涂覆制坯对不锈钢/低合金钢复合界面影响

为探究涂覆铁钴镍夹层法制备不锈钢/低碳钢复合板坯对复合板界面洁净度的影响,运用Procast仿真软件,利用正交试验法,确立夹层涂覆优选工艺参数.依据仿真结果制备带涂覆夹层复合板坯,通过与固态夹层嵌入法制得复合板坯对比,分析不同组坯方式对轧制成形后微观组织和力学性能的影响.试验结果表明,两类组坯方式的复合板夹层均可阻隔碳...     

服役环境下TA2/Q235爆炸复合板剪切断口分形表征

为了定量研究服役条件下TA2/Q235爆炸焊接复合板剪切强度与断口分形维数及多重分形谱的关系,明确适合TA2/Q235复合板的最佳分形表征方法,通过热处理模拟服役过程,对服役后的样品开展剪切测试,并引入分形理论对剪切断口进行表征,建立了剪切强度与分形维数及多重分形谱的定量关系。结果表明,200、400和600℃服役后,样品剪切强度与断口多重分形谱宽度负相关;结合残余应力消除及再结晶长大对TA2/Q235爆炸复合板剪切断口形貌影响规律的分析,相比分形维数,多重分形谱能更准确地描述断口力学信息。     

真空制坯热轧钛/钢复合板工艺及性能

钛/钢复合板的需求量日益增多，真空制坯热轧复合法（VRC）是制备高性能钛/钢复合板的有效工艺。介绍了钛/钢复合板制备工艺的国内外现状和工艺特点。依托863重点项目“钛/钢复合板研究与生产技术开发”和十三五重大课题“容器板轧制复合原理与关键技术”，利用真空制坯热轧复合法（VRC）在实验室和钢厂进行了一系列钛/钢复合板的轧制试验，对复合板的界面组织与力学性能进行了分析。实验室制备的钛/钢复合板，界面生成了明显的TiC层，未发现氧化物等杂质，断口有大量韧窝生成，复合界面平均拉剪强度达到了230MPa。钢厂试生产的钛/钢复合板，宽幅达到3500mm，界面生成连续的β- Ti层，拉剪断口未检测到氧化物，拉伸、冲击、弯曲等力学性能均满足国家标准，剪切强度均在196MPa以上，已达国内领先水平。     

Analysis of the single-fiber-composite test to measure the mechanical properties of metal-ceramic interfaces

Tensile stress-strain curves for a metal-ceramic single fiber composite show load drops associated with every fiber break. Each curve exhibits a limited number of load drops that are characteristic of the level of the fiber-matrix bonding. A detailed analysis of these stress-strain curves gives the following results: (a) the magnitude of the load drops depends not only on the fiber strength but also on the work-hardening behavior of the metal matrix and the length of the shear relaxation zone at the interface; (b) the distribution of the magnitude of the load drops is determined by the random truncation of the shear relaxation length as part of the fiber fragmentation process; (c) the first load drop can be systematically used to determine the in situ Weibull strength statistics and a scaling law for the ceramic fiber; (d) the slope of the reloading portion immediately after a load drop is proportional to the fundamental work-hardening rate of the metal; (e) the interfacial (yield) shear strength of the metal-ceramic interface is described in terms of the total number of load drops and the magnitude of the first load drop. These results are applied to the case of copper-sapphire and copper-niobium-sapphire interfaces. An interlayer of niobium, approx. 30 nm thick, increases the interfacial shear strength by a factor of two. The interfacial shear strengths determined in the present study are lower by an order of magnitude compared to the values obtained with the thin film multiple cracking technique. This difference is explained by different mechanisms of shear relaxation at the interface after fracture of the ceramic phase.     

Experiments on fracture behavior of single fiber-brittle zone model composites

Single fiber-brittle zone model composites were prepared by the electroless plating method, in order to know the effect of the interfacial bonding strength between the fiber and brittle zone on the fracture strength of the composites. For the case of weak inter-facial bonding, the notch formed by the fracture of the brittle zone at an early stage of deformation was unable to extend into the fiber due to a premature interfacial debonding. Therefore no deleterious effect of the brittle zone on the fiber strength was found. For the case of strong interfacial bonding, the formed notch extended into the fiber, resulting in loss of the fiber strength. The strength of such a composite was well explained by the theory recently proposed by Ochiai and Murakami. The important parameters to describe the fracture behavior of the fiber coated with the brittle zone, the strain energy release rate of the fiber and the permissible thickness of the brittle zone, below which the strength of the fiber is not reduced, were experimentally determined.     

