Band 105, Heft 1

Conductive polymers are widely studied as microwave absorbing materials due to their light weight, corrosion resistance, good and flexible processibility and variability of conductivity. Among them, polyaniline (PANI) microwave absorbing materials have been studied most extensively because of their easier and inexpensive preparation methods, good environmental stability in both doped and undoped forms, excellent physical and chemical properties, high conductivity at microwave frequencies and unique doping mechanism with its ease of protonic acid doping in the emeraldine form. In this paper, the preparation and the microwave properties of PANI/inorganics composites and PANI/insulating polymer composites are thoroughly reported.

An effective approach to establish the atomic mobility parameters of quaternary Cu-rich fcc Cu–Mn–Ni–Zn alloys is presented through assessments of the critically-reviewed experimental diffusivities available in the literature by means of DICTRA (DIffusion Controlled TRAnsformation) software. In the quaternary Cu-rich fcc Cu–Mn–Ni–Zn alloys, atomic mobilities in ternary fcc Cu–Mn–Ni and Cu–Ni–Zn boundary systems were directly taken from our previous work, while atomic mobilities in ternary fcc Cu–Mn–Zn boudnary system were assessed as a function of temperature and composition in this work. Since no experimental data were available, the atomic mobility database for fcc Ni–Mn–Zn alloys was not assessed but just directly extrapolated based on the three constituent binary alloys. Considering that the accurate quaternary interdiffusion coefficients were usually absent in the literature, atomic mobilities in fcc Cu–Mn–Ni–Zn alloys were extrapolated based on the assessed atomic mobilities in the 4 ternary boundary systems. On the basis of the obtained mobility parameters, simulations of a series of ternary and quaternary diffusion couple experiments were performed. The concentration profiles and the diffusion paths in diffusion couples were well reproduced by the presently obtained parameters. Furthermore, 3D views of the concentration profiles, diffusion fluxes, chemical potential and quaternary interdiffusion coefficients surfaces were calculated with the obtained atomic mobilities to analyze the uphill diffusion and zero-flux plane phenomenon in some quaternary diffusion couples. In addition, simple criteria for judging whether the uphill diffusion and/or zero-flux plane can occur are also proposed.

Fe 60 Si 40 (at.%) alloys were synthesised using a planetary ball mill. X-ray diffraction was used to identify and characterise various phases formed during the milling process. Mössbauer and electromagnetic methods were used to characterise the variations in structure and their influence on the local change of magnetic properties. The shape of hyperfine field distributions used to describe the Mössbauer spectra is discussed. It was found that after 4 h of milling, α-FeSi and Fe 3 Si starts to form. The coexistence of the α-FeSi phase and Fe 3 Si was found between 8 and 16 h. After 32 h of milling, the powder was completely transformed into the alloy phase (Fe 3 Si). The value of the mean particle size of our samples decreases with increasing milling time. It reaches the value of 0.42 μm after 56 h of milling. The crystallite size was reduced to 13 nm after milling. The coercitive field H C decreases with increased milling time.

CeMg 12 + 100 wt.% Ni composite hydrogen storage alloys were prepared using ball-milling. The phase structure, morphologies, and hydrogen absorption and desorption kinetics of these alloys were systematically investigated. The results show that the milled CeMg 12 + 100 wt.% Ni alloys consisted of Mg 2 Ni and Ni phase with nanocrystalline and amorphous structures. Additionally, the volume fractions of the phase increased with prolonged ball-milling times, which improved the hydrogenation rates and the hydrogen storage capacities of the alloy samples. However, the dehydrogenation kinetics of the alloy samples were also impaired by the increased milling times. The poor dehydriding kinetics of the alloy samples milled for 80 h and 100 h were primarily attributed to grain size effects.

In this study we used RF plasma-assisted molecular beam epitaxy for the epitaxial growth of single-crystalline indium nitride (InN) thin films on aluminum nitride buffer layers/Si (111) substrates. We then used scratch techniques to study the influence of the c -axis orientation of the InN films and the beam interactions on the tribological performance of these samples. When grown at 440, 470, and 500 °C, the coefficients of friction were 0.18, 0.22, and 0.26, respectively, under a normal force ( F n ) of 2000 μN; 0.19, 0.23, and 0.27, respectively, under a value of F n of 4000 μN; and 0.21, 0.24, and 0.28, respectively, under a value of F n of 6000 μN. These measured values increased slightly upon increasing the growth temperature because of the resulting smaller sizes of the apertures and/or pores in the inner films. The sliding resistance of the ploughed area was observed. The contact sliding line became increasingly noticeable upon increasing the value of F n ; the plot of the friction with respect to the penetration depth revealed a significant relation in its adhesion properties presentation.

AA6063 is an aluminium alloy with moderate strength. This type of alloy is widely used in the construction and automotive industries. In this article, the role of axial thrust in the formation of microstructure and fracture surface of the weld zone in friction stir welded AA6063 aluminium alloy is discussed. Butt joints were fabricated at five axial thrusts of 4 kN, 5 kN, 6 kN, 7 kN and 8 kN using an unthreaded tool pin. The rotational speed and translational velocity of the tool were maintained constant at 1500 revolutions per minute and 25 mm min −1 respectively. Specimens were prepared from the joints, and tensile testing was carried out. The ultimate tensile strength and percentage of elongation were calculated. Vickers hardness was measured in the weld zone at mid-thickness on the advancing and retreating sides. The microstructure and fracture surface of the joints were also examined. It was found that the joint produced at the axial thrust of 6 kN exhibited superior ultimate tensile strength, higher percentage of elongation and higher micro-hardness. This joint exhibited a superior quality weld zone without kissing bond and tunnel defects.

