The band structure, the density of states and optical absorption properties of Cu-doped ZnO were studied by the first-principles generalized gradient approximation plane-wave pseudopotential method ...based on density functional theory. For the Zn
Cu
O (
= 0,
= 0.0278,
= 0.0417) original structure, geometric optimization and energy calculations were performed and compared with experimental results. With increasing Cu concentration, the band gap of the Zn₁
Cu
O decreased due to the shift of the conduction band. Since the impurity level was introduced after Cu doping, the conduction band was moved downwards. Additionally, it was shown that the insertion of a Cu atom leads to a red shift of the optical absorption edge, which was consistent with the experimental results.
Amorphous soft magnetic composites have been attracting attention because of its low core loss under high frequency application. It is demanded that the powder for fabricating amorphous soft magnetic ...composites has amorphous structure and nearly spherical shape, which facilitates the uniform coating of insulator on the surface of powder particles. In this paper, amorphous Fe73.5Si13B11Cr1C1.5 (at%) powder was produced by gas-water combined atomization process which takes advantages of both gas atomization and water atomization, and its properties was compared with powder produced by gas atomization and water atomization. Gas-water combined atomization powder with particle size of −60 μm were found to be amorphous with low coercivity, and the shape of particles was nearly spherical. The permeability of magnetic powder cores prepared with three kinds of powder first increased and then decreased with annealing temperature, and the core loss first decreased and then increased. The cores prepared with gas-water combined atomization powder showed the best overall properties, with an effective permeability of 26.9, a relative permeability of 83.3% under a superimposed DC magnetic field of 7.96 kA/m, a core loss of 258 mW/cm3 under a frequency of 100 kHz, and a magnetization intensity Bm of 0.05 T after annealing at 793 K in nitrogen gas.
•Fe73.5Si13B11Cr1C1.5 soft magnetic powder with amorphous microstructure is produced by gas-water combined atomization.•The cooling rate of gas-water combined atomization is close to water atomization, but higher than gas atomization.•The magnetic powder cores made of gas-water combined atomized powder have the high DC BIAS characteristics and low loss.
•The behavior of Pb in geopolymer depends on the chemical property of the Pb compound.•Pb participates in the formation of geopolymer network, forming leaded amorphous gel.•Dissolution of lead ...compounds is a vital step in the formation of leaded geopolymer.•Pb compounds, soluble in alkali, are chemically bonded into the geopolymer gel.•PbS, inert to alkali, is trapped in the geopolymer by physical encapsulation.
Geopolymer possesses good immobilization capacity for Pb. There are two rival interpretations regarding the immobilization mechanism of Pb. This research investigates the behavior of 3 Pb compounds in geopolymer and clarifies the immobilization mechanism. When Pb contamination is added in the form, soluble in sodium hydroxide solution, the Pb is converted to an amorphous form and participates in the formation of geopolymer network. Successful immobilization of these species relies on chemical bonding and physical encapsulation. On the contrary, the Pb compound inert to sodium hydroxide solution is segregated from the binder and trapped by physical encapsulation.
Brittle film fracture induces ductile substrate cracking at relatively low strain levels Instead of protecting the ductile substrate, the brittle film causes its premature fracture. Display omitted
...Film and substrate mechanical integrity is essential for the whole system’s performance. In the present study, cracking of brass ductile substrate induced by brittle TiN film fracture was observed. Counter-intuitively, instead of protecting the ductile substrate, a brittle film can cause its premature fracture, as demonstrated here experimentally. Brittle film fracture could induce cracking of ductile substrate at considerably low strain level. Analytical calculation based on energy conservation during crack propagation is presented to explain this phenomenon of film-induced cracking. It is shown that crack depth penetrated into the substrate is a function of both crack velocity and the number of dislocations emitted from the crack tip. Relatively thick brittle films and fast propagating cracks favor fracture of the ductile substrates. The critical crack velocity, which can induce the cracking of brass substrate, is 61m/s. The presence of brittle film could not only prevent dislocations escaping from the surface of the crystal and inhibit dislocations emitting from surface dislocation sources, but also initiate a channel crack with high velocity due to brittle fracture. Both of them contribute to crack propagation in soft brass substrate. This study provides an alternative view to the notion that a brittle film can protect the ductile substrate from damage.
