等离子喷涂热障涂层材料弹性模量与硬度的压痕测试分析

采用纳米压痕法,研究了经高温热循环处理后的等离子喷涂热障涂层材料弹性模量和硬度的抛物线式演变规律,并采用 Weibull统计分析方法对纳米压痕测试数据进行了处理和分析,提高了实验数据的可靠性.结果表明,经过高温热循环处理之后,不同位置处的热障涂层弹性模量和硬度都呈现出明显的各向异性分布.随着热循环次数的增加,涂层表面和...     

香螺壳的结构和微观力学性能

测量产自黄/渤海海域的香螺贝壳的硬度和弹性模量,研究了贝壳的结构与性能之间的关系.结果表明,香螺贝壳主要由方解石和文石两种矿物镶嵌在有机质中构成,方解石结构为不均匀的柱状晶,文石结构为多级超微的交错纹状结构,其中第三级结构为10-80 nm的纳米级纤维.文石的力学性能优于方解石的性能.贝壳类复合材料的压痕效应主要源于裂纹扩展,而微观裂纹扩展与晶体类型以及晶体结构的排列方式是密切相关的.方解石裂纹形状曲折、不规则且沿着方解石层的边界扩展,抗裂纹扩展能力较差;而文石压痕周围平直清晰,裂纹沿着其二级结构界面扩展,性能较好.     

Friction and wear properties of quasi-periodic material coatings

Quasicrystalline (QC) materials are of interest not only because of their unique structure, but also because they exhibit unusual properties which are potentially useful in industrial applications. In the present study a range of aluminium-based QC alloys, in the form of plasma-sprayed coatings, has been produced and evaluated. For the first time the influence of heat treatment on the structure and properties of these coatings has been systematically investigated. Of the nine QC coatings investigated, those of the Al-Cu-Fe-Cr system and the Al-Pd-Mn system showed the most promising combination of good hardness with low coefficient of friction.     

Analysis of micro--macro material properties and mechanical effects of damaged material containing periodically distributed elliptical microcracks

The existence of numerous microcracks causes changes in the stiffness or fracture toughness of materials. In this paper, the manifestations of mechanical properties in the damaged materials caused by the microcracks are evaluated by the present homogenization method based on the superposition method together with the VNA solution. Moreover, it is known that the stress concentration at the macrocrack tip decreases due to the stress relaxation effect caused by the existence of the microcracks. In order to evaluate the manifestations of mechanical behavior, the mechanical effects of the existence of the microcracks on the macrocrack, the component separation method for mixed-mode stress intensity factors of the macrocrack in the damaged materials is newly developed in this paper. Various numerical analyses are successfully conducted for the two topics, the mechanical properties of the damaged materials and the mechanical behavior of the macrocrack in the damaged materials.     

Novel approach for fabrication and characterisation of porosity-graded material

A novel continuously graded material that is based on a porosity-graded structure was successfully synthesised via a cold pressing-vacuum sintering-dissolution process (SDP) of powder metallurgy technology. Microscopic observations and the Archimedes method were used to confirm the newly synthesised porosity-graded material, the mechanical properties and the modulus. The results show that the density continuously increased from 1.4 to 2.7?g?cm^?3, and there was no obvious interfacial transition layer. In addition, the hardness and elastic modulus were obtained from nanoindentation tests and display a stepwise feature along the gradient direction. Moreover, we found that the fractography changes from typical ductile fracture to ductile and cleavage fracture with an increase in the porosity.

Highlights

• A porosity graded material has been successfully synthesised by powder metallurgy.

• The density continuously transit from 1.4 to 2.7?g?cm^?3, and it has no obvious interfacial transition layer.

• The stepwise feature of density and modulus shows great potential in the shields of spacecrafts.

     

Microstructure and fracture morphology of thermally sprayed refractory metals and ceramics

The microstructural characteristics such as porosity, splat morphology and grain size of thermally sprayed coatings made of both ceramic and refractory metals are investigated. Al₂O₃ and Cr₂O₃ coatings represent ceramic materials while pure W and Mo coatings represent the refractory metals. The used deposition technology (RF-plasma, gas stabilized or water stabilized DC plasma) was found to influence the coatings microstructure to a great extent by providing different particle impact velocities and temperatures. At the same time the substrate temperature plays an important role as is shown for refractory metal coatings deposited at different substrate temperatures. Generally, all investigated coatings contained intrasplat cracks, intersplat pores and voids, individual splats of different degree of deformation and different degree of intersplat sintering, crystal grains formed inside individual splats or extending through many of them. It is shown that the size and abundance of the above-mentioned microstructural features predetermine the fracture morphology of the coating as well as mechanical properties. __________ Translated from Problemy Prochnosti, No. 1, pp. 89–92, January–February, 2008.     

Procedure for the determination of torsional deformation relationships for anisotropic materials

The paper presents a procedure for the determination of torsional deformation relationships for prismatic specimens made of anisotropic material and construction of deformation curves under these conditions Translated from Problemy Prochnosti, No. 3, pp. 116–123, May–June, 2009.     