Three typical superlight Mg–Li alloys (Mg-5Li-3Al-2Zn, Mg-8Li-3Al-2Zn and Mg-14Li-3Al-2Zn) with the matrixes of alfa(Mg), alfa(Mg) + beta(Li) and beta(Li), respectively, are prepared. The microstructures of the alloys are characterized using optical microscopy and X-ray diffraction. The corrosion resistant properties of the alloys are characterized by means of hydrogen evolution, weight loss and potentiodynamic polarization. The alloys are also oxidized at elevated temperature. The microstructure and corrosion resistant property of the alloys after oxidation are also characterized.

The effect of Al 2 O 3 coating on oxidation and hot corrosion was investigated at 700 °C in an atmosphere of 9 %O 2 + 0.2 %HCl + 0.08 %SO 2 + N 2 . Isothermal oxidation testing indicated that the coating was very effective in reducing the oxidation rate of γ-TiAl. The technology of magnetron sputtering used in this study allowed the deposition of a coating that ensured the improvement of high temperature oxidation resistance without interference in mechanical properties of the alloy.

The homogenization practice for direct chill cast AlSi1MgMn billets was investigated. It takes 8 h at 570 °C and at least 4 h at 580 °C to even out the Mg and Si distribution in the aluminium matrix and to obtain relatively small discrete α c -Al 12 (Fe, Mn) 3 Si particles with a “necklace” configuration. Once Mg and Si are solutionized, the equilibrium β-Mg 2 Si phase precipitates during post-soaking cooling at ≥ 500 K h –1 . β′-Mg 2 Si precipitates are also identified in samples cooled at ≤ 250 K h −1 . Hardness produced in this cooling rate range is relatively lower suggesting improved extrudability. These billet samples are fully solutionized at 500 °C during billet pre-heating. Typical press exit temperatures may suffice for adequate age hardening in billet samples soaked at 580 °C for 8 h and subsequently cooled at 250 K h −1 . This is a very attractive feature as it implies a full age hardening capacity even without the need for a separate solution heat treatment.

The microstructures, martensitic transformation, mechanical and shape memory properties of (Ni 53 Mn 22 Co 6 Ga 19 ) 100–x Y x ( x = 0, 0.1, 0.3) high-temperature shape memory alloys were investigated. It was found that small Y addition results in the refinement of grain size and the increase of γ phase volume fraction. These changes can effectively improve the tensile ductility and fracture strength of two-phase Ni 53 Mn 22 Co 6 -Ga 19 alloy, up to the maximum values of 10.1 % and 592 MPa respectively at x = 0.1. However, it is proposed that Y(Ni, Mn) 4 Ga precipitate forms in the alloys with the addition of Y, and its amount increases with further increasing Y addition. The growth of the Y(Ni, Mn) 4 Ga precipitate results in a decrease in the tensile ductility at x = 0.3. Results further show that shape memory properties of the studied alloys are closely related to the refinement of grain size and the alloy yield strength. While adding 0.1 at.% of Y, the shape memory effect and recovery rate decrease, resulting from the refinement of grain size, compared to those of two-phase Ni 53 Mn 22 Co 6 Ga 19 alloy. Subsequently they increase with further increasing Y content to 0.3 at.% due to the decrease in the alloy yield strength.

A simple thermal treatment induced transition from Zn 3 (OH) 2 (BDC) 2 (MOF-69c) to Zn 4 O(BDC) 3 (MOF-5) is reported. Phase crystallinity, pore characteristics and hydrogen storage capacities of the resulting crystals were investigated. It is shown that the structural transition from Zn 3 (OH) 2 (BDC) 2 (MOF-69c) to Zn 4 O(BDC) 3 (MOF-5) could be induced by simply employing the optimal thermal treatment conditions of 200 °C for 48 h in open air. The resultant relatively lower specific surface area of MOF-5 crystals compared to MOF-69c was in agreement with the increased pore diameter and decreased hydrogen storage capacity at 1 bar and 77 K.

Alumina-based refractories are the most commonly used materials for lining electrical furnaces. Bauxite and aluminate chamotte were selected, bound with aluminate cement, and their thermal stability was studied using differential scanning calorimetry and thermogravimetry. Their loss on ignition, after firing at 1000 °C, was determined. The main changes in mass observed were attributed to the removal of moisture at temperatures up to 140 °C and to the dehydration of calcium aluminate cement at 200–300 °C. Boehmite (500 °C) and bayerite transformations (650–700 °C) were recorded for bauxite samples, while chamotte samples exhibited changes due to goethite conversion to hematite (400 °C) and spinel formation at 900 °C. Water removal was then examined in detail through differential scanning calorimetry tests. Experiments for loss on ignition showed that particle size of refractory bauxite does not affect mass changes during firing, while chamotte samples were found to show greater loss at particle sizes 200–315 μm, due to impurities and low melting point compounds.

A rapid and simple method has been developed for the magnetization of non-magnetic materials. The postmagnetization procedure employs magnetic iron oxide microparticles (prepared using a microwave assisted procedure from ferrous sulphate) which are thoroughly mixed with the powder material to be modified. After drying, stable magnetically responsive materials have been formed.