Deformation structure and the tensile fracture characteristics of a cold worked 1080 pearlitic steel

The tensile mechanical properties, deformation structure, and tensile fracture characteristics of a 1080 perlitic steel were examined at various reduction ratios of cold work. The final tensile fracture ductility exhibited an unusual behavior in that this parameter first decreased and then increased with increasing reduction ratio. At a reduction ratio of 1.92, the cold worked material exhibited greater tensile ductility than the as-heat treated material even though the yield strength was greater by more than 400 pct. Microscopic regions of structural damage in the form of shear bands were observed at all reduction ratios, but appeared to become less detrimental to the subsequent tensile ductility as the reduction ratio increased. The fracture mode observed on the broken tensile specimens changed from predominantly cleavage to completely fibrous as the amount of cold reduction was increased. These observations are thought to result from a complex interaction between the interfacial strength of the shear bands, interlamellar spacing and texture effects and the stress state during deformation.     

Tailoring interfacial shear strength of SiC fiber-reinforced brittle matrix composites

The interfacial shear strength of Nicalon SiC fiber-reinforced glass-ceramic matrix composites was aimed to be tailored via two methods: (1) varying of the thickness of the carbon-rich interfacial layer between the fiber and the matrix by controlling hot pressing period and (2) formation of the secondary interfacial layer, TaC, at the carbon/matrix boundary by doping the Ta₂O₅ matrix addition. In the series of composites with varying carbon-rich layer thickness, fiber/matrix debonding mostly occurred at the carbon/matrix boundary and hence the increase in the carbon-rich layer thickness did not cause any apparent changes in the interfacial shear strength. In the TaC formed series of composites, the interfacial shear strength was affected considerably by the presence of the TaC phase at carbon/matrix boundary. The Ta₂O₅ addition to control the quantity of the TaC phase has shown to be a useful method to tailor the interfacial shear strength of SiC fiber/glass-ceramic composites.     

Energy-Based Modeling Approach for Debonding of FRP Plate from Concrete Substrate

For concrete beams and slabs strengthened with bonded fiber reinforced plastic (FRP) plates, plate debonding from the concrete substrate is a common failure mode. In this paper, the debonding process is modeled as the propagation of a crack along the concrete/adhesive interface, with frictional shear stress acting behind the crack tip. Crack propagation is taken to occur when the net energy release of the system equals the interfacial fracture energy. The analysis is first performed for the special case with constant shear stress along the debonded interface, and then for the general case with slip softening in the debonded zone. From the results, a direct correspondence between energy-based and strength-based analyses can be established for arbitrary softening behavior along the interface. Specifically, through the proper definition of an effective interfacial shear strength, the conventional strength-based approach can be employed to give the same results as the much more complicated energy-based analysis. Also, based on the relation between the effective shear strength and other material parameters, it is possible to explain the very high interfacial shear stresses observed in experimental measurements. As an application example, distribution of plate stress and interfacial shear stress for the linear softening case is derived. The model results are found to be in good agreement with experimental measurements, showing that the simple linear softening model can describe the debonding process in real material systems.     

Control of the mechanical properties of metal-ceramic interfaces through interfacial reactions

The use of interfacial reactions to control the structure and shear strength of metal-ceramic interfaces was studied in the NiO-Pt system. Interfaces were formed by hot1pressing together thin NiO single crystals and thick Pt polycrystalline films. Suitable choice of the annealing temperature, time and oxygen partial pressure allowed the introduction at the interface of a layer of either an intermetallic compound NiPt with thickness between 1 and 65 nm or a Ni-Pt solid solution.The shear strength of the NiO-Pt interface with and without the different interlayers present was measured by the periodic cracking method. Compared to its originally hot pressed state the shear strength of the NiO-Pt interface was increased by a factor of at least 4 by the presence of the NiPt and by ∼10 by the solid solution. The use of interfacial reactions to control interfacial strength may also be applicable in other metal-ceramic systems where the metal and the cation form intermetallic compounds, and where the oxidation potentials of the metal and the cation are significantly different.     

