Cr coatings with a thickness of about 19 μm were synthesized on Zr-4 cladding using plasma-enhanced arc ion plating. A Zr-Cr micro-diffusion layer was formed via Cr ion cleaning before deposition to ...enhance the interface bonding strength. Cr coatings exhibit an obvious columnar crystal structure with an average grain size of 1.26 μm using SEM (scanning electron microscopy) and EBSD (electron backscatter diffraction) with a small amount of nanoscale pores on the surface. A long-term aqueous test at 420 ± 3 °C, 10.3 ± 0.7 MPa and isothermal oxidation tests at 900~1300 °C in air were conducted to evaluate the Cr-coated Zr-4 cladding. All the results showed that the Cr coatings had a significant protective effect to the Zr-4 alloy. However, the corrosion deterioration mechanism is different. A gradual thinning of the Cr coating was observed in a long-term aqueous test, but a cyclic corrosion mechanism of void initiation-propagation-cracking at the oxide film interface is the main corrosion characteristic of the Cr coating in isothermal oxidation. Different corrosion models are constructed to explain the corrosion mechanism.
The effects of CuSO4 concentration, voltage and treating time on the hemisphere emissivity and corrosion resistance of AZ31B magnesium-alloy black micro-arc oxidation coatings were studied by ...orthogonal experiment. The microstructure, phase composition, corrosion resistance and hemisphere emissivity of the coating were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, electrochemical test and infrared emissivity spectrometer, respectively. The results showed that the influences of each factor on corrosion current density and the hemisphere emissivity are as follows: voltage > treating time > CuSO4 concentration. The black MAO coatings are mainly composed of WO3, MgAl2O4, CuAl2O4, MgO, CuO and MgF2. The CuO and CuAl2O4 phases are the main reasons for blackness of the coatings. The coating exhibits the best corrosion resistance under the conditions of CuSO4 concentration 1.5 g/L, oxidation voltage 500 V and treating time 10 min. Additionally, the variation trends of hemispherical emissivity and roughness of the black MAO coating are the same when the composition of the coatings is similar. When the concentration of CuSO4 is 1.5 g/L, the oxidation voltage is 450 V and the treatment time is 10 min, the coating with the highest hemispherical emissivity of 0.84 can be obtained.
This paper aims to explore the shared features of effective professional development programmes for improving teachers' assessment literacy (AL). On the basis of the literature review of 17 empirical ...studies related to teachers' AL improvement, the features of effectiveness can be categorized into three themes: 1) What (Content): The programme content should be contextualized and tailored to the teacher's assessment training needs; 2) How (Method): The delivery method should help to build a collaborative learning community, advocate active engagement, and provide continuing professional development opportunity; and 3) Why (Orientation): The programme should be oriented to cultivate teachers as reflective practitioners and to facilitate their identity (re)construction as assessors. The implications for future research are also discussed to direct further efforts in teachers' AL improvement.
The effects of (NH4)2ZrF6 concentration, voltage and treating time on the corrosion resistance of ZK61M magnesium alloy micro-arc oxidation coatings were studied by orthogonal experiments. The SEM ...result shows that the surface roughness and porosity of MAO coatings increased with (NH4)2ZrF6 concentration, voltage and treating time as a whole, except the porosity decreased with treating time. EDS, XRD and XPS analysis show that (NH4)2ZrF6 was successfully incorporated into coatings by reactive incorporation, coatings are dominantly composed of ZrO2, MgO, MgF2 and amorphous phase Mg phosphate. Potentiodynamic polarization was used to evaluate the corrosion property of coatings. When the concentration of (NH4)2ZrF6 is 6 g/L, the voltage is 450 V, and the treating time is 15 min, the coating exhibits the best corrosion resistance which corrosion current density is four magnitudes lower than substrate attributed to the incorporation of ZrO2 and the deposition of MgF2 in the micropores.
Chromium (Cr) coating is a potential candidate material for improving the oxidation resistance and extending rail service life of zirconium (Zr) alloys used in nuclear fuel cladding materials. This ...study investigates the effect of temperature on the effectiveness of Cr coating on Zr-4 alloy deposited using arc ion plating, revealing the microstructure evolution mechanism of Cr coating in high temperature steam environments. The research results indicate that the oxidation of the Cr coating is slow at 900-1000 °C and that the surface oxide layer, to some extent, hinders the diffusion of oxygen from the outside to the inside. However, at higher temperatures, the oxidation rate of the Cr coating is accelerated, and large bubbles and voids are formed at the interface between the Cr2O3 layer and the residual Cr layer, resulting in the fracture of the oxide layer. At this time, the protective performance of the Cr coating is completely lost. Note that the simultaneous inward diffusion of oxygen and outward diffusion of Zr trigger the occurrence of redox reactions, generating a ZrO2 network. Changes in steam temperature significantly affect the oxidation behavior of Cr coating. As a driving force, temperature accelerates the diffusion of oxygen to the substrate. Conversely, the formed zirconia network also promotes the failure of the Cr coating.
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•The effect of temperature on microstructure of Cr coating in high-temperature steam environment was investigated.•Different sizes of ZrO2 products were found above the Cr oxide layer.•Cr coated Zr-4 alloy exhibits parabolic oxidation kinetics and significant weight increase.•ZrO2 network structure accelerates the degradation and failure of Cr coating.•The invasion of hydrogen promotes the initiation and development of cracks.
