Role of stored energy in static recrystallization of cold rolled copper single and multicrystals

The intragranular work-hardening state has been investigated in moderately cold rolled copper single and multicrystals. Every grain/sample has been individually investigated by X-ray diffraction profile analysis which allows the determination of the dislocation density and of the outer cut-off radius of the dislocation structure, the two principal parameters of the stored energy. It has been found that the stored energy varies substantially with the initial orientation, leading to a strong variation of the critical recrystallization temperature from grain to grain. On the other hand, in situ annealing reveals a discontinuous progress of recrystallization characterized by a strong influence of the heterogeneity of the stored energy.     

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。     

A quantitative analysis of the evolution of texture and stored energy during annealing of cold rolled copper

The experimental evolution of the global texture during recrystallization of cold rolled copper is presented after various rolling reductions. After presentation of the method used for the decomposition of the orientation distribution functions obtained from X-ray diffraction measurements into gaussian peaks, the behavior of each texture component is studied. This quantitative analysis coupled with stored energy measurements also obtained by X-ray diffraction allows the oriented nucleation and growth mechanisms to be linked to stored energy variations. The proposed mechanisms are then confirmed by local observations obtained by EBSD.     

Lattice orientation dependence of the stored energy during cold-rolling of polycrystalline steels

During cold deformation, about 10% of the energy spent is stored in the polycrystalline material in the form of the elastic energy associated to crystal defects. The latter can be measured experimentally by calorimetry, X-ray diffraction. In this work, we propose a direct calculation based on an elastic-plastic self-consistent model. The part of the stored energy related to second order (intergranular) stresses is estimated for a cold-rolled Ti–IF steel. The stored energy as well as the accumulated plastic strain are reported as a function of the final crystallographic orientation of the grains. Along the α-fiber, the stored energy increases from {001}<110> to {111}<110> while the plastic strain decreases. This dependence with the crystallographic orientation is in good agreement with experimental results. With respect to recrystallization, experiments show that {111}-grains nucleate first. This highlights the specific role of second order (intergranular) stresses for recrystallization.     

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.     

连续铸造铜单晶的力学性能和电阻率

采用自制水平单晶连铸设备制备铜单晶, 并对铜单晶的力学性能和电阻率进行了测试分析。结果表明,铜单晶与多晶铸棒比,抗拉强度降低２０ ．８５ ％ ,屈服强度降低８６ ．５４ ％ ,延伸率增加８０ ．２４ ％ , 断面收缩率增加３９４ ．５０ ％ ; 与轧制棒比, 抗拉强度降低６５ ．９７ ％ , 屈服强度降低９８ ．２７ ％ , 延伸率增加２７０ ．００ ％ , 断面收缩率增加４ ．００ ％ ; 与多晶铸棒比电阻率降低１５ ．５７ ％ , 与定向凝固铸棒比电阻率降低４ ．２４ ％ 。因此, 连铸铜单晶具有非常优异的塑性加工性能和低电阻率     

单晶/多晶镍轴向拉伸力学性能的分子动力学模拟

为提高航空发动机推重比采用整体叶盘新技术却带来了盘叶连接区域高风险失效问题。本文采用分子动力学对连接区单晶/多晶镍(SPSNi)的力学性能进行模拟,首先通过对比了不同晶态镍拉伸原子图。发现,由于单晶/多晶界面的存在使得拉伸后界面处的非晶化程度加剧,易于孔洞萌生,加剧了SPSNi突然断裂的风险。最后重点研究了单晶/多晶镍的应变率效应与温度效应。当应变率大于1í10_⁸s_^-1小于2í10_¹⁰s_^-1时,SPSNi对加载应变率几乎不敏感,屈服强度小幅上升。超过2í10_¹⁰s_^-1之后,其屈服强度随着应变率的增加而迅速下降。这是因为在高应变率下,SPSNi的FCC原子大规模迅速转变为无序的非晶结构,导致了晶体镍承载能力迅速下降。可以将应变率2í10_¹⁰s_^-1作为SPSNi拉伸变形的阈值。不同温度下,SPSNi屈服强度随温度的增大而线性下降。这是由于在温度的影响下,位错网络的初始镶嵌结构逐渐变得不规则,初始失配应力随着温度的升高而下降。     

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.     

多向锻造纯钨形变储存能及动态再结晶行为分析

对纯钨烧结体进行多向锻造试验,运用OM和DSC分析了纯钨多向锻造组织演化规律及形变储存能的变化,结合XRD、EBSD对纯钨形变储存能的来源及动态再结晶行为进行了研究。结果表明:多向锻造后纯钨内部孔隙明显减少,热变形过程中的动态再结晶导致晶粒显著细化,变形后保留在晶粒及亚晶内部的高密度位错结构导致形变储存能的增加,再结晶晶粒主要沿能量较高的晶界及晶界交汇处分布,其动态再结晶机制为形变诱导晶界迁移机制与亚晶粗化及晶粒机械破碎的混合机制,多向锻造后纯钨再结晶温度基本不变,材料热稳定性有所提高。     

单晶SiC基片的铜基研磨盘加工特性研究!

