多晶与单晶铜塑性变形行为的相关性

利用TEM分析拉伸变形多晶铜中不同取向晶粒的位错组织, 研究了多晶与单晶形变行为的相关性. 结果发现, 多晶铜中诸晶粒的形变显微组织可分为3种不同类型, 而且组织类型与其相应晶粒的晶体学取向存在密切的相关性; 根据多晶中不同类型组织的体积含量, 结合相应取向单晶的应力应变曲线, 计算出了多晶的应力应变曲线, 其结果与实测曲线相似.     

强塑性循环变形中单晶铜和多晶铜的力学性能

分别用小通道角模具(模具Ⅰ)和大通道角模具(模具Ⅱ)以及A路径和Bc路径对单晶铜和多晶铜进行等通道角挤压(ECAP)实验,对挤压后的组织进行光学显微镜(OM)和扫描电镜(SEM)观察,对挤压后的单晶铜组织进行XRD分析,研究单晶铜和多晶铜在挤压中的变形行为。结果表明:单晶铜在两种路径挤压后的抗拉强度无明显差异,用模具Ⅰ挤压时其力学性能的变化幅度较大,经多道次挤压后,其显微组织沿压力轴方向具有明显的定向排列特征。多晶铜在A路径挤压时,其抗拉强度的上升幅度明显比在Bc路径挤压时大。随着挤压道次的增加,两种材料的组织均匀化程度和硬度增大,其断裂方式逐渐由韧性断裂向脆性断裂方向转变。     

9R structure in drawn industrial single crystal copper wires

By using transmission electron microscopy, the microstructures of drawn industrial single crystal copper wires produced by Ohno Continuous Casting(OCC) process were analyzed. The results show that the typical microstructures in the wires mainly include extended planar dislocation boundaries, a small fraction of twins and some dislocation cells sharing boundaries parallel to drawn direction. Besides the typical microstructures, 9R structure configurations were observed in the wires. The formation of 9R polytypes may be caused by the coupled emission of Shockley dislocations from a boundary.     

Theoretical analysis of texture evolution in cold rolling process of single crystal aluminum

The crystal plasticity finite element method（CPFEM）, which incorporates the crystal plasticity constitutive law into the finite element method, was developed to investigate the rolling processes of the cubic oriented and Goss oriented Al single crystal. The simulation results show that after rolling the crystal predominantly rotates around the transverse direction（TD） for both orientations. The rotations around the rolling direction（RD） and the normal direction（ND） are negligible. The reduction plays a significant role in the texture evolution. The TD rotation angle increases with increasing reduction. The deformation bands exist in the rolled specimens with the cubic initial orientation. Compared with the cubic oriented specimens, the TD rotation angles in the Goss oriented specimens are very small.     

热型连铸技术在单晶铜生产中的应用状况

热型连铸是一项近净成形（near—net—shape）技术，它是将定向凝固和连铸技术结合起来的一种新型工艺。通过对有关文献的综述介绍了热型连铸技术的特点和目前国内外研究、应用现状，重点介绍了热型连铸技术在单晶铜生产中的应用、单晶铜的性能特点以及市场需求，提出了该技术的局限性及今后的改进方向和发展前景。     

Effect of Benzotriazole on the dissolution of copper single crystal planes in dilute sulphuric acid

The kinetics of the dissolution of copper single crystal planes in aerated 0·1N H₂SO₄ containing various concentrations (10⁻⁶−10⁻²M) of Benzotriazole have been studied. The dissolution rates which were controlled by surface reaction, were a function of the temperature, crystallographic orientation and the concentration of Benzotriazole. The stabilities of the crystal planes were in the order (100) > (110) > (111). At 7·5 × 10⁻³M Benzotriazole, Cu-Benzotriazole film appeared on the surface, bringing mechanical passivity. Benzotriazole acted as cathodic inhibitor at low concentrations and anodic inhibitor at high concentrations. The corrosion potentials of the crystal planes were in the order (100) > (110) > (111) at all concentrations of benzotriazole.     

On the origin of sliver defects in single crystal investment castings

The origin of sliver defects in seeded single crystal castings has been determined to be the deformation of dendrites in the mushy zone through microstructural characterization of a series of castings with a geometry sensitive to these defects. The extent of bending and torsion of the dendrites in the as-cast microstructure and the net misorientation was quantified from electron backscattered diffraction data using a bespoke data analysis method. At the point of initiation of the sliver defects, deformation was localized at the mould wall, indicating that these defects arise as a result of the bending moments generated by differential thermal contraction between the mould and the dendrites. The comparative susceptibilities of dendrites to deformation under converging and diverging growth with respect to the mould wall were distinguished. The experimental observations were supported by continuum finite element simulations using ProCAST?, which confirmed the occurrence of high stresses in the constricted channel where sliver defects form. Contrary to foundry wisdom, ancillary observations demonstrated that the oxide at the seed melt-back interface played no role.     