The role of metal plasticity and interfacial strength in the cracking of metal/ceramic laminates

Two models based on elastic-plastic fracture mechanics and fiber bridging are developed to study the role of plastic yielding in metals and the interfacial strength of metal/ceramic laminates. There are two types of damage observed in metal/ceramic laminates: multiple cracking and macroscopic crack propagation. The former occurs around the macroscopic crack tip and thus distributes the damage and enhances the composite's toughness. The present models establish that there exists a critical metal/ceramic layer thickness ratio above which multiple cracking dominates and that this ratio decreases (hence increasing the possibility of multiple cracking) as the ratios of metal yield stress over ceramic strength, metal modulus over ceramic modulus, and metal/ceramic interfacial strength over ceramic strength increase. Good agreement between the present models and experimental results is observed for both damage modes, i.e. multiple cracking vs macroscopic crack propagation, and for critical stress intensity factors. The elastic-plastic fracture mechanics and fiber-bridging models predict that multiple cracking is ensured if the metal layer thickness is 2.5 times larger than the ceramic layer thickness, regardless of the metal/ceramic properties.     

Effect of Concrete Composition on FRP/Concrete Bond Capacity

External bonding of fiber-reinforced plastics (FRP) to concrete members has been established as an efficient and effective method for structural strengthening and retrofitting. Direct shear test is often employed to study the crack-induced debonding failure in reinforced concrete members flexurally strengthened with FRP composites. In many existing models, the bond capacity (which defines ultimate load capacity of the specimen in the direct shear test) is considered to be strongly dependent on the compressive or tensile strength of the concrete. However, since debonding behavior is affected by interfacial friction due to aggregate interlocking within the debonded zone, the concrete composition should also play an important role in determining the bond capacity. In this study, the direct shear test is performed with 10 different compositions of concrete. The test results indicate that the bond capacity has little correlation with either the concrete compressive or splitting tensile strength. On the other hand, the bond capacity is found to have reasonable correlation with the concrete surface tensile strength but correlates very well with the aggregate content. As a geometry independent parameter corresponding to bond capacity, the interfacial fracture energy is empirically proposed to relate to these two parameters. The consideration of aggregate content leads to much better agreement between predicted bond capacity and test result. Hence, the effect of concrete composition on the FRP/concrete bond should be considered in practical design.     

钢-铝固液相浸镀复合板的轧制处理

研究了轧制处理后钢-铝固液相浸镀复合板的界面剪切力学性能,确定了压下率与界面剪切强度之间的关系.结果表明:压下率为2.73%时,可消除由1.2mm厚08Al钢板和1.0mm厚工业纯铝构成的2.2mm厚钢-铝固液相浸镀复合板的界面附加应力,从而获得最大界面剪切强度为83.5MPa.     

Influence of fabrication technique on the fiber pushout behavior in a sapphire-reinforced NiAl matrix composite

Directional solidification (DS) of “powder-cloth” (PC) processed sapphire-NiAl composites was carried out to examine the influence of fabrication technique on the fiber-matrix interfacial shear strength, measured using a fiber-pushout technique. The DS process replaced the fine, equiaxed NiAl grain structure of the PC composites with an oriented grain structure comprised of large columnar NiAl grains aligned parallel to the fiber axis, with fibers either completely engulfed within the NiAl grains or anchored at one to three grain boundaries. The load-displacement behavior during the pushout test exhibited an initial “pseudoelastic” response, followed by an “inelastic” response, and finally a “frictional” sliding response. The fiber-matrix interfacial shear strength and the fracture behavior during fiber pushout were investigated using an interrupted pushout test and fractography, as functions of specimen thickness (240 to 730 μm) and fabrication technique. The composites fabricated using the PC and the DS techniques had different matrix and interface structures and appreciably different interfacial shear strengths. In the DS composites, where the fiber-matrix interfaces were identical for all the fibers, the interfacial debond shear stresses were larger for the fibers embedded completely within the NiAl grains and smaller for the fibers anchored at a few grain boundaries. The matrix grain boundaries coincident on sapphire fibers were observed to be the preferred sites for crack formation and propagation. While the frictional sliding stress appeared to be independent of the fabrication technique, the interfacial debond shear stresses were larger for the DS composites compared to the PC composites. The study highlights the potential of the DS technique to grow single-crystal NiAl matrix composites reinforced with sapphire fibers, with fiber-matrix interfacial shear strength appreciably greater than that attainable by the current solid-state fabrication techniques.     