The mechanical properties and physical characteristics of aluminum alloy composites can be significantly improved by adding reinforcing phases. However, the high loading of the reinforcement phase in ...Al7075-Al
2
O
3
composites has not been thoroughly studied. In this work, a combination of semisolid metal powder processing and powder metallurgy is used to process and manufacture Al7075-Al
2
O
3
composites with a high reinforcement fraction of > 40 vol.%. The effects of processing parameters on the microstructures and mechanical properties of the composite material are discussed in detail. The loading limits of the high volume Al
2
O
3
reinforcement in Al7075 composites are identified and linked to the processing parameters. A methodology is introduced to estimate the consolidation temperature of Al7075 alloy using compaction testing. Al
2
O
3
particles (the average particle size of 120 µm) were mechanically milled with Al7075 powder (the average particle size of 20 µm) for 10 min and 5 h using a high-energy planetary ball mill. The mixture was then compacted in the semisolid state at 615 °C under the compaction pressures of 50 MPa and 100 MPa. By increasing the milling time from 10 min to 5 h, the deformation of aluminum powders and the fracture of Al
2
O
3
reinforcement particles occur, restricting the loading limit of reinforcement. The milling time also shows a dominant effect on the powder morphology, microstructure, and mechanical properties of Al7075-Al
2
O
3
composites. Increasing compaction pressure from 50 to 100 MPa significantly improved the compressive strength of the composite from 218 to 652 MPa. Al7075-Al
2
O
3
composite with 40 vol.% of reinforcing phase exhibits the highest hardness of 198.2 HV and 96.9% relative density when it is milled for 5 h and compacted at 100 MPa. However, this composite shows the highest strength of 652 MPa when it is milled for 10 min. By increasing the reinforcing phase to 50 vol.% and 60 vol.%, the hardness, density, and compressive strength of composites decreased. The composites with 60 vol.% of reinforcing phase appeared overloaded. Results show that semisolid metal powder processing has huge potential for the fabrication of high loading Al
2
O
3
in Al7075 matrix with near theoretical density.
The effects of Co on the Cu-Ni-Co-Si alloys' microstructure and mechanical properties were investigated. The Cu-1.5Ni-1.0Co-0.6Si and Cu-1.5Ni-1.5Co-0.6Si alloys with combined aging and 40–80% cold ...rolling were also investigated. The hardness, electrical conductivity, and microstructure were characterized, complemented by X-ray diffraction analysis and transmission electron microscopy. At 450 °C alloys aging, the aging precipitated phases are β-Ni3Si and Co2Si. Specifically, the orthorhombic (Ni, Co)2Si precipitates were found, which have the same crystal structure as the Ni2Si precipitates. The crystal orientation relationship between the matrix and the precipitates is: 112Cu//112β//012p, (11¯1)Cu//(11¯1)β//(021)p; 001Cu//001β//001p, (220)Cu//(110)β//(100)p. With the increasing Co content, the properties of the alloy were degraded. However, Co can promote the growth of the precipitates and accelerate precipitation during the aging process. After aging at 500 °C for 2 h, the hardness and conductivity of the Cu-1.5Ni-1.0Co-0.6Si alloy with 40% deformation were 250 HV and 43% IACS, respectively.
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•Aging and structure transformation of Cu-Ni-Co-Si alloy were studied.•Three precipitated phases are (Ni, Co)2Si, β-Ni3Si and Co2Si.•Crystal orientation relationships between matrix and precipitates were determined.•Addition of Co can improve the hardness and conductivity of Cu-Ni-Co-Si alloy.
