Microstructure, mechanical properties and electrical conductivity of industrial Cu-0.5%Cr alloy processed by severe plastic deformation

Microstructure, mechanical properties and electrical conductivity of industrial Cu-0.5% alloy subjected to equal channel angular pressing (ECAP) by route A and cold rolling with and without aging treatment were investigated. The lamellar grains in thickness of 100 nm were obtained after eight ECAP passes. They were not further pancake shaped, but fragmentary and obtained less sharp boundaries with more dislocations in addition to cold rolling. After aging at 450 °C for 1 h, high density of dislocations and some coarse grains were observable after ECAP and the additional cold rolling, respectively. The tensile tests show that tensile strength arrived at 460 MPa and 484 MPa after four and eight passes of ECAP, respectively, the corresponding tensile strength increased to 570 MPa and 579 MPa after the additional cold rolling. However, the electrical conductivity was not more than 35% IACS. It was proved that four passes of ECAP followed by 90% cold rolling and aging at 450 °C for 1 h offered a short process for Cu-0.5%Cr alloy to balance the paradox of high strength and electrical conductivity, under which the tensile strength 554 MPa, elongation to failure 22% and electrical conductivity 84% of IACS could be obtained. The high strength was explained by precipitation strengthening and fine grain strengthening.     

Texture and microstructure evolution in ultrafine-grained AZ31 processed by EX-ECAP

Extruded AZ31 alloy was processed by equal channel angular pressing (ECAP) up to 12 passes at 180 °C following route B_c, i.e. rotating the sample 90° between individual passes. Microstructure evolution was investigated using EBSD and TEM, as a function of strain imposed by ECAP. The first ECAP pass resulted in the formation of a new texture component which relates to the bimodal grain structure observed in this specimen. The grains larger than 10 μm show the orientation changes corresponding to the ECAP shear, which is characterised by the rotation of the basal poles by approximately 40° from the initial orientation. The fine grains with the average size of 1 μm maintain the initial orientation. The character of the bimodal grain structure and the distinct texture components between large and small grains remained unchanged up to 4 ECAP passes. Further ECAP pressing to 8 and 12 passes leads to a grain refinement through the whole sample volume and the orientation changes of all grains corresponding to the ECAP shear.     

Grain refinement in as cast Al–Mg–Mn alloy during high temperature equal channel angular pressing

Abstract

An as cast Al–Mg–Mn alloy with coarse equiaxed grain structure was processed by equal channel angular pressing (ECAP) at 350°C up to eight passes. Systematic studies were made on the microstructural evolution during ECAP by optical microscopy, electron backscattered diffraction and TEM. Equal channel angular pressing led to a considerable grain refinement, resulting in an average cell size of about 1 μm and a fraction of high angle boundaries of 75% after eight pressing passes. Deformation bands were not developed during the ECAP process, and a reasonably equiaxed substructure was obtained even after one pass. The main mechanism of grain refinement was attributed to the continuous dynamic recrystallisation based on the motion of deformation induced dislocations. Discontinuous recrystallisation at grain boundaries and triple junctions also contributed to the refinement, which played an important role especially at high strain of eight passes.     

Ultra-fine grained bulk CP-Ti processed by multi-pass ECAP at warm deformation region

In order to refine the grain size of commercially pure titanium (CP-Ti) to a submicrometer scale, equal channel angular pressing (ECAP) was attempted at a temperature range of 200–300 °C. The experiments revealed that, 250 °C was the minimum temperature at which ten passes of ECAP could be performed in a 105° die without the cracking of billets. An ultrafine-grained (UFG) microstructure with a mean grain size of 183 nm was achieved after 10 passes. The processed CP-Ti displayed high tensile strength of 892 MPa and high elongation to failure of 20.5%. The enhancement in mechanical properties is explained in terms of grain refinement and dislocation density increasing. The high ductility of UFG pure Ti with the absence of strain hardening behavior is attributed to its enhanced strain rate sensitivity.     

Microstructure and mechanical properties of ultrafine grain ZK60 alloy processed by equal channel angular pressing

The microstructure evolution and tensile properties of ZK60 magnesium alloy after equal channel angular pressing (ECAP) have been investigated. The results show that the two-step ECAP process is more effective in grain refinement than the single-step ECAP process due to the lower deformation temperature, a mean grain size of ~0.8 μm was obtained after two-step ECAP process at 513 K for four passes and 453 K for four passes. The EBSD examination reveals that ZK60 alloy after two-step ECAP process exhibits a more homogeneous grain size and misorientation distribution than single-step ECAP process. Both alloys after ECAP process present similar strong {0002} texture. The tensile strength of two-step ECAP alloy has also been improved compared with the single-step ECAP alloy. The strengthening effect was mainly ascribed to grain refinement.     

