Volume 109, Issue 5

By applying vibrations to a granular media differing in size and density, various segregation states can be established. If an additional rotational motion is engaged, the effective force is no longer gravity but a centrifugal one, leading to a radial segregation. In this contribution, an experimental setup is presented which utilizes these effects. This setup is used to produce a cylindrical metal matrix composite consisting of silicon carbide and aluminium having a radial gradient. The influence of different material- and process-specific parameters on the segregation behaviour was investigated. The evaluation of micrographs of the pressed and sintered samples shows that both positive and negative gradients can be achieved. The rotation speed and the grain size ratio were identified as significant factors. The variation of the vibration amplitude leads to opposite effects. On the one hand, the gradient intensity increased. On the other hand, the variances of the SiC distribution in the tangential or radial directions increased as well. In addition, it has been shown that the effects of different grain shapes are marginal.

We performed nanoindentation measurements on as-cast and high-pressure-torsion deformed Pd-based metallic glass samples with spherical indenters of radius 1, 5 and 8 μm. The different serrated behaviors observed during nanoindentation were connected to the microstructural changes evidenced indirectly by differential scanning calorimetry and directly by electron microscopy. On the deformed sample, the discontinuities remained with the 1-μm indenter, decreased in intensity with the 5-μm indenter and disappeared with the 8-μm indenter. The different plastic zone sizes below the indenters can explain this effect since a larger plastic zone offers more possibility for interactions with pre-existing shear bands.

In pyrometallurgy, freeze lining technology is used to ensure the integrity of the furnace wall. This involves cooling down the wall and solidifying part of the liquid bath material onto the wall, creating a protective layer. In the current study, the cooled probe technique was used to perform a series of laboratory experiments, producing freeze linings under controlled conditions in the CuO x –FeO y –MgO–SiO 2 system. Earlier research has shown the bath–freeze lining interface temperature at thermal steady state can be at subliquidus temperatures under certain conditions. The current study focuses on the effect of bath temperature on this bath–freeze lining interface temperature and has indicated that increasing the bath temperature increases the interface temperature. Furthermore, the crystals forming the interface did not include the primary phase and formed a non-planar interface at thermal steady state.

The decomposition of Al 4 O 4 C in the presence of C at 1 473–1 873 K in vacuum was researched using the condensation products with high content of Al 4 O 4 C, formed in the carbothermal reduction of Al 2 O 3 , as the raw materials. The results showed that Al 4 O 4 C decomposed into gaseous products at 1 573–1 873 K in vacuum. It was speculated that Al 4 O 4 C decomposed into Al-containing gaseous species, CO and O 2 , and then the O 2 reacted with C to form CO. The reaction of the O 2 with C made the decomposition of Al 4 O 4 C take place more easily. With the decrease in temperature, the Al-containing gaseous species and CO formed condensates mainly consisting of Al 4 O 4 C, Al 4 C 3 and Al 2 O 3 , and also containing Al at experimental temperatures of 1 773 K and 1 873 K.

Pure ZnS and doped Zn 0.95 M 0.05 S ( M = Cr, Ni, Co, Fe and Mn) nanorods were successfully prepared by a hydrothermal method. The effects of the variety of doped elements on the crystal microstructure, morphology, optical and magnetic properties of the samples were investigated by means of X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray energy dispersive spectrometry, photoluminescence spectroscopy, UV–Visible diffuse reflectance spectroscopy and vibrating sample magnetometry. The experimental results show that all samples synthesized by this method possess single phase wurtzite structure with good crystallization, transition metal ions ( M = Cr, Ni, Co, Fe and Mn) substitute for the lattice site of Zn 2+ and generate single-phase Zn 0.95 M 0.05 S nanostructures. The morphologies of the samples are one-dimensional nanorods with good dispersion. The optical band gap of doped Zn 0.95 M 0.05 S decreases as the doping ion radius increases, and red shift occurs compared to undoped ZnS nanocrystals. Photoluminescence spectra exhibit clear ultraviolet emission and blue emission. Magnetic measurements indicate that the undoped and doped ZnS samples are ferromagnetic at room temperature.

Aluminium (Al) substituted nickel ferrite (NiAl x Fe 2 - x O 4 with x = 0.0, 0.5 and 1.0) nanoparticles were synthesized by the technique of co-precipitation. The microstructural and optical properties of nickel ferrite nanoparticles were meticulously evaluated from X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and UV–vis spectroscopy. The X-ray diffraction pattern of nanoparticles confirmed the single phase of cubic spinel structure. The particle size of nickel ferrite nanoparticles was in the range of 25–35 nm, while the lattice parameter “ a ” decreased with respect to Al content. The presence of Ni, Fe, Al, and O elemental peaks in the energy dispersive X-ray spectrum confirmed the formation of nickel ferrite nanoparticles. The functional groups of Al–Ni spinel ferrite phase were further confirmed from Fourier transform infrared spectroscopy. Two major absorption bands in the IR spectrum were observed at 600 cm −1 (the high frequency band, ν 1 ) and 450 cm −1 (the low frequency band, ν 2 ) from tetrahedral (A) and octahedral (B) interstitial sites in the spinel lattice. The magnetic hysteresis curves were recorded with respect to Al concentration at room temperature using vibrating sample magnetometry. The magnetization and coercivity of nickel ferrite were decreased as the Al contents increased.

