Effect of thermal cycling on the adhesion strength of Ti/Ni/Ag films on AlN substrate

The adhesion strength of Ti/Ni/Ag multi-layers on AlN substrates before and after thermal cycling treatment was studied. The Ti/Ni/Ag layers with thicknesses of 0.6, 1.0, and 0.2 μm, respectively, were deposited sequentially on bulk AlN substrates using direct current (DC) sputtering. Thermal cycling test (TCT) was conducted for 0, 15, 100, and 300 cycles to measure the adhesion strength of Ti/Ni/Ag on AlN. The adhesion strength of the deposited specimen increased slightly over 15 thermal cycles and increased abruptly after 100 thermal cycles. After 100 thermal cycles, Ti reacted with AlN substrate to form TiN and TiO. The formation of TiN and TiO at the Ti/AlN interface may be responsible for the increase of the adhesion strength after a large number of thermal cycles.     

Extended networks formed by coordination polymers in the solid state

Coordination polymers based upon the self-assembly of metal ions with bridging ligands often show fascinating extended network structures in the solid state. In principle, variation of the molecular components used in the construction of such networks (i.e. metal ion, bridging ligand, co-ligands and counter-anion) affords an almost limitless range of materials that, it is anticipated, will have interesting physical and electronic properties. Thus, linking different metal ions showing different stereochemical preferences with designed bridging-ligands of varying topology and connectivity means that many different network topologies can be accessed. The enormous number of variables associated with coordination network construction means that a ‘combinatorial chemical apporach’ is an appropriate methodology for screening product structures. As it can be difficult to control and predict the nature of the network polymer produced, current research continues to search for an understanding of how building-block design can be used to control extended network structure so that functional materials can be targeted specifically.     

Calculation of adhesion strength at the interface of a coated particle embedded within matrix under multiaxial load

Analytical and finite element solutions of the stress fields around a particle under multiaxial thermomechanical load are derived as functions of the properties of the particle, the matrix and an interphase. The motivation for these calculations is to answer the question of how to load a sample containing a particle to measure the adhesion strength at the interfaces. The calculations provide the stress field and show that an interphase with a Young's modulus lower than that of the matrix reduces stress concentration in the neighbourhood of the particle. The superposition of loads in different directions results in the creation of a more or less uniform distribution of tensile stresses (hydrostatic tension) around the particle, a stress situation that allows the determination of adhesion strength. The ratio of the applied stresses in different directions determines the extension of the area which is under high tensile loads. This provides the basis to develop a test technique for the examination of statistical effects which in addition to the bonding quality may influence adhesion strength at interfaces.     

Evaluation of adhesion strength and toughness of fluoridated hydroxyapatite coatings

Adhesion strength and fracture toughness are two crucial mechanical properties for bioceramic coatings on metal implants directly affecting successful implantation and long-term stability. In this study, the adhesion strength of sol-gel derived FHA coatings on Ti6Al4V substrates was measured by pull-out tensile test, and the toughness was assessed by energy release method. With increase of the degree of fluoridation, the adhesion strength increases up to about 40% and the fracture toughness increases about 200 to 300%. Contrary to the wide-spread belief, it is interesting to note that after soaking in the Tris-buffered physiological saline solution (for 21 days), the adhesion strength increases about 60% as compared with the as-deposited coating, instead of decreasing. The mechanism of the increase is discussed.     

Analysis of the formed track in solid state materials using atomic force microscopy

The track formation in solid state materials, from the theoretical point of view, is still under study. One way to understand the track formation mechanisms and radiation damage of the charged particles in some materials such as polymers, glasses and minerals, is to analyse the surface topography effects. In this work, the track formation analysis in polycarbonate material is presented using an atomic force microscope (AFM) to characterise the evolution of the track on the material surface and beyond a thin layer of the surface material. The AFM is very useful to obtain valuable information at the level of the atomic structure of the materials and of the nuclear tracks, due to its high resolution and very easy operation involving also a simple sample preparation. The results show the development of the formed track by means of induced surface effects after being exposed to ionising radiation and chemical etching.     

Influence of deformation-induced heating on the bond strength of rolled metal multilayers

The bond strength of various metal multilayers produced by cold rolling of metal foils with different thermal conductivity was investigated. Results indicated that the metallic multilayer system with low thermal conductivity exhibited relative high bond strength while high thermal conductivity metal system may fail to be roll-bonded together. The relationship between the deformation-induced localized heating and the bond strength were discussed.     

