Tension-Compression Asymmetry in Ultrafine-grained Commercially Pure Ti Processed by ECAP

A homogenous microstructure of ultrafine-grained (UFG) commercially pure (CP) Ti characterized by equiaxed grains/subgrains with an average grain size of about 150 nm and strong prismatic fiber texture were obtained after 4 passes of equal channel angular pressing (ECAP).Tension–compression asymmetry in yield and work hardening behavior of UFG CP Ti were investigated by uniaxial tension and compression tests.The experimental results reveal that UFG CP Ti exhibits a relatively obvious tensioncompression asymmetry in yielding and work hardening behavior.The basal and prismaticslip are suppressed either for tension or compression,which is the easiest to activate.The tension twin system{1012}<1011> easily activated in compression deformation due to the prismatic fiber texture based on the Schmidt factor,consequently resulting in a lower yield strength under compression than tension.ECAP can improve the tension-compression asymmetry of CP Ti due to grain refinement.The interaction among the dislocations,grain boundaries and deformation twins are the main work hardening mechanisms for compression deformation,while the interaction between the dislocations and grain boundaries for tension deformation.Deformation twins lead to the higher work hardening under compression than tension.

Thickness-related synchronous increase in strength and ductility of ultrafine-grained pure aluminum sheets

To explore the specimen size effect of mechanical behavior of ultrafine-grained(UFG)materials with different structures,UFG Al sheets processed by equal channel angular pressing(ECAP)were selected as target materials and the dependency of tensile behavior on sheet thickness(t)was systematically investigated.The strength and ductility of ECAPed UFG Al sheets were improved synchronously as t increased from 0.2 to 0.7 mm,and then no apparent change occurred when t reached to 0.7 and 1.0 mm.The corresponding microstructure evolved from dislocation networks in equiaxed grains into the walls and subgrains and finally into the dominated cells in elongated grains or subgrains.Meanwhile,dense shear lines(SLs)and shear bands(SBs)were clearly observed and microvoids and cracks were initiated along SBs with the increase of t.These observations indicated that the plastic deformation of UFG Al sheets was jointly controlled by shear banding,dislocation sliding,and grain-boundary sliding.Furthermore,the propagation of SBs became difficult as t increased.Finally,the obtained results were discussed and compared with those of annealed UFG Al and UFG Cu.

Effect of processing route on grain refinement in pure copper processed by equal channel angular extrusion

An experimental study of the microstructures in pure copper billets processed by 8 passes of equal channel angular extrusion （ECAE） via an extended range of processing routes with a 90° die is carried out. Each processing route is defined according to the inter-pass billet rotation angle （χ）, which varies from 0° to 180°. According to the generation of high-angle boundaries and reduction of grain size by electron backscatter diffraction （EBSD） measurements, the grain refinement is found to be most efficient for route with χ=90°and least efficient with χ=180°, among the seven routes studied. This trend is supported by supplementary transmission electron microscopy （TEM） measurements. Comparison of the EBSD and TEM data reveals the importance of considering the non-equiaxity of grain structures in quantitative assessment of microstructural differences in ECAE-processed materials.

Primary-transient creep and anelastic backflow of pure copper deformed at low temperatures and ultra-low strain rates

Creep and anelastic backflow behaviors of pure copper （4N Cu） with grain size dg=40 μm were investigated at low temperatures of T〈0.3Tm （Tm is melting point） and ultra-low creep rates of ε≤1×10^-10 s^-1 by a high strain-resolution measurement （the helicoid spring specimen technique）. Analysis of creep data was based on the scaling factors of creep curves instead of the conventional extrapolated steady-state creep rate. Power-law creep equation is suggested to be the best for describing the primary transient creep behavior, because the pre-parameter does not apparently change with elapsed time. The observed anelastic strains are 1/6 of the calculated elastic strains, and linear viscous behavior was identified from the logarithm plot of the anelastic strain rate versus anelastic strain （slope equals 1）. Therefore, the creep anelasticity is suggested to be due to the unbowing of there-dimensional network of dislocations.

Effect of pulse magnetic field on solidification structure and properties of pure copper

The application of pulse magnetic field to metal solidification is an advanced technique which can remarkably refine solidification structure. In this paper, the effect of pulse magnetic field on solidification structure, mechanical properties and conductivity of pure copper was experimentally investigated. The results showed that the solidification structure transformed from coarse columnar crystal to fine globular crystal with increasing pulse voltage. Increasing pulse voltage also improved the tensile strength. However, with the increase of pulse voltage, the elongation and electrical resistivity firstly decreased, then increased when the pulse voltage beyond a critical value. Moreover, in some conditions, pulse magnetic field can simultaneously improve the conductivity and mechanical property of pure copper.

