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Carbon fiber reinforced aluminum matrix composites (C f /Al) are widely used in various industries. But they are difficult to join because it is hard to realize the wetting and continuity of the carbon fiber in joint. To solve this problem, C f /Al are joined by ultrasonic soldering in this work. Results show that the C f /Al can be wetted within 5 s under ultrasonic. Transmission electron microscope result shows that the surface of the wetted carbon fiber is covered by an amorphous-nanocrystalline layer, which is formed due to the high solder velocity, temperature and pressure caused by cavitation. Carbon fibers flow into the solder after the Al matrix is eroded, guaranteeing its continuity in the joint. Limited carbon fibers flow into the joint at low ultrasonic power of 333.3 W, while a fully carbon fiber reinforced composite joint is obtained at 1000 W. The soldered joints have higher strength than the C f /Al substrate, and its formation mechanism is discussed. [ABSTRACT FROM AUTHOR]

The process condition is one of the major factors to the quality of the matched cold-pressing joining between dissimilar sheets. The material AA1100 pure aluminum sheets and 304 stainless steel sheets were taken for experimental studying in this article. It was reached systematically that the effects of process conditions such as the loading pressure, the thickness of the aluminum sheets, and the joint structure on joining process and quality. As results shown, there was shunt behavior on the joint area of the aluminum sheet. The thickness of the joining decreased from the center to the both sides sequentially. The thickness of the aluminum sheets was proportional to the joining strength, and the loading pressure was inversely proportional to the joining strength when the other parameters were all the same. The technical reserves for the development of cold-pressing joining deformation joining for dissimilar sheets were provided in this study. [ABSTRACT FROM AUTHOR]

• High-strength Ti 2 AlNb sheet was fabricated by hot packed rolling the spark-plasma-sintered pre-alloyed powders. • Extreme high tensile strength of 1532 MPa without any post heat treatment was obtained after two rolling passes. • The micro-sized O and nano-sized O phases contributed to the high tensile strength of the sheet. In this work, we fabricated high-strength Ti 2 AlNb sheets by hot packed rolling the spark-plasma-sintered pre-alloyed powders at the B2 + O phase field. We rolled the sheets with three different schemes, namely, sheet A (thickness reductions of 42% + 42%), sheet B (30% + 30% + 30%), and sheet C (30% + 21% + 21% + 21%). Results showed that the spheroidizing of the O phase occurred during the multiple rolling processes, and sheet C consisted of only spherical O phases. The mechanical property tests showed that Ti 2 AlNb sheets with tensile strengths higher than 1400 MPa could be obtained without any post heat treatment. Both micro-sized O and nano-sized O phases contributed to the excellent mechanical properties of the sheets. The multiple rolling processes resulted in slight decreases in tensile strength but an increase in ductility. All sheets showed brittle fracture mode with reduction of area smaller than 5%. [ABSTRACT FROM AUTHOR]

In this work, a novel "spark plasma sintering (SPS) of pre-alloyed powder followed by a hot packed rolling" method is proposed to fabricate the Ti 2 AlNb sheet. Ti 2 AlNb sheets with high tensile strength and good ductility are obtained without any post heat treatment. Ti 2 AlNb compact is first prepared by SPS of the pre-alloyed powders. The compact sintered at 1060 °C consists of only B2 phases with an average grain size of 25.88 μm. No α 2 phase forms after rolled at 1030 °C and the B2 grain size increases by increasing the rolling passes because of the fast grain growth of B 2 grains. Numerous ultrafine O phases precipitated inside the B 2 matrix after cooled in air, and they contribute to the excellent strength and ductility of the sheets. The mechanical property tests showed that the sheets rolled by 2 passes (thickness reduction: 42% + 42%) and 4 passes (30% + 21% + 21% + 21%) had the maximum tensile strength of 1239.03 MPa and the maximum elongation of 9.49%, respectively. All the rolled sheets presented ductile fracture mode with numerous dimples on the fracture surface. • A novel "SPS of pre-alloyed powder followed by hot packed rolling" method is proposed to fabricate Ti 2 AlNb sheet. • Ti 2 AlNb sheets with high strength and good ductility can be obtained without any post heat treatment. • The nano-sized O phases precipitated from B 2 matrix contribute to the excellent properties of the sheets. [ABSTRACT FROM AUTHOR]