Dynamic deformation behavior of an oxide-dispersed tungsten heavy alloy fabricated by mechanical alloying

The objective of this study is to investigate the dynamic deformation and fracture behavior of an oxide-dispersed (OD) tungsten heavy alloy fabricated by mechanical alloying (MA). The tungsten alloy was processed by adding 0.1 wt pct Y₂O₃ powders during MA, in order to form fine oxides at triple junctions of tungsten particles or at tungsten/matrix interfaces. Dynamic torsion tests were conducted for this alloy, and the test data were compared with those of a conventional liquid-phase sintered (LPS) specimen. A refinement in tungsten particle size could be obtained after MA and multistep heat treatment without an increase in the interfacial area fraction between tungsten particles. The dynamic test results indicated that interfacial debonding between tungsten particles occurred over broad deformed areas in this alloy, suggesting the possibility of adiabatic shear-band formation. Also, oxide dispersion was effective in promoting interfacial debonding, since the fine oxides acted as initiation sites for interfacial debonding. These findings suggest that the idea of forming fine oxides would be useful for improving self-sharpening and penetration performance in tungsten heavy alloys.     

Theoretical prediction of tensile strength of fibers as a function of thickness of brittle zones on fiber surfaces

A theoretical model of longitudinal strength of fibers as a function of the thickness of brittle zones on fiber surfaces was presented. Unifying parameters, corresponding to a formation of a notch due to a premature failure of the brittle zone, to an extension of the notch and to an interfacial debonding between the fiber and the brittle zone, were derived by modifying Weibull theory, fracture mechanics and shear lag analysis of Dow, respectively. A framework for interpreting the interrelation between the magnitudes of these unifying parameters and the failure mode of the fiber/brittle zone composites was carried out. It was shown that, if the thickness of the brittle zone is thicker than a critical value and if the interfacial bonding is stronger than a critical value, the fiber strength is reduced. Some examples of combinations of these unifying parameters given as a function of the thickness of the brittle zone were presented and the failure mode of the fiber/brittle zone composite was described schematically also as a function of the thickness of the zone.     

Effect of heat treatments on interfaces of hot rolled Q235- TA2 clad plate with a niobium interlayer

The normalization process and high- temperature temper process were used to investigate the effect of heat treatments on the microstructure and mechanical properties of bond interfaces. The SEM and EDS were used to discuss the microstructure and element diffusion after heat treatment. And the interfacial bond strength was obtained by compression shear test on the testing machine. With the fractured surface morphology analysis, the composition of phases at the bond interface was analyzed by XRD. The experimental results show that a small quantity of brittle intermetallic compound Fe2Nb phases are observed at the bonding interface of the Q235- Nb bonds after heat treatment, and needle structure is formed at Nb- Ti interface after normalization treatment. The compression shear strength of normalized specimens(171MPa) at 900?? is slightly higher than that of the high- temperature tempered specimens(162MPa) processed at 650??. Observation of fracture surfaces demonstrations that the failure takes place through the bonding interface of the Q235- Nb bonds during all the shear tests, the compression shear strength is lower at Q235- Nb interface than at Nb- Ti interface.     

银铜侧向复合材料界面结合机理分析

本文采用“包覆锭坯+扩散烧结+冷轧复合”联合工艺制备了银铜侧向复合带材,利用金相显微镜（OM）、扫描电镜（SEM）和能谱仪（EDS）观察分析银铜复合界面结构和元素分布,并分析其银铜复合界面的结合机理。结果表明,银铜复合界面形成过程为：1）银铜接触界面处凹凸不平的表面在轧制力的作用下相互咬合,形成机械结合界面;2）接触面在轧制力的作用下,银铜表面氧化膜破裂,新鲜表面质点间在轧制变形热的作用下产生原子结合;3）在扩散烧结过程中,银铜界面处的原子在高温作用下被激活,银铜原子相互扩散,在界面处发生银铜共晶反应形成液相金属层,随着烧结时间的延长,其共晶反应液相层厚度逐渐增加,随后冷凝结晶,使银铜实现侧向冶金结合。4）在后续中间退火过程中,共晶层与两侧的铜、银基体相互扩散,铜、银原子向更深的方向逐渐扩散,在靠近共晶层铜侧和银侧逐步形成固溶体层,使银与铜的结合强度进一步提高。银铜侧向复合界面结合机理包含机械咬合结合、接触共晶反应自钎焊结合和原子扩散结合3种,复合界面结合强度较好,剪切强度达220 MPa。     

