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991.
The as-cast and heat-treated microstructures and mechanical properties of the AZ91 magnesium alloys with and without minor Sc addition were investigated and compared in this paper. The results indicated that adding0.15–0.45 wt% Sc to the as-cast AZ91 alloy not only could modify and refine the Mg_(17)Al_(12) phase but also suppress the formation of the Mg_(17)Al_(12) phase. At the same time, the grains of the Sc-containing as-cast AZ91 alloys were also effectively refined. As a result, the mechanical properties at room temperature(RT) for the Sccontaining as-cast AZ91 alloys were effectively improved. In addition, adding 0.15–0.45 wt%Sc to the AZ91 alloy promoted the formation of the continuous precipitates(CP) during the aging treatment in spite of that the formation of the discontinuous precipitates(DP) was simultaneously suppressed. Accordingly, the Sc-containing as-aged AZ91 alloys obtained the relatively higher mechanical properties at RT than the as-aged AZ91 alloy. 相似文献
992.
Yunsong Zhao Chenguang Liu Yuanyuan Guo Yanfei Liu Jian Zhang Yushi Luo Dingzhong Tang 《自然科学进展(英文版)》2018,28(4):483-488
Boron is added into single crystal superalloys as a micro-alloying element to strengthen low angle grain boundaries.However,systematic investigations on the effect of boron on microstructures of single crystal superalloys are limitedly reported.The effect of boron on as-cast and heat-treated microstructures was investigated in two experimental Ni-based single crystal superalloys containing 3 wt% Re.The current results indicated that the volume fraction of(γ+γ′)eutectic and M_3B_2 borides was evidently increased,while the number of micropores was evidently decreased with the addition of 0.02 wt% boron.The(γ+γ′)eutectic could not be dissolved completely due to the lower incipient melting temperature caused by the formation of M_3B_2 borides.Meanwhile,the M_3B_2 borides were found to be enriched with indispensable strengthening elements Cr,Mo,W and Re,and this may lower the strengthening effect and cause stress concentration during high temperature creep. 相似文献
993.
The hydrogen storage of(TiZr_(0.1))_xCr_(1.7-y)Fe_yMn_(0.3)(1.05x1.2,0.2y0.6)alloys,prepared by Ar plasma arc melting,were investigated by X-ray diffraction,pressure-composition-temperature(PCT).The results indicated that all(TiZr_(0.1))_xCr_(1.7-y)Fe_yMn_(0.3)(1.05≤x≤1.2,0.2≤y≤0.6)alloys were determined as C14-type Laves phase,the cell parameters a,c and unit cell volume of(TiZr_(0.1))xCr_(1.1)Fe_(0.6)Mn_(0.3)(1.05≤x≤1.2)alloys increased with increasing the(TiZr)super-stoichiometry from 1.05 to 1.2,and the value of a/c almost unchanged.The hydrogen absorption and desorption plateau pressure decreased from 5.6,4.4–2.6,2.2 MPa with the increase of(TiZr)super-stoichiometry from 1.05 to1.2 at 274 K respectively,and the hydrogen desorption plateau pressure decline was not obvious when the(TiZr)super-stoichiometry exceeded 1.15.The(TiZr_(0.1))_(1.1)Cr_(1.1)Fe_(0.6)Mn_(0.3)alloy had the best comprehensive properties about the maximum and reversible hydrogen storage capacity was 1.79 and 1.45 wt%respectively.The cell parameters a,c and unit cell volume of(TiZr_(0.1))_(1.1)Cr_(1.7-y)Fe_yMn_(0.3)(0.2≤y≤0.6)alloys increased as the ratio of Fe/Cr content decreased.The hydrogenation and dehydrogenation plateau pressure decreased from 4.5,3.4–1.0,0.9 MPa respectively and the maximum hydrogen storage capacity increased from 1.79 to 2.0 wt%as the Fe content reduced from 0.6 to 0.2 at274 K.The maximum and the reversible hydrogen storage capacity were about 2.0 and 1.65 wt%as the ratio of Fe/Cr was 0.13(ie,(TiZr_(0.1))_(1.1)Cr_(1.5)Fe_(0.2)Mn_(0.3)alloy),its relative molar enthalpy of dissociation hydrogen was24.30 kJ/mol H_2. 相似文献
994.
Selective functionalization of mesoporous silica nanospheres (MSNs) is crucial for nanoengineering of MSNs.
Herein, we have combined “surface-protected etching strategy” and “cationic surfactant assisted etching
strategy” to prepare functionalized MSNs with externally attached amino groups. The externally attached NH2
groups endow the catalysts with excellent catalytic performance for nitroaldol reaction between nitromethane
and benzaldehyde. In addition, those NH2-MSNs can also be used to support gold nanoparticles, which display
very good catalytic performance for reduction of 4-nitrophenol. It can be envisioned that the synthesis protocol
developed in this work could also be extended to nanoengineered MSNs, which provides opportunities for nanoreactors
design. 相似文献
995.
This paper reports the ferroelectricity in antiferromagnetic SmCrO_3 with a reasonably large value of spontaneous electric polarization(70μC/cm~2mC cm~(-2)at 50 K)based on the measurement of pyroelectric current.The experimental results showed that the temperature of the onset of polar order was evidently higher(about220 K)than the Neel temperature(T_N=197 K)in the magnetodielectric studies.The calculated magnetodielectric effect(MDE)value was explicitly negative with maximum|MDE|values of about 3.6%around 230 K.The absence of a convincing signature in MDE at antiferromagnetic ordering temperature T_Nindicated the absence of magnetoelectric coupling around this temperature regime.The results further confirmed that the onset of polar order can be attributed to the structural distortion,rather than the canted noncollinear magnetic structure. 相似文献
996.