Microstructures and properties of ultrafine-grained pure titanium processed by equal-channel angular pressing and cold deformation

Equal-channel angular pressing (ECAP) has been used to refine the grain size of commercially pure (CP) titanium as well as other metals and alloys. CP-Ti is usually processed at about 400 degrees C because it lacks sufficient ductility at lower temperature. The warm processing temperature limits the ability of the ECAP technique to improve the strength of CP-Ti. We have employed cold deformation following warm ECAP to further improve the strength of CP-Ti. Ti billets were first processed for eight passes via ECAP route Bc, with a clockwise rotation of 90 degrees between adjacent passes. The grain size obtained by ECAP alone is about 260 nm. The billets were further processed by cold deformation (cold rolling) to increase the crystalline defects such as dislocations. The strength of pure Ti was improved from 380 to around 1000 MPa by the two-step process. This article reports the microstructures, microhardness, tensile properties, and thermal stability of these Ti billets processed by a combination of ECAP and cold deformation.     

Investigation on nanocrystalline iron‐cobalt‐vanadium alloy processed by equal channel angular pressing (ECAP)

Nanocrystalline iron‐cobalt‐vanadium alloy was fabricated by Equal‐Channel Angular Pressing (ECAP). Microstructural evolution at different passes of ECAP and the effect of φ in the ECAP were researched. The results revealed that a phase slowly turned to γ phase and followed the form of dislocation cells in the iron‐cobalt‐vanadium alloy with the increase of severe plastic deformation. At last, it became reasonably finer bands of subgrains. The results with intersect at an angle φ of 90° was better than with at an angle φ of 120°. After three passes of ECAP, at an angle φ of 90°, the nanocrystalline microstructure could be obtained. The grain size was reduced from 30 μm in the initial state to 400nm.     

Microstructure evolution and hardness variation during annealing of equal channel angular pressed ultra-fine grained nickel subjected to 12 passes

The microstructure, thermal stability and hardness of ultra-fine grained (UFG) Ni produced by 12 passes of equal channel angular pressing (ECAP) through the route Bc were studied. Comparing the microstructure and hardness of the as-ECAPed samples with the published data on UFG Ni obtained after 8 passes of ECAP through the route Bc reveals a smaller average grain size (230 nm in the present case compared with 270 nm in 8-pass Ni), significantly lower dislocation density (1.08 × 10¹⁴ m⁻² compared with 9 × 10¹⁴ m⁻² in 8-pass Ni) and lower hardness (2 GPa compared with 2.45 GPa for 8-pass Ni). Study of the thermal stability of the 12-pass UFG Ni revealed that recovery is dominant in the temperature range 150–250°C and recrystallisation occurred at temperatures >250 °C. The UFG microstructure is relatively stable up to about 400 °C. Due to the lower dislocation density and consequently a lower stored energy, the recrystallisation of 12-pass ECAP Ni occurred at a higher temperature (~250 °C) compared with the 8-pass Ni (~200 °C). In the 12-pass Nickel, hardness variation shows that its dependence on grain size is inversely linear rather than the common grain size^−0.5 dependence.     

Effect of equal channel angular pressing on fracture toughness of Al-7075

In this paper, influence of equal channel angular pressing (ECAP) on the fracture behavior of Al-7075 alloy is experimentally investigated. The specimens are successfully processed by ECAP methodology up to four passes using different routes. Transmission electron microscope (TEM) images showed that after four passes of ECAP, the average grain size is refined from 40 μm to less than about 500 nm. The percentage increase in yield strength, ultimate strength and microhardness of the specimens after four ECAP passes was 230, 90 and 110 respectively. Standard tests on the disk-shaped compact DC(T) specimens showed that fracture toughness is decreased up to 8% at the first ECAP pass while after four passes, this parameter roused to 17% higher than that of annealed condition. Furthermore, scanning electron microscope (SEM) micrographs demonstrated that ductile fracture mechanism with large dimples occurred in the annealed samples, changed to limited ductile fracture with fine dimples after ECAP process. This research provides new insights into the effect of ECAP and grain refinement on the fracture behavior of materials.     

Mechanical behaviour and texture of annealed AZ31 Mg alloy deformed by ECAP

Abstract

AZ31 Mg alloy samples were processed by equal channel angular pressing (ECAP) at 220°C for four passes. An average grain size of ～1·9 μm with reasonable homogeneity was obtained. The ECAP process imparted large plastic shear strains and strong deformation textures to the material. Subsequent annealing of the equal channel angular pressed samples produced interesting mechanical behaviours. While yield strength increased and ductility decreased immediately after undergoing ECAP, annealing at temperatures <250°C restored ductility significantly at a small decrease in of yield strength. Annealing at temperatures >250°C reduced yield strength without additional improvement in ductility. It is believed that the combination of stress relief via dislocation elimination, refined microstructure and the retention of a strong ECAP texture at low annealing temperatures enhance ductility. High temperature annealing breaks down the ECAP texture resulting in no further improvement in ductility. The results show that the mechanical properties of the alloy can be positively influenced by annealing after ECAP to achieve a combination of strength and ductility.     

