查看更多>>摘要：Transition elements are important alloying elements in aluminum alloys, whilst there was a blank of the role of Ti in cast Al-Li-Cu alloys. In this study, the impact of 0.1 and 0.2 wt% Ti additions on Al-2.5Li-1.5Cu-1Zn-0.5Mg(?0.2Zr) alloys has been investigated by microstructure characterizations and tensile tests. The optical microscopy results showed that the grains were significantly refined as the transition elements presented. There was little poisoning phenomenon in the alloys containing both Zr and Ti for the limited holding time during the smelting process. The age-hardening and mechanical properties were prominently enhanced with the addition of Ti and Zr after ageing at 150 oC. The results of transmission electron microscopy showed that dispersed and dense θ? (Al2Cu) precipitates distributed in the alloy containing 0.2 wt% Ti, while T1 (Al2CuLi) phases dominated in the alloy containing 0.2 wt% Ti and 0.2 wt% Zr, accompanied by a moderate number of S? (Al2CuMg). The coarsening rates of δ?(Al3Li) and δ?-precipitation free zones (PFZs) decreased gradually with the content of transition elements increasing, but the case in the 0Zr2Ti alloy was abnormal for the interaction between θ? and δ?. The best comprehensive mechanical properties of YS = 374 MPa, UTS= 527 MPa and EL = 7.1% could be obtained by 2Zr2Ti alloy after ageing at 150 °C for 64 h.
查看更多>>摘要：Recent studies demonstrate that Al-Si alloys, which are conventionally used in as-cast form, can be transformed to profiles through high temperature plastic deformation. However, rare attention is paid to room temperature deformation of Al-Si alloys. In this work, an Al-6Si-3Cu alloy with excellent mechanical performance was produced through combined heat treatment and room temperature rolling, which is superior to other recently developed Al-Si alloys. Specifically, the alloy processed by a combination of solid solution treatment and room temperature rolling has an ultimate tensile strength (UTS) of 429.8 MPa and an elongation (EL) of 5.8%, exhibiting an improvement of 105% and 76% compared to the as-cast alloy, respectively. Subsequent artificial aging further enhances the EL to 9.9% but decreases the UTS to 387.4 MPa, which exceed that of the as-cast alloy by 200% and 85%, respectively. Detailed microstructure observations were performed to reveal the underlying mechanisms behind the enhancement of strength and ductility. Results presented in this work may shed some light on the development of strong and ductile Al-Si alloys.
查看更多>>摘要：The thermoelastic martensitic transformation in the polycrystalline Ti29.7Ni50.3Hf10Zr10 alloy was studied using high-resolution and in situ neutron diffraction in the temperature range of 25–250 °C. The thermal expansion tensors of the B19′ martensite and austenite were determined. B19′ martensite is characterized by a strong anisotropy of the thermal expansion coefficients. The analysis of the diffraction peak integrated intensities suggests that nearly 10% of austenite, which is partly disordered, does not take part in martensitic transformation. The volume effect of the transformation in the Ti29.7Ni50.3Hf10Zr10 alloy was 0.79%. The simultaneous addition of Hf and Zr atoms into the TiNi matrix leads to the deterioration of the crystallographic compatibility between martensite and austenite, which may be responsible for the large thermal hysteresis and volume changes upon transformation.
查看更多>>摘要：This paper discusses the effect of deep cryogenic treatment (DCT) on the evolution of natural and artificial aging of Al-Mg-Si alloy EN AW 6026. This study provides the first research and evidence of DCT effect on dispersoids and their development in aluminum alloys. DCT induces reformation and regrowth of dispersoids during natural aging from a preferential cuboidal shape to spherical, which is also distinguishable by the change in chemical composition. Additionally, with DCT the dispersoids form in a denser manner, which consequently influences the hardness evolution with aging time. The study also reveals that the exposure duration to DCT (from 24 to 48 h) increases the DCT impact on the hardness evolution during natural aging of selected alloy. The influence of homogenization temperature on the DCT performance is also researched in connection to modified natural aging, which is correlated to the presence and formation of secondary phases during homogenization. Furthermore, DCT also promotes the formation of β'' precipitates and at the same time retards the formation of larger β' precipitates during artificial aging. After artificial aging, both dispersoids and precipitates display a denser population and more elongated shape aligned along the< 100 > axis of the aluminum matrix with DCT compared to conventionally heat-treated samples without DCT. The microstructural changes during DCT application are strongly linked to the modification of dispersoids with homogenization and artificial aging that influence the content of alloying elements in the matrix.
查看更多>>摘要：A novel Z-scheme 3D flower-like NH2-UIO-66/BiOCl composite was fabricated by a facile solvothermal method. The structural characterization results demonstrate that NH2-UIO-66 is embedded on the smooth surface of the flower-like BiOCl, forming a tight contact interface. As a visible light collector, NH2-UIO-66 expands the optical absorption range of BiOCl, which is confirmed by the UV-Vis diffuse reflectance spectra (DRS). By combining UV-Vis DRS, Mott-Schottky (MS) plots and VB-XPS, a well-matched band structure between NH2-UIO-66 and BiOCl is obtained. Photoelectrochemical characterizations indicate that the synergistic effect between NH2-UIO-66 and BiOCl interfaces facilitates the separation and transfer of photogenerated electron-hole pairs. In the case of photocatalytic performance experiments, the removal efficiency of the prepared NU66/BOC composites for TC-HCl was higher than either NH2-UIO-66 or BiOCl under simulated solar irradiation. NU66/BOC-20 exhibited the best performance with Kapp value (0.01269 min?1), which is 84 and 3 times more than the pristine NH2-UIO-66 (0.00015 min?1) and BiOCl (0.00410 min?1), respectively. In addition, NU66/BOC-20 composite demonstrates remarkable stability with a TC-HCl removal rate of 83% in the third cycle. The radical quenching experiments indicate that the primary active species is superoxide radicals (·O2?) while holes (h+) play a role to some extent. Based on the above experimental results and in-situ irradiated XPS, Z-scheme was proposed to explain the electron transfer pathway in the photocatalytic process.
