ECAPed Samples Research Articles

ZK60 alloy processed by ECAP: Microstructural, physical and mechanical characterization

Lately, magnesium alloys have been extensively investigated through severe plastic deformation (SPD) methods in order to extend their application to structural components. In the present work, as-extruded ZK60 magnesium alloy samples were subjected to 4 passes of equal-channel angular pressing (ECAP) at a processing temperature of 250°C, following route Bc. The microstructural evolution of the deformed grains was analyzed using electron back-scattered diffraction (EBSD). The Orientation Imaging Microscopy (OIM) maps, together with the grain boundary misorientation distribution showed a reduction in the grain size accompanied by a large proportion of high angle grain boundaries. Calorimetric analysis showed a slight increase in the recrystallization temperature of the ECAPed magnesium samples. Mechanical tests showed an improvement in the elongation-to-failure after 4 ECAP passes, which were about 2 times higher than in the as-extruded sample. Also a brittle to ductile transition was observed.

Ageing Characteristics of Equal Channel Angular Pressed Al-Mg-Si Alloy

This study investigated the effect of severe plastic deformation (SPD) and artificial ageing treatment on mechanical properties of cast Al-Mg-Si alloy. 6061-T6 aluminum alloy was remelted and casted into a rod of 13mm in diameter and 60mm in length. The rod samples were then subjected to equal channel angular pressing (ECAP) for SPD process, up to 2 passes, through Bc route. Cast and ECAPed samples were solution heat treated at 530 °C, quenched in water and held at 180 °C at various ageing time to determine the effect of artificial ageing. Cast alloy consisted of α phase grains that were surrounded by Mg2Si particles locating at the grain boundaries. The hardness increased with accumulative applied strain by 2-pass ECAP process with the value of 99.4 Hv. For heat treated samples, maximum hardness was achieved after 5-hour ageing.

Microstructures, mechanical behavior, cellular response, and hemocompatibility of bulk ultrafine‐grained pure tantalum

Bulk ultrafine-grained (UFG) pure Ta had been successfully prepared by equal channel angular pressing (ECAP) technique till eight passes. The 1st, 2nd, 4th, and 8th ECAPed Ta samples were investigated in the current study, with the 0th ECAPed Ta sample as the microcrystalline counterpart control. The microstructure and grain size distribution were characterized by X-ray diffractometer patterns, scanning electron microscopy, and transmission electron microscopy analysis by means of histogram. Although the mechanical behavior of all the experimental samples were analyzed through uniaxial tensile measurement and microhardness test, in vitro biological interactions onto the substrates such as protein adsorption, cellular responses derived from different types of cell lines, and the activity of erythrocyte and platelets were further evaluated and specifically assessed by bicinchoninic acid assay, enzyme-linked immunosorbent assay, and the method of colorimetric reading. A superior percentage of protein adsorption can be observed on the substrate of the UFG 8th ECAPed Ta (around 90%), even above those on the tissue culture plate (control) and the other ECAPed Ta samples. Furthermore, the UFG 8th ECAPed Ta shows no cytotoxic within 4 days culture when incubated with the murine fibroblast cell lines (L929). In addition, a priority order in the growth of endothelial cells (ECV304) other than vascular smooth muscle cells was observed in the case of the UFG 8th ECAPed Ta. In terms of hemolysis rate and adhered platelets (both the amount and the individual morphology), an evolutionary outcome of preferentially enhanced hemocompatibility can be concluded for the case of the UFG 8th ECAPed Ta.

Enhanced biodegradation behavior of ultrafine-grained ZE41A magnesium alloy in Hank's solution

The biodegradation behavior of an ultrafine-grained (UFG) magnesium alloy ZE41A containing rare-earth (RE), obtained through multi-pass of equal channel angular pressing(EACP), was investigated by electrochemical measurements in Hank's solution. The highest value of charge transfer resistance was obtained in the electrochemical impedance spectroscopy plots of the ECAPed samples with the largest pressing pass, while a movement of corrosion potential toward noble direction and a decrement of corrosion current density were observed in the potentiodynamic polarization curves of the ECAPed samples with further pressing passes. These results indicated that ECAP could be an efficient way to reduce the biodegradation rate of the ZE41A alloy.