Effects of microrolling parameters on the microstructure and deformation behavior of pure copper

Microrolling experiments and uniaxial tensile tests of pure copper under different annealing conditions were carried out in this paper. The effects of grain size and reduction on non-uniform deformation, edge cracking, and microstructure were studied. The experimen- tal results showed that the side deformation became more non-uniform, resulting in substantial edge bulge, and the uneven spread increased with increasing grain size and reduction level. When the reduction level reached 80% and the grain size was 65 μm, slight edge cracks occurred. When the grain size was 200 μm, the edge cracks became wider and deeper. No edge cracks occurred when the grain size was 200 μm and the reduction level was less than 60%; edge cracks occurred when the reduction level was increased to 80%. As the reduction level increased, the grains were gradually elongated and appeared as a sheet-like structure along the rolling direction; a fine lamellar structure was obtained when the grain size was 20 lam and the reduction level was less than 60%.

Work hardening of adhesively bonded pure copper single lap joints

To explain the reason why work hardening occurs in epoxy adhesive bonded zone of pure copper adherends after tensile shear strength testing, an elasto-plastic finite element model was established to analyze the effect of different adherends thickness of 2mm and 4mm on the shear strength as well as the level of work hardening in copper adherends of single lap joint. The numerical simulation results show that the axial or equivalent stress overrun the yield strength of the pure copper adherend is the main reason why the work hardening occurs on the bonded zone of the adherends after the shear strength testing. The elasto-plastic finite element simulation results are agreed with the experimental ones. The thicker its adherends are, the more serious the work hardening is.

Microstructure and mechanical properties of laser welded joints of pure copper and 304 stainless steels

A continuous wave diode laser with an output power of 2.8 kW was used to join pure copper and 304 stainless steel with a thickness of 1 mm. The focused laser beam with a diameter of O. 8 mm was irradiated on the copper side of the butt joints. In process of laser welding, effects of processing primary parameters on tensile strength of the joints were investigated. The interfacial characterizations of the joints were investigated by metallographic microscope, scanning electron microscope （SEM） and energy dispersive X-ray spectroscope （EDS）. The results showed that the element diffusion and solution occur and metallurgical bonding was achieved between pure copper and 304 stainless steel. The maximum tensile strength of the joints was 209 MPa when the laser power of welding was 2. 4 kW and welding speed was 12 mm/s.

Microstructure and properties of pure iron/copper composite cladding layers on carbon steel

In the present study, pure iron/copper composite metal cladding was deposited onto carbon steel by tungsten inert gas welding. The study focused on interfacial morphological, microstructural, and mechanical analyses of the composite cladding layers. Iron liquid–solid-phase zones were formed at copper/steel and iron interfaces because of the melting of the steel substrate and iron. Iron concentrated in the copper cladding layer was observed to exhibit belt, globule, and dendrite morphologies. The appearance of iron-rich globules indicated the occurrence of liquid phase separation（LPS） prior to solidification, and iron-rich dendrites crystallized without the occurrence of LPS. The maximum microhardness of the iron/steel interface was lower than that of the copper/steel interface because of the diffusion of elemental carbon. All samples fractured in the cladding layers. Because of a relatively lower strength of the copper layer, a short plateau region appeared when shear movement was from copper to iron.

Electrolytic Sampling from Pure Copper and Common Brasses Ⅰ: Calculation of the Mass Dissolved from the Samples according to Faraday's Law

In a procedure for electrolytic dissolving pure copper and common brasses, the approximate electrochemical mole mass(k) of the sample was determined in accordance with the brand of the sample, a stitable electrolyte was selected to make the current efficiency equal to 100%, and then the dissolved mass of samples was calculated according to Faraday's law(m=klt).Three representative samples were sampled by the electrolytic dissolution method and the calculated dissolved amounts were equal to the values by weighing the anode.The cxperimental results of zinc and copper in the anode liquor are in agreement with certified values.