Effect of the nature of fillers and ultraviolet irradiation on the mechanical properties of epoxy composite coatings

The effect of ultraviolet irradiation, the physical nature and percentage of fine-grained fillers on the mechanical properties of composites has been studied. It has been found that the ultraviolet irradiation of epoxy compositions causes a decrease in the adhesive strength and an increase in the cohesive strength of protective coatings. This has been proved to be due to a change in the course of physicochemical processes at the filler/epoxy oligomer interface, owing to which external surface layers, which have a considerable extent and a high degree of cross-linking, are formed around fine particles in the matrix. Translated from Problemy Prochnosti, No. 4, pp. 117–123, July–August, 2009.     

On the determination of interfacial stresses in a composite material

The conventional finite element method has been modified to allow the elastic stresses along the fibre matrix interfaces of a composite to be determined with improved accuracy. The results obtained by this 'modified' method are compared with both a photoelastic and some traditional finite element solutions.     

Fe3B基纳米复合永磁材料的微结构和性能

利用差热(扫描)分析、X射线、透射电镜、振动样品磁强计研究了添加Co、Dy对Fe3B／Nd2Fe14B 纳米复合永磁材料的微结构和性能的影响．结果表明：添加适当的微量元素可以提高Nd4．5Fe77B18．5纳米复合永磁材料的内禀磁性,改进微结构,从而提高材料的永磁性能．在Nd4．5Fe77B18．5中添加1％-3％(原子分数)的Co、Dy明显地降低材料的晶化温度和最佳热处理温度、提高了2：14：1相的居里温度、改善了纳米复合永磁材料的微观结构,从而提高材料的永磁性能．与Nd4．5Fe77B18．5相比,Nd3．5Fe74Co3DylBl8.5的永磁性能为：Br=1.06T,jHc=328kA／m,(BH)max=108．9kJ／m^3,分别提高了26％,17％和104％．     

Nanomechanical evaluation of nickel-titanium surface properties after alkali and electrochemical treatments.

In this paper, the suitability of alkali treatment followed by heat treatment at 600 degrees C, and spark oxidation for nickel-titanium, intended for medical applications such as pins, wires and clamps, was evaluated on the basis of nanomechanical and wear testing. In addition, the chemical composition and topography of the surface layer, wetting ability, corrosion resistance and influence of the heat treatment on structure of the alloy were also investigated. The results showed that the highest hardness was observed for alkali-treated samples, and this could be correlated with the structure of the sample that contained martensite and a higher phase transformation temperature. This treatment caused a very large increase of nickel in the top layer and decreased resistance in pitting corrosion. These results disqualified the treatment to be considered as useful for medical applications. On the other hand, the hardness of the oxidized samples was at the same level as that obtained for ground reference samples. Moreover, the oxide layer was enriched with phosphorus, and it was predominantly composed of TiO2 and phosphorus oxides. This 3.1 microm thick layer had good adhesion to the substrate as indicated by scratch testing and wear resistant in nanowear testing. However, the oxidation did not significantly increase the corrosion resistance of the alloy compared with reference samples.     

离心铸造制备Al－Ti系金属间化合物梯度功能材料的组织及耐磨性的研究

为获得表面具有耐磨、耐热、耐蚀而整体又具有较好强韧性的低密度材料，以缓解各种应力（热应力，压应力等），提高材料的使用性能，作者采用离心铸造工艺，通过改变合金成分、转速，获得组织，成份，硬度均呈梯度分布的材料。显微组织分析表明：外表层组织主要有ＴｉＡｌ和ＴｉＡｌ＿３初生金属间化合物组成，离心转速和合金含量愈高，则外表层初生金属间化合物含量愈多，且金属间化合物显微硬度呈梯度分布，显微硬度和耐磨性呈很好的对应关系，最后作者提出该工艺下材料的形成机制，合金元素传质和初生相沉积随凝固同时进行，为进一步定量地控制该材料组织提供理论依据。     

铸铁表面激光熔敷层的抗裂性和耐磨性

采用免预热多道搭接的激光熔敷工艺,在铸铁表面制备出抗裂耐磨的激光熔敷层,研究了激光功率和扫描速度对熔敷层抗裂性的影响。适当的激光功率和扫描速度可以使铁基熔敷层的裂纹率最低．随着Ni含量的增加,熔敷层内奥氏体相体积分数增加;K可促进共晶碳化物团球化,熔敷层抗裂性增强．通过对铸铁表面激光熔敷层裂纹的萌生与扩展的动态观察,揭示了熔敷层开裂的微观机制．裂纹易在粗大渗碳体区或石墨与奥氏体的界面处萌生,奥氏体可明显抑制裂纹的扩展．Ti含量增加使熔敷层中原位自生的TiC的体积分数增大,熔敷层磨损质量损失减少,耐磨性增强．     

