Effects of Fe concentration on microstructure and corrosion of Mg-6Al-1Zn-xFe alloys for fracturing balls applications

Mg-6Al-1Zn-xFe (x = 0, 1, 3, 5 and 7 wt%) alloys were prepared by powder metallurgy and followed by hot extrusion. Majority of Fe element exists as insoluble particles in the alloys. The as-extruded alloys showed higher degradable rates but less stable mechanical properties than as-annealed alloys. Corrosion rate of all the alloys increased with increasing Fe concentration, reaching 2.4 mL cm⁻² h^-1. 0.2% yield strength of all the alloys was higher than 150 MPa. In short, Mg-6Al-1Zn-xFe alloys have an attractive combination of corrosion and mechanical properties, which holds a bright future for fracturing balls applications.     

Electrically conducting polyolefin composites containing electric field-aligned multiwall carbon nanotube structures: The effects of process parameters and filler loading

The characteristics of network formation of multiwall carbon nanotubes (MWCNTs) inside ethylene–octene copolymer (EOC) melts under an alternating current (AC) electric field and the resulting electrical conductivity improvements are studied by combining dynamic and steady state resistivity measurements. Fine MWCNT dispersion during melt compounding of the samples is accomplished by means of a novel non-specific, non-covalent functionalization method. It is found that the electrified composite films exhibit nanotube assembly into columnar structures parallel to the electric field, accompanied by dramatic increases in electrical conductivity up to eight orders of magnitude. Experimentally acquired resistivity data are used to derive correlations between the characteristic insulator-to-conductor transition times of the composites and process parameters, such as electric field strength (E), polymer viscosity (η) and nanotube volume fraction (ϕ). Finally, a criterion for the selection of (η, E, C) conditions that enable MWCNT assembly under an electric field controlled regime (i.e., minimal Brownian motion-driven aggregation effects) is developed. The correlations presented herein not only provide insights in the MWCNT assembly process, but can also guide the experimental design in future studies on electrified composites or assist in the selection of process parameters in composites manufacturing.     

Enhanced energy storage performance of BNT-ST based ceramics under low electric field via domain engineering

Lead-free bulk ceramics for advanced pulse power capacitors possess low recoverable energy storage density (W_rec) under low electric field. Sodium bismuth titanate (Bi_0.5Na_0.5TiO₃, BNT)-based ferroelectrics have attracted great attention due to their large maximum polarization (P_m) and high power density. The BNT-ST: xAlN ceramics are designed and fabricated to get high W_rec and large P_m under low electric field simultaneously. An excellent large P_m (49.04 μC/cm²) and W_rec (2.07 J/cm³) under low electric field (160 kV/cm) are acquired in BNT-ST: 0.1 wt% AlN. The domain structure evolution and polarization switching are investigated systematically using piezoresponse force microscopy (PFM). The introduction of AlN promotes the formation of thermal conductive network and the crystallization of ceramics, thus improving thermal stability and increasing P_m significantly. The higher density of domain walls and the larger negative built-in voltage may be beneficial to increase breakdown field strength (E_b), while the more 180° domains induce by electric field and the better domain switching behavior contribute to a significant increase in P_m. The enhanced E_b and super high P_m are favorable for obtaining high W_rec under low electric field which will boost the application of BNT-based ferroelectrics in advanced pulse power capacitors.     

Dielectric behavior and magnetical response for porous BFO thin films with various thicknesses over Pt/Ti/SiO2/Si substrate

A novel sol–gel method has been developed to deposit multiferroic nanocrystalline bismuth ferrite (BFO) thin films over Pt/Ti/SiO₂/Si substrate by spin-coating technique with various thicknesses. It is found that the deposition parameters significantly influence the quality and the thickness of BiFeO₃ films. The films are all uniform and adherent to Pt/Ti/SiO₂/Si substrate. The spin-coated films are characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), Atomic force microscope (AFM), photoluminescence spectroscopy (PL) and Fourier transform infrared spectroscopy (FTIR). Rhombohedral structure of BFO is confirmed from the XRD and FT-IR studies. The SEM image shows a porous structure formation of BFO over Pt/Ti/SiO₂/Si substrate. The surface outgrowth for the films at various thicknesses is measured from root mean square (RMS) and surface roughness through AFM. The step height and the RMS are found to be high for the film at 500 nm in comparison with thickness of 200 nm. The influence of the dielectric properties of the porous BFO at different thicknesses is studied using LCRQ meter. Finally, the magnetic behavior of film is compared with M–H hysteresis loop and Magnetoresistance (MR) studies.     

