Band 106, Heft 1

We introduce a new thermo-mechanical approach for producing layered bulk samples built-up from the constituent phases of structural materials for the analysis of multiphase co-deformation phenomena. Following a thermo-mechanically controlled roll-bonding procedure, the intrinsic properties of the microstructural components as well as their mutual mechanical interaction and interfacial phenomena can be systematically investigated in highly controlled model microstructures of reduced complexity. The effectiveness of the approach is demonstrated on two examples where austenite or martensite layers, respectively, are introduced in a bulk ferritic matrix, representing in either case components of high strength steels. Special emphasis is laid on how the plasticity of martensite within ferrite, as a key parameter required for understanding and optimising dual phase steels, can be investigated following the proposed approach.

Sheets of Mg-4Er (wt.%) alloy were prepared by multi-pass hot rolling and subsequent annealing. The annealed sheets could be cold-rolled to a high reduction of 95% (corresponding to a rolling strain of 3) by one-pass rolling at room temperature. The evolution of the deformed microstructure of Mg-4Er alloy was investigated during the cold-rolling process. The results suggest that multiple dislocation slips are the predominant deformation mode responsible for the remarkable rolling plastic strain. Meanwhile, the multiple dislocation slips are favorable to a continuous restoration process, which can accommodate the rolling strain by absorbing the deformation energy.

In the present work, the effects of cold work and aging parameters on the microstructure and precipitation kinetics of Ni-Span-C 902 superalloy were studied. The solution treated alloy was cold-rolled to different deformations from 30 to 60% followed by aging in the temperature range of 450–850°C for different times, from 10 2 to 10 5 seconds. The results showed that the 50% cold-rolled alloy attained its maximum hardness by aging at 650°C for 10 5 seconds. This was concurrent with the fine distributed gamma′ precipitates that appeared in the microstructure. By increasing temperature from 750 to 850°C, overaging occurred due to the increase in gamma′ particle size and the formation of epsilon-phase. The estimated activation energy of the precipitation reaction, based on Johnson–Mehl–Avrami–Kolmogorov analysis, was determined to be 254 kJ · mol −1 for the 50% cold-rolled alloy.

The microstructural, electrical and mechanical characteristics of conventionally and rapidly solidified Ni-23 wt.% Al alloys after heat treatments were investigated. The microstructures of Ni-23Al alloys were examined by means of scanning electron microscopy and the phase composition was identified using X-ray diffraction analysis. The phase transitions during the solidification process were investigated using differential thermal analysis under an Ar atmosphere. X-ray diffraction analysis indicated that the Ni-23Al samples showed an intermetallic γ′-Ni 3 Al phase, and we observed the intermetallic γ′-Ni 3 Al phase together with the β-NiAl phase after heat treatment at 700–900°C for 24 h. We performed electrical resistivity measurements by using the four-point probe technique in the temperature range 100–900°C. The resistivity of Ni-23 wt.% Al samples increases linearly with temperature. Vickers microindentation tests were carried out on the heat-treated samples with loads ranging from 392.26 mN to 1174.86 mN at room temperature. We found that the microhardness and effective elastic modulus values increased with increasing temperature and these values showed peak load dependence. The tensile and compressive stress values of the Ni–Al alloys also decreased with increasing temperature.

In this study, the influences of reinforcement volume fraction and the ratio of the reinforcement particle size to the matrix particle size on the wear behaviour of Al/SiC metal matrix composites were investigated by use of a model function obtained from an artificial neural network. Hardness and ball-on-disc wear tests were applied to Al/SiC composites manufactured via a powder metallurgy method. The results indicate that as the reinforcement volume fraction and the ratio of the reinforcement particle size to the matrix particle size increase, the wear loss decreases except in two cases; in the first case (vol.% ≤ 7.5), as the ratio of the reinforcement particle size to the matrix particle size rises, the wear loss increases and then decreases. In the second case, the decreasing trend of wear loss at high values of volume fraction (≥ 15%) declines and then increases where the value of the reinforcement to the matrix particle size ratio is about 1.

Various Ni–Zn–P alloy coatings were deposited onto aluminum substrates using electroless plating from a sulphate bath containing varying amounts of zinc (II) ions. Different techniques, such as scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, were employed to characterize the morphology, composition and structural properties of the resulting films. The effect of varying Zn content on the corrosion properties of the coatings was tested in 3 wt.% NaCl media, by means of current–potential curves, potential transients and electrochemical impedance spectroscopy measurements. It was found that increasing ZnSO 4 concentration from 5 to 25 g l −1 in the plating bath, increases the Zn content in the film from 9.90 wt.% to 12.7 wt.%, reduces the film thickness, modifies the surface morphology and significantly reduces the corrosion rate.

A new joining method, termed resistance spot welding with a rivet, was tried to weld steel to aluminum alloy. Scanning electron microscopy studies of the interfacial microstructures revealed the presence of an FeAl reaction layer at the rivet/aluminum alloy interface, and of FeAl 3 at the steel/aluminum alloy interface. A tensile shear load of a maximum of 3.85 kN was obtained at a welding current of 21 kA. The results reveal that resistance spot welding with a rivet is an effective method for joining steel and aluminum alloy.