采用铜基螺旋槽研磨盘对6H-SiC单晶基片的Si面和C面进行了单面研磨加工,研究研磨压力、研磨盘转速和金刚石磨粒尺寸对SiC基片材料去除率和表面粗糙度的影响。结果表明,单晶SiC的C面和Si面具有明显的差异性,C面更易加工,其材料去除率比Si面大。研磨压力是影响材料去除率和表面粗糙度的主要原因,研磨压力越大,材料去除率越高,但同时表面粗糙度变大,较大的研磨压力会导致划痕的产生。在达到最佳表面粗糙度时,C面加工所需的转速比Si面大。磨粒团聚会严重影响加工表面质量,采用粒度尺寸3 μm的金刚石磨料比采用粒度尺寸1 μm的金刚石效果好,经粒度尺寸3 μm的金刚石磨料研磨加工5 min后,Si面从原始粗糙度R_a 130 nm下降到R_a 5.20 nm,C面下降到R_a 5.49 nm,表面质量较好。      

热型连铸单晶铜的性能

利用自制的热型连铸设备生产了单晶铜棒材，对其铸态、冷加工态、退火态的力学性能与电学性能进行了系统的测试与研究。结果表明：和多晶铜相比，单晶铜在铸态时具有良好的塑性和较低的电阻率，并具有优异的室温延展性，其延伸率可达6100％以上；冷拉拔加工后单晶铜表现出更大的加工硬化现象，但采用合理的退火工艺可使其加工硬化得到缓解。     

蓝光激光定向能量沉积纯铜零件的工艺及性能

金属高反材料对短波长激光拥有较高的吸收率,文中使用大功率蓝光激光器作为能量源在不锈钢基板上进行纯铜的沉积,将激光功率、扫描速度和送粉速率从5个水平形成不同的工艺参数组合进行全因子试验. 先从宏观尺寸分析了工艺参数对沉积层的影响,后从相对密度、组织结构和力学性能3个方面对多道多层工艺进行探究. 结果表明,单位送粉激光能量(laser energy per unit powder feed,LEPF)在2.592 ~ 6.048 kJ/g范围内可进行稳定的连续沉积,而当LEPF值大于6.050 kJ/g时,因用于沉积的激光能量过多而导致气孔出现. 使用LEPF值为4.53 kJ/g打印出了表面质量较好的纯铜薄壁圆筒零件. 通过正交扫描得到最高相对密度为99.10%的纯铜块状样件,并观察到了两种孔隙:近球形的气体包封孔隙(I型)以及未熔合和未熔化的粉末孔隙(II型). 最后进行拉伸测试,从结果发现,远离基板成形位置抗拉强度为196.55 MPa,靠近基板成形位置的断后伸长率为26.72%.     

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.     

Effect of heat treatment on microstructure and properties of single crystal copper cold-welded joints

With the means of electron backscattered diffraction (EBSD), mechanical properties test and digital eddy current metal conductivity, the single crystal copper cold- welded joint was tested and analyzed, the structure change of cold- welded joint and the effect of heat treating on the structure and property of cold- welded joint were discussed. The results show that: The deformation area of the single crystal copper cold welded joint is broken, the crystalline grain at the interface of the joint is refined, and the single crystal structure is still maintained in the base metal area. The hardness of the deformation area increases greatly, the conductivity of the joint does not change much, and the tensile strength of the joint reaches about 70% of that of the base metal. At the interface of the heat treating joint, the single crystal structure of the deformation area and the base metal area are destroyed, and the grains grow up at the interface and the orientation is different. The hardness of the joint interface is much lower than that of the non-heat treating joint, the electrical conductivity of the joint is good, and the tensile strength of the joint is higher than that of the base metal.     

单晶铜在ECAP过程中的织构转变和强化行为

由于优秀的导电性能,单晶铜已经在各个领域得到了广泛的应用。然而,较低的强度性能严重阻碍了其进一步的发展和使用。所以,使用ECAP技术对单晶铜进行强化,同时研究采用三个不同路径挤压时对材料性能的影响。使用电子背散射衍射和 X 射线衍射来对 6 道次 ECAP 变形过程中单晶铜的织构进行检测。模具的内角为 120°,挤压路径为 A、Bc、C。结果表明： 5 道次挤压后,A 路径,Bc路径和 C 路径的强度和延伸率分别为 405MPa 、30%,395 MPa、26.7%,385 MPa 、27.9%。6 道次挤压后,A 路径的织构为{112}<110>以及较弱的{110}<112>织构;Bc 路径为{001}<110>织构;而 C 路径的织构已经产生了分散。当采用 C 路径进行几道次的挤压后,首先在其极图中出现了双织构并存的情况,随后 A 路径极图中同样出现了双织构。而在 Bc 路径极图中,并没有其他的织构出现。在挤压过程中材料的导电性只有少量的下降,且全部在 98%IACS 以上。可以看出,在合适的应变量下,ECAP 可以使单晶铜强度明显提高而且导电性损失很小。同时,采用不同的挤压路径可以显著影响材料的性能,例如采用A路径挤压出的材料有最高的强度,C路径挤压出的材料有最好的导电性能。