To investigate the effect of the content of yttrium nitrate on the microstructure and properties of micro-arc oxidation coatings on a ZK61M magnesium alloy, this study successfully prepared a ...ZrO2-Y2O3-containing composite ceramic coating on a ZK61M magnesium alloy by using micro-arc oxidation (MAO) technology, adding different amounts of yttrium nitrate (0 g/L, 0.15 g/L, 0.45 g/L, and 0.75 g/L) to a zirconate electrolyte with the main components of 6 g/L of (NH4)2ZrF6, 4 g/L of NaH2PO4, 1 g/L of NaF, and a pH value of 7.5–8.0. The microstructure, phase composition, corrosion resistance, and friction coefficient of the coating were investigated using a scanning electron microscope, an energy spectrometer, an X-ray diffractometer, a photoelectron spectrometer, an electrochemical tester, and a friction and wear tester, respectively. The results showed that the composite ceramic coating was composed of c-ZrO2, t-ZrO2, m-ZrO2, MgO, Y2O3, and MgF2. Among the MAO coatings prepared in this experiment, it was when the concentration of the Y(NO3)3 was 0.75 g/L that the coating exhibited the best corrosion resistance and wear resistance. The corrosion current density (Icorr) was 1.415 × 10−8 A·cm−2, which was four orders of magnitude lower than that of the substrate. The friction coefficient and wear volume of the coating were reduced by 30.77% and 96.55% compared to the substrate, respectively.
In this paper, a new approach of single-valued neutrosophic linguistic (SVNL) distance measure is proposed in multiple-attribute group decision-making (MAGDM). The combining idea of the weighted ...average and the ordered weighted average is a SVNL distance. Firstly, we propose a new SVNL weighted distance measure, it is a SVNL combined and weighted distance (SVNLCWD) measure, which can reflect decision-makers'(DMs) attitudes towards the importance and weights of the argument. Secondly, a SVNLCWD-TOPSIS approach for MAGDM problems with SVNL information is proposed, and then a modified relative coefficient is proposed to sort the potential schemes. Finally, the validity and feasibility of the model are verified by an example of a low carbon logistics service provider selection.
A single-valued neutrosophic set is a special case of neutrosophic set, which can describe a great deal of imprecise, uncertain and inconsistent information in the real world. Aiming at the problem ...of multi-attribute decision-making with the decision information presented as the form of single-valued neutrosophic sets (SVNSs). In this paper, a new method for multi-attribute decision-making (MADM) under single-valued neutrosophic environment is proposed. Firstly, the concepts of neutrosophic sets and single-valued neutrosophic sets are introduced, a distance formula based on single-valued neutrosophic sets is given. Secondly, the weighted comprehensive decision matrix is constructed. In addition, TOPSIS method is extended to single-valued neutrosophic environment, the relative closeness coefficient is used to sort the alternatives, the optimal decision-making scheme is obtained. Finally, a numerical example is given to illustrate the feasibility and effectiveness of the proposed method.
Micro-arc oxidation (MAO) coatings were obtained from an AZ91D magnesium alloy at different oxidation times (5, 10, 15, and 20 min), using a zirconium salt electrolyte system, with (NH4)2ZrF6 as the ...main salt. The morphology of the coatings was studied using a scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM). Energy dispersive spectrometry (EDS), X-ray diffractometry (XRD), and X-ray photoelectron spectroscopy (XPS) were employed to determine the type of element and the composition of its phase. The potentiodynamic polarization curve (PDP) was applied to illustrate the corrosion resistance of the coatings. We found the coatings had minor porosity and the best compactness when the MAO treatment time was 10 min. The coatings mainly comprised MgO, ZrO2, MgF2, and Zr3O2F8 phases and amorphous magnesium phosphate. Among the MAO coatings prepared in this experiment, the 10 min coating had the lowest corrosion current density (Icorr), and the Icorr was 4.864 × 10−8 A/cm2, which was three orders of magnitude lower than the uncoated AZ91D magnesium alloy.
Micro-arc oxidation (MAO) coatings were obtained from an AZ91D magnesium alloy at different oxidation times (5, 10, 15, and 20 min), using a zirconium salt electrolyte system, with ...(NHsub.4)sub.2ZrFsub.6 as the main salt. The morphology of the coatings was studied using a scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM). Energy dispersive spectrometry (EDS), X-ray diffractometry (XRD), and X-ray photoelectron spectroscopy (XPS) were employed to determine the type of element and the composition of its phase. The potentiodynamic polarization curve (PDP) was applied to illustrate the corrosion resistance of the coatings. We found the coatings had minor porosity and the best compactness when the MAO treatment time was 10 min. The coatings mainly comprised MgO, ZrOsub.2, MgFsub.2, and Zrsub.3Osub.2Fsub.8 phases and amorphous magnesium phosphate. Among the MAO coatings prepared in this experiment, the 10 min coating had the lowest corrosion current density (Icorr), and the Icorr was 4.864 × 10sup.−8 A/cmsup.2, which was three orders of magnitude lower than the uncoated AZ91D magnesium alloy.
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