. The results obtained showed that the towpreg consolidation could be successfully predicted using the model under study.

Abstract: A bis-sulphur silane (BTESPT) was used to produce thin protective layers on AA2024- T3, a structural aluminium alloy widely used in the aeronautic industry, being the coatings analysed ex-situ by ellipsometry. Despite a slight degree of film anisotropy evidenced by measurements at different angles of incidence, an optical model of a single homogeneous phase could be employed to describe the silane based layer. The information obtained allowed to characterize the influence of the operational deposition parameters on the film thickness and structural organization of the silane phase (evaluated by its optical absorption). It is shown that the silane concentration of the solution and immersion time determine the final thickness of the formed layer while the curing time does not affect significantly this parameter. On the other hand, it was observed a marked decrease of the optical absorption of the coatings submitted to curing temperatures of at least 100°C, which should be ascribed to a structural reorganization phenomena induced by the removal of water molecules from the film. The data gathered by ellipsometry were successfully corroborated by independent surface profilometry analysis of the films.

Abstract: In this work, W-S-Ti films were deposited by r.f. magnetron sputtering, using simultaneously WS2 and Ti targets. The atomic percentage of Ti in the coating was varied from 0 at.% up to 28 at.%. No significant variations in the S/W ratio with the increase of Ti content were observed. The increasing Ti contents in the films led to a gradual loss of crystallinity. Coatings with contents greater than ≈ 16 at.% only presents a broad peak characteristic of amorphous structures. Alloying the films with Ti led to significant improvements in the hardness (from 0.3 to 8.9 GPa). Also, the adhesive critical load continuously grew with the increase of the Ti content in the films. The wear coefficient of the films dropped more than one order of magnitude with the increase of Ti content whereas the friction coefficient was kept fairly constant with just a small increase in relation to single W-S film. In conclusion, to have a good tribological performance, the addition of Ti to the films should be balanced in order that the increase of the mechanical properties does not lead to severe loss of the self-lubricant properties.

Abstract: In the present work a monocrystalline Cu-13.5Al-4Ni (wt.%) alloy with shape memory effect (SME) submitted to thermal cycling inside the critical range was investigated in terms of number of cycles and resulting structural changes. Attention was paid to the structural changes associated with reversible β1↔γ’1 martensite transformation. The monocrystalline Cu-Al-Ni alloy was produced in Russia, according to a specific technology. The structural characteristic of the alloys was studied through optical microscopy and X-ray diffraction methods using Cu-Kα radiation. Differential scanning calorimetry permitted the determination of the temperature range as well as a thermal effect due to the β1↔γ’1 martensitic reversible transformations, before and after 100, 200 and 300 thermal cycles.

Abstract: The aim of this research is to study the effect of the welding process on the microstructure and mechanical properties of friction stir welded joints in aluminium alloys 2024- T3, 5083-O and 6063-T6. A small loss of hardness and strength was obtained in welds in alloys 2024-T3 and 5083-O as opposed to welds in alloy 6063-T6, where a substantial softening and a drop of strength were observed. In alloy 6063-T6 a strength efficiency of only 45 to 47% was obtained.