河南龙门店银矿断裂构造分形特征分析

龙门店银矿断层发育,主要有NE、NW和NNE向3组断裂,其中NE和NNE向断裂与成矿关系密切,矿体的形成与分布严格受断裂控制。为研究断裂分维特征与矿体的关系,采用计盒维数法计算出龙门店银矿断裂的分维值为1.295,中部分维值为1.319,性质偏于剪性;与成矿有关的NE-NNE向断裂在全区和矿区中部的分维值分别为1.197和1.237,为剪性断裂。二者判定系数R²均＞0.98,说明矿区断裂具有良好的自相似性。与成矿相关的NE-NNE向断裂分维值D＞1.17所圈闭的太华群片麻岩是有利的成矿部位,全区断裂分维值D＞1.25作为辅助指标。采用分维值定量描述断裂的自相似性,对成矿预测有一定的指导作用。     

Brazing of Ti-6Al-4V and niobium using three silver-base braze alloys

Evaluations of the (infrared)-brazed Ti-6Al-4V and niobium joints using three silver-base braze alloys have been extensively studied. According to the dynamic wetting angle measurement results, the niobium substrate cannot be effectively wetted by all three braze alloys. Because the dissolution of Ti-6Al-4V substrate causes transport of Ti into the molten braze, the molten braze dissolved with Ti can effectively wet the niobium substrate during brazing. For infrared-brazed Ti-6Al-4V/Ag/Nb joint, it is mainly comprised of the Ag-rich matrix. The TiAg reaction layer is observed at the interface between the braze and Ti-6Al-4V substrate. In contrast, Ti-rich, Ag-rich, and interfacial TiAg phases are found in the furnace-brazed specimen. The dominated Ti-rich phase in the joint is caused by enhanced dissolution between the molten braze and Ti-6Al-4V substrate. The infrared-brazed Ti-6Al-4V/72Ag-28Cu/Nb joint is mainly comprised of the Ag-rich matrix and Ag-Cu eutectic. With increasing the brazing temperature or time, the amount of Ag-Cu eutectic is decreased, and the interfacial Cu-Ti reaction layer(s) is increased. The infrared brazed joint has the highest average shear strength of 224.1 MPa. The averaged shear strength of the brazed joint is decreased with increasing brazing temperature or time, and its fracture location changes from the braze alloy into the interfacial reaction layer(s) due to excessive growth of the Cu-Ti intermetallics. The infrared-brazed Ti-6Al-4V/95Ag-5Al/Nb joint is composed of Ag-rich matrix and TiAl interfacial reaction layer. With increasing the brazing time, the amount of Ag-rich phase is greatly decreased, and the interfacial reaction layer becomes Ti₃Al due to enhanced dissolution of Ti-6Al-4V substrate into the molten braze. The average shear strength of the infrared-brazed joint is 172.8 MPa. Additionally, the existence of an interfacial Ti₃Al reaction layer significantly deteriorates the shear strength of the furnace-brazed specimen.     

Assessment of the Performance of Sn–3.5Ag/Cu Solder Joint Under Multiple Reflows,Thermal Cycling and Corrosive Environment

The solder joint performance of Sn–3.5Ag/Cu combination was studied under multiple reflows, thermal cycling and exposure to the corrosive environment. Factorial experiment was carried out to assess the effect of individual parameters and the interaction of parameters on the shear strength of the solder joint. The results showed that the combination of thermal cycling and immersion in corrosive media resulted in the maximum decrease in the shear strength followed by the combination of multiple reflows and corrosive media. The shear strength reduced with the increase in immersion duration in corrosion medium. Factorial experiment was analyzed using analyis of variance (ANOVA). The results indicated that the individual parameters had a significant effect, whereas the effect of interaction of these parameters was less significant on the performance of the solder joint. Fracture surface indicated mixed mode of failure and the occurrence of fracture predominantly in the bulk solder.