硬质涂层力学性能可靠测量的两步压入法

正确测量涂层的硬度等力学性能一直是硬质涂层生产和研究中亟待解决的问题。本文提出的采用力学探针对涂层进行两步压入的实验方法可以在未知涂层厚度的条件下通过大载荷逐步加载展示出涂层厚度对载荷选择的要求,从而正确选择加载载荷进行小载荷压入实验。由此方法得到的涂层硬度值和其它力学性能指标具有准确和可靠的特点。     

无钴p型方钴矿热电材料的制备及热电性能研究

采用熔体旋甩结合热压烧结技术,制备了无钴p型方钴矿热电材料。利用X射线衍射仪以及扫描电子显微镜对其组织结构进行分析,并对烧结后的样品进行热电性能研究。结果表明,Fe和Ni可有效地取代Co,获得纯的方钴矿相。另外,即使无钴样品的高温ZT值略低于参比样品,但功率因子及低温ZT值基本相当,这对节约Co这一战略资源以及实现产业化应用具有重要的意义。     

钛基-TiN-TiC系梯度薄膜材料的生物摩擦磨损特性研究

在ＳＲＶ试验机上用血清润滑对钛合金及钛基－Ｔｉｎ－ＴｉＣ梯度薄膜与ＵＨＡＭＷＰＥ摩擦副摩擦磨损性能进行了测试与比较,并对其磨损机理进行了分析。研究结果表明,钛基－ＴｉＮ－ＴｉＣ梯度薄膜材料表面硬度得到提高,达到２６３０ＨＶ,与基力,生物耐磨性明显提高,为发展耐磨性好的人工关节材料探索了一条新的途径。     

Ultrasonic technique as tool for determining physical and mechanical properties of frozen soils

Ultrasonic velocities of compressional and shear waves in frozen sand, silty-sand and silt were measured at subfreezing temperature and the relationship between acoustic and physical-mechanical properties examined. Ultrasonic measurements revealed that the influence of temperature on ultrasonic velocities is due to the phase transition from water to ice. Different methods were proposed to determine the amount of unfrozen water in frozen soils. The unfrozen water content was measured directly by time domain reflectometry and compared to predicted values using different theoretical approaches. The prediction models showed good agreements with measured values at low temperatures. However, the shape of the curves obtained did not completely satisfying as the estimated unfrozen water fraction near 0 °C was significantly greater than the measured values. Finally, based on the elastic wave theory and measured acoustic velocities the elastic constants of the frozen soils were calculated. The changes in elastic constants were found to be related to the increase in ice content, ice stiffness by ice cementation and a decrease in unfrozen water content.     

A non-destructive evaluation of the material properties of a composite laminated plate

A non-destructive method for the evaluation of material properties of a rectangular, anisotropic, homogeneous plate with four free edges is presented. The method consists of two steps. In the first step, a certain number of the plate's natural frequencies are experimentally measured. In the second step, the plate rigidities are varied in a theoretical model, so that the calculated natural frequencies match as close as possible the corresponding experimental values. Two such models are presented, based on the Classical Lamination Theory and on a Higher Order Shear Deformation Theory. High order Lagrange polynomials are used as deflection functions and the Rayleigh-Ritz procedure is employed to arrive at the solution. The identification of the plate rigidities is done by means of an iterative Bayesian parameter estimation method, where possible measurement errors or rigidities' uncertainties can be taken into account.     

Structural,mechanical, and electrical properties of carbon nanoparticles synthesized from diesel

We studied the elemental analysis, structural morphology, mechanical, and electrical properties of carbon nanoparticles synthesized from diesel. The spherical carbon particle size in the range of about 10 to 80 nm in diameter was observed in scanning electron microscope (SEM) studies that were identified by Atomic force microscopy (AFM) study as an aggregation of carbon particles of average size 2.5 nm. The surface rms of carbon nanoparticle thin film (CNTF) was measured directly by AFM and found 0.22 nm. The Derjaguin–Muller–Toporov (DMT) elastic modulus of carbon nanoparticles (CNPs) was measured by PeakForce QNM mode of AFM. The minimum and maximum elastic modulus was measured of 0.40 GPa and 43.89 GPa, respectively. The resistivity, conductivity, magneto resistance, mobility, and average Hall co-efficient were measured by “Ecopia Hall-effect measurement system” by four-point Van der Pauw approach at ambient condition. We demonstrated I–V characteristic at the Indium/CNTF thin film interface, which is accompanied by rectifying behavior.     

On the determination of mechanical properties of composite laminates using genetic algorithms

This paper describes a method which combines finite element analysis and genetic algorithms (GAs) for identifying the elastic constants of composite laminates by using vibration test data. A procedure updates the elastic constants in a numerical model so that the output from the numerical code fits the results from vibration testing. In this approach, the elastic constants can be readily identified in a single test without damaging the structure. The GA, developed on a personal computer using the language MATLAB, applies the general-purpose numerical code MSC-NASTRAN to carry out the modal analysis.