Al2O3-Cu/(25)W(5)Cr and Al2O3-Cu/(35)W(5)Cr electrical contact materials were fabricated by vacuum hot-pressing sintering and internal oxidation. The relative density, electrical conductivity, and ...Brinell hardness were measured. The microstructure was analyzed by scanning electron microscopy and transmission electron microscopy. JF04C electrical contact testing apparatus were used to investigate the electrical contact performance of composites. Arc erosion morphologies were analyzed by scanning electron microscopy and three-dimensional profilometer. The material transfer as well as electrical contact performance were studied during contact make and break operations at 30 V DC with current between 10 and 30 A. It indicates that the nano-Al2O3 particles pinned dislocations. Material transfers from the cathode to the anode. With the melting, evaporation, and sputtering of Cu during arcing, W particles gather and generate needle-shaped skeletons. Finally, liquid droplets, needle-like structures, craters, and bulges were formed on electrode surfaces after arc erosion. Furthermore, their quantity and morphology are affected by tungsten content. When the content of W in the dispersed copper matrix increases from 25 wt% to 35 wt%, welding force is reduced during the steady operations. In addition, when the arc duration is greater than 8.86 ms, the Al2O3-Cu/(35)W(5)Cr contact material has a shorter average arc duration than Al2O3-Cu/(25)W(5)Cr at the same arc energy.
Liquid droplets, needle-like structures, craters, and bulges were formed on the electrode surfaces after arc erosion. Display omitted
•Vacuum hot-pressing sintering was combined with internal oxidation to fabricate Al2O3-Cu/(W, Cr).•The mass transfer directions of the two composites are from the cathode to anode.•Liquid droplets, needle-like structures, craters and bulges formed on electrode surfaces.•The 35 wt% W composite experienced shorter arc duration.
The aim of this study is to develop a new method for the preparation of high-value, environmentally friendly products from tailings. Magnetic Fe3O4 nano-powder was synthesized by ultrasonic-assisted ...chemical co-precipitation utilizing high purity iron separated from iron ore tailings by acidic leaching method. Magnetite particles with 15nm average diameter were characterized by X-ray diffraction, field-emission scanning electron microscopy and vibrating sample magnetometer. Surfactant influence on particles shape and size was investigated. Fe3O4 nanoparticles coated with C12H25OSO3Na exhibit better dispersion and uniform size. The product consisted of ferrous ferrite (Fe3O4) nanosized cubic particles with a high level of crystallinity and exhibit super-paramagnetism based on magnetization curves lacking hysteresis.
► Fe3O4 nano-powder was synthesized by ultrasonic-assisted chemical co-precipitation. ► Fe3O4 nano-powder coated with C12H25OSO3Na show better dispersion and uniform size. ► Nanoparticles synthesis requires no protecting gas, and can be easily implemented.
Titanium alloy fatigue limit is reduced by brittle coatings.
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•Tension-tension fatigue tests of TC4 alloy with brittle coatings were conducted.•Fatigue crack initiated in brittle ...coatings and propagated to the interface.•The fatigue limit stress is significantly reduced due to the brittle coatings.•The model of coating cracking-induced fatigue decrease is proposed.
In order to study the coating effects on fatigue crack initiation mechanism in Ti-alloys, two types of brittle coatings, CrAlN and TiN, were deposited on the surface of TC4 titanium alloy by physical vapor deposition. The tension-tension fatigue tests and the in-situ observations of fatigue crack morphology were performed to study the coating effects on the fatigue crack initiation and propagation in the Ti-6Al-4V alloy. It was found that the 510–530 MPa TC4 fatigue limit is reduced to 315–330 MPa due to the CrAlN coating. The brittle coatings impeded the deformation of the TC4 samples at the beginning stage of fatigue tests, while coating cracking promoted the elongation of the tested samples. Fatigue crack was found to be initiated in the brittle coatings and propagated to the coating-substrate interface, inducing micro-damage of the substrate surface. The fracture surface of coated and uncoated samples was quite different, and the formation of non-propagating fatigue cracks was also observed. The coating cracking-induced low cyclic stress substrate damage model was proposed. This study should be of significance for the coating improvement and provides a theoretical basis for improving fatigue properties of coating materials.
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