Qingfeng Guan

Adhesion Strength of Thermal Barrier Coatings with Thermal-Sprayed Bondcoat Treated by Compound Method of High-Current Pulsed Electron Beam and Grit Blasting

Microstructural characteristics and adhesion properties of air plasma spraying, thermal barrier coatings (TBCs) having thermally sprayed bond coats treated by high-current pulsed electron beam (HCPEB) irradiation, and a combination treatment of HCPEB and grit blasting were investigated. Microstructure observations revealed that the original coarse surface of thermally sprayed bond coat was significantly changed to interconnected bulged nodules with a compact appearance after HCPEB irradiation. With further grit blasting treatment, these series of bulged nodules appeared with successive and uniform jagged edges. Surface roughness of the bond coat after compound treatment became higher due to these bulged nodules with jagged edges, which was conducive to ceramic deposition. The results of the tensile test revealed that the adhesion strength of thermally sprayed TBCs with the bond coats conducted by a compound treatment was obviously increased. The combination treatment of HCPEB and grit blasting improved the interfacial bonding strength as well as the interfacial homogeneity.

Blue photoluminescent Si nanocrystals prepared by high-current pulsed electron beam irradiation

Si nanocrystals (Si-ncs) were prepared from n-type Si (100) wafers by using high-current pulsed electron beam irradiation in vacuum. High density (9.7 × 1014 cm−2) ultrafine Si-ncs (∼3 nm) embedded in amorphous Si layers (∼60 nm) exhibit blue photoluminescence emission at room temperature which can be attributed to the quantum confinement size effect. The pulse number is a key parameter which influences the photoluminescence intensity. Possible formation mechanisms of Si-ncs are discussed.

Microstructures of pure nickel induced by high-current pulsed electron beam irradiation

The characteristics of surface feature and microstructure of the near-surface of nickel were investigated after high current pulsed electron beam (HCPEB) irradiation. Based on a physical model, the temperature profile was simulated. The depth of heat-affected zone, the initial melting position, heating rate and quenching rate were computed. The initial coarse-grained structure on the surface was refined, of which the size is about 70 nm. The TEM observations indicate that dislocation wall, sub-dislocation wall, twin and twin boundary steps were achieved on the surface of material after HCPEB irradiation. Furthermore, huge numbers of vacancy defect clusters including dislocation loops, stacking fault tetrahedras (SFT) and voids were also formed within the sublayer of the irradiated surface. The fact that supersaturation vacancies migrated towards the surface along grain boundaries and/or various dislocation configurations led to the formation of microporous feature on the irradiated surface.

Preparation of polypyrrole–TiO2 and its adsorption and photocatalytic degradation of salicylic acid

AbstractPolypyrrole–TiO2 composited photocatalysts have been prepared by sol–gel method. The as-prepared photocatalysts were characterized by scanning electron microscopy, X-ray diffraction, and FT-IR. The results showed that the polypyrrole–TiO2 consists of well-defined hollow tubes with the size of inner diameter 0.5–1 μm, and the hollow tubes exhibited non-crystal phase and it was well-formed anatase phase at high temperature treatment. The performances of polypyrrole–TiO2 were tested by adsorption and degradation of salicylic acid. The adsorption equilibrium data, at different temperatures, were described by the Langmuir, Freundich, Temkin and Dubinin–Radushkevich isotherm models. The results showed that the Langmuir model was well fit to the equilibrium adsorption data, and the adsorption capacities could reach 32.4 mg g−1. The photocatalytic degradation activity of salicylic acid with polypyrrole–TiO2 was investigated under visible light irradiation. It was revealed that the degradation rate of sali...