Microstructure and strength of pure Cu with large grains processed by equal channel angular pressing

The pure Cu rods with an initial grain size of 410 μm were treated by using equal channel angular pressing (ECAP). The deformed microstructure and mechanical properties of ECAPed Cu samples were investigated. Special attention was paid on the refinement of grain size and local micromechanics of ECAPed Cu samples. The original coarse grains were refined to 320 μm after 4 passes. The final grains were composed of dislocation cells with a size of 500 nm–3 μm after 5–8 passes. The yield strength reached a saturation value of 368 MPa after 5 passes. The maps of microhardness distribution illustrated the inhomogeneity of local mechanical properties. The dislocation subdivision was the main deformation mode to refine the grain size, while twin fragmentation was restrained by dislocation slips for the reason of large initial grain size. Furthermore, the strengthening of ECAPed Cu was discussed.     

Twist-channel angular pressing: effect of the strain path on grain refinement and mechanical properties of copper

Substructural characteristics of Cu (99.97%) were examined after the Twist channel angular pressing (TCAP) process carried out at ambient temperature. Grain refinement efficiency and resulting thermal stability were evaluated after three passes with respect to utilization of various strain paths. Results were obtained using light microscopy and X-ray diffraction methods; Mechanical properties of extruded materials were also tested. Thermal stability was studied after application of three annealing cycles. Based on the findings, Bc route is the most efficient strain path with respect to the grain refinement; higher speed of extrusion (10 mm/s) corresponds with suppression of the static recrystallization. Measured strength, obtained after three passes (route A), achieved values around 440 MPa homogeneously along the cross section of the extruded material. Homogeneity of deformation was also confirmed by micro-hardness tests. The grain size, determined after three passes, averaged out 1.2 μm. Application of TCAP (three passes) brought markedly homogeneous deformation throughout the processed sample in comparison with classical ECAP process.     

Texture and mechanical properties of single crystal copper during equal channel angular pressing by route C

Single crystal copper has excellent electrical and thermal conductivity, but the lower strength seriously limited its application. Traditional strengthening methods, such as alloying, will severely damage its conductivity. Severe plastic deformation is the most effective methods for increasing the metals strength and not reducing the conductivity. The microstructure and texture evolution of single crystal copper (99.999 %) during equal channel angular pressing by route C was investigated by scanning electron microscopy, X‐ray diffraction, electron backscatter diffraction and transmission electron microscopy, the mechanical properties and conductivity were tested, and the influence mechanism of texture and microstructure on mechanical properties and conductivity were analyzed. The results show that during equal channel angular pressing, the original <111> orientation gradually changed to <001>, accompany lots of low‐angle grain boundaries were formed. With strain increasing, the high‐angle grain boundaries increased gradually, and the deformation bands with <110> orientation was formed in the single crystal structure, which plays a positive role on the conductivity. After 5 passes, the tensile strength of single crystal copper increased from 168 MPa to 415 MPa by route A and 385 MPa by route C, and the elongation declined sharply from 63 % to 30 % and 27.9 %, respectively. After 16 passes, the hardness increased from 60.4 HV to 130.8 HV and the conductivity only slightly down.

     

Investigation of texture and mechanical properties of copper processed by new route of equal channel angular pressing

The evolution of crystallographic texture and the mechanical properties of copper subjected to severe plastic deformation (SPD) using equal channel angular pressing (ECAP) were investigated. Samples were subjected to ECAP under two different processing routes: B₆₀ and B_C. As the cross sections of the samples were circular, a new route with a rotation angle of 60° in the same direction between consecutive passes was introduced. The material exhibited texture development similar to the simple shear texture in both routes and the most significant changes in texture strength in both processing routes took place after the second pass. Microstructure of ECAP processed samples were investigated using electron backscatter diffraction (EBSD) analysis. Comparison of the EBSD data with optical micrograph of the initial sample confirmed that ECAP process has led to a significant decrease in grain size. Significant increases in hardness and tensile strength were observed after the first pass of ECAP. Variations of tensile strength as a function of the number of passes were related to the dislocation densities and the average boundary spacing.     

