电学参数对胶体中工业纯钛微弧氧化膜特性的影响

利用自制多功能微弧氧化(MAO)电源对处在胶体中的工业纯钛表面进行了MAO处理,比较系统地研究了电压脉冲的峰值(U)和占空比(d)对膜层的生长特性、微观结构、相结构和处理后试样耐腐蚀性能的影响.结果表明,随着U的增加或d的加大,膜厚几乎呈线性增加,膜表面微孔尺寸和粗糙度逐渐增大,微孔密度逐渐减小.膜层主要由致密层组成,除U=450V,d=10%时制备试样的膜层中含有少量锐钛矿相TiO2外,其他试样的膜层全由金红石相TiO2组成;在30%硫酸溶液中的耐腐蚀测试表明,MAO处理后试样的耐腐蚀性能与U和d密切相关,随着U的增加或d的加大,试样的耐腐蚀能力逐渐增强.     

Transmission electron microscopy of dislocations in cementite deformed at high pressure and high temperature

Polycrystalline aggregates of cementite (Fe₃C) and (Fe,Ni)₃C have been synthesised at 10 GPa and 1250 °C in the multianvil apparatus. Further, deformation of the carbides by stress relaxation has been carried out at temperature of 1250 °C and for 8 h at the same pressure. Dislocations have been characterised by transmission electron microscopy. They are of the [1?0?0] and [0?0?1] type, [1?0?0] being the most frequent. [1?0?0] dislocations are dissociated and glide in the (0?1?0) plane. [0?0?1] dislocations glide in (1?0?0) and (0?1?0). Given the plastic anisotropy of cementite, the morphology of the lamellae in pearlitic steels appears to have a major role in the strengthening role played by this phase, since activation of easy slip systems is geometrically inhibited in most cases.     

Effects of torsional deformation on the microstructures and mechanical properties of a CoCrFeNiMo0.15 high-entropy alloy

Abstract

The effects of torsional deformation on the microstructures and mechanical properties of a CoCrFeNiMo_0.15 high-entropy alloy have been investigated. The torsional deformation generates a gradient microstructure distribution due to the gradient torsional strain. Both dislocation activity and deformation twinning dominated the torsional deformation process. With increasing the torsional equivalent strain, the microstructural evolution can be described as follows: (1) formation of pile-up dislocations parallel to the trace of {1 1 1}-type slip planes; (2) formation of Taylor lattices; (3) formation of highly dense dislocation walls; (3) formation of microbands and deformation twins. The extremely high deformation strain (strained to fracture) results in the activation of wavy slip. The tensile strength is very sensitive to the torsional deformation, and increases significantly with increasing the torsional angle.     

Development of Surface Nano-Crystallization in Alloys by Surface Mechanical Attrition Treatment (SMAT)

Nanometer-sized grain structures that exhibit a large number of grain boundaries on the surface of a bulk material demonstrate excellent properties relative to their coarse-grained (CG) equivalents. Surface modification using surface mechanical attrition treatment (SMAT) is an option that cab be used to tailor the corrosion, tribological, mechanical, and chemical reaction properties of a surface. SMAT is an effective route to create the nanostructured surface layer. The SMAT process has unique advantages compared with the other coating and deposition techniques for surface nanocrystallization. For example, SMAT does not alter the chemical composition of the nanocrystalline surface layer in the matrix. In addition, SMAT has been demonstrated to activate the material surface layer by surface modification and enhance the atomic diffusivity. This article presents a review of the advantages offered by the SMAT technique for the creation of high performance surface layers. The influence of the created nanocrystalline layer on mechanical, physical, and chemical properties is assessed. Developments and the current status of the surface nanolayer that are formed are evaluated from a physical approach. Finally, prospects for the future development of grain refinement on the surface of a material matrix and potential applications are presented.     