The relationship between crystal orientations and meso-mechanical properties of β phase Ti-7333 titanium was investigated through the combination of nanoindentation experiments and simulation. The crystal plasticity finite element(CPFE) model for nanoindentation of single body-centered cubic crystal was established based on the experimental data. And the crystal plasticity constitutive law was implemented to simulate the nanoindentation process, obtaining satisfied results with an acceptable error. From the simulated pileup morphology patterns with different crystal orientations, it was found that the β phase experienced a symmetrical and orientation-related deformation process. Meanwhile, the strain-rate sensitivity(SRS) of β phase was investigated through nanoindentation tests based on continuous stiffness measurement(CSM) under different strain rates,varying between 0.2, 0.05 and 0.01 s~(-1). Two grains with different orientations exhibited similar SRS exponents,m, calculated from the experimental results. 相似文献
997.
Tongjin Zhou Wei Feng Huibin Zhao Yu Meng Huaxia Zhang Hongsheng Ding Zichen Wang 《自然科学进展(英文版)》2018,28(1):45-53
In order to comprehensively understand the forming mechanism of abnormal phases solidified in a nickel-base cast superalloy with additives of tungsten and molybdenum, the coupling effects of W and Mo on the microstructure and stress-rupture properties were investigated in this paper. The results indicated that the precipitation of primary α-(W, Mo) phase depended tremendously on the amount of W and Mo addition. When the total amount of W and Mo was greater than 5.79 at%, α-(W, Mo) phase became easily precipitated in the alloy.With increasing of Mo/W ratio, the dendrite-like α-(W, Mo) phases were apt to convert into small bars or blockylike phases at the vicinities of γ′/γ eutectic. The morphological changes of α-(W, Mo) phase can be interpreted as the non-equilibrium solidification of W and Mo in the alloy. Since the large sized α-(W, Mo) phase has detrimental effects on stress-rupture properties in as-cast conditions, secondary cracks may mainly initiate at and then propagate along the interfaces of brittle phases and soft matrix. During exposing at 1100 ℃ for 1000 h, the α-(W, Mo) phases transformed gradually into bigger and harder M_6C carbide, which results in decreasing of stress-rupture properties of the alloy. Finally, the alloy with an addition of 14W-1Mo(wt%) maintained the longest stress lives at high temperatures and therefore it revealed the best microstructure stability after 1100 ℃/1000 h thermal exposure. 相似文献
998.
Hematite(α-Fe_2O_3)has been extensively studied as a promising photocatalyst,with the capacity to split water under visible light.To tune its electronic structure and improve the performance for oxygen evolution reaction(OER),high-quality single crystals ofα-Fe_2O_3nanoparticles were synthesized and doped by various transition metals(M=V,Cr,Mn,Zn,Co,Ni,Cu,Nb,Mo,Ti)by a molten-salt flux method.Optical,electronic and catalytic properties of transition-metal-dopedα-Fe_2O_3(TM-dopedα-Fe_2O_3)have been systematically investigated.Cobalt has been identified as the best dopant forα-Fe_2O_3,reducing the OER overpotential by 0.16 V with respect to the undoped. 相似文献
999.
The low quantum efficiency arising from poor charges transfer and insufficient light absorption is one of the critical challenges toward achieving highly efficient water splitting in photoelectrochemical cells. Three dimensions(3D) structures and heterojunctions have received intensive research interests recent years due to their excellent ability to separate photo-generated charges as well as the enhanced light harvesting property. Herein,3 D Cu O/WO_3 structure was fabricated through a facile solvothermal method followed by chemical bath deposition. The loading of Cu O clusters on WO_3 nanoflake arrays results in a much improved photocurrent density compared with that of pristine WO_3 nanoflake arrays, which reaches 1.8 m A/cm2 at 1.23 V vs. the reversible hydrogen electrode. The electrochemical impedance spectroscopy measurement demonstrates that the improved performance of Cu O/WO_3 electrode is attributed to the accelerated charge transfer kinetics as a result of the desirable band alignment in Cu O/WO_3 heterojunction. This work demonstrates a facile strategy to construct superior WO_3 electrode, which will ultimately allow for efficient storage of solar energy into hydrogen. 相似文献
1000.
Yan M Zhaoxin Du Xiaoming Cui Jun Cheng Guolong Liu Tianhao Gong Huimin Liu Xiaopeng Wang Yuyong Chen 《自然科学进展(英文版)》2018,28(6):711-717
The microstructure and mechanical properties of Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe high strength titanium alloy sheets prepared by unidirectional cold rolling and two-step cross cold rolling were investigated. Results showed that the β phase grains were refined significantly by cold rolling followed by solution treatment for a short time.Compared to unidirectional cold rolling, the short time solution treatment after two-step cross rolling could significantly reduce the non-uniformity of the microstructure of the alloy sheets. After aging treatment at 550 ℃,the anisotropy of the mechanical properties still existed in the unidirectional rolled sheets, and the tensile strength was highest along the rolling direction. After solution and aging treatment, the anisotropy of the mechanical properties of the two-step cross rolling process sheet was not obvious than unidirectional cold rolling,and alloy had good strength and plasticity matching. 相似文献