Sealing problems, subsequent cleaning processes and poor force transmission effect etc. series of problems which strongly restrict the development and application of traditional medium pressure-based sheet forming technology. To overcome these problems, the magnetorheological fluid (MRF) can be used as the alternative force transmission medium. In this study, the deep drawing process of a 304 stainless steel sheet using MRF was investigated. The die cavity was filled with MRF and electric current was used to quantitatively adjust the magnetic fields distribution, which then controls the deformation behavior of the forming sheet. As compared to the conventional deep drawing process, experimental results clearly show that significant improvement in the produced sample quality was obtained when using the MRF with the electric current of 2 A. These improvements include: the height of the boundary circle reduces by 20%, the wall thickness distribution is more uniform, the rebound ratio correspondingly reduces from 9.6% to 0.67%, and the degree of sticking mode and the size precision are significantly increased. The results of this study provide scientific guidance to solve the bottleneck in the traditional deep drawing forming technology. The potential applications of the MRF-based new deep drawing technology to improve the product quality were explored. [ABSTRACT FROM AUTHOR]

• Ti x VNbMoTa refractory high-entropy alloys with ultra-fine grains were fabricated by MA and SPS. • The mechanical alloying time of the milling powders with high Ti content was extended by the severe agglomeration. • The fluctuation of yield strengths is attributed to the changes of strengthening effect. Ti x VNbMoTa refractory high-entropy alloys (RHEAs) were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS) based on classic VNbMoTaW RHEA. The effect of Ti content on the microstructures and mechanical properties of the Ti x VNbMoTa RHEAs were systematically investigated. The results showed that the milling powders with more Ti content were agglomerated severely in the early stage of the MA process, leading to the extension of mechanical alloying time. The mechanically alloyed powders in all groups exhibited single body-centered-cubic (BCC) phase after the MA process. The sintered alloys were consisted of ultra-fine matrix and precipitation phase. The grain sizes of the matrix and precipitation phases, as well as the volume fraction of the precipitation phases were increased with the increase of Ti content. The MA and SPS processes and the replacement of Ti not only greatly reduce the densities, but also significantly improved the ductility, strength and specific strength of the alloys. The yield strengths were decreased first and then increased with the increase of Ti content in the Ti x VNbMoTa RHEAs, which is mainly attributed to the weakened effect of grain boundary strengthening, and the enhanced effect of the substitution solid solution strengthening and the interstitial solid solution strengthening. The rapidly increased sizes and volume fractions of the precipitated phases in Ti1.5 and Ti2 destroyed the continuity of matrix and the coordination of deformation, resulting in the decrease of ductility. [ABSTRACT FROM AUTHOR]

In this study, the scanning electron microscope (SEM) and electron backscattering diffraction (EBSD) was used to investigate the evolution of the TiB whiskers (TiBw) orientation, microstructure, and texture during hot rolling. The mechanical properties at room-temperature were tested for as-rolled composites in different loading directions. Based on the calculated and measured Schmid Factors (SFs), the effect of texture on the modes of dislocation slip in different directions was researched. A generalized shear-lag model was modified to evaluate the strengthening contribution of TiBw in different directions. The effects of matrix texture, TiBw orientation, and Hall-Petch (H–P) relationship on the anisotropy of mechanical properties of as-rolled composites were comprehensively analyzed. Results show that recrystallization (DRX) mechanisms include continuous DRX (CDRX) and discontinuous DRX (DDRX) during hot rolling. When the rolling reduction was 70%, the matrix alloy displayed the {11 2 ‾ 0} <10 1 ‾ 0> texture (the crystal c-axis point to the TD, i.e. T-Texture) and recrystallization texture. With the increase of rolling reduction, the strength of as-rolled composites increased. The best mechanical properties were obtained in the rolling direction (RD) at 60% rolling reduction, in which the tensile strength and plasticity were increased by 14% and 17.3% respectively compared with as-sintered composites. The prismatic slip and the basal slip were activated in RD and transverse direction (TD) respectively during room-temperature tensile. The strengthening contribution of TiBw decreases from RD to TD. Analysis of the synergistic effect of TiBw load-transfer reinforcement and H–P reinforcement on property anisotropy shows that the combination of the H–P relationship and TiBw orientation weakens the as-rolled composites anisotropy. 1. The microstructure and texture evolution of TiBw/TA15 during hot rolling is analyzed. 2. The Schmid Factors of different slip systems for ideal T-texture are calculated. 3. The shear-lag model is modified to evaluate the strengthening effect of TiBw. 4. The synergistic effects of TiBw and grain size on the anisotropy are analyzed. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new process of diffusion bonding in air for Al–Mg–Li alloy was proposed, which greatly reduced the welding cycle and equipment requirements. • The Cu coating nano-interlayer not only inhibited the formation of oxide film but also promoted atomic diffusion. • The shear strength of Al-Mg-Li alloy joint was 187.9 MPa reaching up to 90.6% of that in BM. • The width of Al-Al diffusion interface was only about 1 μm and the joint was enhanced by nano-MgO. The process of diffusion bonding in air was successfully used to join 5A90 Al–Mg–Li alloy, which can greatly reduce the welding cycle and equipment requirements. Before diffusion bonding, the Cu nano-coating prepared on the surface of Al–Mg–Li alloy by ultrasonic electrodeposition was used as interlayer to hinder the formation of oxide film and increase the atomic diffusion. The effects of coating thickness, diffusion temperature and interlayer types on the microstructure and performance of joints were investigated. When the diffusion temperature was 530 °C and the coating thickness was 5.12 μm, the optimal shear strength of the joint with 1 μm-thick diffusing interface was 187.9 MPa, which was 90.6% of that in base metal. As the decomposition of unstable Li 20 Mg 6 Cu 13 Al 42 , Cu atoms diffused into the Al matrix to precipitate Al 6 CuMg 4 , and enhanced nano-MgO phase was formed in situ. In addition, the element diffusion behavior and formation mechanisms of the joints were discussed in detail. [ABSTRACT FROM AUTHOR]