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 410μm 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 320μm after 4 passes. The final grains were composed of dislocation cells with a size of 500nm–3μm after 5–8 passes. The yield strength reached a saturation value of 368MPa 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.

Wettability and In Vitro Bioactivity Studies on Titanium Rods Processed by Equal Channel Angular Pressing

Commercial purity titanium (CP-Ti) was processed by equal channel angular pressing (ECAP) with a channel angle of 120° with the aim of studying the effect of microstructure on the wettability and bioactivity. Solid and tubular Ti rods of 6 mm diameter were ECAPed at room temperature. During ECAP of tubular specimens, hydroxyapatite was filled in the tube. Grains and sub-grains of size approximately 1 μm were observed using transmission electron microscopy in both solid and tubular samples. Vickers microhardness measurements and surface energy calculations showed good improvement for ECAPed samples. This can be attributed to the fine grain structure achieved after processing. However, tubular sample showed marginally higher hardness and wettability. In vitro bioactivity studies carried out using 1.5× SBF indicate enhanced bioactivity in ECAPed samples. Also, cell response using rat skeletal muscle (L6) cells was found to be promising for both solid and tubular ECAPed specimens.

Hydrogen storage properties of pure Mg after the combined processes of ECAP and cold-rolling

Abstract Commercial Mg was processed by two combined processes: ECAP and cold rolling. Samples were first processed by ECAP for four passes using route Bc, at 300 °C and ram speeds of 3 and 25 mm/min. The ECAPed samples were cold-rolled in several passes. The cold rolled samples, which presented a favorable (0 0 2) texture, presented faster hydrogen absorption kinetic than the just ECAPed samples. No significant changes of desorption temperatures were found. The good results observed in the ECAPed plus cold rolled samples were explained by the acquired preferred orientation and by the increase of defects after cold rolling.

THE IMPACT TOUGHNESS OF HYPOEUTECTIC AlSi7Mg0.3 ALLOY PROCESSED BY ECAP

The effect of the pre-ECAP heat treatment and ECAP (Equal Channel Angular Pressing) processing on the impact toughness and fracture morphology of the AlSi7Mg0.3 alloy was investigated. The pre-ECAP heat treatment (annealing at 550°C followed by quenching and ageing at 250°C) of as -cast alloy improved its ductility, which was necessary for its severe plastic deformation. The pre-ECAP heat treatment followed by ECAP processing (4 passes at room temperature using A-route) of as-cast alloy homogenized the distribution of silicon and intermetallic phase particles in the solid solution matrix and improved its impact toughness. The as-cast alloy sample was fractured mostly in brittle manner. The fracture cracks initiated and propagated mainly along eutectic particles networks. T he fracture surface of ECAPed sample showed a typical ductile characteristic. The fracture propagated along and/or across banded distribution of eutectic particles and across bands of solid solution matrix.

Stored energy and recrystallization kinetics of ultrafine grained titanium processed by severe plastic deformation

Equal channel angular pressing (ECAP) was conducted at 250°C on commercial purity titanium up to 10 passes. An ultrafine-grained microstructure with a mean grain size of about 183nm was obtained. The evolution of stored energy and recrystallization temperature was studied by differential scanning calorimetry. The activation energy involved in the recrystallization process was also determined. The results show that with increase of ECAP passes up to 6 the recrystallization temperature increases. Also, it is seen that with increasing ECAP passes up to 8 the stored energy increases, beyond which it saturates at a value of about 58J/mol. For the recrystallization of 10 passes ECAP-ed samples, average activation energy of about 342kJ/mol was determined.

Microstructural Characterization of an Al-Mg-Si Aluminum Alloy Processed by Equal Channel Angular Pressing

In the present work, a peak-aged 6061 Al-Mg-Si aluminum alloy was subjected to equal channel angular pressing (ECAP) at 110 °C. The microstructure of the sample was characterized by high-resolution transmission electron microscope and weak-beam dark-field method. It was shown that the dislocation density in some local areas is much lower than the average dislocation density expected in the usual alloys processed by severe plastic deformation. High-resolution transmission electron microscope observations indicated that many full dislocations were dissociated into partial dislocations connected by stacking faults. In addition, a Z-shaped defect (i.e., a type of dislocation locks) probably formed by the reactions of the partials in different {111} planes was first observed in the ECAPed alloy. Furthermore, the precipitation behavior and sequence in the present ECAPed sample were identified by high-resolution transmission electron microscopy.

