Volume 112, Issue 1

Recently, Fe-based superconductors have shown promising properties of high critical temperature and high upper critical fields, which are prerequisites for applications in high-field magnets. Critical temperature, T c , is an important characteristic correlated with crystallographic and electronic structures. By doping with foreign ions in the crystal structure, T c can be modified, which however requires significant manpower and resources for materials synthesis and characterizations. In this study, we develop the Gaussian process regression model to predict T c of doped Fe-based superconductors based on structural and topological parameters, including the lattice constants, volume, and bonding parameter topological index H 31 . The model is stable and accurate, contributing to fast T c estimations.

Zinc oxide nanoflakes were synthesized using the wet precipitation method from aqueous solutions of zinc nitrate and sodium hydroxide. The obtained materials were characterized by means of X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and nitrogen adsorption–desorption methods. The presence of sodium lauryl sulfate in the preparation of zinc oxide resulted in thinner, larger size, and higher specific surface area nanoflakes. The saturated adsorption capacities of zinc oxide nanoflakes for HCN, NO 2 , and SO 2 were 216 mg g –1 , 81 mg g –1 , and 38 mg g –1 , respectively. These results suggest that the material is a potential candidate for the removal of these toxic gases.

Two methyl-modified Al 2 O 3 /SiO 2 xerogels, i. e. AIP-Al 2 O 3 /MSiO 2 and ANN-Al 2 O 3 /MSiO 2 xerogels, were prepared using aluminum isopropoxide and aluminum nitrate nonahydrate as the aluminum precursors, respectively. The appearance, density, viscosity, Gibbs activation energy for viscous flow and reaction rate constant of the sols were analyzed and compared. Their microstructures were characterized by means of powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and nitrogen adsorption–desorption measurements. The results show that the Al–O–Si bond is formed in the AIP-Al 2 O 3 /MSiO 2 and ANN-Al 2 O 3 /MSiO 2 xerogels. The ANN-Al 2 O 3 /MSiO 2 sol has a smaller mean particle size and greater sol stability than the AIP-Al 2 O 3 /MSiO 2 sol. Meanwhile, the ANN-Al 2 O 3 /MSiO 2 xerogel has a smaller pore size and higher porosity. The total pore volume and specific surface area of the ANN-Al 2 O 3 /MSiO 2 xerogel are 27.27% and 29.36% larger than those of the AIP-Al 2 O 3 / MSiO 2 sample, respectively. The saturated adsorption capacity of the ANN-Al 2 O 3 /MSiO 2 xerogel to methylene blue is 7.15% larger than that of the AIP-Al 2 O 3 /MSiO 2 xerogel.

SiC nanoparticles play an important role in Cu–MWCNTs nanocomposites. So far, the effect of SiC volume fraction has not been considered on the properties of Cu–MWCNTs–SiC hybrid nanocomposites. Copper-based hybrid nanocomposites with 2 vol.% carbon nanotubes and 1–3 vol.% SiC nanoparticles were prepared via powder metallurgy. The composite powders were compacted and then sintered at 850, 900 and 950 °C for 1 h. Increasing the volume fraction of SiC nanoparticles restricts the grain growth, decreases the friction coefficient, and increases the hardness and wear resistance of prepared nanocomposites. The coefficient of friction and wear rate of Cu–MWCNTs–SiC hybrid nanocomposites decreased with increasing SiC content. Nanocomposites sintered at 900 °C exhibited higher hardness and wear resistance compared to other samples. The highest hardness and wear resistance were related to the Cu-2 vol.% MWCNTs-3 vol.%SiC hybrid nanocomposite sintered at 900 °C, which shows approximately 24 and 78% improvement over the pure copper specimen, respectively. Wear resistance and hardness were reduced for samples sintered at 950 °C.

In this study, novel Co 60 Fe 18 Ti 18 B 4 alloy powders have been synthesized with high compositional homogeneity using a high-energy ball milling technique. The structural, morphological and mechanical properties of the nanosized alloyed powders were examined using different analytical techniques, including scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffraction. According to the X-ray diffraction analysis for both Co powder and Co 60 Fe 18 Ti 18 B 4 alloy powders, with increasing milling time, the content of Co-based (hcp) solid solution decreased and Co-based (fcc) solid solution increased. The mechanical properties of the material were also investigated by Vickers micro-hardness testing. The micro-hardness value of the Co 60 Fe 18 Ti 18 B 4 alloy was found as 120.08 HV. After sintering (1 h– 1000 °C), the hardness improved remarkably (536.32 HV). Furthermore, results indicate that the synthesized Co-based alloy powder has both glassy and nanocrystalline phase forms.