Mechanical properties,microstructure and texture of single pass equal channel angular pressed 1050, 5083, 6082 and 7010 aluminum alloys with different dies

Four important commercial aluminum alloys, namely 1050, 5083, 6082 and 7010AA are processed through a single pass via two equal channel angular pressing (ECAP) dies with different geometries (die angles of 90° and 120°). Electron back scattered diffraction (EBSD) is applied on the flow plane of the processed samples. Large scans with a step size of 7 μm for grain size distribution and texture measurements, as well as small scans with a step size of 0.1 μm for determination of cell size distribution, were performed. Hardness and simple compression are employed to evaluate the mechanical properties of the ECAP processed samples. Shear bands in the ECAP processed 7010AA was a major feature that led to failure in all samples subjected to further simple compression. The hardness as well as the stress–strain behavior was similar in the ECAP processed 6082 and 5083AA. The die geometry and the strain involved in the single pass influenced the overall texture intensity developed in the wrought alloys (1050 and 5083AA) and had minimal influence on the texture intensity of the heat treatable alloys (6082 and 7010AA). Low angle grain boundaries dominated the microstructure of all alloys for all testing conditions.     

Ultrafine pure aluminium through back pressure equal channel angular consolidation (BP-ECAC) of particles

Pure Al particles were synthesised into bulk materials using back pressure equal channel angular consolidation (BP-ECAC) and further deformed up to 4 passes of ECAP at 100 °C with the application of 50 MPa in back pressure. Ingot metallurgy (IM) Al was processed under the same conditions to provide comparison. The microstructures were characterised using TEM for grain size and shape as well as misorientations. In general, the grains were finer and misorientations larger in the PM (powder metallurgy) materials than in the IM materials. The tensile strength of the PM materials was significantly higher than that of the IM materials. Different work hardening behaviours were observed between the materials after 1 pass and those after 4 passes.     

Significantly enhanced tensile strength and ductility in nickel aluminium bronze by equal channel angular pressing and subsequent heat treatment

Nickel aluminium bronze (NAB) was subjected to equal channel angular pressing (ECAP) at 400 °C for up to 4 passes in routes B_A and C, respectively, followed by isothermal heat treatment with a view to improving the κ phase structures and tensile properties. The lamellar κ_III structure was completely broken after 4 passes in route B_A although route C was less efficient. Spheroidisation and coarsening of the highly deformed κ_III continued during heat treatment especially at ≥600 °C. At 800 °C, both the lamellar structure and the fine κ_IV particles transformed completely into a coarse globular morphology with no distinction between the primary and eutectoid α. Significant increases in strength were achieved by ECAP, reaching a maximum yield strength of 960 MPa with a good ductility of ~14 %. Heat treatment after ECAP was shown to considerably improve tensile ductility to >30 % while keeping the strength high at ~700 MPa, a significant enhancement compared to the as-received NAB.     

超细晶铜力学和阻尼性能及微观结构研究

在众多阻尼材料中,金属阻尼材料既能满足高阻尼减振降噪性能,又具有较高的强度,是理想的阻尼材料.为了提高商业纯铜的力学性能,分析晶粒细化程度对纯铜力学性能和阻尼性能的影响,在室温下对商业纯铜棒进行12道次BC路径等通道转角挤压(ECAP)实验.对挤压后样品进行单轴微拉伸试验和高循环拉伸疲劳试验研究其力学性能;通过动态力学...     

Mechanical Properties,Fatigue Life,and Electrical Conductivity of Cu–Cr–Hf Alloy after Equal Channel Angular Pressing

Structure, mechanical, and service properties of a Cu–Cr–Hf alloy after quenching, equal‐channel angular pressing (ECAP), and subsequent aging have been studied. The positive effects of ultrafine‐grained structure formation (grain/subgrain size of ≈200 nm) during ECAP and strengthening particles precipitation upon subsequent aging at 450 °C on the mechanical and fatigue properties of the alloy are shown. Ultrafine‐grained Cu–Cr–Hf alloy after aging shows increasing in the fatigue limit on the basis of 10⁷ cycles from 185 to 375 MPa relative to that of the initial coarse‐grained state. The alloy after ECAP and aging also exhibits sufficient elongation to failure (11.4%) and good electrical conductivity (78%IACS).     

Effect of grain refinement on the mechanical properties of Cu–Al–Be–B shape memory alloy

In this work, the mechanical properties of equal channel angular processing (ECAP)-processed fine- and coarse-grained Cu–11.42Al–0.35Be–0.18B shape memory alloys (wt.%) were evaluated using tensile testing. After eight passes of ECAP and subsequently quenching from 600 °C to RT, the mean grain diameter was refined from 227 μm to 42 μm with grain boundaries purified. The fine-grained alloy exhibited good mechanical properties with a high tensile strength (703 MPa) and featured deeper and closer dimples on its fracture surface. The micro cracks were more refined, and the cracks extension along the grain boundaries was improved in the fine-grained alloy. These changes can be attributed to improvement of martensite morphology, structural refinement and grain boundary purification.