Effect of water on monetite synthesis in the solid state

Synthesis of calcium hydrogen phosphate CaHPO₄ can be carried out with a milling apparatus into which solid calcium dihydrogen phosphate Ca(H₂PO₄)₂.H₂O and tricalcium phosphate Ca₃(PO₄)₂.1/6H₂O mixtures are introduced. The effect of water vapor pressure P_H2O on this reaction has been investigated. At a given temperature (60°C) the curves of degree of conversion as a function of milling time depend on P_H2O. Formation of brushite CaHPO₄.2H₂O during the course of reaction can be noted for a particular range of water vapor pressure.If some amounts of brushite are added to the initial mixture, the kinetics of the reaction developed under water vapor are increased. Experiments on the evolution of products after a milling treatment give evidence of the important dependence of the reaction rate on water vapor pressure.     

Measurement of the tunnel rate in SIS' tunnel junctions as function of bias voltage

Cryogenic detectors with superconducting tunnel junctions can provide an energy resolution improved by at least one order of magnitude compared with standard semiconductor detectors. While the detection principle was already demonstrated many years ago, the past years were dedicated to the transition from the laboratory sample to practical detectors. Our most favored detector design gives rise to tunnel junctions with electrodes of unequal energy gaps. In such hetero tunnel junctions bias conditions can be established which cause a negative signal current. We report the experimental verification of this effect, and we discuss the yield of charge signal of cryogenic detectors based upon superconducting tunnel junctions.     

Residual fatigue strength assessment of concrete considering tension softening behavior

In this study, the residual strength of plain concrete beams under fatigue loading is assessed. The quasi-brittle nature of the material is considered by including the effect of tension-softening taking place in the fracture process zone. A two step approach is followed. In the first step, the effective critical crack length for unstable fracture to occur is determined by using two different methods, namely a modified LEFM based fatigue crack propagation law and the crack resistance method. In the second step, the moment carrying capacity as a function of increasing effective crack length is obtained in order to assess the residual strength of the member. A parametric study is performed by considering three different softening laws: linear, bilinear and power laws. It is seen that the bilinear softening law matches close to the experimental predictions of other investigators.     

热输入对Q890高强钢焊缝组织及性能的影响

针对国内某钢厂最新研制的Q890高强钢,采用三种不同的热输入对其进行气体保护焊接,研究了不同热输入对焊缝金属组织、硬度及冲击韧性的影响.结果表明,3种热输入下,焊缝组织主要以板条贝氏体为主,并含有粒状贝氏体、少量的板条马氏体和残余奥氏体.随着热输入的增大,焊缝组织中贝氏体铁素体板条粗化,板条马氏体逐渐减少,而粒状贝氏体逐渐增多,部分残余奥氏体由薄膜状向块状转变;焊缝金属硬度随着热输入的增大而下降;焊缝金属的冲击韧性亦呈逐渐下降的趋势.     

集料-基体协调性对混凝土强度影响的试验研究

研究了集料-基体两相协调性对混凝土强度的影响.试验研究了碎石、钢、砂浆、陶粒和加气混凝土5种强度差异较大的集料在3种不同强度等级基体下的混凝土抗压强度及其发展规律.研究结果表明粗集料和砂浆基体对混凝土抗压强度影响十分显著.在基体强度一定时,粗集料强度达到一定程度后再增加对提高混凝土强度作用不大;当集料强度比基体强度低时,单纯通过增大基体强度来提高混凝土强度效果不明显;集料与基体的差异对强度发展规律和混凝土绝对强度有很大影响.只有在两者相互协调的基础上,才能充分发挥集料和基体的作用.     

Cyclic strength of parts with overlapping zones formed by roller burnishing

The authors study residual stresses in and cyclic strength of shaft with overlapping zones formed during roller burnishing. The most significant decrease in fatigue strength is shown to occur in the presence of an overlapping zone with the areas arising due to a lowered roller burnishing pressure in the second pass. __________ Translated from Problemy Prochnosti, No. 3, pp. 144–148, May–June, 2006.     

药用PVC硬片／铝箔热合强度不合格影响因素研究

本文研究了药用聚氯乙烯（PVC）硬片／铝箔的热合强度不合格影响的因素,通过材料鉴别和热合强度比较,得出PVC硬片热溶出物对其热合强度影响较小;铝箔内层粘合胶种类不同对其热合强度有影响,需指定铝箔与PVC硬片一一对应关系才能降低检验的风险性;铝箔内层粘舍胶涂布均匀性是影响其热合强度主要因素,同一样品不同部位热合强度差异比较明显;最后样品热合强度值会随着放置时间的增加而增加,于12h后达到平衡。