Route Bc Research Articles

Analysis of plastic deformation of semi-crystalline polymers during ECAE process using 135° die

In this paper, analysis of plastic deformation of high density polyethylene (HDPE) and polypropylene (PP) during an equal channel angular extrusion (ECAE) process is investigated. The effects of ram speed, number of passes, processing route and temperature are tested experimentally using a 135◦ die. The results show that the pressing force decreases with an increase in the number of passes and reaches a saturation state rapidly for routes A and C compared to routes BA and BC. Furthermore, it is found that the reduced curvature of the extruded samples is obtained by route C, however, the maximum warping is obtained by route A. A slight influence of temperature on the reduction of the warping is observed on the extruded samples. In order to predict the plastic strain inside the extruded samples, an elastic viscoplastic model is identified using compressive tests at different strain rates and coupled with the finite element method (FEM). A good correlation is found between the numerical modeling and experimental findings. FEM results show that the PP samples display a higher level of plastic strain compared to HDPE samples. However, almost the same degree of strain heterogeneity is obtained for both polymers. Finally, in order to reduce the warping and improve the strain homogeneity, a controlled back-pressure with small corner angle is expected to be an adequate solution.

High cycle fatigue of ARMCO iron severely deformed by ECAP

The high-cycle fatigue behavior of ARMCO iron severely deformed by Equal Channel Angular Pressing (ECAP) at room temperature through route Bc until 8 passes, with an average grain size of ~365nm, was studied and compared with the same material in the annealed state with an average grain size of ~72µm. The fatigue limit of the 8 passes ECAPed sample increased with respect to the annealed material by more than 250% rising from 274MPa to 717MPa. Striations and dimpled relief were observed on the fracture surfaces of the fatigued ultrafine and coarse grain fatigue samples. The microstructure was characterized by Electron Backscattered Diffraction (EBSD) before and after the fatigue tests and it was observed in both samples an increment in the fraction of Low Angle Grain Boundaries (LAGB) at high number of cycles to failure. A texture analysis for the materials after the fatigue failure was done. This study shown a preferential orientation towards the γ fiber for both conditions.

Effect of Equal Channel Angular Pressing on the Microstructure and Mechanical Properties of Hybrid Metal Matrix Composites

Objectives: The objective of the present study is to prepare Al6061-Gr-SiChybrid composites by stir casting route and the effect of Equal Channel Angular Pressing (ECAP) on the microstructure and mechanical properties of Al6061-Gr-SiC hybrid composites will be evaluated. Methods: In the present study, Al6061 is selected as matrix material. The reinforcement materials chosen are graphite (Gr) and Silicon carbide (SiC) particles of 10-30 μm size. The hybrid composites have been prepared by stir casting route in which the amount of Gr particles are kept at 3wt% and SiC particles are varied from 2-10wt% in steps of 2wt% . The cast hybrid composites are subjected to annealing treatment at 400oC for 4 hours and specimens have been prepared from these composites for ECAP process. The ECAP process was carried out at room temperature using a die with channel angle of 120o and Bc route was adopted for successive passes. The influence of ECAP on microstructure and mechanical properties of Al-Gr-SiC hybrid composite was evaluated. Findings: The microstructural study revealed that the composites are free from defects and also the distribution of reinforcement particles in the matrix are fairly uniform. Significant improvement in micro hardness and tensile strength was observed as the wt% of SiCp increases in as cast Al6061-Gr- SiC hybrid composites. After ECAP process, the size and distribution of the reinforcement particles are not changed but significant reduction in the grain size of the matrix alloy was observed. The micro hardness and tensile test results revealed that, there is a significant improvement in the micro hardness and the Ultimate tensile strength of ECAP processed hybrid composites. The enhancement in mechanical properties are mainly attributed to the grain refinement of the matrix alloy and strain hardening of hybrid composite materials by ECAP process. Applications: The ECAP process had a profound effect in enhancing the mechanical properties of hybrid composites. These composite materials have great impact in automobile, military and aerospace industries.