A Strengthening Model of Cu-Cr <i>In Situ</i> Fibrous Composites Produced by Equal Channel Angular Pressing

The composite filament structure was produced in the Cu-5.7%Cr and Cu-12.4%Cr as-cast alloy ingots by using equal channel angular pressing (ECAP) at room temperature. Optical and TEM microstructure, micro-hardness, tensile strength and electrical conductivity of ECAPed samples were investigated. The rotation and spreading of Cr particles took place during ECAP, and resulted in long thin in-situ filaments. The tensile strength increased with the number of the ECAP passes. A strengthening model was recommended to predict the enhancement of the tensile strength in Cu-Cr in situ fibrous composites.

J045051 ECAP加工を施したAl-Al_3Ti複相材料におけるAl_3Ti粒子破壊挙動の3次元組織解析([J045-05]知的材料・構造システム(5))

Microstructural evolution of Al-Al_3Ti multi-phase material by equal-channel-angular pressing (ECAP) is 3-dimenstionally investigated. The Al-Al3Ti multi-phase materials have Al_3Ti platelet particles in Al matrix. Especially, the distribution changes of the Al3Ti particles with ECAP are focused in this study. The Al_3Ti platelet particles are fragmented by ECAP under all of processing routes. When the Al-Al_3Ti specimen is deformed by ECAP under route A, the fine Al3Ti particles are homogeneously distributed along to deformation axis and the plane normal of the Al_3Ti particles are aligned perpendicular to deformation axis. On the other hand, the Al_3Ti particles in the specimens deformed under route Bc and route C are gathered and form several groups. Moreover, orientation distribution of the Al_3Ti particles in the specimen deformed under route Bc is random, and the Al_3Ti particles in the ECAPed sample under route C are aligned. The differences of the Al_3Ti particle distribution depending on the processing routes comes from shear deformation mechanism and plastic flow of the A1 matrix. Furthermore, it is found that fragmentation of the Al_3Ti particles by ECAP are preferentially occurred on (112)_<A13Ti>.

Mechanical Properties of Ultrafine-Grained Al Alloy for Engineering Machinery

Three groups of commercial 1050 Al alloy were subjected to equal channel angular pressing (ECAP) at room temperature using route A, route C and route Bc, respectively. Mechanical properties and fracture modes of as-annealed and ECAPed samples were investigated. The microhardness of 1050 Al fabricated by ECAP increases by a factor of about 1.5 compared to the as-annealed state. The ultimate tensile strength (UTS) increases significantly after ECAP, while the elongation decreases. But they are strongly dependence on the number of ECAP passes and the pressing route. The UTS and elongation of the samples processed by route Bc are best, consequently, the static toughness U of the samples is enhanced. Besides, all specimens subjected to ECAP deformation failed in a ductile manner.

A comparison between equal channel angular pressing and asymmetric rolling of silver in the severe plastic deformation regime

The structure evolution and mechanical properties of silver generated by equal channel angular pressing and by rolling and asymmetric rolling in the severe plastic deformation regime is investigated. Experimental investigations are combined with finite element analyses to improve the understanding on strain distribution developed during asymmetric rolling and to evaluate the equivalent strain accumulated after a large number of passes. The silver samples could be successfully deformed by both processing techniques up to strain values exceeding 8. The ECAP processed materials featured a submicrometer-size equiaxed grain structure with sharp grain boundaries, while symmetric and asymmetric rolling led to subgrain structures with a higher dislocation density at grain interiors and less defined grain boundaries. Accordingly, the tensile properties achieved after the different processing routes differed. In ECAP samples the strength improved at first passes and then showed a plateau for the whole range of imposed strain. In rolled silver, the achieved strength almost continuously improved even at larger strains. The finite element model showed that surface strain effects related to local friction between working rolls and sample surface regions promote an additional deformation, especially in asymmetric rolling, leading to a significant contribution at large plastic strains and generate discrepancies with equivalent strains assessed by continuum theories.

