Band 109, Heft 2

This work attempts to quantitatively describe the microstructural evolution in a new commercial 6 ××× aluminum alloy developed in an industrial laboratory (Al-0.87Si-0.81Mg-0.51Zn-0.46Cu-0.19Fe-0.09Mn, in wt.%), during solidification by using the phase-field simulation supported by experimental measurements. Coupling to the CALPHAD thermodynamic and atomic mobility databases is attained for providing energy and diffusivity information during the phase-field simulation. Two different resolutions are used in order to resolve the primary α-(Al) dendrite and the faceted β-AlFeSi eutectic phase in the phase-field simulations. The phase-field simulated microstructure morphology is verified by experimental results. Moreover, the microsegregation and back-diffusion phenomena in the primary α-(Al) dendrite are also analyzed.

The hydrogenation and corrosion behaviour of La 2 Ni 9  · CoSn 0.2 alloy was analysed in respect of its use in Ni–MH batteries. It has been proved that the presence of tin in the alloy causes a decrease in hydrogen equilibrium pressure. In the electrochemical studies several techniques, such as chronopotentiometry, multi-potential steps, linear sweep voltammetry and the potentiokinetic polarization were applied to characterize the electrochemical properties of a La 2 Ni 9 CoSn 0.2 powder composite electrode. During long cycling, powder particles undergo micro-cracking or other forms of surface development causing a progressive increase in the exchange current density of the H 2 O/H 2 system, but, on the other hand, this increase favours corrosion processes such as the electrode material's oxidation. This is also reflected in the capacity loss values.

The isothermal sections of the Co–Ni–Ti system at 950 and 1 000 °C were investigated experimentally. Diffusion couples were measured by electron probe microanalysis to construct the phase relations at 950 °C, whereas eleven key alloys annealed at 1 000 °C were investigated using X-ray diffraction and electron probe microanalysis. The ternary phase, τ-(Co,Ni) 3 Ti (hP24-VCo 3 ), was observed at both temperatures. At 950 °C, continuous solid solutions are formed between CoTi 2 and NiTi 2 as well as between CoTi and NiTi. Eight 3-phase regions, i. e. Ni 3 Ti + (Co,Ni)Ti + τ, Ni 3 Ti + γ-(Co,Ni) + τ, τ + c-Co 2 Ti + (Co,Ni)Ti, τ + c-Co 2 Ti + Co 3 Ti, τ + Co 3 Ti + γ-(Co,Ni), c-Co 2 Ti + h-Co 2 Ti + Co 3 Ti, L + β-(Ti) + (Co,Ni)Ti 2 and L + (Co,Ni)Ti 2  + (Co,Ni)Ti, were constructed at 1 000 °C. Considerable ternary solubilities in Ni 3 Ti, Co 3 Ti and c-Co 2 Ti were determined.

The magnetorheological properties of a series of magnetorheological elastomers with ferromagnetic particles of different mass fractions and different diameters are investigated. The aim is to provide a basis for the preparation of high-performance material. The shear behavior of the magnetorheological elastomers is also investigated as a function of temperature. The results essentially reveal the temperature-dependent nature of the variable stiffness of the magnetorheological elastomers. A modified Gauss distribution columnar model of ferromagnetic particles (with a temperature-dependent magnetic permeability) and a modified super-elastic rubber matrix (with a linear thermal expansion coefficient) is developed and used to explore the nature of the temperature-dependent variable stiffness. The results suggest that the interaction between the rubber matrix and ferromagnetic particles is the most critical factor responsible for the temperature dependence and not the features of the two components themselves. On the basis of System Identification Theory, a fitting polynomial is added to modify the constitutive model, which can represent the interaction between the rubber matrix and ferromagnetic particles. Polynomial data fitting and a theoretical model were used to derive an expression for the temperature dependence. As a result, the magnetic field-induced shear modulus was obtained as a semi-empirical model. This was then used to draw maps of the temperature-induced and magnetic field-induced shear modulus. The calculated results were compared with the experimental data and the errors found to be acceptable, which verifies the effectiveness and reliability of the semi-empirical model. Finally, the temperature dependence of the shear modulus is converted into the temperature dependence of the shear stiffness.

We have synthesised two kinds of graphitic carbon nitride (g-C 3 N 4 ) through a pyrolysis process involving urea and melamine. The obtained products were characterised by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV–vis diffuse reflection spectroscopy, and nitrogen adsorption–desorption. The product derived from the urea shows a mesoporous honeycomb-like nanosheet structure (denoted by h-g-C 3 N 4 ): compared with the bulk product obtained from melamine (denoted by b-g-C 3 N 4 ), the h-g-C 3 N 4 showed better adsorption and higher photo-activity for rhodamine B (RhB) reduction. The h-g-C 3 N 4 also shows good reusability after cyclic adsorption–regeneration. The present results evinced an efficient design, an eco-friendly and convenient photocatalyst, and a tunable photo-reactivity for use in sustainable light-to-energy conversion.