Spark plasma sintering (SPS) is a powder metallurgy technique developed for consolidating metallic and/or ceramic particles in very short times. High heating and cooling rates can prevent excessive grain growth, favoring densification. The spark plasma sintered materials' final properties are strongly related to the reinforcement types and percentages as well as to the processing parameters employed during synthesis. The present paper analyses the effect of 3 and 6 wt.% of nanosized SiO 2 particles addition on the mechanical and microstructural behavior of Al-based metal matrix composites produced via SPS. The microstructural and mechanical behavior was analyzed as a function of the SPS parameters: heating rate, sintering temperature and pressure. Low percentages of silica particles are very effective for improving mechanical properties. High reinforcing percentages lead to agglomeration and drops in the composite's mechanical properties.

Novel LaFe 11.6 Si 1.4 H y magnetocaloric composites were prepared with Sn powder and a 3-d Ni-coating steel substrate using a hot-pressing technique. By selecting low-melting-point pure Sn powder as an adhesive, and a 3-d Ni-coating steel substrate as the supporting skeleton, the LaFe 11.6 Si 1.4 H y magnetocaloric composites exhibited good mechanical properties, a strong magnetocaloric effect (MCE), and a high thermal conductivity. The magnetic entropy change of the LaFe 11.6 Si 1.4 H y magnetocaloric composites was optimised by adjusting the Sn concentration. By controlling the Sn concentration, the 0.7 mm-thickness LaFe 11.6 Si 1.4 H y magnetocaloric composites with 10 wt.% Sn powder had a porosity of as low as 4.5 %, a thermal conductivity of 8 W m −1 K −1 , and a magnetic entropy change of 7.9 J kg −1 K −1 , a magnetic entropy change of 7.9 J kg −1 K −1 , and adiabatic temperature change of 6.4 K.

Ti-6Al-4V samples were fabricated by selective laser melting (SLM) with a series of different laser energy inputs. The microstructure presented a feature of fine acicular martensite due to the high cooling rate of the SLM process. All the relative density, micro-hardness and tensile properties initially increased and then decreased with increasing laser energy density. The fracture morphology exhibited a mixed mode of complex ductile and brittle fracture. All the results indicated that the laser energy density has a crucial effect on the microstructures and mechanical properties of the SLMed Ti-6Al-4V alloy. The correlations between the laser energy density and the microstructures and mechanical properties of the SLMed Ti-6Al-4V alloy were studied.

The paper presents comparative results of NiTi corrosion resistance tests of the alloy in initial state and after oxidizing and oxynitriding in low temperature plasma. These processes allow obtaining TiO 2 or composite TiO 2 + TiN layers with a titanium nitride (TiN) interlayer. Corrosion resistance tests of diffusion layers produced on NiTi were carried out via electrochemical impedance spectroscopy and the potentiodynamic method in Ringer's solution at 37 °C. The results were complemented with analysis of the alloy's structure, surface topography, and elemental distribution in the layers. The results showed an increase in corrosion resistance of NiTi alloy both after glow-discharge oxidation and oxynitriding. Significant shortening of the passive range of oxynitrided layers may result both from differences in surface topography and the thickness of the oxide layers.

In this study, AISI 321 austenitic stainless steel samples were surface treated using severe shot peening (SSP) with 1 000 % and 1 300 % coverages. Microstructural features including the grain size, phase transformation, and formation of sub-surface microcracks were investigated at the rough top surface and about 40 μm depth (top surface after grinding and removal of initial rough surface layer created by SSP). In addition, microhardness variations were thoroughly analyzed in-depth. Experimental results demonstrated that for both 1 000 % and 1 300 % coverages, the microstructures of top surface and 40 μm depth are respectively composed of equiaxed nano-grains and lamella-shaped cells; however, enhanced imparted strain in the case of 1 300 % coverage leads to the formation of considerable amounts of strain-induced martensite (α′) phase in the surface layers and consequently, due to strength increase and lack of deformability, some microcracks are created in the sub-surface layers (up to 20 μm depth).

The effects of two conventional heat treatments and one innovative processing by laser surface remelting of modified X37CrMoV5-1 tool steel on its abrasion wear resistance were investigated. Conventional heat treatments consisted of quenching from 990 °C, individually followed by two different tempering treatments to achieve secondary hardness either at 520 °C or 560 °C. Laser surface remelting was performed using optimized parameters of continuous laser beam scanning mode. The results showed that the highest wear resistance was obtained for almost carbide-free, surface remelted microstructure with the highest hardness due to microstructural refinement and martensitic transformation hardening. The observed differences in wear resistance among individual material states are discussed in relation to their microstructures, hardness, and wear mechanisms characteristics.

Coarse microstructures and severe macrosegregation always occur in large-sized billets prepared by normal direct chill casting, and cannot be eliminated during subsequent deformation or high temperature annealing. This study proposes a new melt treatment method coupled to annular electromagnetic stirring and intercooling, and applies it to direct chill casting of large-sized 2219 aluminum alloy billets. Compared to the normal direct chill casting, the microstructure and second phase were refined and homogenized, and the macrosegregation of Cu was alleviated. Accordingly, the average tensile and yield strengths, elongation and hardness were significantly improved and remained relatively stable at different positions on the billet. Tensile fracture tests showed that annular electromagnetic stirring coupled with intercooling decreases the amount of porosity in the structure.