Homogenization of ECAPed Al 2024 alloy through age-hardening

Mechanical properties of aluminum alloys can be improved by obtaining ultra-fine grained structures via severe plastic deformation methods such as equal channel angular pressing (ECAP). In practice, however, the final structure may not be as homogeneous as desired. Thus, elimination of the inhomogeneity of ECAPed samples is a challenging task. In the case of age-hardenable alloys, a combination of ECAP and aging might provide new means of obtaining microstructural homogeneity. In this study, the effect of post-ECAP aging on the microstructural homogeneity of 2024 Al–Cu–Mg alloy was investigated. Following solutionization and rapid cooling, some samples were aged at 190°C for various times. Another group of samples were similarly aged after one-pass ECAP through a 120° die. Throughout the aging of the samples, maps of microhardness variation were acquired in order to monitor the precipitation behavior. It was observed that considerable homogenization in the microstructure of the ECAPed samples was reached, especially right after peak aging. The homogenization level was characterized with the hardness inhomogeneity index. EBSD and TEM investigations were performed to observe variations in the homogeneity of the microstructure.

Microstructural homogeneity, texture, tensile and shear behavior of AM60 magnesium alloy produced by extrusion and equal channel angular pressing

Equal channel angular pressing (ECAP) experiments with various pass numbers were conducted for the extruded AM60 magnesium alloy to investigate the influence of the operation on the microstructure and mechanical properties of the alloy. By this means, the grain structure of the material was refined from 19.2μm to 2.3μm after 6 passes at 220 °C. The shear punch testing (SPT) and uniaxial tensile tests were employed to evaluate the mechanical properties of the extruded and ECAPed samples. Both the yield stress (YS) and ultimate strength (US) obtained from the shear punch and tensile tests increased just after two passes but decreased with further pressing, though the grains became finer with increasing the pass number. The 6-pass ECAPed AM60 showed lower yield stress and higher ductility compared with the as-extruded material, indicating that texture softening overcame the strengthening effects of the grain refinement. The good correlation between the shear and tensile data obtained in the present investigation showed that SPT was a useful method for evaluation of the mechanical properties of the ECAPed fine-grained materials. The Vickers microhardness was also recorded on the polished cross sections of each sample and the results were plotted in the form of color-coded maps in order to provide a graphical presentation of the hardness distribution. It was found that the improvement in the homogeneity of hardness with a greater number of passes was due to a reasonably homogeneous microstructure throughout the product.

Study of vacancy-type defects by positron annihilation in ultrafine-grained aluminum severely deformed at room and cryogenic temperatures

Commercial-purity aluminum was processed by equal-channel angular pressing (ECAP) at room temperature (RT-ECAP) and cryogenic temperature (CT-ECAP) with liquid nitrogen cooling between two successive passes. It was found that the RT-ECAPed samples showed equiaxed microstructure after 4 and 8 ECAP passes, while the CT-ECAPed samples displayed slightly elongated microstructure and slightly smaller grain size. Moreover, the CT-ECAPed samples had higher hardness values than the RT-ECAPed samples subjected to the same amount of deformation. Positron annihilation lifetime spectroscopy (PALS) was used to investigate the evolution of vacancy-type defects during the ECAP deformation process. The results showed that three types of defects existed in the ECAPed samples: vacancies associated with dislocations, bulk monovacancies and bulk divacancies. The CT-ECAPed samples had a higher fraction of monovacancies and divacancies. These two types of defects are the major vacancy-type defects that can work as dislocation pinning centers and induce hardening, resulting in higher hardness values in the CT-ECAPed samples. A quantitative relationship between material hardness and the defect concentration and defect diffusion coefficient has been established.

