Foam metals have become a hot choice for protection due to their excellent specific strength and energy absorption capabilities, and the advancement of light-weighting has posed higher performance requirements and challenges for foam metals. Herein, the disordered-ordered interpenetrating porous composite (Al foam /ZL111 Al-alloy) was prepared via a combination technique of melt foaming and infiltration casting methods. The corresponding quasi-static mechanical properties of characteristic units were analyzed, and the mechanical properties of the composite structural characteristic units may be greatly improved compared to the single structure. The compressive strength of the composite is increased by 66% compared to the sum of their single components, and the plateau stresses were increased by 204%. In order to further improve the comprehensive mechanical properties of the composite structure, the characteristic unit was subjected to T6 heat-treatment and tested in quasi-static compression. The specific compressive strength, plateau stress, and energy-absorbing capacity of the T6 heated unit were enhanced by 73.54%, 107%, and 83.18%, respectively, compared with those before heat treatment. According to the microstructure examination, it can be seen that the eutectic silicon is transformed from the original lamellar to the equiaxed spherical shape after the T6 heat treatment, which reduces the elastic modulus of the material to a certain extent, but significantly improves the compressive strength and plateau stress of the material, and thus improves the energy-absorbing capacity of the composite structure. The interpenetrating porous composite structure can effectively retain the respective advantages of the single component and thus show excellent energy absorption ability, therefore, an appropriate heat treatment of the bi-continuous interpenetrating porous metal (alloy material) structure is an effective means to improve the comprehensive mechanical properties of the material.
The superplastic deformation behavior of Ti65 Ti-alloy was studied via tensile testing in temperature range of 900~960 oC at strain rate range of 0.001~0.03 s-1 in terms of the effect of temperature and strain rate on the superplastic properties of the alloy. Meanwhile, the strain rate sensitivity index m, stress index n and deformation activation energy Q of the alloy were acquired. The grain size, grain orientation and distribution in the area nearby the tensile fracture of the test alloy were characterized by electron back-scattered diffraction (EBSD) technique. The results show that with the increase of temperature the flow stress of Ti65 Ti-alloy is reduced and the elongation is elevated. With the reducing strain rate, the flow stress decreases, and the elongation first increases and then decreases. At the deformation temperature of 960 oC and strain rate of 0.003 s-1, the maximum elongation of the alloy reached 1108%, namely its superplasticity is the best. Correspondingly, the strain rate sensitivity index m is 0.42, the stress index n is 2.5, and the superplastic deformation activation energy Q is 393 kJ/mol, which illuminated that the predominate deformation mechanism is grain boundary sliding and dislocation sliding for Ti65 Ti-alloy. During the superplastic deformation process under different conditions, the Ti65 Ti-alloy undergoes significant dynamic recrystallization, generating uniformly distributed fine equiaxed grains. As the deformation temperature rising and the strain rate reducing, the degree of discontinuous dynamic recrystallization enhances. The grain size of Ti65 Ti-alloy increases with the increase of deformation temperature, and while increases first and then decreases with the increase of strain rate.
Diatoms were prepared by adding extraction solution prepared from ionic rare earth ores to diatom culture media. The results indicate that high concentrations of rare earth extraction solution inhibited the growth of diatoms. An appropriate amount of rare earth extraction solution was added to cultivate diatoms, and diatom frustules modified with rare earth ions were used as rare earth ion doped diatom anode materials for lithium-ion batteries. The natural hollow porous structure of diatom frustules provided enough buffering space for the volumetric strain of SiO2. The doping of rare earth ions reduced the electrochemical impedance of the anode electrode of diatom frustules, significantly improving its long cycle and rate performance. The specific discharge capacity of the diatom frustule anode (DBS@C-REE-10) prepared with 10 mL/L rare earth extract after 150 cycles was 879 mAh·g-1, which was much greater than that of the diatom anode without rare earth ion modification.
Tungsten and tungsten-based materials are one of the most promising candidate of the first wall material faced plasma atmospheres for future nuclear fusion devices, and their brittleness and mechanical properties have always been the focus of attention. Herein, the tensile behavior at 300~800 °C of W-Y2O3 composites after recrystallization annealed at different temperatures and pure W after stress relief annealed were comparatively assessed at 300~800 °Cvia high temperature tensile testing machine, in terms of the effect of addition of rare earth oxide Y2O3 on the mechanical properties of W-composites. It was found that with the increasing temperature, the tensile strength of W and W-Y2O3 composites decreased gradually, and the corresponding break elongation increased first and then decreased; while the tensile behavior of W and W-Y2O3 composites all follow the ductile-brittle transition process, namely brittleness-pseudoplasticity-intrinsic plasticity. If tensile testing at the same temperature, W-Y2O3 composites exhibit better high plastic behavior than pure W. Whereas, W-Y2O3 composites present the best plasticity and toughness at 600 oC, with a break elongation even up to ~46%. In addition, from the acquired tensile curves, it is found that the temperature at which pure W exhibits plastic behavior is near 400 °C, while the temperature at which W-Y2O3 exhibits plastic behavior is near 300 °C. The constitutive equation of their strain hardening stage shows that pure W followed the power function strengthening behavior dominated by Hollomon's equation, while W-Y2O3 shows logarithmic function strengthening behavior in the early stage of uniform plastic deformation, and the same power function strengthening behavior as that of pure W in the later stage of uniform plastic deformation. It follows that the addition of Y2O3 can significantly enhance the plasticity and toughness of W composites, while reducing their brittleness and ductile-brittle transition temperature.