The oxidation behavior of two kinds of H13 steel powders were studied at different temperatures in air. Both oxidation kinetics and oxidation products were investigated, and the effect of powder particle size distribution on the powder oxidation was also evaluated. In addition, elemental and microstructural analyses were also conducted to characterize the oxide phase formation. Results showed that chromia and spinel were the main phases for both samples after oxidation for 24 h, irrespective of significant descaling.

The influence of the carbon introduction method on the microstructure and the mechanical properties of sinters produced from iron-based powders by diffusion-alloying sintering has been studied. Two methods of carbon introduction were tested: (1) Premixing of the base powder with graphite, and (2) Coating of the base powder with a carbon-containing substance. The results obtained could be summarized as (1) The microstructure and the mechanical properties depend on the method of carbon introduction; (2) The sinters produced from coated powders possess finer micro-structure, improved homogeneity, and in two out of three of the studied compositions, better mechanical properties. Based on the results obtained, a reasonable assumption was made that the method of carbon introduction affects the dissolution rate of the carbon additive, thus affecting the micro-structure and the mechanical properties of the sinter.

Deformation modes and twin hardening of pure magnesium under compression in respect of the initial structure and texture were studied in the present work. In general, samples had two types of texture with different alignment of c -axis in respect to a compression direction. In the first case, most of the grains have the c -axis parallel to the compression direction and in the second case, the c -axis was perpendicular with the compression direction. It was found that coarse grained material deformed by slip despite the type of the texture, while the fine grained samples, with c -axis perpendicular to the compression direction, deformed by twinning. The samples which deform by twinning exhibited the highest yield point. It was concluded that combination of the fine grained structure and hard type texture components may introduce twinning as the main deformation mode and may increase the mechanical properties of magnesium and its alloys. The model for twin induced hardening is proposed where twins act as the grain refinement factor.

This paper is focused on the mechanism of kink band formation. In the general case, lattice rotation in a kink band may be realized by two sequentially activated simple elastic shears in nearly perpendicular planes. In the case of zinc crystals, compressed along (0001) plane at the temperature 523 K, the first shear may result from stress-induced temporary lattice instability (movement of atoms towards metastable positions in tetrahedric holes), while the second shear occurring along a temporary ‘new-positioned’ basal plane immediately ‘rebuilds’ the stable lattice.

High strength and lightweight materials are currently used in the automobile and defence sectors. In this framework, aluminium-based composites are a suitable choice due to their improved properties. The present study deals with the development of surface composites of A359/Si 3 N 4 via friction stir processing. The varying percentage of reinforcement (2% to 6%) is the main criterion behind the study to observe its influence on mechanical, wear, thermal and corrosion properties. Investigations of microstructure and morphological characterization of the developed samples were conducted by optical light microscopy and scanning electron microscopy. Identification of the alloying elements, reinforcement materials and phase distribution is observed by EDS mapping. In addition, Raman spectroscopy and X-ray diffraction analysis were also conducted to validate the structural composition. As a research outcome, the effect of varying reinforcement percentage was examined on the tensile strength supported by fractographic analysis and hardness values. Apart from this, wear, thermal expansion and corrosion tests were conducted to assess the behavior of samples in different operation conditions. The results reveal the maximum tensile strength (478 MPa) and maximum hardness (119 HRB) with minimum wear loss (3.3 mg m –1 ), maximum thermal expansion (8.2 mm 3 ) and maximum weight loss due to corrosion (0.0058 g) for A359/6%Si 3 N 4 composite.

The 25Cr2MoVA steel was subjected to various heat treatments. We found that the hardness increased when the quenching temperature was in the range of 870 – 910 °C, and then it decreased for the temperature of 910 – 990 °C. The maximum hardness was 553 HV after quenching from 910 °C. Following quenching from 910°C, the 25Cr2Mo-VA steel was tempered in the temperature range of 560 to 750 °C. With an increase in the tempering temperature, the hardness and tensile strength of the material decreased, while the impact toughness increased; the corrosion resistance increased initially and then decreased. The best heat treatment process for the 25Cr2MoVA steel involved quenching form 910 °C and tempering at 650°C for 1 h, the hardness was 362 HV, the tensile strength reached 1 310 MPa, the impact energy reached 149 J, and the material exhibited the best corrosion resistance.