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[en] Pre-alloyed powders of oxide dispersion strengthened (ODS) steels were produced by atomization. The atomized powders without mechanical alloying (MA) and with short-time MA were consolidated by hot isostatic pressing (HIP). The morphology and microstructure of the atomized and the MA powders were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microstructure of 9Cr–ODS steels with different MA time was characterized by high-resolution transmission electron microscopy (HRTEM), electron backscatter diffraction (EBSD) and atom probe tomography (APT). The results showed that high-density of nanosized precipitates and ultrafine grains are formed in the ODS steels using the processing route, which remarkably reduce MA time. The yield strength and ultimate tensile strength of ODS steels are improved with the increase of MA time
[en] Tunneling magnetoresistance (TMR) has been achieved for Fe-Cr-O granular films prepared by RF cosputtering methods. These films are composed of nanoscaled Fe granules with an average diameter of 18-28 nm embedded in the crystalline insulating Cr2O3 matrix, and Fe volume fraction fv ranges from 15% to 55%. Ferromagnetic properties exist in all samples. With the decrease of fv, TMR increases from -0.24% for fv=55% to -1.9% for fv=39%, the maximum, then decreases to -0.23% at fv=28%. It is interesting that TMR becomes positive 2% at fv=15%. The relationship between lnρ(0) and 1/T1/2 shows a clear linear relation in the temperature range from 200 to 290 K for the sample with the maximum negative TMR, indicating a tunneling conductive mechanism. Beyond this temperature range (5-200 K) the relationship is obviously nonlinear, implying that some other effects may exist, which needs to be further studied. Our results imply that superparamagnetic state of the metal granules is not the necessary condition for TMR, and it may not be the main factor affecting the TMR, while the microstructure of films, such as the interfaces between the metal and oxide may be important to TMR as the electronic structure of metal-oxide interface can influence the spin polarization
[en] Highlights: • The 14Cr-ODS ferritic alloys with Y2O3, La2O3 and CeO2 additions were produced by mechanical alloying (MA) and spark plasma sintering (SPS). • High-density nanoscale Y2Ti2O7, La2Ti2O7 and Ce2Ti2O7 oxides were identified by high resolution transmission electron microscope (HRTEM) in three kinds of 14Cr-ODS steels, respectively. • The contribution of nanoscale oxides to yield strength is dominating. - Abstract: 14Cr oxide dispersion strengthened (ODS) alloys with the additions of Y2O3, La2O3 and CeO2 (denoted as 14Y, 14L, and 14C), respectively, were produced by mechanical alloying (MA) and spark plasma sintering (SPS). The effects of Y2O3, La2O3 and CeO2 on the microstructures of 14Cr-ODS alloys were characterized by using electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM), and the mechanical properties were evaluated using microhardness and tensile test. The results showed that ultra-fine grains with random crystallographic orientations are formed in the SPSed ODS alloys. High-density nanoscale Y2Ti2O7 oxides in 14Y, La2Ti2O7 oxides in 14L and Ce2Ti2O7 oxides in 14C are observed, respectively. The average oxide size increases while the areal number density of them decreases in order of 14Y, 14L and 14C. The yield strength of 14Y alloy is higher than that of 14L and 14C. The contributions of Hall-Petch strengthening and dispersion strengthening to yield strength in the three kinds of alloys are estimated.