单机架可逆冷轧机工作辊热变形计算

在分析了影响冷轧工作辊热变形的因素基础上,用数值积分的方法计算了冷轧过程中的塑性变形功和摩擦热,进而用简化方法计算了工作辊周向热流,从而确定轧辊表面温度后,采用差分法计算了工作辊内部的温度场以及热变形,并开发了相应的计算程序。用该程序计算并分析了某单机架可逆冷轧机工作辊温度场和热凸度规律,实例证明,该方法精度满足实际要求,为该轧机板形控制提供了分析依据。     

Effect of halide ions on the dissolution of copper single crystal planes in dilute sulphuric acid

The rates of dissolution of copper single crystal planes in dilute sulphuric acid containing various concentrations (10⁻⁸ to 10⁻²M) of Cl⁻, Br⁻ and I⁻ are determined at 30°C. The dissolution rates, which are controlled by transport process in solution, are a function of the temperature, stirring rate, oxygen solubility, crystallographic orientation and the concentration of halide ions. Halide ions acted as anodic inhibitor at low concentrations and cathodic inhibitor at high concentrations. The changes in the dissolution rates have been attributed to specific adsorption of halide ions or precipitation of cuprous halides on the surface of the crystal planes.     

On the influence of cold work on the oxidation of some stainless steels

Oxidation experiments, performed by means of light interference microscopy, give information of the initial oxidation on a microscopic scale. A thin oxide layer on the substrate gives rise to an interference colour, which is directly correlated to the thickness of this layer. It is shown that not all stainless steels react in the same way to the same pretreatments. The oxidation behaviour of drawn AlSI 304 and AlSI 321 is completely different from that of Incoloy 800 H, while the undeformed and recrystallized samples all show the same oxidation behaviour. It is suggested that this behaviour of AlSI 304 and AlSI 321, is caused by the formation of α martensite in the deformed austenitic matrix.     

Effect of crystalline anisotropy and forming conditions on thinning and rupturing in deep drawing of copper single crystal

Copper single crystal has excellent electrical properties and ductility, and it has a peculiar application in micro-manufacturing. In this paper, a specific mold was designed and made in order to conduct deep drawing of copper single crystal and evaluate the crystalline orientation effect to the local thinning and rupturing in the process. As a contrast, a finite element subroutine (VUMAT in ABAQUS) based on the crystal plasticity theory was developed to simulate the deep drawing process according to the experimental configurations. The results show that the (1 1 0) blank has better deep drawing performance than (0 0 1) blank; The crack of (0 0 1) blank originates at 〈1 0 0〉 orientation in the plane because 〈1 0 0〉 orientation has poor plasticity; friction is a crucial factor to the forming quality in a small scale deep drawing process; the simulations are in good agreement with the experiments, which also indicates the crystal plasticity model is very necessary to study the plastic forming of metallic material, especially the crystalline characteristics should be considered in the research.     

Retention of the Goss orientation between microbands during cold rolling of an Fe3%Si single crystal

An FeSi single crystal with an initial {1 1 0}〈0 0 1〉 orientation, also referred to as Goss orientation, was cold rolled up to a thickness reduction of 89%. Most of the crystal volume rotated into the two symmetrical {1 1 1}〈1 1 2〉 orientations. However, a weak Goss component remained in the highly strained material, even though the Goss orientation is mechanically unstable under plane strain loading. Two types of Goss-oriented regions were discernable in the material subjected to 89% reduction. It appeared that these two types of Goss regions have different origins. Goss grains that were found aligned in shear bands form during straining. A second type of Goss region was found between microbands where the initial Goss orientation was retained.     

Spatial orientations and structural irregularities associated with the formation of microbands in a cold deformed Goss oriented Ni single crystal

The crystallographic nature of microband boundaries was investigated in a Goss oriented nickel single crystal following cold deformation in channel die plane strain compression. Standard electron backscatter diffraction (EBSD), three-dimensional (3-D)-EBSD and transmission electron microscopy (TEM) were used in the investigation. When viewed in the three orthogonal sections microband boundary traces were classically aligned in the transverse direction section at an acute angle from the rolling direction (RD), but appeared wavy in the normal direction (ND) section. The latter observation may lead to the conclusion that microband boundaries are non-crystallographic. 3-D EBSD was used to reconstruct actual microbands in a deformed volume that revealed significant new information about their structure. Here microband surfaces are largely planar over large distances, but frequently interrupted by local distortions and undulations due to interactions between intersecting non-coplanar microbands. The combined EBSD/TEM investigation has revealed that microband boundaries are aligned close to an active {1 1 1} slip plane (i.e. they are crystallographic), but the undulations and distortions they contain are non-crystallographic in the sense that they deviate from an active slip plane. The non-crystallographic features of microbands (as revealed by their wavy structure in the ND section) may be explained by the crystallographic oscillations of up to ±7.5° towards RD that occur during plastic deformation. Such oscillations result in varying fractions of slip on a given {1 1 1} plane, resulting in varying degrees of interaction between the two sets of non-coplanar microbands. These local and intense microband interactions result in their deviation from their active slip planes.     