Change in electrical resistivity of commercial purity aluminium severely plastic deformed

Commercial purity aluminium sheets were severely plastic deformed by accumulative roll bonding (ARB). Changes in electrical resistivity at 77 K and microstructure during the ARB process were traced up to 12 cycles, which corresponded to an equivalent strain of 10. The resistivity at 77 K increased with increasing number of ARB cycles, then saturated after about the sixth ARB cycle with a maximum increment of resistivity from starting material of about 1.1 nΩ m. Since lattice defects affect the resistivity of metals, the internal dislocation density and the density of grain boundaries were evaluated from scanning transmission electron microscopy images using Ham's method and grain boundary maps obtained from electron back-scattering diffraction, respectively. The relationship between the change in resistivity and the lattice defects is discussed.     

The effect of nanostructured surface layer on the fatigue behaviors of a carbon steel

A nanostructured surface layer was formed on a carbon steel by means of surface mechanical attrition treatment (SMAT). The microstructure of the surface layer of the SMATed sample was characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Microhardness and residual stress distribution along the depth from the SMATed surface layer were measured at the same time. Fatigue behaviors of the carbon steel subjected to the SMAT process were investigated. A nanostructured layer with average grains size of ∼12.7 nm was formed, of which microhardness is more than twice as high as that in matrix and residual compressive stress can reach about −400 MPa with maximum depth of ∼600 μm. The fatigue strength of as-received sample is 267 MPa and that of SMATed sample is 302 MPa based on fatigue life 5 × 10⁶ cycles. The SMAT process has improved the fatigue strength by as much as 13.1% for the carbon steel. It is shown that the SMAT is an effective method to render the material with the features, such as a nanostructured and work-hardened surface layer as well as compressive residual stresses, which can pronouncedly improve the fatigue strength of the carbon steel.     

Size effects of nano-spaced basal stacking faults on the strength and deformation mechanisms of nanocrystalline pure hcp metals

The size effects of nano-spaced basal stacking faults (SFs) on the tensile strength and deformation mechanisms of nanocrystalline pure cobalt and magnesium have been investigated by a series of large-scale 2D columnar and 3D molecular dynamics simulations. Unlike the strengthening effect of basal SFs on Mg alloys, the nano-spaced basal SFs are observed to have no strengthening effect on the nanocrystalline pure cobalt and magnesium from MD simulations. These observations could be attributed to the following two reasons: (i) Lots of new basal SFs are formed before (for cobalt) or simultaneously with (for magnesium) the other deformation mechanisms (i.e. the formation of twins and the < c + a > edge dislocations) during the tensile deformation; (ii) In hcp alloys, the segregation of alloy elements and impurities at typical interfaces, such as SFs, can stablilise them for enhancing the interactions with dislocation and thus elevating the strength. Without such segregation in pure hcp metals, the < c + a > edge dislocations can cut through the basal SFs although the interactions between the < c + a > dislocations and the pre-existing SFs/newly formed SFs are observed. The nano-spaced basal SFs are also found to have no restriction effect on the formation of deformation twins.     

The influence of the initial structural state of armco iron on the ultrasonic treatment effect

Methods of diffraction electron microscopy have been used to examine the types of dislocation substructures formed in the surface layer of armco-iron specimens subjected to ultrasonic treatment. It is shown that banded or equiaxed ultrafine-grained structure can be generated in the material depending on its initial structural state. The special features of the plastic deformation and fracture of the ultrafine-grained surface layers of the specimens under uniaxial tension are described. The extent to which the mechanical properties of the examined material are improved by ultrasonic treatment has been found to depend on its initial state. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 74–82, January, 2009.     

热处理对CH薄膜表面粗糙度及力学性能的影响

利用低压等离子体化学气相沉积法制备厚度约为7 m的辉光放电聚合物薄膜,将制备的薄膜样品放入通有氩气保护的热处理炉中加热至300 ℃,分别进行6,10,24 h的保温热处理。通过白光干涉仪观察分析了不同保温时间下辉光放电聚合物薄膜的表面粗糙度; 利用傅里叶变换红外吸收光谱分析了300 ℃条件下不同保温时间对薄膜结构的影响; 采用纳米压痕仪表征了不同保温时间热处理后,薄膜硬度及模量的变化。结果表明:随着保温时间的增加,薄膜的表面均方根粗糙度由12 nm降至4.43 nm。薄膜结构中甲基的相对含量减少,双键的相对含量增加,碳链变长,同时薄膜网络结构的交联化程度增强。硬度和模量随着保温时间的增加先减小后增大。     

