Volume 110, Issue 5

The aim of the present work is to find the relationship between a decrease in transformation temperature and an increase in dislocation density during thermal cycling of NiTi alloy. The resistivity is used as a measure of the dislocation density variation and it allows one to find a linear dependence of the increment in the transformation temperatures on the dislocation density variation starting with the fifth thermal cycle. It is found that the thermal cycling of NiTi alloy within a temperature range of 473 to 273 K is accompanied by less dislocation density variation than in a range of 413 to 273 K. The dependence of transformation temperatures on increase in dislocation density in the first five cycles is not linear, hence it is concluded that the dislocation density variation is not the unique reason for a decrease in transformation temperature during the thermal cycling of equiatomic NiTi alloy.

The decrease in the X-ray diffraction Bragg peak intensity from concentrated multicomponent alloys (CMA), has been modeled in literature akin to the effect of temperature. In the current work, experiments and computations are used to comprehend the effect of atomic disorder in CMA on the Bragg peaks of powder diffraction patterns. Ni–Co–Fe–Cr–Mn and Cu–Ni–Co–Fe–V have been used as model systems for the study. It is proved that the intensity decrease is not insignificant, but is not anomalous either. A recipe is evolved to compare the Bragg peak intensities across the alloys of a CMA. It is demonstrated that it is incorrect to model the effect of an increase in atomic disorder in a CMA, as a temperature effect. A ‘good measure’ of lattice distortion is identified and further it is established that full width half maximum is a good measure of the bond length distortion. It is demonstrated that the true strain due to bond length distortion is of significantly lower magnitude than that given by a priori measures of lattice strain. In the scheme of categorization of defects in crystals, it is argued that CMA is a separate class (as distinct from type-I and type-II defects); which should be construed as a defected solid, rather than a defect in a solid.

The Al–Fe system has been modeled and optimized with the CALPHAD approach. Heat capacity values from three intermetallic phases (stoichiometric compositions: Al 2 Fe, Al 5 Fe 2 and Al 13 Fe 4 ) were experimentally determined and implemented into the Gibbs energy descriptions, thus the estimated heat capacity from Neumann–Kopp is substituted. From these results together with new literature values, a revised dataset of the binary Al–Fe system is presented. Based on the Compound Energy Formalism, the homogeneity range of the Al 2 Fe and Al 5 Fe 2 phase is represented using a two-sublattice model. In addition, the Al 8 Fe 5 phase has been modeled with a four-sublattice model and the number of sublattices of the Al 13 Fe 4 phase has been changed from a three-sublattice model to a two-sublattice model. The critically assessed parameters provide a consistent thermodynamic dataset and represent most of the relevant thermochemical data as well as phase diagram data within their experimental uncertainties.

The effects of isothermal heat treatment on microstructures of an A356 alloy containing rare-earth gadolinium (Gd) were investigated to obtain an optimum semi-solid structure. Our results revealed that the primary α-Al phase of the semi-solid A356 alloy containing Gd was significantly refined and that its morphology was spherical or near-spherical. Increases in holding temperature and prolongation of holding time led to an initial decrease in size during the primary α-Al phase, followed by a gradual increase. Solid–liquid interfacial tension resulted in the spheroidization of the primary α-Al phase.

The effects of different double ageing processes on the mechanical properties and microstructural evolution in the 1460 alloy were investigated. The corresponding microstructure and mechanical properties of the heat-treated specimens were studied by means of transmission electron microscopy, differential scanning calorimetry, hardness testing and tensile testing. The results show that the elongation of two-step aged (130 °C/84 h + 160 °C/24 h) samples can be increased to 8 % with a minor decrease in tensile strength (450 MPa). Throughout the two-step ageing process, the precipitation behaviour of the alloy exhibited the following characteristics: the δ′ phase formed at lower temperature dissolved into the matrix instead of coarsening and becoming over-aged at the beginning of the second ageing step; finely distributed θ′(Al 2 Cu) and δ′(Al 3 Li) at a steady state were obtained, resulting in a significant improvement in tensile strength; and the peak ductility occurred with the precipitation of T1(Al 2 CuLi) and consumption of δ′(Al 3 Li), as small δ′ particles caused a co-planar slip, resulting in lower ductility.

Additive manufacturing refers to a wide class of manufacturing processes based on the progressive building of functional parts through the addition of material layer upon layer. These technologies were first confined to prototyping, but the subsequent development of additive manufacturing processes for further materials, such as metals, has encouraged their worldwide industrial spread, from the biomedical field to the automotive and the aerospace industries. Additively manufactured parts are required to meet high and stable performance, at least comparable to that of conventional wrought materials, so as to comply with strict and well-defined international standards. This paper presents an investigation into the mechanical properties of AlSi10Mg parts produced by laser powder bed fusion technique, using different spatial orientations within the build volume. The effects of the part position and orientation on the static (tensile) properties of the produced parts were assessed by means of the two-way analysis of variance technique. The build angle was found to be the most effective parameter, while the variability ascribable to the effect of part position resulted mainly as physiological. The fatigue resistance showed a globally decreasing trend with increasing build angle.