Magnesium fluoride (MgF2) – A novel sintering additive for the preparation of transparent YAG ceramics via SPS

The effect of MgF₂ as a sintering additive for the preparation of YAG ceramics via spark plasma sintering (SPS) is investigated with promising results, as nearly complete densification (0.58% porosity) is achieved at relatively low temperature and moderate pressure. Higher temperature and dwell time resulted in a translucent/transparent body. On the other side, significant grain growth was observed with MgF₂ addition.     

Effect of heat treatment on the microstructure and properties of Ni based soft magnetic alloy

A Ni‐based alloy was heat treated by changing the temperature and ambient atmosphere of the heat treatment. Morphology, crystal structure, and physical performance of the Ni‐based alloy were characterized via SEM, XRD, TEM, and PPMS. Results show that due to the heat treatment process, the grain growth of the Ni‐based alloy and the removal of impurities and defects are promoted. Both the orientation and stress caused by rolling are reduced. The permeability and saturation magnetization of the alloy are improved. The hysteresis loss and coercivity are decreased. Higher heat treatment temperature leads to increased improvement of permeability and saturation magnetization. Heat treatment in hydrogen is more conducive to the removal of impurities. At the same temperature, the magnetic performance of the heat‐treated alloy in hydrogen is better than that of an alloy with heat treatment in vacuum. The Ni‐based alloy shows an excellent magnetic performance on 1,373 K heat treatment in hydrogen atmosphere. In this process, the µ_m, B_s, P_u, and H_c of the obtained alloy are 427 mHm^?1, 509 mT, 0.866 Jm^?3, and 0.514 Am^?1, respectively. At the same time, the resistivity of alloy decreases and its thermal conductivity increases in response to heat treatment.     

Effect of stacking fault energy on mechanical behavior of cold-forging Cu and Cu alloys

Cu, Cu–2.87 wt% Mn, Cu–4.40 wt% Mn and Cu-10.19 wt% Mn were prepared by cold-forging. The deformation behavior of Cu–Mn alloys is consistent with the Cu-Al alloys and Cu–Zn alloys but without lowering the stacking fault energy to simultaneously increase the strength and ductility. A series of analysis demonstrate that Cu–Mn alloys have a much smaller twin density than low stacking fault energy (SFE) metals, and dislocation strengthening is the major reason for the higher strength. The role of short range order (SRO) in promoting the mechanical properties has also been briefly discussed.     

Effects of sintering method and BiFeO3 dopant on the dielectric and ferroelectric properties of BaTiO3–BiYbO3 based solid solution ceramics

(0.95–x) BaTiO₃–0.05 BiYbO₃–x BiFeO₃ (x?=?0, 0.01, 0.02, and 0.04) (abbreviated as (0.95–x) BT–0.05 BY–x BFO) ceramics were fabricated by conventional sintering (CS) and microwave sintering (WS) methods. Effects of sintering method and BFO dopant on the microstructure and electric properties of (0.95–x) BT–0.05 BY–x BFO ceramics were comparatively investigated. X-ray diffraction showed that all CS and WS samples presented a single perovskite phase. It was also found that WS ceramics possessed denser microstructure and finer grains compared to CS samples as indicated by the surface morphology characterization. Dielectric measurements revealed that all samples exhibited the weak relaxation behavior; however, the degree of relaxation behavior of BT–BY based ceramic could be strengthened by addition of BFO and by WS method. Moreover, the temperature and frequency stability could be improved with doped BFO. The density of 0.93BT–0.05BY–0.02BFO ceramic was found to be the largest while that of 0.94BT–0.05BY–0.01BFO ceramic was the smallest, thus, the dielectric constant of 0.93BT–0.05BY–0.02BFO was significantly larger than that of 0.94BT–0.05BY–0.01BFO and 0.94BT–0.05BY–0.04 BFO ceramics. minimum dielectric constant of (0.95–x) BT–0.05 BY–x BFO ceramic was obtained at x?=?0.01. Ferroelectric measurements indicated that all samples showed the slim hysteresis loop. The remnant polarization (P_r) and coercive field (E_C) of (0.95–x) BT–0.05 BY–x BFO ceramics first decreased and then increased with increasing x，the minimum values were obtained at x?=?0.01. Moreover, P_r and E_C of WS ceramics were slightly larger than those of CS ceramics, indicating that higher density and larger grain sizes contributed to enhancing the ferroelectric characteristic. These findings indicate that addition of moderate amount of BFO and use of WS technique can strengthen the degree of relaxation behavior and improve the ferroelectric properties of BT–BY based ceramics.