Effect of Equal Channel Angular Pressing on the Microstructure and Mechanical Properties of Al6061-SiCp Composites

In the present study, Aluminium metal matrix composite with Al6061 matrix and SiC (10-30μm) particulate reinforcement of varying composition (2-10wt.%) were prepared by stir casting technique. Significant improvement in tensile strength and hardness was noticed as the wt.% of SiCp increases in as cast Al6061- SiC composites. The cast composites have been subjected to annealing treatment at a temperature of 400oC for 4 hours to homogenize the microstructure. The specimens have been prepared from these composites for Equal Channel Angular Pressing (ECAP). The ECAP process was carried out at room temperature using a die with channel angle of 120° and Bc route was adopted for successive passes. The effect of ECAP on the microstructure and mechanical properties of Al6061 -SiC composite is evaluated. After ECAP process, the size and distribution of the reinforcement particles are not changed but there is a significant reduction in the grain size of the matrix alloy was observed. The hardness and tension tests were conducted at room temperature as per ASTM standards. The results were compared with the base Al6061 material and as cast Al6061-SiC composites. There is a significant improvement in the hardness and the Ultimate tensile strength of ECAP processed composites.

High cycle fatigue behavior of Al1070 alloy severely deformed by equal channel angular pressing process

In the present work, equal channel angular pressing of commercial pure aluminum 1070 was performed up to 4 passes using route Bc. For equal channel angular pressing operation, a suitable die set was designed and manufactured. X-ray diffraction analysis was used to determine the microstructure of the equal channel angular pressing-ed material. The fracture surface morphology and microstructure after fatigue were investigated by scanning electron microscopy. Mechanical properties of the equal channel angular pressing-ed material were evaluated by hardness and tension tests. Also, cyclic deformation behavior of severe plastic deformation Al1070 has been studied and results show a significant variation in hardness, ultimate strength and fatigue properties in high cycle fatigue life. Coefficient of fatigue strength σ′f and Bridgman correction factor have been obtained by S-N curve and tension test specimens, respectively, and compared before and after equal channel angular pressing process. Also an useful relation has been derived between fatigue life ( Nf) and stress amplitude ( σa) in high cycle fatigue region. Results indicated that there was not clear relation between fatigue strength coefficient and true corrected fracture stress in this case.

An investigation of microstructure and mechanical properties during ECAE of commercially pure aluminum

In the present paper commercially pure Al billets were processed by equal channel angular extrusion (ECAE) up to 8 passes via route BC at room temperature. Electron back scattered diffraction (EBSD) were used to evaluate the microstructure of the aluminum. Moreover, the mechanical properties of the processed billets were investigated by tensile and hardness tests. The microstructural and microhardness analyses at various locations of the billet thickness, from the top to bottom surfaces, revealed a significant improvement in homogeneity by increasing the number of passes. It was also found that the yield strength and average microhardness of aluminum is increased significantly up to four passes and then it is decreased when more passes are applied.

Effect of strain path on severely deformed aluminium

The twist channel angular pressing (TCAP) technology was recently developed in accordance to the contemporary trend of increasing the efficiency of severe plastic deformation technologies. This study was aimed to analyse structural changes, particularly grain sizes and orientations and textures, in commercial purity aluminium after a single pass TCAP and to put the structure in connection with the strain path. For comparison, another sample processed by two passes equal channel angular pressing (ECAP), Bc route, was analysed. Three independent shear planes affecting the material during a single pass TCAP caused the grains to refine down to the average size of 5.8µm. The sample after a TCAP pass also exhibited highly developed subgrains. The textures of the samples exhibited differences in preferential orientations and their intensities.

In vitro and in vivo studies of ultrafine-grain Ti as dental implant material processed by ECAP

The aim of this study was to investigate the surface characterization of ultrafine-grain pure titanium (UFG-Ti) after sandblasting and acid-etching (SLA) and to evaluate its biocompatibility as dental implant material in vitro and in vivo. UFG-Ti was produced by equal channel angular pressing (ECAP) using commercially pure titanium (CP-Ti). Microstructure and yield strength were investigated. The morphology, wettability and roughness of the specimens were analyzed after they were modified by SLA. MC3T3-E1 osteoblasts were seeded onto the specimens to evaluate its biocompatibility in vitro. For the in vivo study, UFG-Ti implants after SLA were embedded into the femurs of New Zealand rabbits. Osseointegration was investigated though micro-CT analysis, histological assessment and pull-out test. The control group was CP-Ti. UFG-Ti with enhanced mechanical properties was produced by four passes of ECAP in BC route at room temperature. After SLA modification, the hierarchical porous structure on its surface exhibited excellent wettability. The adhesion, proliferation and viability of cells cultured on the UFG-Ti were superior to that of CP-Ti. In the in vivo study, favorable osseointegration occurred between the implant and bone in CP and UFG-Ti groups. The combination intensity of UF- Ti with bone was higher according to the pull-out test. This study supports the claim that UFG-Ti has grain refinement with outstanding mechanical properties and, with its excellent biocompatibility, has potential for use as dental implant material.

