Equal Channel Angular Processing Research Articles

The Influence of Texture and Grain Size on Compressive Deformation Behavior of Pure Mg through Equal-Channel Angular Processing

Multi-pass of equal channel angular pressing (ECAP) at a single temperature as low as room temperature from 200 °C were measured using electronic back scatter diffraction (EBSD). The effect of texture and grain size on mechanical properties was investigated to realize the strengthening and large plastic deformation mechanism. A room temperature ECAP with multi-pass procedure is effective to product high strength and large plastic Mg, as a result of submicron grain structure and texture strengthening.

Optimization of Strength and Ductility in Ultra-Fine 304 Stainless Steel after Equal-Channel Angular Processing

The microstructure and mechanical properties of 304 stainless steel were investigated which was subjected to equal channel angular pressing (ECAP). Tensile strength, elongation, Vickers hardness of as-ECAPed and annealed ECAPed 304 stainless steel were systematically measured and compared and microstructure evolution during ECAP and ECAP+annealing was observed by OM and TEM. It was found that with the increasing of ECAP passes, the grain size of stainless steel was effectively refined to nanoscale, such as about 50 nm after 8 ECAP-passes. In addition, the dislocation density in ECAPed samplel increased greatly, consequently, the tensile strength and hardness of ECAPed 304 stainless steel increased and elongation decreased remarkably. After annealing at 600°C for 10 min，the ductility of ECAPed stainless steel was improved greatly while grains did not have obvious growth, and strength did not change much. The above results showed that the optimization of strength and ductility in ultra-fined 304 stainless steel can be achieved by appropriate ECAP plus annealing processes.

Structure Property Correlation in Ultrafine Grained Copper Processed by Equal Channel Angular Processing

Ultra fine grained copper is produced by equal channel angular processing (ECAP) routes.Multiple passing through the ECAP die reveals high grain refinement in first few passes.Transmission electron microscopies in to the samples reveal a grain refinement of 150 μm to 500 nm sized grains after 4 passes. Mechanical properties measuerement shows that the severe plastic deformation has improved the structural strength to 410 MPa. Structure property study confirms the Hall petch strengthening mechanism operational during the deformation process. The effect of initial microstructral inhomogeniety is investigated and it is found to have marginal influence in the grain refinement of the multiple pass ECAP. Process modeling study using finite element models reveal the developed shear strain and stress fields during the deformtion process.

Finite Element Simulation of Die Design for Warm Equal Channel Angular Extrusion Process of AZ31 Alloy and its Experimental Investigation

In this paper, a systematic investigation of equal channel angular extrusion/Pressing (ECAE, ECAP) process on the AZ31 alloy and die design is performed by using numerical simulation. The stress distributions on the die were obtained, and general consideration of the die during the whole pressing process was given. The numerical results revealed that effective stress distribution at the corner of the cavity and the extruded load during extrusion processes was effect by channel angles and friction factor. From the simulations, it was found that the closer the die corner is, the higher stress value results can be acquired. And the effective stress concentration in ECAP die cavity corner. The extruding load fell rapidly when the angular angle increasing. With the increase of friction factor, extruding load also increased significantly. The proposed method can serve as preconditions to analyze the abrasion and fatigue of ECA Pressing die. Besides, this method also provides a feasible way for other die stress analysis.

Microstructure and Properties of Magnesium Alloy by Equal Channel Angular Processing

Mg-6Zn-0.6Zr magnesium alloy (ZK60) was extruded by equal channel angular processing (ECAP) equipment via 2, 4, 6 passes at 400°C. The corresponding microstructure and hardness were examined. The change of the crystal plane in this processing was analyzed by X-ray diffraction. The results show that, ECAP favors recrystallization and refines grains with the increase of pass times. The grains are significantly refined to 10um after 6 passes and the hardness is improved to 79.8HV after 4 passes.

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.

WEAR CHARACTERISTICS OF Cu OFHC MATERIAL PREPARED BY ORBITAL FORGING AND ECAP

The paper is focused on the wear mechanism of orbital forged and equal-channel angular extruded Cu OFHC (oxygen-free high thermal conductivity) material. The wear behaviour of the Cu OFHC material is investigated through pin-on-disc tests. Two different processing conditions have been used, equal-channel angular processing (ECAP) and orbital (radial) forging. The wear investigations in this orbital formed material are unique; additionally wear properties show interesting wear characteristics. Particular attention has also been paid to the friction coefficient and to the role of the wear rate.