查看更多>>摘要：In this work, an original color-tunable persistent luminescence (PersL) phosphor based on Pr3+ doped LiTaO3 (LTO) was realized. The PersL emission can be modulated from pale yellow to deep orange-red merely by changing the concentration of Pr3+, which attributed to the concentration quenching resulted from the cross-relaxation (CR) effect. Thermoluminescence (TL) analysis shows that the continuous shallow traps (0.668–0.8 eV) are suitable for PersL. Moreover, it also exhibits excellent photostimulated luminescence (PSL) performance owing to the presence of stable deep traps of 0.916 eV. A possible PersL mechanism of LTO:Pr3+ is put forward to explain this phenomenon. Finally, inspired by this multicolor PersL feature, a quick response code (QR-code) and an arrow pattern are developed, revealing that LTO:Pr3+ is an ideal material for dynamic anti-counterfeiting. Our work is designed to promote the practical applications of PersL materials in information security areas.
查看更多>>摘要：A novel B-based B50Sm10Co40 amorphous alloy was fabricated by melt-spinning technique. The crystallization temperature, Vickers hardness, and Young's modulus of the alloy are 1068 K, 15.2 GPa, and 230 GPa, respectively, much higher than those of a Co-based Co65Sm10B25 amorphous alloy in the same system. Ab initio molecular dynamics simulation based on density-functional theory indicates that the short-range order of the B50Sm10Co40 amorphous alloy is dominated by B-centered tri-capped trigonal prisms (TTPs) and bi-capped square Archimedean antiprisms, whereas the Co65Sm10B25 alloy mainly contains B-centered TTPs and Co-centered distorted icosahedral-like polyhedra, and the fraction of the TTPs is lower than that in the B50Sm10Co40. The dense-packed B-centered prism-type clusters with a high proportion of stable B–B covalent bonds reduce the atomic diffusivity and mobility, and increase the resistance to crystallization and shear transformation, which contribute to the high thermal stability and hardness/modulus of the B-based B50Sm10Co40 amorphous alloy.
查看更多>>摘要：In this work, Ti3SiC2/AgNWs composite powders were synthesized by an alcohol thermal reaction method and added in acrylic epoxy resin to prepare a microwave absorption coating. The characteristics of the composite powders and coatings were analyzed. XRD results verified the successful preparation of AgNWs, and SEM images revealed the AgNWs were intertwined with Ti3SiC2 powders. The introducing of AgNWs was helpful to form a conductive network inside the coatings. And the complex permittivity of the coating was enhanced with the increasing content of AgNWs. What's more, the impedance matching condition and attenuation loss ability of the coatings were optimized, which contributed to enhancing the microwave absorbing performances. The Ti3SiC2/AgNWs/acrylic acid resin coating containing 30% AgNWs exhibited the optimum microwave absorption performance. For the coating with 2.0 mm thickness, the lowest RL value of ? 31.2 dB was obtained at 10.34 GHz, and the effective absorption bandwidth has reached to 3.22 GHz (9.18–12.4 GHz). After incorporating with frequency selective surface (FSS), the microwave absorption performance in the low frequency range is significantly enhanced. The results show that the combination of Ti3SiC2/AgNWs with FSS can tailor the absorption bandwidth and develop a novel microwave absorbing material.
查看更多>>摘要：An oxide dispersion strengthened copper (ODS-Cu) alloy with Zr addition was fabricated by high-energy water-cooled mechanical alloying and spark plasma sintering (SPS). The effects of Zr addition on the material properties and microstructure of ODS-Cu alloys were investigated by comparing with the results of the Cu-1Y2O3 (wt%) ODS alloy. The addition of 0.81 Zr (wt%) to the Cu-1Y2O3 (wt%) alloy was confirmed to increase the Vickers hardness of the ODS-Cu alloy by a factor of 1.5, resulting in an unprecedented value of 243 HV. The excellent strength comes mainly from the strengthening effect caused by the refinement of the dispersed oxide particles. Fine and dense FCC-structured complex Y2Zr2O7 oxide particles were found to be uniformly distributed within the alloy, which are in good coherency with the Cu matrix, allowing the particle size to be less than half of that in Cu-1Y2O3 (wt%) ODS alloy at 7.6 nm. Although a slight decrease in the thermal diffusivity of the ODS-Cu alloy with Zr was observed, which can be attributed to the solid solution effect of the residual Fe in the matrix, this study proposes a suitable thermal aging treatment to restore the thermal diffusivity by precipitating the solute Fe.
查看更多>>摘要：In this work, we have investigated the effect of W addition on microstructure and mechanical properties of equiatomic TiVCr medium entropy alloy films. It is found that a transition from amorphous phase to quasicrystal and nanocrystal occurs with increasing content of W, showing an improved crystallinity of the films. Hardness drastically increases with increasing W addition and reaches the maximum value of 7.2 GPa at 16.0 at% W content, which is two times higher than that of the initial sample. Amorphous phase strengthening, solid solution and precipitation strengthening become the dominant mechanism, responsible for the ultrahigh strengthening effect.
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