噻唑化合物对铜在硫酸中的缓蚀行为研究

利用失重法、极化曲线和电化学阻抗谱等方法研究2,5-二巯基-1,3,4-噻唑(DMTD)对纯铜在0.5 M的硫酸中的缓蚀作用。通过失重法研究缓蚀效果,并以其实验数据探讨吸附模型;采用极化曲线和电化学阻抗图谱研究缓蚀剂性能及机理。失重结果表明四种实验温度下DMTD均可明显减缓纯铜在硫酸溶液中的腐蚀,DMTD分子吸附满足Langmuir等温线;电化学分析可知DMTD抑制纯铜阴阳极腐蚀反应;随着DMTD浓度的增大,吸附膜层缓蚀性能增强;表面形貌观察分别证实了DMTD的缓蚀作用。2,5-二巯基-1,3,4-噻唑(DMTD)可有效抑制纯铜在0.5 mol·L^(-1)的硫酸中的腐蚀。

A gradient nano/micro-structured surface layer on copper induced by severe plasticity roller burnishing

In order to investigate a gradient nano/micro-structured surface layer on pure copper produced by severe plasticity roller burnishing （SPRB） and grain refinement mechanism, the microstructure characteristics and material properties of sample at various depths from the topmost surface were investigated by SEM, TEM, XRD, OM etc. The experimental results show that the gradient nano/micro-structure was introduced into the surface layer of over 100μm in thickness. The remarkable increase in hardness near the topmost surface was mainly attributed to the reduced grain size. The equiaxed nano-sized grains were in random orientation and the most of their boundaries were low-angle grain boundaries （LAGBs）. The coarse grains are refined into the few micro-sized grains by dislocation activities;deformation twinning was found to be the primary form for the formation of submicron grains;the formation of nanostructure was dominated by dislocation activities accompanied with rotation of grains in local region.

稀土Y对铜线材抗氧化行为的影响机理研究

目的针对纯铜线材的抗氧化性能不足问题,通过稀土微合金化制备了含微量Y元素的铜线材,研究稀土Y含量对铜线材抗氧化性能的影响。方法采用扫描电子显微镜(SEM)、EDS能谱仪和X射线衍射仪等表征手段,分析了氧化膜脱落后基体表面形貌以及稀土Y元素在氧化过程中的存在形式与氧化膜的生长过程,揭示了添加稀土元素Y提高纯铜抗氧化性能的作用机理。结果稀土Y的引入提高了纯铜线材的抗氧化性能,在600℃、10 h条件下,Cu-0.03Y线材相对于Cu线材氧化增重率由0.55%降低至0.2%,降幅达63%。稀土元素Y的添加使铜线材的(100)晶面占比减少,(111)晶面占比增多,基体表面易被活化的(100)原子面占比降低,铜线材的抗氧化性能提高。在Cu-0.1Y线材中稀土元素浓度较高时发生偏聚,稀土元素与氧的亲和力大于铜与氧的亲和力,偏聚处形成不连续的稀土氧化物,使氧离子与铜离子的接触反应面积增大,相比Cu-0.03Y线材抗氧化性能降低。结论氧化过程中稀土离子的扩散速率慢、半径大,对铜离子的向外扩散起到阻碍作用,降低了铜离子的扩散速度,提高了铜线材的抗氧化性能。

蓝光激光熔覆纯铜覆层的组织及性能

纯铜材料对红外波段的激光吸收率较低,难以进行传统红外激光熔覆,因此限制了纯铜材料在表面防护领域的应用。本研究采用蓝光激光熔覆技术制备纯铜涂层,通过理论计算结合实验验证获得了其制备工艺参数。随后对纯铜熔覆层的微观组织、显微硬度和摩擦磨损行为进行分析,并结合XRD和EDS研究了蓝光激光熔覆制备的纯铜涂层的元素分布和物相组成。结果表明:采用蓝光激光熔覆技术制备的纯铜材料具有较大的工艺窗口,可获得成形良好的熔覆层。蓝光激光熔覆后,熔覆界面处出现了明显的金属间化合物相NiCu_(4)以及FeCu_(4)。纯铜熔覆层的显微硬度小于基体材料,并且在结合界面存在明显的硬度变化过渡区域,因此涂层和基体之间的稀释区较大。在室温干摩擦磨损条件下,熔覆层的磨损行为以粘着磨损为主,磨粒磨损为辅,并且存在明显的氧化磨损。

