Materials Science Forum Vols. 537-538

Abstract: Polycrystalline diamond layers are mostly used in various fields of industrial application. Mechanical tension is generated due to the different heat expansion coefficients of the substrate and the layer, which leads to fracturing in some cases. In this work a homogeneous polycrystalline diamond structure has been deposited on Si/SiO2 substrate by microwave assisted CVD method (MW-PECVD). An selective etching technique has been used to remove the silicon below the 2.5 micron thick diamond layer. A self-supporting diamond structure has been created this way. Polycrystalline diamond based heaters and thermometers can be made from doped diamond materials, which can resist corrosive and radiative environment.

Abstract: The mechanical behaviour and ballistic performance of carbon, glass (E and S type), aramide and polyethylene fabric reinforced composites with different epoxy resins were studied. The specimens −produced by hand lay-up method− were qualified by low velocity (Charpy and drop weight tests) and high velocity (two different bores ballistic) impact tests. The energy absorption capacity of the composites were found to be strongly affected by material properties of reinforcing fibre, type of fabric structure and elasticity of resin.

Abstract: Availability of a stable carbon nanotube suspension is a prerequisite for production of polymer composites with carbon nanotube as additives. In this work nanotube suspensions, which have been prepared from various nanotubes in different dispersion agents, were compared. Dispersibility of the samples was investigated by scanning electon microscopy and atomic force microscopy. Solution of a non-ionic surfactant was also used successfully as a new dispersion agent. Geometrical parameters of the carbon nanotubes were determined by using atomic force microscopy. Correlation was found between the dispersibility and the parameters of the nanotubes and relative permittivity of the different solvents.

Abstract: Supersaturated Al-4.8Zn-1.2Mg-0.14Zr and Al-5.7Zn-1.9Mg-0.35Cu (wt.%) alloys were processed by Equal-Channel Angular Pressing (ECAP) at 200°C. The crystallite size distribution and the characteristic parameters of the dislocation structure of both Al matrix and precipitates were determined by X-ray diffraction line profile analysis, which has been complemented by transmission electron microscopy (TEM) observations. Results of these investigations show that the bulk ultrafine-grained microstructure with high dislocation density produced by ECAP has strong influence on the precipitation process, resulting in high strength in both alloys.

Abstract: In-situ synthesized Al2O3 reinforced metal-ceramic composite coating was fabricated on lowalloyed carbon steel surface by laser cladding. Injection of the ceramic powder into the melted surface can be difficult due to the effect of surface tension and to the lower density of the Al2O3 particles, compared to that of the steel matrix. These difficulties can be avoided by the in-situ synthesis of Al2O3 particles in the liquid steel matrix. In this paper, the results of experiments performed by laser beam will be introduced, together with the interpretation of these results. Experiments proved that the Al2O3 ceramic phase can be created in-situ in the steel matrix.

Abstract: The devitrification of the Fe-Ni-B-Si amorphous ribbon was investigated by the differential scanning calorimetry (DSC) with scanning and isothermal methods. The devitrification of rapidly quenched ribbons is a multilevel process. On the basis of DSC investigations it was determined that crystallization occurs in three processes up to 700°C in the Fe40Ni40B16Si4 alloy. In the present work the first and second steps have been discussed. The first crystallization step involves the segregation of the Fe-Ni crystalline solid solution from the amorphous matrix. During the second crystallization phase, in addition to austenite, nickel silicide and two types of iron borides crystallize as well. The ribbons were relaxed at 380°C for 2 hours, following the pre-annealing at different temperatures. Pre-annealing was performed in the DSC within the temperature range elapsing from 395°C to 420°C. The preannealing at temperatures below the first exothermal DSC peak has an effect on the crystallization processes. After the pre-annealing the samples were investigated by DSC. The DSC peak of the first crystallization step shifts to higher temperatures and decrease its enthalpy. The scanning DSC measurements, applied after the isothermal pre-annealing, were performed in order to determine the fraction of the ribbon transformed in the primary crystallization step. The second DSC peak shifts to lower temperatures with a maximum of 4°C. The X-ray diffraction (XRD) analyses reveal that the lattice constant changes with the pre-annealing temperatures. Such observation was also supported by the circumstance that the composition of the Fe-Ni solid solution undergoes certain modifications.

Abstract: Nowadays, metal matrix composites have many new areas of application owing to their excellent properties - for example their great tensile strength and high Young’s modulus with its relatively low weight. The aim of this work is to an examination of ceramic fibre-reinforced aluminium matrix composite wires made via continuous process. Furthermore, the research will outline the double composite products that are composite wire-reinforced metal matrix composites. Double composites are examined by tensile tests, bending tests and pressing tests. A lot of research has been done on the thermal aging of composite wires and on measuring the impact energy of thermal-aged specimens. The mechanical test shows us that structures reinforced with the composite wires have a notably higher load-carrying capacity than does a structure reinforced directly with fibres or a structure without any reinforcement.

Abstract: Wood fiber reinforced polypropylene composites of different fiber contents without any treatment were prepared, and tensile tests were carried out on injection molded specimens. With increasing fiber content a decrease of the tensile strength was experienced. The weak adhesion at the fiber-matrix interface and the typical composite failures can be seen on SEM pictures. During the tests acoustic emission was monitored to get more information about the damage mechanism. From the AE counts distribution it can be concluded that the maximum number of AE counts decreases simultaneously with the tensile strength in case of the different composites.

Abstract: Polycrystalline diamond and diamond-like carbon (DLC) films were deposited by microwave chemical vapor deposition (MW-CVD) and by pulsed laser deposition (PLD) respectively. Ar ion bombardment was used to change the properties of these layers. The sp2 bonds were determined directly by reflected electron energy loss spectroscopy (REELS) and further characterization was made by Raman scattering. The polycrystalline diamond showed only very slight π-π* transition at 6.5 eV, but after Ar ion bombardment strong peak was formed but definitely shifted to lower energy compared to the well known π-π* transition of graphite. The as deposited PLD carbon films showed broad peak around 5eV clearly different than the π-π* transition (6.5eV). After Ar+ ion bombardment the peak was shifted also to lower energy range (4-5eV) with a remaining part at 6.5eV. The lower energy part of the peak can be correlated to the transition of sp3 sites, while this change in peak position was not detectable after ion bombardment of the reference HOPG sample, which does not contain sp3 hybridized carbon atoms.

Abstract: Bulk Al6082 alloy is subjected to ECAP using route Bc. This paper focuses on the determination of the anisotropy coefficients and equivalent stress-equivalent strain curve using continuum mechanics equations. Assuming the material to be rigid-plastic, the parameters of the constitutive equation are determined with the aid of measuring the deformation and the uniaxial yield stress during upsetting tests in three perpendicular directions.