Texture evolution and grain refinement of ultrafine-grained copper during micro-extrusion

Samples of oxygen-free high conductivity (OFHC) coarse-grained (CG) and ultrafine-grained (UFG) copper were micro-extruded to an equivalent strain of 2.8 in one pass at room temperature. Samples of the OFHC copper were annealed at 650°C for 2?h to produce CG copper. Some samples were subsequently processed by equal channel angular pressing of eight passes, route Bc, at room temperature to produce the UFG material. Crystallographic texture and misorientation distributions were obtained locally from EBSD mappings at different radial positions after micro-extrusion. To model the strain path during micro-extrusion, the analytic flow line model of Altan et al. [J Mater. Process. Tech. 33 (1992) p.263] was used and also validated by finite element calculations. Modelling was carried out using the viscoplastic self-consistent (VPSC) model and a recently developed grain refinement model. The results showed large texture variations along the cross-section of the extruded sample for both UFG and CG copper. These cyclic drawing textures in UFG copper were simulated in good agreement with experiments using the presented modelling framework.     

EBSD FEG-SEM, TEM and XRD techniques applied to grain study of a commercially pure 1200 aluminum subjected to equal-channel angular-pressing

Microstructural evolution due to equal-channel angular-pressing (ECAP) with increasingly severe deformation was investigated in a commercially pure 1200 aluminum alloy. A true strain of eight produced sub-micrometer scale grains and very fine subgrains in the grain interior. The deformation process was documented and described using field-emission (FEG) gun scanning and transmission electron microscopy techniques. After eight ECAP passes, the high-angle grain boundaries accounted for approximately 70% of all boundaries. The fine spacing resolution of FEG scanning electron microscopy allowed detailed grain and subgrain statistical evaluation in the deformed microstructure; transmission electron microscopic inspection afforded appreciation of the role of very low-angle misorientation boundaries in the microstructure-refining process. ECAP results were compared with those produced by cold rolling. The material's texture evolved in a decreasing trend of Cube {001}100 intensities in favor of Cube rotated toward the normal-to-pressing direction {001}120, while Goss {110}001 and {111}110, {111}112 directions slightly increased with strain.     

Grain refinement and strengthening of a Cu–0.1Cr–0.06Zr alloy subjected to equal channel angular pressing

Abstract

The grain refinement and mechanical properties of a Cu–0.1Cr–0.06Zr alloy subjected to equal channel angular pressing (ECAP) at a temperature of 673 K were examined. The microstructure evolution was characterised by the development of a large number of low-angle subboundaries at small strains. An increase in the true strain resulted in gradual transformation of low-angle subboundaries into high-angle grain boundaries that was assisted by the deformation micro-banding. The development of new ultra-fine grains was considered as a kind of continuous dynamic recrystallization, the kinetics of which was characterised by a sigmoid-type dependence on strain and could be expressed by a modified Johnson–Mehl–Avrami–Kolmogorov equation. ECAP led to significant strengthening of the alloy. The yield strength increased from 105 MPa in the initial state to 390 MPa after 8 ECAP passes. A modified Hall–Petch relationship was applied to analyse the contributions of grain refinement and dislocation density to the overall strengthening. In spite of significant strengthening, the electro-conductivity remained at a level of 80% IACS.     

Study of the grain-boundary structure in submicrocrystalline niobium after equal-channel angular pressing

The method of Mössbauer emission spectroscopy on ^119m Sn nuclei was used to study grain boundaries in submicrocrystalline Nb produced by the method of equal-channel angular pressing (ECAP) of poly-crystalline Nb (99.9%). ECAP included 16 passes at room temperature.     

7050铝合金等通道转角挤压过程中显微结构和力学性能演化的小角x射线散射研究

采用三种等通道转角挤压（ECAP）与热处理相结合的工艺制备了超高强度细晶7050铝合金， 应用小角x射线散射技术定量地分析了ECAP过程中显微结构参数的变化情况，合理地解释了E CAP过程中力学性能的变化，揭示了合金强化机理. 研究发现，“固溶淬火＋ECAP＋时效” 工艺是获得高性能7050铝合金的合适工艺，可以使7050铝合金的抗拉强度提高到677 MPa， 延伸率保持在15％左右. 关键词： 7050铝合金 小角x射线散射 显微结构 力学性能     

Microstructural characterization of ultrafine-grain interstitial-free steel by X-ray diffraction line profile analysis

This paper highlights the microstructural features of commercially available interstitial free (IF) steel specimens deformed by equal channel angular pressing (ECAP) up to four passes following the route A. The microstructure of the samples was studied by different techniques of X-ray diffraction peak profile analysis as a function of strain (ε). It was found that the crystallite size is reduced substantially already at ε=2.3 and it does not change significantly during further deformation. At the same time, the dislocation density increases gradually up to ε=4.6. The dislocation densities estimated from X-ray diffraction study are found to correlate very well with the experimentally obtained yield strength of the samples.     