• DFT and AIMD were combined to study the oxidation mechanism of CrN. • Surface energy of CrN low-index surface was calculated. • The adsorption configuration and electronic structure were analyzed. • The dynamics process of O 2 dissociation and adsorption was studied by AIMD. • The PDOS change during AIMD simulation were analyzed. [Display omitted] Density functional theory (DFT) calculation and ab initio molecular dynamics (AIMD) are combined to investigate the CrN oxidation mechanism. The surface energy, adsorption configuration and electronic structure of oxygen molecule and atom on the CrN (100) surface are investigated through DFT calculation. AIMD calculation is used to investigate the geometric configuration and electronic structure evolution of O 2 molecule adsorption and dissociation process at 1073 K. Results show that the (100) surface has the lowest surface energy. The top site of Cr atom is the most stable adsorption site for oxygen molecules and atoms, and the adsorption energy values are −4.276 eV and −4.975 eV, respectively. Charge density difference results show that both oxygen molecule and atom undergo charge transfer with the Cr atom. The O atom gains electrons while the Cr atom loses electrons. Results of partial density of states show that the Cr O bond is formed due to the hybridization between the O-p and Cr-d orbitals. At 1073 K, AIMD results show that the O 2 molecule automatically dissociates into O atoms, and the dissociated O atoms form stable covalent bonds with the surface Cr atom. The hybridization between the O-p and Cr-d orbitals gradually increases, thereby forming stable adsorption. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations are combined to study the α-Ti oxidation mechanism on atomic scale. The most and second stable adsorption site for O atoms on the surface layer is FCC and HCP site, respectively. The most stable adsorption site of subsurface layer is octahedral site. O atoms all gain electrons from adsorbed Ti atoms and the Ti–O bonds are mainly formed by the hybridization between O-p and Ti-d orbitals. At both 303 K and 873 K, AIMD results show that O 2 molecule gradually dissociate into O atoms on α-Ti (0001) surface and then adsorb on the surface. The increase of temperature accelerates the dissociation rate of O 2 molecule. During the formation of Ti–O bond, O and Ti atom gain and lose electrons, respectively. The partial density of states evolution results show that the Ti–O bond is formed by the gradually strengthened hybridization between O-p and Ti-d orbitals. At 303 K, α-Ti (0001) surface can form a dense oxide film. But a discontinuous and loose oxide film is formed at 873 K and O atoms can penetrate into the octahedral and tetrahedral sites of the subsurface layer. • DFT and AIMD were combined to reveal the α-Ti oxidation mechanism. • Adsorption behavior of O atom on surface and subsurface was studied by DFT. • The dynamic dissociation and adsorption process of O 2 was investigated by AIMD. • The temperature effect on the O 2 dissociation behavior was studied by AIMD. • Electronic structure during DFT and AIMD calculation were investigated. [ABSTRACT FROM AUTHOR]