By spheroiding the GCr15 bearing steel with quenching, high-temperature tempering, secondary quenching and low-temperature tempering, the associated evolution mechanism of the microstructure, especially the coarsening of carbides, and its correlation with hardness was investigated here. The results show that after austenitization at 930 oC followed by water/oil quenching and subsequent high-temperature tempering at 700 oC for spheroidization, the cementite particulates continuously coarsened and their size became more uniform as the time of high-temperature tempering time (6, 12, 24, 48 h) increased. The coarsening of spheroidal cementite followed the Ostwald ripening theory. After the secondary quenching (holding at 840 oC for 10 min) and low-temperature tempering (holding at 160 oC for 2 h), part of the cementite dissolved and its content decreased. Due to the dissolving and coarsening of cementite during the austenitization process in the two-phase region, the average size of the cementite was increased compared to that just after the spheroiding. The simple and efficient quenching and high-temperature tempering processes have achieved spheroidization and size control of the cementite. Longer high-temperature tempering time during the spheroidization process resulted in more large cementite particles, nevertheless, more of which could retain for a longer period during the secondary quenching and low-temperature tempering process. This led to a larger average size of the cementite, and at the same time, the lower carbon content in the austenite made it easier to transform into martensite. The increase of carbide size and spacing weakened the hardening effect, while the increase in martensite content could alleviate the decrease in hardness. The hardness of the spheroidized structure and of the secondary quenching and tempering structure basically met the hardness requirements of GCr15 bearing steel. These research can provide a credible reference for the design of the microstructure and properties, as well as the process design of GCr15 bearing steel.
A Ti-V-Mo composite microalloyed experimental steel was subjected to series heating-deformation treatment via Gleeble-3800 thermal simulation tester, i.e. firstly it was heated to 1250 oC and kept for 180 s, then cooled down to 890 oC and kept for a certain period of time; Subsequently, compression and deformation treatments were carried out; Afterwards, it was cooled to different (final cooling) temperatures and finally water-quenched. The effect of final cooling temperature on the precipitates, microstructure transformation, and hardness of the steel was systematically studied using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Vickers hardness tester. The precipitation behavior of carbides (Ti, V, Mo)C and its influence on the variation of microstructure and hardness of the steels quenched at different final cooling temperatures were clarified. The results indicated that the microstructure of the test steels consist of granular bainite at 590 oC, polygonal ferrite at temperatures ranging from 630 oC to 690 oC and a mixture of ferrite and martensite at 730 oC. With the increasing final cooling temperature, the average grain size of ferrite increased from 2.7 μm to 5.6 μm, and the average size of (Ti, V, Mo)C precipitates increased from 3.45 nm to 4.71 nm. With the increasing final cooling temperature from 590 oC to 730 oC, the hardness increased first, then remain stable and then decreased rapidly. For the isothermal final cooling temperature within the range 630~660 oC, the hardness was up to 485HV, which was due to the saturation of the fine grain strengthening of ferrite and the precipitation strengthening of (Ti, V, Mo)C. The fine grain strengthening caused by ferrite grain refinement and the precipitation strengthening caused by the precipitation of (Ti, V, Mo)C were dominant factors of hardness change at different final cooling temperatures.
A novel piezoelectric ceramics (1-x)K0.5Na0.5(Nb0.95Ta0.05)O3-x(Bi0.5Yb0.5)0.95Li0.05ZrO3 was prepared by the conventional solid-phase sintering method, and then was characterized by means of XRD, SEM, EDS, etc. It can be determined that BYLZ incorporates completely into the KNNT lattice in an atomic substitution manner, thereby forming a single perovskite structure, namely, the ceramics is O phase for x = 0.0, O-T phase for x in the range 0.0 < x ≤ 0.02, R-O-T phase for x in the range 0.03 < x ≤ 0.04, and T phase for x in the range 0.04 < x ≤ 0.05. Performance tests show that ceramics achieve the best performance in the polymorphic phase boundary region of x = 0.04:i.e., d33 = 305 pC/N, kp = 38.17%, εr = 1710, tanδ = 2.5%, Pr = 34.63 μC/cm2, EC= 20.67 kV/cm, and TC = 340 °C.
A novel visible-light-driven 1T/2H O-MoS2@S-pCN photocatalyst was synthesized in situ on sulfur-doped g-C3N4 nanosheets (S-pCN) via hydrothermal method with N, N-dimethylformamide (DMF) as solvent. The prepared 1T/2H O-MoS2@S-pCN photocatalyst was characterized by means of XRD, XPS, FT-IR, SEM and UV-vis. The photoelectrochemical properties of the catalyst and the oxidation-reduction behavior of the mixture of ciprofloxacin (CIP) and hexavalent chromium (Cr(VI)) induced by the catalyst were also studied. The results showed that if 15% 1T/2H O-MoS2@S-pCN photocatalyst was introduced into the mixed solution, the removal rate of CIP and Cr(VI) could reach 97.63% within 2 min and 96.2% within 10 min respectively. Furthermore, after five cycle of use, the excellent photocatalytic performance of the catalyst remained unchanged. The excellent performance of the photocatalyst may be attributed to the existence of heterojunctions, the 1T/2H molybdenum disulfide phase with peculiar structure and oxygen doping in the 1T/2H O-MoS2@S-pCN photocatalyst, which could improve its visible light response and effectively inhibit the electron-hole pair recombination. The mechanism related with the removal of CIP and Cr(VI) by this catalyst may be that CIP was oxidized by active substances (h+, e-, ∙O2-), and Cr(VI) was reduced by active substances (e-, ∙O2-).