Thermodynamics of elastic strength of the metal surface layer

This paper presents a physicochemical model that establishes a connection between the elastic strength of the surface layer (SL) of metal and its surface Gibbs energy. The elastic limit of SL along the low-index face of the metal single crystal under stress during the transition from elastic to plastic deformation was calculated. Calculation shows that the elastic limit of metal SL with fcc and bcc structures is approximately three orders of magnitude higher than the yield strength of these metals in bulk and close to nanohardness of the metals, in particular; for Cu(111) и Al(111), it is 5.3 and 2.8?GPa, respectively. In the light of the proposed model, the effect of lowering the elastic strength of metal SL due to adsorption of surfactant is formulated.     

Effect of fiber content and surface treatment on the mechanical properties of natural fiber composites produced by rotomolding

In this study, natural fibers (agave, coir, and pine) were surface treated with maleated polyethylene (MAPE) with two main objectives: (1) to improve the mechanical properties of natural fiber composites produced by rotational molding and (2) to increase the fiber content in the composite. The rotomolded composites were produced at 0, 10, 20, 30, and 40% wt. of fiber contents (treated or untreated) and characterized in terms of morphology and mechanical properties (hardness, impact, tension, and flexion). The results showed that MAPE surface treatment was more successful for agave and coir than for pine fibers due to their respective chemical composition. In general, surface treatment led to better fiber distribution and a more uniform composite morphology allowing the possibility to use higher fiber contents in rotational molding. At low fiber contents (10 and 20% wt.), the mechanical properties were improved using treated fiber composites (TFC) compared to the neat polymer and untreated fiber composites (UFC). Although the mechanical properties of TFC decreased at high fiber contents (30 and 40% wt.), they were substantially higher (about 160, 400, and 100% for impact, tensile, and flexural properties, respectively) than for UFC.     

Investigation of changes in properties of water under the action of a magnetic field

The properties of water and their changes under the action of a magnetic field were gathered by the spectrum techniques of infrared, Raman, visible, ultraviolet and X-ray lights, which may give an insight into molecular and atomic structures of water. It was found that some properties of water were changed, and a lot of new and strange phenomena were discovered after magnetization. Magnetized water really has magnetism, which has been verified by a peak shift of X-ray diffraction of magnetized water + Fe₃O₄ hybrid relative to that of pure water + Fe₃O₄ hybrid, that is a saturation and memory effect. The properties of infrared and ultraviolet absorptions, Raman scattering and X-ray diffraction of magnetized water were greatly changed relative to those of pure water; their strengths of peaks were all increased, the frequencies of some peaks did also shift, and some new peaks, for example, at 5198, 8050 and 9340 cm⁻¹, occurred at 25°C after water was magnetized. In the meanwhile, the magnetized effects of water are related to the magnetized time, the intensity of an externally applied magnetic field, and the temperature of water, but they are not a linear relationship. The study also showed a lot of new and unusual properties of magnetized water, for example, the six peaks in 3000–3800 cm⁻¹ in infrared absorption, the exponential increase of ultraviolet absorption of wave with the decreasing wavelength of light of 200–300 nm, the frequency-shifts of peaks, a strange irreversible effect in the increasing and decreasing processes, as well as a stronger peak of absorption occurring at 50°C, 70°C and 80°C, the existence of many models of motion from 85°C to 95°C in 8000–10000 cm⁻¹, and so on. These results show that the molecular structure of water is very complicated, which needs further study. Furthermore, the macroscopic feature of mechanics, for instance, surface tension force of magnetized water, was also measured. Experiments discovered that the size in contact angles of magnetized water on the surface of hydrophobic materials decreases, thus the surface tension force of magnetized water decreases relative to that of pure water. It is seen from the above results that the clustering structure of hydrogen-bonded chains and polarization effects of water molecules are enhanced after magnetization. These results are helpful in revealing the mechanism of magnetization of water. Supported by the National Basic Research Program of China (Grant No. 2007CB936103)