Effects of rare earth metal addition on microstructure of hot-dip 55%Al-Zn-Si coatings

Optical microscope(OM),scanning electron microscope(SEM),energy dispersive spectrometer (EDS) and X-ray Diffraction(XRD) were used to study the effects of rare earth on the microstructural characteristics of 55%Al-Zn-1.6%Si hot -dip coatings on steel.The results of OM,SEM and EDS showed that by adding RE into the 55%Al-Zn-1.6%Si bath,the saw-toothed shape of intermetallic reaction layer of coating became smooth,and the thickness of the overlay and intermetallic reaction layer decreased.The XRD results revealed that the intermetallic reaction layer was comprised of two different regions,a bright phase closest to the steel substrate with phases of Fe_2Al_3 and a dark phase closest to the metallic coating with phases of FeAl_3/α-Fe-Al-Si.

Formation of microstructural features in hot-dip aluminized AISI 321 stainless steel

Hot-dip aluminizing（HDA） is a proven surface coating technique for improving the oxidation and corrosion resistance of ferrous substrates. Although extensive studies on the HDA of plain carbon steels have been reported, studies on the HDA of stainless steels are limited. Because of the technological importance of stainless steels in high-temperature applications, studies of their microstructural development during HDA are needed. In the present investigation, the HDA of AISI 321 stainless steel was carried out in a pure Al bath. The microstructural features of the coating were studied using scanning electron microscopy and transmission electron microscopy. These studies revealed that the coating consists of two regions： an Al top coat and an aluminide layer at the interface between the steel and Al. The Al top coat was found to consist of intermetallic phases such as Al_7Cr and Al_3Fe dispersed in an Al matrix. Twinning was observed in both the Al_7Cr and the Al_3Fe phases. Furthermore, the aluminide layer comprised a mixture of nanocrystalline Fe_2Al_5, Al_7Cr, and Al. Details of the microstructural features are presented, and their formation mechanisms are discussed.

Compressible and Lightweight MXene/Carbon Nanofiber Aerogel with “Layer‑Strut” Bracing Microscopic Architecture for Efficient Energy Storage

Two-dimensional MXene has recently captured widespread research attention in energy storage and conversion fields due to its high conductivity,large specific surface area,and remarkable electro-activity.However,its performance is still hindered by severe self-restacking of MXene flakes.Herein,conductive Ti_(3)C_(2)T_(x)/carbon nanofiber(CNF)composite aerogel with typical“layer-strut”bracing 3D microscopic architecture has been fabricated via synergistic assembly and freeze-drying process.In virtu of the strong interfacial interaction between polymeric precursor nanofibers and MXene mono-layers,gelation capability and 3D formability of Ti_(3)C_(2)T_(x) is greatly reinforced,as resulted Ti_(3)C_(2)T_(x)/CNF aerogels possess a highly ordered microporous structure with interlayered CNF penetrating between large size MXene lamellae.This special configuration guarantees the stability and pliability of the composite aerogels.Furthermore,the 3D form interconnected conductive network and the parallell alignment of the pores allow free electrical carriers motion and ion migration.As a result,the prepared Ti_(3)C_(2)T_(x)/CNF aerogel-based electrode exhibits an exceptional gravimetric specific capacitance of 268 F g^(−1) at a current density of 0.5 A g^(−1) and an excellent cycling stability of 8000 cylcles,and the assembled symmetric supercapacitor,delivers a high energy density of 3.425 W h kg^(−1) at 6000 W kg^(−1).This work offers a new route for the rational construction of 3D MXene assembly for advanced energy storage materials.

Density functional theory study on the influence of cation ratio on the host layer structure of Zn/Al double hydroxides

A density functional theory （DFT） study has been carried out for [Zn-1AI（OH2）n＋6（OH）2n-2]^3＋ （n=3-6） and [Znn-1AI（OH2）2n-2（OH）2n-2]^3＋ （n = 7） clusters, which include the basic structural information of the brucite-like lattice structure of Zn/Al layered double hydroxides （LDHs） with Zn/AI molar ratio （R） in the range 2-6, in order to understand the effect of the Zn/Al ratio on the structure and stability of binary Zn/Al LDHs. Based on systematic calculations of the geometric parameters and formation energies of the cluster models, it was found that it is possible for Zn^2＋ and Al^3＋ cations to replace Mg^2＋ isomorphously in the brucite-like structure with different R values, resulting in differences in microstructure of the clusters and unit cell parameter a of the Zn/Al LDHs. Analysis of the geometry and bonding around the trivalent Al^3＋ or divalent Zn^2＋ cations reveals that Al^3＋ plays a more significant role than Zn^2＋ in determining the microstructure properties, formation and bonding stability of the corresponding ZnRAl clusters when R〈5, while the influence of Zn^2＋ becomes the dominant factor in the case of R〉 5. These findings are in good agreement with experiments. This work provides a detailed electronic-level understanding of how the composition of cations affects the microstructure and stability of Zn-containing binary LDH layers.

Surface alloying of Al films/Ti substrate based on high-current pulsed electron beams irradiation

Ti–Al surface alloy was fabricated using a cyclic pulsed liquid-phase mixing of predeposited 100 nm Al film with a-Ti substrate by low-energy high-current electron beam. Electron probe micro-analysis（EPMA）,grazing incidence X-ray diffraction analysis（GIXRD）,transmission electron microscopy（TEM）, and nanoindentation were used to investigate the characterization of Ti–Al surface alloy. The experimental results show that the thickness of alloy layer is ＊3 lm, and the content of Al in the ＊1 lm thickness surface layer is ＊60 at%. The tetragonal TiAl and TiAl2intermetallics were synthesized at the top surface, which have nanocrystalline structure.The main phase formed in the ＊2.5 lm thick surface is TiAl, and there are few TiAl2and Ti3Al phase for the alloy.Dislocation is enhanced in the alloyed layer. The nanohardness of Ti–Al surface alloy increased significantly compared with a-Ti substrate due to the nanostructure and enhanced dislocation. Since the e-beam remelted repeatedly, the Ti–Al surface alloy mixed sufficiently with Ti substrate. Moreover, there is no obvious boundary between the alloyed layer and substrate.