Fatigue properties of ultra-fine grain Cu–Cr alloy processed by equal-channel angular pressing

A precipitation-hardening copper based alloy (Cu–0.6wt.% Cr) was selected and the ultra-fine grain (UFG) microstructure was obtained by equal channel angular pressing (ECAP). The alloys tensile behaviors and fatigue properties were investigated experimentally, the results indicated that the Cu–Cr alloy processed by ECAP possessed high strength and sufficient ductility and the 12-passes ECAPed sample with UFG under strain controlled fatigue exhibited cyclic softening and lower fatigue limit compared to the unECAPed one. Moreover, the shear bands on the surface of cycled samples were also studied by scanning electron microscopy, the results showed that the oriented distribution of defects along the shear plane in the last ECAP processing was one of the major mechanisms of SBs formation.

Effect of Annealing on the Microstructure, Texture and Mechanical Properties of Severely Deformed Interstitial Free Steel

Ti-stabilised interstitial free (IF) steel initially subjected to 8 passes, route BC equal channel angular pressing (ECAP) was further cold rolled (CR) at room temperature to 95% thickness reduction. Both samples were isothermally annealed at 710 °C following which their microstructures and micro-textures were compared via electron back-scattering diffraction (EBSD). The mechanical properties first obtained by shear punch testing (SPT) were later corroborated by uniaxial tensile tests. In the case of the ECAP material, continuous recrystallisation is followed by abnormal growth at prolonged annealing times with minor increases in high angle boundary (HAGB) fraction. On the other hand, the additionally CR material shows continuous recrystallisation accompanied by a reduction in the HAGB fraction. After 15 s annealing, the ECAP and CR samples exhibit a good strength-ductility balance; which corresponds to ~52% and ~67% softening, respectively.

MICROSTRUCTURES AND MECHANICAL PROPERTIES OF 0Cr13 FERRITIC STAINLESS STEEL PROCESSED BY EQUAL-CHANNEL ANGULAR PRESSING AND SUBSEQUENT ANNEALING TREATMENT

In comparison with austenitic stainless steel,the ferritic stainless steel has obvious advantage in price due to its lower nickel content.However,the relatively poor ductility and toughness limit its applications.To overcome these shortcomings,a new thermo-mechanical approach, involving processing by severe plastic deformation and proper annealing treatment to introduce a bimodal grain size distribution,was adopted for achieving high work-hardening capability,superior strength-ductility combination and good impact toughness in metallic materials.In this work,the combined effects of severe plastic deformation and partially recrystallization on the microstructures and mechanical properties of a ferritic stainless steel were investigated and compared with the traditional forging and annealing process.An solution-treated ferritic stainless steel(0Cr13,AISI 405) was subjected to equal-channel angular pressing(ECAP,an important kind of severe plastic deformation) for two passes at room temperature and subsequent annealing treatments.Optical microscope(OM) and transmission electron microscopy(TEM) observations showed that ultratine-grained(UFG) structure was obtained in the ECAP-processed sample.After subsequent annealing at 650—750℃for 1 h,partial recrystallization occurred and the remaining island-like UFG grains(10%—35%volume fraction) distributed uniformly.Statistical measurements indicated that the microstructures of the annealed ECAP samples exhibited a bimodal grain size distribution including relatively coarse recrystallized grains(CRGs) and remaining ultrafine grains(UFGs).The average grain size for CRGs determined from OM observations was 5.1—8.3μm and the average grain size for UFGs measured from TEM observations was 418—525 nm.By contrast,the annealed forged sample(700℃) exhibited a unimodal grain size distribution with average grain size of about 74μm.Tensile and impact tests showed that the strength of 0Cr13 ferritic stainless steel could be improved greatly through grain refinement by ECAP process,and the strength-ductility combination could be modulated via sacrificing some strength for ductility by subsequent annealing treatment.In comparison with the conventional sample (forging+annealing at 700℃),the tested steel processed by the optimal processing involving ECAP deformation and annealing treatment at 700℃showed higher yield strength,uniform ductility and static toughness(enhanced by 10%,35%and 70%respectively),simultaneously a comparable impact toughness(212 J/cm~2).The refined microstructure and higher work-hardening capacity were responsible for the improved mechanical properties of the annealed ECAP samples and the strengthening mechanisms were discussed based on the experimental results.