Synchrotron X-ray microbeam diffraction measurements of full elastic long range internal strain and stress tensors in commercial-purity aluminum processed by multiple passes of equal-channel angular pressing

Synchrotron X-ray microbeam diffraction was used to measure the full elastic long range internal strain and stress tensors of low dislocation density regions within the submicrometer grain/subgrain structure of equal-channel angular pressed (ECAP) aluminum alloy AA1050 after 1, 2, and 8 passes using route BC. This is the first time that full tensors were measured in plastically deformed metals at this length scale. The maximum (most tensile or least compressive) principal elastic strain directions for the unloaded 1 pass sample for the grain/subgrain interiors align well with the pressing direction, and are more random for the 2 and 8 pass samples. The measurements reported here indicate that the local stresses and strains become increasingly isotropic (homogenized) with increasing ECAP passes using route BC. The average maximum (in magnitude) LRISs are −0.43 σa for 1 pass, −0.44 σa for 2 pass, and 0.14 σa for the 8 pass sample. These LRISs are larger than those reported previously because those earlier measurements were unable to measure the full stress tensor. Significantly, the measured stresses are inconsistent with the two-component composite model.

Microstructural evolution and fracture mechanism of a new Al–Zn–Mg–Cu–Zr alloy processed by equal-channel angular pressing

Equal-channel angular pressing (ECAP) is considered to be one of the most effective processing procedures to produce ultrafine-grained (UFG) materials. A new Al–Zn–Mg–Cu–Zr alloy was subjected to ECAP experiment in Route BC (i.e ., rotated 90° in the same sense between each pass). The effect of ECAP on the microstructural evolution and fracture mechanism of the alloy was analyzed by optical microscope (OM), X-ray diffraction (XRD), tensile test (at room temperature), and scanning electron microscope (SEM). The results show that the main strengthening phase of the alloy is MgZn2, whose content increases apparently after ECAP, the dislocation density increases by one order of magnitude, the hardness value of the 1 pass ECAPed sample increases by 53 %, the ultimate tensile strength (UTS) increases by 29 %, and the true strain increases by 15.4 %. But the further increase in the strength with the passes increasing would cost a slight drop in the true strain. The morphology of the tensile dimples is converted from elongated one to equiaxed one with a uniform distribution of size and depth after pressing.

Microstructural evolution and micro/meso-deformation behavior in pure copper processed by equal-channel angular pressing

Pure copper was processed by equal channel angular pressing (ECAP) using route Bc with a die channel angle of 110°. Electron back scattered diffraction (EBSD) and transmission electron microscopy (TEM) were used to analyze the microstructure and texture during ECAP processing and after combining ECAP with micro-compression. Ultrafine-grained pure copper with an average grain size of ~0.5µm was achieved after ECAP processing through 12 passes. The anisotropic behavior during micro-compression is caused by the micro-texture of pure copper introduced by ECAP processing. Three kinds of strain softening behaviors are found during micro-compression tests in pure copper processed by ECAP. The strain softening of micro/meso deformation in UFG pure copper is caused by the accelerated dislocations annihilation due to the high dislocation recoveries at HAGBs, which is consistent with the deformation mechanism of grain boundary sliding and grain rotation.

Structure and properties of AlMg alloy after combination of ECAP and post-ECAP ageing

Equal channel angular pressing technique (ECAP) was used before and after solution heat treatment to obtain grain refinement and strengthening of commercial Al–Mg casting alloys. The experiments were performed to investigate the strengthening effect of the alloy after various post-ECAP ageing treatments. The alloys were severely deformed at room temperature following route Bc and die channel angle of 120°. It was found that heat treatment before and after ECAP significantly affect and improves mechanical properties of aluminium alloys. It was also proven that the severe plastic deformation causes grain refinement which directly influence on properties of AlMg alloys. An increase of strength and ductility was achieved by appropriate selection of post-ECAP ageing. It is also proven that the good strengthening effect is also achieved at temperatures lower than those usually used for ageing. Based on the findings above, the tensile properties and hardness of Al–Mg alloys are discussed.