Formation mechanism of nanostructures in austenitic stainless steel during equal channel angular pressing

An ultra-low carbon austenitic stainless steel was successfully pressed from one to eight passes by equal channel angular pressing (ECAP) at room temperature. By using X-ray diffraction, optical microscopy and transmission electron microscopy, the microstructural evolution during ECAP was investigated to reveal the formation mechanism of strain-induced nanostructures. The refinement mechanism involved the formation of shear bands and deformation twins, followed by the fragmentation of twin lamellae, as well as successive martensite transformation from parent austenitic grains with sizes ranging from microns to nanometres through the processes γ(fcc)?→?ε(hcp)?→?α′(bcc). After pressing for eight passes, two types of nanocrystalline grains were achieved: (a) nanocrystalline austenite with a mean grain size of ～31?nm and (b) strain-induced nanocrystalline α′-martensite with a size of ～74?nm. The formation mechanisms are discussed in terms of microstructural subdivision via deformation twinning and martensite transformation.     

Synthesis of copper alloys with extended solid solubility and nano Al2O3 dispersion by mechanical alloying and equal channel angular pressing

Cu–4.5 wt % Cr and Cu–4.5 wt % Cr–3 wt % Ag alloys, with and without nanocrystalline Al₂O₃ dispersions (particle size <10 nm), were synthesized by mechanical alloying/milling and consolidated by equal-channel angular pressing (ECAP) at ambient temperature. Microstructural characterization and phase analysis by X-ray diffraction, as well as scanning and transmission electron microscopy, provided evidence for the formation of a Cu-rich extended solid solution with nanometric (<30 nm) crystallite size after 25 h of milling, with uniformly dispersed alumina nanoparticles embedded in it. Consolidation of Cu–4.5 wt % Cr–3 wt % Ag alloy with 10 wt % nanocrystalline Al₂O₃ by eight ECAP passes was shown to result in a composite with an exceptionally large hardness of 390 VHN and enhanced wear resistance. The electrical conductivity of the pellets of the latter alloy without Al₂O₃ is about 30% IACS (international annealing copper standard), whereas pellets with 5 or 10 wt % Al₂O₃ dispersion exhibit a conductivity of about 20–25% IACS. Thus, the present room temperature synthesis and consolidation route appear to offer a promising avenue for developing high-strength, wear/erosion-resistant Cu-based electrical contacts with nano-ceramic dispersion.     

Enhanced corrosion resistance and cellular behavior of ultrafine-grained biomedical NiTi alloy with a novel SrO-SiO2-TiO2 sol-gel coating

NiTi alloy has a unique combination of mechanical properties, shape memory effects and superelastic behavior that makes it attractive for several biomedical applications. In recent years, concerns about its biocompatibility have been aroused due to the toxic or side effect of released nickel ions, which restricts its application as an implant material. Bulk ultrafine-grained Ni50.8Ti49.2 alloy (UFG NiTi) was successfully fabricated by equal-channel angular pressing (ECAP) technique in the present study. A homogeneous and smooth SrO-SiO₂-TiO₂ sol-gel coating without cracks was fabricated on its surface by dip-coating method with the aim of increasing its corrosion resistance and cytocompatibility. Electrochemical tests in simulated body fluid (SBF) showed that the pitting corrosion potential of UFG NiTi was increased from 393 mV(SCE) to 1800 mV(SCE) after coated with SrO-SiO₂-TiO₂ film and the corrosion current density decreased from 3.41 μA/cm² to 0.629 μA/cm². Meanwhile, the sol-gel coating significantly decreased the release of nickel ions of UFG NiTi when soaked in SBF. UFG NiTi with SrO-SiO₂-TiO₂ sol-gel coating exhibited enhanced osteoblast-like cells attachment, spreading and proliferation compared with UFG NiTi without coating and CG NiTi.     