A gradient layer of Al/Cr diamond-like carbon film has been prepared by magnetron sputtering on 2024 Al-alloy. Emphasis has been placed on the anti-corrosion and tribological properties of the Cr-doped diamond-like film. Experimental research: scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectrometry, nano-indentation testing, potentiodynamic polarization, electrochemical impedance spectroscopy and tribological tests were undertaken to investigate the surface morphology, surface structures, chemical composition, anti-corrosion and mechanical properties of the as-prepared gradient diamond-like carbon film. The results indicated that the Cr-doped diamond-like carbon film with intermediate transition chromium layer showed improvements with regards to hardness and corrosion prevention due to the dense surface structure and decreased electrical conductivity. Cr-doped diamond-like carbon film also displayed excellent tribological properties such as a low friction coefficient and wear rate during tribological testing.

In the present study, ZnSe ceramics were sintered at different temperatures in the range of 900 °C to 1 100 °C by spark plasma sintering. Microstructure, hardness, phase composition, and the optical properties of the ceramics were investigated by scanning electron microscopy, micro-Vickers hardness, X-ray diffraction and Fourier-transform infrared spectroscopy. The results indicated that temperature has a strong effect on grain growth as well as on reducing porosity and improving the properties. The optimal combination of properties (99.5 % density, 165 kg mm −2 hardness and 30 % transmission) was achieved after sintering at 1 100 °C for a holding time of 10 min with an applied pressure of 90 MPa. Furthermore, the grains tended to orient along the spark plasma sintering direction via preferential grain growth that was observed by X-ray diffraction and scanning electron microscopy.

In recent years, topological crystalline insulators have attracted increased attention due to practical demands of tunable electronic, spin electronic and thermoelectric devices. As an important topological crystalline insulator, mono-crystalline SnTe octahedra with {111} dominated surfaces, were successfully synthesized on a large scale via a surfactant-free hydrothermal synthesis route in this work. Important controlling factors for phase and morphology, i.e. reaction temperature, reactant concentration and stoichiometric ratio, are discussed in detail. The results indicated that high temperature is favorable for forming pure phase, and excessive Sn suppresses the appearance of SnTe with octahedral morphology. Lower reactant concentration is beneficial to preparing uniform SnTe octahedra via the selective growth mechanism. Crystallographic characteristics of the SnTe octahedra were investigated using focused ion beam, electron backscattered diffraction and transmission electron microscopy analysis. The hexagonal-like micro-plate (cut from an octahedron) was confirmed as mono-crystalline by the corresponding three Euler angle maps, the Kikuchi diffraction pattern and selected-area diffraction. It can be further deduced from the multiple experimental results that surfaces of octahedral SnTe are dominated by {111} crystallographic planes and the average size is 1–3 μm. Controllable mono-crystalline octahedra would effectively promote the development of topological crystalline insulators and their micro devices.

In this study, in order to investigate the mechanical heterogeneity of a Ti6Al4V titanium alloy laser-welded joint, microstructural examinations, microhardness tests and shear punch tests were carried out. Meanwhile, hole drilling was deployed to measure the residual stress in the joints. In residual stress simulation studies, the complex phenomenon of welding was numerically modelled by indirectly coupled transient, non-linear thermo-mechanical analysis. An elongated combined heat source was used here for modelling the temperature field. The effects of the residual stress after welding, both for considering and neglecting mechanical heterogeneity, were investigated systematically. The obtained results indicate that the residual stress of the simulation, when mechanical heterogeneity is considered closely, matches the experimental data.

Electron beam melting was utilized to investigate the behavior of carbon flow by melting 100 g of multi-crystalline silicon in an electron beam furnace for five minutes. Carbon and nitrogen are the constituent impurities in contaminated Si samples with an average weight of 13 % and 9, respectively. The electron beam melting experiment caused redistribution of the impurities along the periphery and bottom of the Si sample with a pie-shaped structure. Investigations through scanning electron microscopy and energy dispersive X-ray spectroscopy confirmed that the impurities were silicon nitride and silicon carbide. It was determined that Si 3 N 4 has a rod-shaped microstructure, whereas SiC has a granular morphology. By segregating the impurities redistributed through this technique, pure Si was obtained in the remaining sample.

Cobalt-based nanoparticles are promising candidates towards countless biomedical applications due to their unique characteristics. Co 3 O 4 nanoparticles were synthesized by applying the sol-gel technique and finally sintered at various temperatures (700, 800, 900 °C). The crystal size, morphology, purity, and optical properties were determined using a variety of advanced characterization techniques. To investigate photodynamic therapy feasibility by using Co 3 O 4 nanoparticles in the liver cells, in-vitro cancerous liver cells (HepG2 cells) were exposed to light of wavelength 655 nm (red light) for 30 min at 50 mW cm −2 and in dark as well. After assessment of cell viability analysis, it is concluded that light-induced photodynamic therapy shows significant phototoxic effects based on temperature dependency.