In this study, 4A duplex stainless steels were prepared via remelting in an intermediate frequency furnace and subsequently solution treated at different temperatures. The effects of solution treatment on the mechanical properties and corrosion resistance of 4A duplex stainless steel were investigated. Microstructures were characterized via optical microscopy and scanning electron microscopy. The mechanical properties were evaluated via hardness test, tensile test, and impact test experiments. The point corrosion resistance was studied via chemical immersion and potentiodynamic anodic polarization. The results showed that with increasing solution temperature in the range of 1 223 – 1 423 K, the tensile strength and hardness first decreased and then increased, and minimum values were obtained at 1 323 K. The σ phase precipitated at the boundaries of the α/γ phases in samples solution treated at 1 223 K, decreasing both impact energy and pitting potential of the experimental steels. When experimental steels were solution treated at 1 373 K for 2 h, a suitable volume fraction of α/γ was uniformly distributed throughout the microstructure, and the steels exhibited optimal mechanical properties and pitting corrosion resistance.

The effect of heat treatment and chromium contents (up to 9.1 wt.%) on the wear resistance of spheroidal carbide cast iron (9.5 wt.% V) was studied using optical and scanning electron microscopy, X-ray diffractometry, dilatometry and three-body abrasive testing. It was found that quenching from 760 °C and 920 °C improved the alloys’ wear resistance compared to the as-cast state due to the formation of metastable austenite transforming into martensite under abrasion. The wear characteristics of alloys studied are 1.6 – 2.3 times higher than that of reference cast iron (12 wt.% V) having stable austenitic matrix. Chromium addition decreases surface damage due to the formation of M 7 C 3 carbides, while it reduces wear resistance owing to austenite stabilization to abrasion-induced martensite transformation. The superposition of these factors results in decreasing the alloys’ wear behaviour with chromium content increase.

The present study was performed mainly on A413.1 alloy. Measured amounts of La, Ce or La+Ce, Ti and Sr were added to the molten alloy in the form of master alloys. Samples sectioned from castings obtained from thermal analysis experiments were used for preparing samples for metallographic examination. The results show that addition of rare earth ( RE ) metals to Al–Si alloys increased the α-Al nucleation temperature and depressed the Al-Si eutectic formation temperature, thereby increasing the solidification range. Depending upon the alloying elements/additives, a large number of RE -based intermetallics could be formed: Al 4 (Ce,La), Al 13 (Ce,La) 2 Cu 3, Al 7 (Cu,Fe) 6 (Ce,La) 6 Si 2, Al 4 La, Al 2 La 5 Si 2, Al 2 Ce 5 Si 2, Al 2 (Ce,La) 5 Si 2. Under an electron microscope, these phases appear in backscatter imaging mode in the form of thin grayish-white platelets on the dark gray Al matrix. The average thickness of these platelets is about 1.5 μm. When the alloy is grain refined with Ti-based master alloys, precipitation of a gray phase in the form of sludge is observed: Al 12 La 3 Ti 2 , or Al 12 (Ce,La) 3 Ti 2. Regardless the alloy composition, the RE /Al ratios remain constant in each type of intermetallic. Rare earth metals have a strong affinity to react with Sr (resulting in partial modification of the eutectic Si particles) as well as some transition elements, in particular Ti and Cu. Iron has a very low affinity for interaction with RE metals. It is only confined to Fe-based intermetallics.

Fe–Co-based soft magnetic alloys with excellent magnetic properties were prepared by metal injection moulding and hot isostatic pressing. The effect of processing parameters on microstructure and magnetic properties of the alloy were investigated. Good magnetic performance of Fe-50 %Co alloy with a maximum permeability of 9550, saturation induction of 2.42 T, and coercive force of 68.14 A m –1 was achieved. Hot isostatic pressing processing resulted in a near-full density and the achieved saturation induction exceeded the reported value (1.99 to 2.26 T) of Fe-50 %Co produced by metal injection moulding.

A solid-state route was developed to prepare rhombohedral phase Mg 2 SiNi 3 with the dimensions of about 300 nm by using metallic magnesium, nickel oxide and silicon as starting materials at 700 °C in an autoclave reactor. The obtained product was investigated by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Magnetic measurement at room temperature indicated that the values of saturation magenetization and coercivity of the obtained Mg 2 SiNi 3 were 0.31 emu g –1 and 65.20 Oe, respectively.