[Display omitted] • DFT and AIMD were combined to study the Ti 2 AlC oxidation mechanism. • Surface energy of different Ti 2 AlC (0001) surfaces was calculated. • The adsorption configuration and electronic structure were analyzed. • The dynamics process of O 2 dissociation and adsorption was investigated by AIMD. • The PDOS changing process during AIMD simulation was analyzed. Ti 2 AlC oxidation mechanism was investigated by density functional theory (DFT) and ab initio molecular dynamics (AIMD). DFT results showed that the most stable adsorption site was HCP hollow sites, followed by FCC. O atom gained electrons, while Al atom lost electrons through the hybridisation of O-p and Al-s/p orbitals. AIMD results show that O 2 molecule gradually dissociated into O atoms at 1273 K and formed Al-Ti mixed oxide film. The hybridisation between O-p and Al-s/p orbitals formed Al-O bond, while the hybridisation of O-p and Ti-d orbitals formed Ti-O bond. [ABSTRACT FROM AUTHOR]

The nanostructured Cu coatings were electrodeposited with different vibration, such as vibration-free, agitation and ultrasonic.Ultrasonic could help to refine grains and optimize the comprehensive performance of the coating. The effect of vibration on the thermal stability of pure Cu coatings was investigated with the coatings annealing at 450 °C, 500 °C and 550 °C. Both agitation and ultrasonic can suppress the nanograins coarsening and the effect of ultrasonic was more excellent. Ultrasonic can not only increase the content of nanotwins and triple junctions but also induce the relaxation of GBs. Therefore, the ultrasonic deposited nanograins in the low-energy state exhibit superior thermal stability. The mechanisms of the thermal stability in the electrodeposited coatings were studied from thermodynamics and dynamics. By comparing dislocation density, stacking faults energy and grain boundaries energy, it was proved that the driving force of grain growth in the ultrasonic deposited coating was lowest. Both the methods of isothermal measurements and Kissinger showed that the ultrasonic could increase the activation energy of grain growth to inhibit grain boundary mobility. • The ultrasonic deposited nanograins annealed at 550 °C for 3600 s only grew from 29.4 nm to 178.7 nm. • Ultrasonic cavitation promoted the formation of nanotwins and relaxation of GBs. • Ultrasonic reduced driving force of grain growth and GBs mobility effectively by analysis of thermodynamics and dynamics. • Electrodeposition combining with ultrasonic provided an important route to stabilize nanomaterials without alloying. [ABSTRACT FROM AUTHOR]

The hot deformation behaviors of an ultrafine-grained MoNbTaTiV refractory high entropy alloy (RHEA) fabricated by powder metallurgy (P/M) were investigated using isothermal compression tests in the deformation temperature range of 1100 °C ~ 1300 °C and the strain rate range of 0.0005 s−1–0.5 s−1. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques were used to analyze the effect of the deformation temperatures and the strain rates on the flow stress behaviors and microstructural evolution during hot deformation. The results showed that the flow stresses exhibit typical dynamic recrystallization (DRX) characteristics, but show work hardening characteristics at 1100 °C and 0.5 s−1 deformation conditions and at 1200 °C and 0.5 s−1 deformation conditions. With increasing deformation temperature and decreasing strain rate, the maximum compressive stresses were dramatically decreased, and the average grain sizes also slowly increased. The limited growth of grains was due to the sluggish diffusion effect of high entropy alloys (HEAs) and the pinning effect of the ultrafine precipitated phases. The dominant DRX process gradually changed from discontinuous dynamic recrystallization (DDRX) to continuous dynamic recrystallization (CDRX) with increasing deformation temperature and decreasing strain rate. Both of these DRX processes were promoted by the ultrafine precipitated phases. The dominant deformation mechanism at low deformation temperature and high strain rate was grain deformation. Grain boundary gliding became the dominant deformation mechanism at higher deformation temperature and lower strain rate, but it was inhibited to some extent by grain growth and the ultrafine precipitated phases distributed at grain boundaries. [ABSTRACT FROM AUTHOR]

This work focused on the microstructure, morphology and thermal stability of a MoNbTaTiV refractory high-entropy alloy synthesized by mechanical alloying. The mechanically alloyed powder with a uniform chemical distribution and an average grain size of less than 15 nm was obtained after 40 h milling process. With a refinement of the grain size and an increase of the lattice strain, the milled powder transformed from large and inhomogeneous to refined and homogeneous. The mechanically alloyed powder exhibited excellent thermal stability at 1200 °C. • MoNbTaTiV refractory high-entropy alloy was synthesized by mechanical alloying. • The alloyed powder presented a uniform chemical distribution and an average grain size of less than 15 nm. • The alloyed powder exhibited refinement and homogeneous size distribution. • The alloyed powder maintained bcc phase and nanoscale grain size at 1200 °C. [ABSTRACT FROM AUTHOR]