Equal-channel angular pressing and annealing of a twinning-induced plasticity steel: Microstructure, texture, and mechanical properties

In this work, a high-manganese Fe–23Mn–1.5Al–0.3C Twinning-Induced Plasticity (TWIP) steel was subjected to plastic shear deformation using Equal-Channel Angular Pressing (ECAP) at 300 °C following route BC and additional annealing. The microstructure evolution during both deformation by ECAP and subsequent annealing was investigated and correlated with the mechanical properties. The successive grain refinement during ECAP was promoted by two parallel mechanisms, namely dislocation driven grain fragmentation and twin fragmentation, and accounted for the ultra-high strength. In addition, due to the relatively low volume fraction of deformation twins after ECAP at 300 °C, further contribution of deformation twinning during room temperature deformation allowed additional work-hardening capacity and elongation. During subsequent recovery annealing the ultra-fine grains and deformation twins were thermally stable, which supported retainment of the high yield strength along with regained uniform elongation. For the first time, the texture evolution during ECAP and during the following heat treatment was analyzed. After 1, 2, and 4 ECAP passes a transition texture with the characteristic texture components of both high- and low-SFE materials developed. During the following heat treatment the texture evolution proceeded similar to that observed in the same material after cold rolling. Retaining of the ECAP texture components due to oriented nucleation at grain boundaries and triple junctions as well as annealing twinning accounted for the formation of a weak, retained ECAP texture after recrystallization.

Effect of different c/a ratio on the microstructure and mechanical properties in magnesium alloys processed by ECAP

Three magnesium alloys, AE21, AE42 and LAE442, were prepared by ECAP employing 1–12 passes. The microstructure evolution during ECAP was systematically analyzed by EBSD. The AE21 and AE42 alloys show typical texture after ECAP with grains predominantly oriented with basal planes inclined by ∼55° from processing direction. This texture results from activation of basal slip during ECAP following the route BC. The LAE442 alloy showed different texture formation, which is fully explained by different c/a ratio and activation of non-basal slip. The differences in the microstructure evolution resulted in different performance in mechanical loading. In the present study a complex investigation of mechanical properties is performed using uni-axial tensile and compression deformation tests and also by Vickers indentation that simulates multi-axial deformation. Resulting microhardness evolution was therefore correlated to grain size according to Hall–Petch relation and to the evolution of dislocation density measured by positron annihilation spectroscopy. On the other hand, the yield stress in the tensile and compression uni-axial deformation tests was determined mainly by the texture. It was shown that by tailoring the c/a ratio the typical texture development could be effectively suppressed in magnesium alloys processed by ECAP and in such way the negative effect of texture on strength can be avoided.

Ultra-High-Strength Interstitial-Free Steel Processed by Equal-Channel Angular Pressing at Large Equivalent Strain

The billets of interstitial-free (IF) steel are deformed by equal-channel angular pressing (ECAP) at 298 K (25 °C) adopting the route BC up to an equivalent strain (e vm) of 24. The evolution of microstructures and their effects on the mechanical properties are examined. The microstructural refinement involves the elongation of grains, the subdivision of grains to the bands with high dislocation density, and the splitting of bands into the cell blocks and then cell blocks into the cells. The widths of the bands and the size of cells decrease with strain. The degree of reduction in the grain size is highest at the low strain level. However, most of the boundaries at this stage are of low-angle boundaries (at e vm = 3). Thereafter, the misorientation angle increases by progressive lattice rotation with strain. The coarse bands transform step by step from the lamellar structure to the ribbon-shaped grains and finally to the near-equiaxed grain structures with the subgrains of a saturated low-angle grain boundary fraction of 0.34 at very large strain >15. The as-received coarse-grained microstructure (grain size of 57.6 ± 21 µm) has been refined to 257 ± 48 nm at an equivalent strain of 24. The strength increases considerably up to e vm = 3 due to grain refinement and high dislocation density. However, the strengthening at later stages is mainly due to the increase in misorientation angle and refinement. Initial yield strength of 227 MPa is increased to a record value of 895 MPa on straining up to e vm = 24 at 298 K (25 °C). Uniform elongation decreases drastically at low equivalent strain but it regains marginally later. The ECAPed sample fails by a ductile fracture at e vm = 0.6 to 6 but by a mixed mode of ductile–brittle fracture at larger strain of 9 to 24.