[en] An efficient algorithm is presented in this paper to improve the perturbation efficiency of the adaptive downhill simplex simulated annealing (ASSA) method for magnetotelluric inversion with oblique correlated misfit valleys. The correlated model space is rotated to a less dependent space which is defined by the eigenvectors of the parameter covariance updated progressively by the inversion itself. The downhill simplex step and rotation work together to decorrelate the correlated model space. The application to two synthetic cases and real data indicates that ASSA in the rotated space generally has a better convergence and efficient behaviour than ASSA without rotation. In the rotated space, the high rejection rates, which occurred in the unrotated space, are avoided. At low temperature, the estimated covariance can be used to approximate the global covariance. For all cases, ASSA in the rotated space gives better inversion results
[en] To study the effects of zirconium (Zr) addition on the microstructure, hardness and the tensile properties of oxide dispersion strengthened (ODS) ferritic-martensitic steels, two kinds of 9Cr-ODS ferritic-martensitic steels with nominal compositions (wt.%) of Fe-9Cr-2W-0.3Y_2O-3 and Fe-9Cr-2W-0.3Zr-0.3Y_2O_3 were fabricated by the mechanical alloying (MA) of premixed powders and then consolidated by hot isostatic pressing (HIP) techniques. The experimental results showed that the average grain size decreases with Zr addition. The trigonal δ-phase Y_4Zr_3O_1_2 oxides and body-centered cubic Y_2O_3 oxides are formed in the 9Cr-Zr-ODS steel and 9Cr non-Zr ODS steel, respectively, and the average size of Y_4Zr_3O_1_2 particles is much smaller than that of Y_2O_3. The dispersion morphology of the oxide particles in 9Cr-Zr-ODS steel is significantly improved and the number density is 1.1 x 10"2"3/m"3 with Zr addition. The 9Cr-Zr-ODS steel shows much higher tensile ductility, ultimate tensile strength and Vickers hardness at the same time
[en] This paper presents development of 130mm S460G1-Z35 by using low carbon Nb-Ni-Mo-V-Ti micro-alloying design and two-stage rolling, quenching and tempering process. For the super heavy gauge high-strength structural steel, the yield strength is higher than 450MPa, the tensile strength is higher than 550MPa, the elongation is greater than 20%, the low temperature(-40) impact energy value is not less than 250J, the z-direction section shrinkage is more than 65%, and the welding performance is good. The plate are successfully applied to the engineering construction of the city of dreams in Macau. (paper)
[en] Anatase TiO2 films are deposited on glass substrates at different oxygen partial pressures of 0.8-1.6 Pa. Room temperature N ion implantation is conducted in the films at ion fluences up to 5 × 1017 ions/cm2. UV-visible absorption and photoluminescence (PL) are investigated. With the increase of N ion fluences, the band gap of TiO2 decreases and the absorbance increases. X-ray photoelectron spectroscopy (XPS) confirms the formation of O-Ti-N nitride after implantation, resulting in the red shift of the band gap. The PL intensity of the deposited films increases with the increasing oxygen partial pressure and decreases remarkably due to the irradiation defects induced by ion implantation. (authors)
[en] An experimental setup referring to the optical element configuration of National Ignition Facility was built. The energy loss from mitigation cone by CO_2 laser was tested. The results showed that the loss ratio had a linear correlation with the density of mitigation cone while the density was low. The energy would lose faster with the increase of density if the mitigation cone was larger. Density of mitigation cone must be small than 2 cm-2 to ensure the loss ratio less than 3%. (authors)
[en] In this work, diamond-like-carbon (DLC) films were deposited onto polycarbonate (PC) substrates by radio-frequency plasma-enhanced chemical vapor deposition (RF PECVD), and silicon films were prepared between DLC and PC substrates by magnetron sputtering deposition so as to improve the adhesion of the DLC films. The deposited films were investigated by means of field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Subsequently, the following frictional and optical properties of the films were measured: the friction coefficient by using a ball-on-disk tribometer, the scratch hardness by using a nano-indenter, the optical transmittance by using a UV/visible spectrometer. The effects of incident power upon the frictional and optical properties of the films were investigated. Films deposited at low incident powers showed large optical gaps, which decreased with increasing incident power. The optical properties of DLC films correlated to the sp2 content of the coatings. High anti-scratch properties were obtained at higher values of incident power. The anti-scratch properties of DLC films correlated to the sp3 content of the coatings
[en] Highlights: ► Comb-like CdS nanobelt/ZnO nanorod heterostructures were synthesized. ► ZnO nanorods epitaxially grew on the (1 0 0) surface of the CdS nanobelts along [1 0 0]. ► A preliminary growth mechanism was proposed. - Abstract: Comb-like CdS nanobelt/ZnO nanorod heterostructures were synthesized by a two-stage method. X-ray diffractometer, scanning electron microscopy, transmission electron microscopy were used to characterize and analyze the as-synthesized products. The results demonstrate that the CdS nanobelt backbones grow along [2 1 0] and the ZnO nanorod branches epitaxially grow on the (0 0 1) surface of the CdS nanobelt with a growth direction of [0 0 1]. The as-prepared heterostructures exhibit an important feature of single-crystallinity. At room temperature, the comb-like CdS nanobelt/ZnO nanorod heterostructures show strong green emission.