The broad interest in the thermophysical properties of gallium-based melts is stimulated by their extensive use in various applications, such as sliding contacts, heat-sensitive elements of liquid-metal thermometers and thermocouples, carrier liquid for conducting magnetic fluids and the working medium for physical modeling in solidification and magnetohydrodynamic studies. The electrical conductivity, thermal conductivity, viscosity, density and thermoelectric power were determined for different alloy compositions in a wide temperature range below and above the liquidus. Respective scaling relations are proposed. A comparison with data available in literature is given.

Co(OH) 2 –graphene composite was prepared through a simultaneous hydrothermal method. The structure, morphology and electrochemical performance of the obtained samples were systematically investigated by means of X-ray diffraction and transmission electron microscopy. Furthermore, cyclic voltammetry measurements showed that the Co(OH) 2 –graphene electrode material had an excellent electrochemical capacitance.

An alternative approach for preparing anisotropic MnAlC powders is reported. [001] textured MnAlC flakes with various sizes and thicknesses were fabricated by surfactant-assisted ball-milling (SABM) of bulk ingots. After ball-milling for 8 h the flakes have thicknesses below 200 nm and aspect ratios as high as 10 2 ∼10 3 . After being annealed at suitable temperatures, both bulk and SABMed powders can transform from ∊-phase to τ-phase completely. C-doping cannot prevent the decomposition of the τ-phase into the β+γ 2 phases after annealing at above 500°C. The magnetic properties are strongly dependent on both the fraction of the τ-phase and the thickness. A high coercivity of ∼242.8 kA m −1 has been achieved in SABMed powders. The coercivity value is 128.8% higher than the experimental value for bulk materials.

93W-4.9Ni-2.1Fe (wt.%) alloys were fabricated by means of conventional two-stage sintering, direct microwave sintering and improved two-stage sintering. A more homogeneous microstructure was found in both the direct microwave sintered alloy and the improved two-stage sintered alloy. Numerous pores were present in the direct microwave sintered alloy, but few could be seen in the improved two-stage sintered alloy. The mechanical properties of the improved two-stage sintered alloy were greatly enhanced as compared to those of the direct microwave sintered alloy. These findings suggested that the improved two-stage sintering had little negative effect on absorbing microwaves and could reduce pore defects, which implied a promising sintering process for tungsten heavy alloys and others with liquid stage sintering.

The Pb content effect of chemical solution deposited lanthanum-doped lead zirconate titanate (PLZT) (Pb:La:Zr:Ti = Pb:3:30:70, Pb = 105∼117) was studied for conductive aluminum-doped zinc oxide (AZO) and tin-doped indium oxide (ITO) deposited as top electrodes by means of pulsed laser deposition. The crystallinity, surface morphology, ferroelectric properties and hydrogen degradation resistance of the ITO/PLZT/Pt and AZO/PLZT/Pt capacitors were evaluated. All the PLZT films showed perovskite phase (revealed by X-ray diffraction patterns) and showed similar surface morphology and grain size (revealed by scanning electron microscopy images). PLZT capacitors with a Pb content of 113 exhibited the largest remnant polarization (at 15 V (300 kV cm − 1 )), however, the difference in hydrogen degradation resistance was small between the four levels of Pb content.

In this study, La–Zn-substituted SrFe 12 O 19 ferrites were synthesized using the traditional ceramic process. The by-products of iron oxide scales from a steel plant were used as the main raw materials. The influence of the La–Zn substituent and the calcination temperature on the microstructure and magnetic properties of Sr 1 − x La x Fe 12 − x Zn x O 19 ferrites was investigated. The results showed that with the increase in the x value, the crystalline lattice constant of the a - and c -axes and the cell volume decreased. There was no α-Fe 2 O 3 phase in the ferrites when the value of x was 0.3. The corresponding saturation magnetization ( M s ) and remnant magnetization ( M r ) values were, respectively, about 65 emu g − 1 and 39.5 emu g − 1 . Both values of M s and M r rise to the maximum value. When the calcination temperature was reduced from 1200°C to 1150°C, the average particle size decreased from 0.9 μm to 0.7 μm and M s remained at 65 emu g − 1 . However, the coercivity increased from 2690 Oe to 3100 Oe.

This study focuses on the electrochemical behavior of brass in acidic and alkaline tap water. Both conditions were studied using corrosion potential, cyclic polarization and electrochemical impedance spectroscopy. Weight loss experiments were also performed to validate corrosion behavior. It was evaluated from corrosion potential values and Pourbaix diagrams that brass surface was aggressively attacked at low pH due to dissolution of zinc-rich phase and solvation of cuprite and zincate at high pH by breakdown of the passive film. Under near neutral conditions the increase in charge transfer resistance corresponded to formation of a stable passive film. Brass exhibited peculiar behavior at pH 1 and 12 by showing low charge transfer resistance due to preferential attack of zinc and solvation of copper/zinc rich phases, respectively, as validated by impedance spectroscopy.