Development of Texture in Interstitial-Free Steel Processed by Equal-Channel Angular Pressing

Ti + Nb-stabilised interstitial-free steel is deformed by equal-channel angular pressing (ECAP) adopting a route BC up to an equivalent strain of 24. Upon ECAP the grain size decreases to ultrafine level and it becomes strongly textured. At evm = 0.6-6, components of both {110} fiber, \( J_{\uptheta } \), \( \bar{J}_{\uptheta } \) and of 〈111〉 fiber, D 1θ, D 2θ with common components of E θ, \( \bar{E}_{\uptheta } \) are existing but after evm ≥9, only 〈111〉 fiber components are observed. At large strain, evm = 9-24, 〈111〉 fiber texture is recorded with monoclinic symmetry. At evm = 0.6, coarse grains get split into deformation bands. Fragmentation of bands (at evm = 3) suppress \( \bar{J}_{\uptheta } , \) \( J_{\uptheta } \) components. At evm = 6, formation of lamellar structures increases intensity of mainly D 1θ, D 2θ. At evm = 9, oriented ribbon grains result in strong D 1θ, D 2θ components with 〈111〉 fiber. At evm = 15-24, conversion of ribbon grains to near-equiaxed shaped grains maintains 〈111〉 fiber texture with enhanced intensity of D 1θ and D 2θ components.

Microstructure and mechanical properties of 7005 aluminum alloy processed by room temperature ECAP and subsequent annealing

A coarse-grained microstructure of the extruded 7005 aluminum alloy was processed by equal channel angular pressing (ECAP) via route BC at room temperature. Microstructural evolution of the alloy processed by ECAP with different passes and subsequent annealing treatment were analyzed by using optical microscope, transmission electron microscope and electron backscatter diffraction. The results revealed that grains were refined gradually, and the low angle boundaries were progressively transformed to high angle boundaries by an increasing ECAP passes. After 7 ECAP passes, the average grain size decreased to ∼0.87 μm, and the fraction of high angle boundaries increased to ∼65.5%. Furthermore, the results of tensile testing indicated that the yield strength was remarkably increased from ∼170 MPa before ECAP to ∼389 MPa after 7 ECAP passes, and the corresponding tensile strength increased to ∼400 MPa after 7 ECAP passes, maintaining an appropriate elongation of ∼13%. After annealing treatment at 150 °C for 1 h, the samples processed by 7 ECAP passes obtained large elongation of ∼16%, and still maintained a high yield strength of ∼337 MPa and tensile strength of ∼350 MPa, which may be attributed to the recovery effects.

Effect of severe plastic deformation on an extruded ZK60 magnesium alloy

ABSTRACTEqual channel angular pressing (ECAP) was carried out on extruded ZK60 magnesium alloy until an equivalent strain of ∼4 (corresponding to 4 passes) at 523K following route Bc. The effect of the deformation on both microstructure and texture was investigated by analysis of inverse pole figures and pole figures respectively, determined by EBSD. Additionaly, the mechanical properties were evaluated through tensile tests. The ECAPed processed ZK60 alloy showed the presence of dynamic recrystallization (DRX) process, correlated with a strong basal fiber texture. The presence of pyramidal slip was also observed, which can be correlated with the presence on twin-oriented boundaries in the material. Both the grain size reduction and the existence of texture influenced the ductility of the magnesium alloy processed by ECAP, as the ductility of the ZK60 alloy after four ECAP passes increased two times in comparation with the initial (un-processed) material.

Superplastic Behavior of an AA2139 Subjected to ECAP

An AA2139 alloy belonging to Al-Cu-Mg-Ag system was subjected to thermomechanical processing (TMP) included solution treatment at 525°C for 1 h, quenching in water, over-aging at 380°C for 3 h followed by equal-channel angular pressing (ECAP) at 250°C to a total strain of ~12 via route BC. This TMP produced a partially recrystallized structure with fine crystallites having an average size of ~0.9 μm and a fraction of high-angle boundaries of ~56%. Tensile test was performed in the temperature interval 300-500°C at initial strain rates ranging from ~1.8×10-4 to ~1.7×10-1 s-1. It was shown that the highest elongation-to-fracture of ~660% appears at a temperature of 400°C and an initial strain rate of 1.4×10-3 corresponding with the coefficient of sensitivity coefficient, m, of 0.34.

Dislocation study of ARMCO iron processed by ECAP

ABSTRACTThe aim of this work was to study the deformation behavior of an Armco iron after severe plastic deformation by equal channel angular pressing (ECAP). Particular attention was paid to predict the dislocation density by different approaches like the model proposed by Bergström. Experimental measures of dislocation density by different techniques are used in the discussion. Cylindrical samples of ARMCO iron (8mm of diameter, 60mm of length) were subjected to ECAP deformation using a die with an intersecting channel of Φ=90° and outer arc of curvature of ψ= 37° die. Samples were deformed for up to 16 ECAP passes following route Bc. The mechanical properties of the material were measured after each pass by tensile tests. The original grain size of the annealed iron (70 μm) was drastically reduced after ECAP reaching grain sizes close to 300nm after 16 passes.