Volume 111, Issue 2

The liquidus projection and the isothermal section at 1 300 °C of the Nb–Si–V ternary system were experimentally studied. Using scanning electron microscopy, electron probe microanalysis and X-ray diffraction, the primary solidification phases and the precipitation paths in each region of the liquidus projection as well as the equilibrium relations of the phases in the isothermal section were determined. Ten primary solidification regions were found in the liquidus projection and eight three-phase equilibrium regions were observed in the isothermal section at 1 300 °C. The compounds βNb 5 Si 3 with V 5 Si 3 and NbSi 2 with VSi 2 are the phases of the same structure but different compositions and form two linear compounds βNb(V) 5 Si 3 or V(Nb) 5 Si 3 and Nb(V)Si 2 or V(Nb)Si 2 , respectively The ternary linear compound (Nb,V) 2 Si with the stoichiometry about 2 : 1 of (Nb + V) : Si was found in both the liquidus projection and the isothermal section at 1 300 °C.

In this study, pure Al foam and 2, 5, 10 wt.% cubic boron nitride Al composite foams were manufactured to reveal the effects of cubic boron nitride addition on the properties of Al foam materials. Cellular morphology investigations and quasi-static compression test results were correlated with the effect of foaming agent behavior, compacting pressure, amount of ceramic addition, and compressive properties. The cubic boron nitride reinforced Al foams exhibited superior compressive properties and energy absorption behavior. The compressive properties were enhanced by increasing the cubic boron nitride content and compacting pressure. The maximum mechanical properties were achieved in 10 wt.% cubic boron nitride aluminum composite foams. The results revealed that these composite foams are possibly a candidate for specific high technology applications with high mechanical properties.

In this study, the applicability of dynamic equal channel angular pressing for grain refinement and improvement in the properties of a two-phase Cu-30 %Zn alloy was investigated. Simulation and experiments were performed to study the deformation characteristics. The parameters for the multi-pass extrusion simulation were consistent with those in the experiments. The experimental results are in good agreement with the simulation. A homogeneous microstructure and grain refinement are readily achieved. The hardness increases rapidly by 170 % compared to the annealed samples, and its distribution is approximately uniform throughout the 2-pass deformation. Microstructural analysis indicates nanotwins of ~5–10 nm width and high-density dislocations.

Although drawing forming limit diagrams is a suitable tool for analyzing material formability, it can only be used when loading is proportional. In other words, when the ratio between main strains stays unaffected during the formation process. Since forming limit diagrams are strictly dependent on strain path, the significance of the limit increases. As the path of the strain changes in a formation process, the forming limit diagrams and therefore the designer's decision changes as well. In order to eliminate this issue, stress-based forming limit diagrams (SFLD) which are independent from the strain path are gaining attention. This paper gives an efficient method to determine the SFLDs and can accurately predict the location for the onset of failure, including strain rate calculations. Furthermore, introducing a damage function based on a simple continuum damage mechanics is dependent on the stress state (Triaxiality and Lode parameters). As a characterization parameter, elastic modulus is eventually chosen to measure the ductile damage in the process of plastic deformation of the material. Furthermore, a UMAT subroutine is developed in finite element simulation by ABAQUS according to original formulations, in order to analyze and link the related essential models. To examine the accuracy of the results from the present simulative study and compare with the experimental results, applicability is considered. Forming limit tests are also performed for St 13 sheets measuring the FLD and then transforming to SFLD. It should be noted that the rule of these simulative SFLDs is in good agreement with the experimental points. Results revealed that the level of the stress-based forming limit diagram for the material St 13 increases with enhancing the strain rate.

In the present paper, a new method for producing ultrafine grained microtubes of AZ31 magnesium alloy is proposed. The method consists of performing isothermal hot micro-backward extrusion on severe plastic deformation processed samples. One-pass equal channel angular pressing (ECAP) and cyclic extrusion compression angular pressing forward extrusion (CECAP-FE) were performed on an as-cast coarse-grained Mg-3Al-1Zn magnesium alloy before microtube fabrication. Microstructure and microhardness of the samples before and after micro-backward extrusion and deformation force during the fabrication process were studied. As a result, it was revealed that the proposed method performed on CECAP-FEed precursors could effectively produce ultrafine grained AZ31 magnesium alloy microtubes with excellent microhardness, good uniformity in shape, microstructure, and microhardness.