Metallographic and OIM study of weld cracking in GTA weld build-up of polycrystalline,directionally solidified and single crystal Ni based superalloys

Abstract

The repair of gas turbine components is of importance both commercially and scientifically to ensure cost effective repair schemes that will extend the lives of hot end components such as blades and stators. The present communication reports the results of a metallographic and orientation imaging microscopy study of weld cracking observed in the gas tungsten arc repair welds of a polycrystalline (IN738LC), a directionally solidified (Rene 80) and a proprietary single crystal (SX) alloy. The three alloys were welded with low, intermediate and high strength weld fillers, using a weld build-up approach rather than a conventional weld repair of a through thickness crack. This procedure would be applicable for example to worn area on the tips of turbine blades. Inhomogeneous initial microstructures and those from solidification processes led to extensive heat affected zone microfissuring in the IN738LC alloy, associated with MC carbide liquation, liquation of gamma prime (γ′), segregation of boron and strain effects from precipitation of γ′ in both single and double pass welds. As observed previously in a V shaped weld preparation, the extent of microfissuring in alloy IN738LC increased substantially from the use of the low and intermediate strength weld fillers, to extensive heat affected zone microfissuring by using the high strength IN738 filler. In the directionally solidified Rene 80 welds, due to the reduction in grain boundary area per unit volume, only minor heat affected zone cracking was observed, while the SX alloy did not crack at all. The absence of any cracks in the SX alloy welds despite the presence of stray grains in the fusion zone appears to be related to reduced stress levels in the welds due to the choice of welding technique and the welding parameters.     

Thermal stability and strength of deformation microstructures in pure copper

The plastic flow field produced by machining is utilized to access a range of deformation parameters in pure copper: strains of 1–7, strain rates of 1–1000 s^?1 and temperatures as low as 77 K. The strength and stability of the severe plastic deformation microstructures including cellular, elongated, equiaxed and twinned types are characterized. Unique combinations of strengthening and stability are identified in the case of heavily twinned microstructures. These observations offer insights for improving the stability of both single-phase and multicomponent ultrafine-grained alloys.     

Preparation of epitaxial and polycrystalline bismuth titanate thin films on single crystal (100) MgO by chemical solution deposition

Epitaxial and polycrystalline Bi₄Ti₃O₁₂ thin films were prepared on single crystal (100) MgO substrates by a chemical solution deposition process using metal naphthenates as starting materials. Pyrolyzed films (at 500°C) were annealed for 30 min in air at 650, 700, 750 and 800°C, respectively. The effects of annealing temperature on the crystallinity, epitaxy and surface morphology of the films were investigated by X-ray diffraction θ-2θ scans, pole-figure analysis, and atomic force microscopy (AFM). Epitaxially grown films annealed at 700 and 750°C, respectively, showed growth of three-dimensional needle-shaped grains. During annealing at 800°C, grain growth of Bi₄Ti₃O₁₂ may be suppressed by the formation of a titanium-rich phase such as Bi₂Ti₂O₇ owing to Bi volatilization, resulting in lower root mean square roughness than that of film annealed at 750°C.     

Fracture morphology and crack mechanism in pure polycrystalline magnesium under tension-compression fatigue testing

The fatigue fracture was characterized and the fracture behavior was analyzed,using scanning electron microscope(SEM) and electron back-scattered diffraction(EBSD),the fatigue tests of two strain amplitude at room temperature were 0.5% and 1.0% respectively,and the results showed that the fatigue deformation of different strain amplitude produced two typical fatigue fracture morphology,and when the strain amplitude was 1.0%,fatigue fracture mechanism of AZ31 magnesium alloy induced by {1012}twins,when the strain amplitude is 0.5%,it was induced by{1012}-{1012} double twins.In the present study,the average thickness of primary twin is～20 μm at amplitude of 0.5 % and～80 μm at amplitude of 1.%.The thickness of{1012} primary twins was large enough to activate {1012}-{1012} secondary twins at a high strain amplitude,while the thickness of {1012} primary twins was too narrow to activate{1012}-{1012} secondary twins at a low strain amplitude.     

纯铜表面激光熔覆铜合金涂层的组织及耐磨性

采用光学显微镜、扫描电镜、X射线衍射及能谱分析对纯铜表面送粉激光熔覆制备的铜合金涂层进行了分析.结果表明,涂层与基体为冶金结合,无气孔、裂纹等缺陷,涂层稀释率极低,铜合金涂层在凝固过程中通过液相分离形成大量均匀弥散分布的细小球形分离相、富含铜的固溶体和少量大块分离相聚集体;细小分离相的平均直径小于5μm,分离相由富含Fe、Co、Mo的多元金属硅化物组成.富含铜固溶体的硬度为280 HV0.1,大块分离相聚集体的硬度为510 HV0.1.磨损试验结果表明,激光熔覆涂层的耐磨性较纯铜基体有显著提高.