TEM studies of structure in OFHC copper processed by equal channel angular rolling

In this study, UFG (ultrafine-grained) structure formed through ECAR (equal-channel angular rolling) process has been studied by methods of electron microscopy. The microstructure, mechanical properties and microhardness were investigated in OFHC (oxygen free high conductivity) copper after 1st–13th passes. The interpretation of microstructure changes was performed using a model which describes mechanism of UFG structures formation. It was found that ECAR is a tool used for the purpose of achieving significant structural refinement resulting in a final grain size d ～ 400 nm. Moreover, this method provides such specific structural changes which have highly advantageous influence on mechanical properties (yield stress, ultimate tensile strength, reduction of area) as well as microhardness.     

Al-Mn-Ce quasicrystalline composites: Phase formation and mechanical properties

Aluminium-based composites with quasicrystalline particles as reinforcements were synthesized via the powder metallurgy processing route. In order to obtain bulk samples with a nanoscale microstructure most equivalent to that resulting from rapid solidification, powders of Al-Mn-Ce alloys were prepared by pulverization of melt-spun ribbons using a planetary ball mill. Significant differences in the phase formation upon quenching, composite microstructure and thermal stability of the microstructure were found for different alloy compositions. Severe grain growth during the subsequent consolidation by hot extrusion caused the formation of a micrometre-scale composite instead of the nanoscale phase mixture initially existing after rapid solidification. After hot extrusion, the specimens were deformed by compression at a constant compression rate at room temperature. With an ultimate strength of up to 975 MPa and a ductility of more than 4% the material yields excellent properties compared with conventionally produced aluminium-based alloys.     

Three-dimensional quantification of texture heterogeneity in single-crystal aluminium subjected to equal channel angular pressing

Abstract

A three-dimensional crystal plasticity finite element method (3D CPFEM) modelling of a real equal channel angular pressing (ECAP) process for investigating the mechanical properties and texture evolutions of single-crystal aluminium has been developed for the first time. The challenge of modelling such a severe plastic deformation via 3D CPFEM is how to accurately predict the deformation mechanism under the complicated contact conditions between a billet and a die. The validation by comparison with experimental observations demonstrates that the developed 3D CPFEM ECAP model is able to precisely capture the deformation characteristics at the microscale. Furthermore, this research clarified the previously remaining disputes such as the microstructural formation mechanism in the deformed area and the deformation nature in the plastic deformation zone. It is also the first time to extensively discuss the orientation-dependent deformation feature of the ECAP-processed billets, including morphology, lattice rotation angle and grain refinement.     

Quasi-static deformation and final fracture behaviour of aluminium alloy 5083: influence of cryomilling

The commercial aluminium alloy 5083 was processed via cryomilling to produce nanocrystalline (NC) powders with an average grain size of ～25–50?nm. The powders were subsequently degassed at 723 K (450°C), pre-heated and immediately quasi-isostatic (QI)-forged to produce a thermally stable bulk ultrafine grain (UFG) material having average grain size values ranging from 190 to 350?nm, depending on the processing conditions used. In this paper, the tensile properties and fracture behaviour of the bulk UFG material are presented and compared with the tensile properties of its conventionally processed counterpart. The specific influence of preheat temperature on strength and ductility of the alloy is briefly discussed. Three different pre-heat temperatures of 523, 623 and 723?K (250, 350 and 450°C) were chosen and used with the primary objective of controlling grain growth during forging. The influence of preheat temperature on tensile deformation and final fracture behaviour is highlighted. The macroscopic fracture modes of the bulk nanostructured material (BNM) prepared following three pre-heat temperatures are investigated. The microscopic mechanisms controlling tensile deformation and final fracture behaviour are discussed with regards to the intrinsic microstructural effects in the UFG alloy, nature of loading, and the kinetics and mechanisms of deformation.     

Mechanical properties of ferrite-perlite and martensitic Fe–Mn–V–Ti–C steel processed by equal-channel angular pressing and high-temeperature annealing

Using the method of equal-channel angular pressing (ECAP), submicrocrystalline structure is formed in lowcarbon Fe–Mn–V–Ti–C steel with the average grain size 260 nm in the ferrite-perlite state and 310 nm in the martensitic state. It is established that the ECAP treatment gives rise to improved mechanical properties (H_μ = 2.9 GPa, σ₀ = 990 MPa in the ferrite-perlite and H_μ = 3.7 GPa, σ₀ = 1125 MPa in martensitic states), decreased plasticity, and results in plastic flow localization under tensile loading. The high strength properties formed by the ECAP are shown to sustain up to the annealing temperature 500°C.     