Mixed Cu-4Ti (wt.%) and Cu-1.4B (wt.%) powders were separately mechanically alloyed and then homogenized. The obtained powder was laser melted by pulsed Nd:YAG laser and heat treated at 900 °C for 10 h in argon. 3D compacts were characterized by means of digital camera images, optical microscopy and scanning electron microscopy. Microstructure after laser melting varies regionally due to mixing of two different mechanically alloyed powders and contains in-situ formed microparticles of primary TiB 2 . Formation of secondary TiB 2 nanoparticles was possible only after high temperature heat treatment (900 °C, for 10 h) as concluded from X-ray diffraction analysis, chemical analysis, and microhardness tests of laser melted and heat treated parts. Copper matrix was strengthened to a significantly higher extent after the formation of secondary TiB 2 nanoparticles.

The present work is focused on the investigation of hardness and scratch behavior of mechanically alloyed and various temperature (300 °C–500 °C) spark plasma sintered Al 86 Ni 8 Y 6 glassy alloys. Glassy alloy sintered at higher temperature, exhibited significantly improved hardness attributed to the increase in metallurgical bonding, relative density and nanocrystalline phases. A large variation in hardness of sintered alloys was attributed to the diffusion controlled crystallization mechanism depending on the nucleation rate during spark plasma sintering, which led to the different degree of microstructural phase evolution in a different part of the sample as confirmed by the scanning probe microscopy revealing the varying depth of indentation. Nanoindentation conducted at lower load resulted in higher hardness attributed to the indentation size effect. The scratch test exhibited decrease in coefficient of friction from 0.40 to 0.30 with the increase in sintering temperature from 300 °C to 500 °C, attributed to decrease in surface roughness.

Our goal is to investigate the physical, magnetic and dielectric properties of cadmium ferrite nanoparticles. Here we report the synthesis of nanosized cadmium ferrite (CdFe 2 O 4 ) spinel ferrite by the sol-gel process using citric acid as a complexing agent. We assessed the properties of nano-CdFe 2 O 4 by a variety of analytical and physical techniques. X-ray diffraction and Fourier transform infrared spectroscopy were performed to confirm spinel phase formation. Surface morphology images and compositional features were obtained using electron microscopy and other imaging techniques. Transmission electron microscopy analysis revealed the formation of nanoparticles with an average particle size of 40 nm. The magnetic properties were characterized by a highly sensitive magnetometer system (SQUID VSM) at room temperature revealing that the sintered sample of cadmium ferrite nanoparticles is ferromagnetic. We also studied dielectric behavior of the sintered pellet of the sample. We determined the frequency dependence of the dielectric permittivity, the loss factor and the impedance of the samples in the frequency range from 100 Hz to 20 MHz, at temperatures from 308–428 K at an interval of 40 °C. The dielectric behavior of ferrites is explained by the interface polarization, arising from the heterogeneous nature of its structure. Further research, both in terms of the preparation and characterization of ferrites, is warranted to better understand the nature and application of ferrites.

Novel SnO/BN photocatalysts were prepared via ultrasonic reaction. Their phase composition, morphology, and photocatalytic performance were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and diffuse reflection spectra. The morphological results indicated that BN nanosheets were loaded on the surface of SnO flakes. By modifying BN, the visible light response of SnO was improved. The SnO/BN photocatalysts exhibited enhanced photocatalytic activity for the degradation of methyl orange, and a degradation efficiency of at least 95 % under visible light irradiation was observed after 60 min.

The anti-solvent recrystallization process for the preparation of salt microparticles is introduced. The micron size of salt particles was confirmed by scanning electron microscopy. The preparation conditions such as the antisolvent types, dripping acceleration, stirring time, the volume ratio of antisolvent and solvent, and adding sequence of solvent were optimized. The experimental results indicated that these preparation conditions were as follows: The saturated salt solution was added into absolute alcohol at a dripping acceleration of 10 mL · min −1 , a stirring time duration of 30 min, and an antisolvent and solvent volume ratio of 4 : 1. Salt microparticles with an average diameter of about 6.3 μm, uniform size distribution and better crystallization were obtained under the above optimization conditions.

Copper has emerged as a suitable substrate material for the synthesis of graphene using chemical vapour deposition (CVD). It is imperative to make the CVD process sustainable. Understanding the growth of graphene on electroplated Cu substrates is an important step towards realising this objective. In this work graphene was grown on commercial and electroplated copper substrates. Raman spectroscopy was used to analyse the synthesised graphene and comment on the suitability of electroplated Cu substrates for graphene synthesis