红壤模拟液中单宁酸对铜的缓蚀作用

采用动电位极化曲线和电化学阻抗谱研究了酸性红壤模拟液中单宁酸对纯铜接地材料腐蚀行为的影响。结果表明:当单宁酸质量浓度为0.1~4.0g/L时,随着单宁酸质量浓度的增加,其对铜的缓蚀效率增大;添加单宁酸可有效抑制铜的腐蚀反应过程;在该土壤模拟溶液体系中,单宁酸属于一种阴极缓蚀剂。Mott-Schottky曲线分析结果表明,在酸性红壤模拟液中,铜表面生成的膜具有p型半导体性质,随着单宁酸质量浓度增加,受主浓度降低,铜表面膜层的耐蚀性更强。单宁酸分子在铜表面的吸附最趋向Langmuir吸附模型,当单宁酸质量浓度为0.1~4.0g/L时,其在铜表面的吸附自由能小于0,大于-40kJ/mol,单宁酸在铜表面发生的是自发进行的物理吸附过程。

微合金化元素对纯铜热稳定性和导电性的影响

利用光学显微镜(OM)、透射电镜(TEM)和电导率测试等研究了添加微量合金化元素对4N纯铜的晶粒尺寸热稳定性和导电性的影响,分析了合金元素与基体中微量杂质元素S的相互作用。结果表明:添加微量Ti元素及微量Cr、Ni和Ag元素均可显著提高4N纯铜晶粒尺寸的热稳定性,经900℃×30 min高温处理后,Cu、Cu-Ti和Cu-Cr-Ni-Ag的晶粒尺寸分别为158.57、86.06和48.35μm,即热稳定性Cu-Cr-Ni-Ag>Cu-Ti>Cu。同时,添加微量合金化元素后纯铜的导电率仍较高,Cu、Cu-Ti和Cu-Cr-Ni-Ag导电率分别为101.87、101.64和99.98%IACS。分析认为热稳定性的提高主要与TiS相、CrS相的钉扎以及Ni和Ag固溶拖拽有关,微量Ti和Cr可与杂质S反应形成六方结构TiS相和单斜结构CrS相,且均与基体呈非共格关系,特别是CrS相较TiS相更为细小、数量更多。

超/特高压直流输电工作环境中纯铜部件点蚀行为

超/特高压输电是实现全球能源互联的核心技术。作为应用最广泛的输电系统导体材料,铜及铜合金的耐蚀性被重点关注。在超/特高压直流输电过程中,周围环境存在较大磁场,导致铜部件的服役环境与普通输电环境不同。采用动电位极化、电化学阻抗谱和元素分析等方法对纯铜在超/特高压环境下的电化学腐蚀行为进行了研究。结果表明:在超/特高压环境下,纯铜在3.5%NaCl溶液(质量分数)中的极限扩散电流高于无磁场条件下的极限扩散电流,并且无磁场条件下的反应电阻比施加了0.1 T磁场条件下的反应电阻明显提高。结合电化学阻抗谱、X射线衍射及元素分析可知,0.1 T磁场会使纯铜的耐蚀性降低,主要腐蚀产物为氧化亚铜。

多道次连续挤压对铜组织和性能的影响

连续挤压技术是一种高效率、节能和成本低廉的绿色塑性成型的方法,其最大特点就是利用了摩擦力作为驱动力和热源,大大减低了生产成本。选择Φ8 mm纯铜进行多道次重复连续挤压,实验设备型号为TLJ250连续挤压机,挤压轮转速选取为6 r/min。实验结束后,分别对经1~3道次连续挤压后的铜产品进行拉伸试验、硬度试验以及金相组织的观察。经过多道次连续挤压后,纯铜粗大晶粒都发生了不同程度的破碎,形成数量众多且等轴细小的均匀晶粒。第2道次延伸率较第1道次提升4.6%,第3道次较第1道次提升4.9%。但是,第2道次的抗拉强度比第1道次降低12.96 MPa,第3道次比第1道次的抗拉强度降低11.65 MPa。纯铜产品的硬度值经过多道次连续挤压后,略有增加。

高纯铜带耐高温性能的研究进展

随着5G电子通信、新能源汽车等产业的发展,高纯铜带在电子器件中的应用愈来愈广泛,同时电子器件封装、热沉等技术发展对其提出了苛刻的耐高温性能要求。高纯铜带对杂质控制要求非常严格,不能采用第二相来调控耐高温性能,因此是当前研究的一大难点。本文综述了高纯铜带耐高温性能的最新研究进展,从制备工艺和组织控制两个角度出发,着重探讨了电解、压延、气相沉积制备的高纯铜带高温下晶粒长大机理的研究进展,针对织构和晶界工程对高纯铜带耐高温性能当前存在的问题和解决办法进行了讨论,并对其发展方向进行了展望。