Annealing behaviour of ultrafine-grained aluminium

Ultrafine-grained (UFG) aluminium, processed under fast cooling rate conditions (12?K?s^?1) following hot rolling (water quenched) exhibits enhanced thermal stability due to an increase in concentration of solid solution atoms, relative to the furnace cooled material. The influence of fraction recrystallized on yield stress and uniform elongation is reported to exhibit a slight deviation from the linear behaviour that is anticipated on the basis of the rule-of-mixtures. This result was rationalized on the basis of differences in the spatial distributions of the UFG and coarse grains and/or dislocation recovery mechanisms.     

Relaxation and hysteresis internal friction in ultra-fine-grained copper at temperatures of up to 400°C

The temperature- and amplitude-dependent internal friction and elastic moduli of copper samples (99.95% Cu) subjected to deformation by equal channel angular pressing with a pass number of 1, 4, and 8 along the Bc route in the hertz range of loading frequencies at room temperature and temperatures of up to 400°C are investigated. The effect of deformation and subsequent recrystallization on the parameters of thermally activated internal friction peaks due to grain-boundary relaxation and the recrystallization of intensively deformed copper, and on amplitude-dependent internal friction due to dislocation hysteresis, is determined.     

Mechanism for improvement in mechanical and thermal stability in dispersed phase polymer composites

We report substantial improvement in the mechanical stability, thermal stability, and conductivity of four series of ion-conducting dispersed phase composite polymer electrolytes (CPEs). Tensile strength of filler-dispersed composite films was ≥2 MPa in contrast to ~1 MPa for undispersed polymer–salt complex. Similarly, elongation at break has shown an increase by ~200–300% in the composite films. Filler-induced enhancement in thermal and mechanical stability has clearly been noticed. The improvement in the mechanical stability is also accompanied by a corresponding increase in electrical conductivity in the composite films by 1–2 orders of magnitude at lower (2 wt.%) of the filler loading. A mechanism for the improvement in mechanical stability has been proposed. The strength of the mechanism lies in evidenced polymer–filler interaction among the composite components. Suppression of thermal degradation and increased mechanical strength of the CPEs on filler addition has been explained on the basis of transient cross-linking of the polymeric segments and filler–polymer bridging effect.     

The effect of hardening by annealing in ultrafine-grained Al–0.4Zr alloy: influence of Zr microadditives

Influence of annealing on the microstructure and mechanical properties has been studied for Al–Zr (0.4 wt.%) alloy with the ultrafine-grained (UFG) structure formed by high-pressure torsion (HPT) at room temperature. A drastic hardening effect by short-term annealing in the temperature range of 90–280°С was observed for the HPT-processed Al–Zr alloy. The effect of hardening by annealing for the HPT-processed Al–Zr alloy is compared with that for the HPT-processed commercial purity (CP) Al. It was shown that addition of 0.4 wt.% Zr in Al does not cause a significant impact on the magnitude of hardening by annealing up to 150°С, however it leads to a shift of its maximum to higher annealing temperatures and expansion of the thermal stability range of strength up to 280°С. The kinetics of hardening by annealing for CP Al and Al–Zr alloys in the UFG state has been studied for the first time. It was shown that in both materials the strength first increases linearly with the duration of annealing and then reaches saturation. The temperature dependence of the rate of hardening by annealing was analysed through an Arrhenius law, and apparent activation energy was extracted for both systems. The addition of Zr results in the reduction of the activation energy of annealing-induced hardening by ～2 times. Possible physical mechanisms controlling the kinetics of hardening by annealing are discussed for the ultrafine-grained CP Al and Al–Zr alloy.     

铜铝复合管在空调器室内外机连接管中应用的试验研究

主要针对铜铝复合管在家用空调器室内外机连接管的应用替代铜管进行了试验研究。从力学性能、弯曲性能、工艺性、耐压性和耐腐蚀能力几个方面分别对Φ6.35×0.6、Φ9.52×0.7和Φ12.7×0.8的三种型号铜铝复合管连接管进行性能试验。结果表明:三种型号的铜铝复合管连接管延伸率都大于40%,不低于铜管的延伸率,抗拉强度在150～180MPa之间具有良好的弯曲性能,扩口率在65～89%之间,不低于铜管的扩口率(≥50%)。三种规格的铜铝复合管安全承受压力均大于常用制冷剂R22和R410a所要求的耐压强度。经过500h的盐雾实验后,压力测试焊接点无泄漏。最大承受压力超过15MPa,满足空调室内外连接管的使用要求。同时将三种规格的铜铝复合管接入空调器在焓差实验室进行性能测试,表明:与原机型铜连接管相比,使用铜铝复合管连接管的空调器制热量、制冷量和能效比的变化低于1%,对空调器的性能基本没有影响。与铜管相比,在相同条件下,可以降低成本23～35%。