Microstructures and corrosion mechanism of AISI 304L stainless steel irradiated by high current pulsed electron beam

AISI 304L austenite stainless steel was irradiated by a high-current pulsed electron beam (HCPEB) source in different process. The microstructures were investigated in detail by electron microscopy. The relationship between corrosion resistance and the microstructures has been established. Our experimental results suggest that much abundant defect structures were formed within the irradiated surface which promoted the formation of a compact and thick passive layer during the process of corrosion experiment in simulated sea water. This passive layer effectively prevented corrosive anionic species from passing through the surface oxidation layer and delayed the corrosion process, leading to the improvement of irradiated materials’ corrosion performance. However, the craters on the treated surfaces may be turn into new active points on the metal surface which favored local pitting. Our experimental results demonstrate the potential of proper HCPEB processing for improving the corrosion resistance of metallic materials.

Crater Formation on the Surface of Pure Metal and Alloy Irradiated by High Current Pulsed Electron Beam

Abstract A detailed investigation concerning the formation mechanism of craters of pure metal and alloy surface after high-current pulsed electron beam (HCPEB) processing has been carried out. After HCPEB irradiation, typical craters were homogeneously distributed on the entire surface of 3Cr13 stainless steel, resulting from local sublayer melting and eruption through the solid outer surface. Comparatively, almost no craters were created of pure zirconium, which was associated with the shallow melting site and incomplete treated surface. Furthermore, a large number of ultrafine grains were formed on the irradiated surface, indicating that surface melting was the dominant interaction mechanism between HCPEB irradiation and pure zirconium. It is apparent that “crater free” phenomenon plays a dominant role in surface modification of zirconium and zirconium alloys.

Effect of thermocycling on the microstructure of Ti-6Al-4V alloy in simulated low Earth orbit space environment

The study of material damage and its physical mechanisms, the deep understanding of material performance degradation processes, and the improvement of key materials and devices used in a space environment are undoubtedly of critical scientific importance. This work investigated the mechanical properties and microstructures of the Ti-6Al-4V alloy subjected to thermocycling in a simulated low Earth orbit (LEO) space environment by using microhardness tests, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results revealed an initial increase in hardness with the number of cycles, followed by a subsequent decrease. After 300 thermal cycles, many cavities were formed at the two-phase interface of the Ti-6Al-4V alloy. The dominating structures were transformed into dislocation cell substructures of larger size. After 500 cycles, the central structures in the sample were subgrains evolving by dislocation cells, as well as intragranular twins and jogs structures. The relationship between microstructural evolution and thermal fatigue in LEO space environment was discussed, which may help predict the fatigue damage of materials.摘要本文通过模拟空间环境中冷热循环实验条件, 利用光学显微镜、 X射线衍射仪、 透射电子显微镜及显微硬度仪分析了低地球轨道冷热循环作用下TC4钛合金的微观结构状态和性能的演化行为. 实验结果表明, 随着循环次数的增加, 样品的硬度迅速增加到最大值, 在随后的冷热循环过程中样品出现了循环软化现象; 冷热循环300次后, α和β相的界面出现大量孔洞, 样品中的典型结构转变为尺寸较大的位错胞状亚结构, 晶界容易成为应力集中的区域并萌生微裂纹; 500次循环样品中的典型结构为位错胞演化而成的亚晶以及晶内的孪晶和割阶结构. 本文详细讨论了低地球轨道冷热环境下TC4钛合金微观结构的演变规律和冷热疲劳之间的关系.

Rare earth texture analysis of rectangular extruded Mg alloys and a comparison of different alloying adding ways

The microstructures and textures of four rectangular extruded Mg alloys, Mg–3Gd, Mg–3Nd, Mg–1Gd–1Nd and Mg–1.5Gd–1.5Nd (all in wt%) were investigated by using optical microscopy (OM), X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). The results demonstrate that the extruded alloys all reveal fully recrystallized microstructure and weak non-basal texture. For textures of the four extruded alloys, it is shown that the basal planes of majority grains tilt away from the sheet plane normal toward the extrusion direction. Compared with two binary alloys, the ternary alloys possess weaker texture strengths. Through orientation distribution function analysis, two types of rare earth textures, {01

Effects of Cr-doping on the optical and magnetic properties in ZnO nanoparticles prepared by sol–gel method

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