Vickers and Knoop Micro-hardness Behavior of Coarse-and Ultrafine-grained Titanium

The present study focuses on the relationship of hardness with grain size for commercially pure titanium (Cp-Ti) and ultra fine grained titanium (UFG-Ti) produced by equal channel angular process (ECAP) of Cp-Ti). Vickers and Knoop indentations of UFG-Ti at different loads was ∼2.5 times harder than those of Cp-Ti. X-ray diffraction (XRD) analysis showed peak broadening in UFG-Ti due to reduced grain size and micro-lattice strains. Scanning electron microscopy (SEM) revealed that ECAP had reduced the grain size of Cp-Ti by ∼10 times. Weibull statistics showed UFG-Ti with lower dispersion in hardness values compare to Cp-Ti indicating a more uniform microstructure.

Sensitivity analysis of the ECAE process via 2k experiments design

In this work the theoretical solutions based upon the upper-bound theorem recently proposed by Perez and Luri [Mech. Mater. 40 (2008) 617] for the equal channel angular extrusion process (ECAE) are analyzed by performing a 25 central composite factorial analysis. The uniaxial mechanical properties of commercial pure aluminium are considered by assuming isotropic nonlinear work-hardening combined to von Mises and Drucker isotropic yield criteria to predict the ECAE load and the effective plastic strain. From the proposed 25 factorial analysis, the main parameters affecting the ECAE pressure may be ranked as: (1) Friction factor, (2) die channels intersection angle, (3) outer and (4) inner die corners fillet radii and lastly, (5) plunger velocity. Alternatively, the effective plastic strain is mainly controlled by the die channels intersection angle and, in a less extent, by the outer and inner die corners fillet radii.

Multi-Scale Modeling of Texture Evolution in Beryllium and Zirconium during Equal Channel Angular Extrusion

This work studies the deformation mechanisms active in two pure hexagonal close packed metals, beryllium (Be) and zirconium (Zr), during equal channel angular extrusion processing. An experimental-theoretical approach is employed to assess their relative contributions through measurement and calculation of texture evolution. A new multi-scale constitutive model, incorporating thermally activated dislocation density based hardening, is shown to effectively predict texture evolution as a function of processing route, number of passes (up to four), initial texture, pressing rate, and processing temperature. Texture predictions are shown to be in very good agreement with experimental measurements. Also, it is found that the two most active deformation modes in Be are basal slip and prismatic slip, where the predominant one is interestingly found to depend on die angle. Deformation in Zr during the first pass is predicted to be accommodated not only by its easiest mode, prismatic slip, but by basal slip and tensile twinning.

A new method of characterizing equivalent strain for equal channel angular processing

In order to establish the quantitative relationship between equivalent strain and the performance index of the deformed material within the range of certain passes for equal channel angular processing (ECAP), a new approach to characterize the equivalent strain was proposed. The results show that there exists better accordance between mechanical property (such as hardness or strength) and equivalent strain after rolling and ECAP in a certain range of deformation amount, and Gauss equation can be satisfied among the equivalent strain and the mechanical properties for ECAP. Through regression analysis on the data of hardness and strength after the deformation, a more generalized expression of equivalent strain for ECAP is proposed as: e=k0exp[-(k1M-k2)^2], where M is the strength or hardness of the material, k1 is the modified coefficient (k1 ∈((0, 1)), k0 and k2 are two parameters dependent on the critical strain and mechanical property that reaches saturation state for the material, respectively. In this expression the equivalent strain for ECAP is characterized novelly through the mechanical parameter relating to material property rather than the classical geometry equation.

The mechanism of nanostructured steel fracture at low temperatures

Microstructural aspects of deformation and fracture of steel which is nanostructured using the technique of equal-channel angular pressing and thermal processing at low temperature (−60°C) are considered in the paper. The methods of optical and atomic-force microscopy are used to investigate deformation surfaces. The fracture character change (from a brittle cleavage to a ductile shear) at low temperatures is shown to be associated, on the one hand, with a fuzzing of grain boundaries during pressing with solid structural phases and, on the other hand, by the replacement of the prevalent plastic deformation carriers.

High Strength Ti of Substantial Interstitial Contents Produced by Back Pressure Equal Channel Angular Consolidation of Dehydrided Particles

Back pressure equal channel angular (BP-ECA) processing was utilised to consolidate a dehydrided (DH) Ti powder of high interstitial content (1.15 wt.% O, 0.09 wt.% N) at 630°C into fully dense bulk ultrafine-grained (UFG) Ti. The consolidated samples showed an increase in the contents of oxygen (1.34 wt.%) and nitrogen (0.3 wt.%). The measured densities of 4.53 g/cm3 for the consolidated samples after 1 and 3 passes were very close to the theoretical value of pure Ti. TEM revealed the formation of a bimodal microstructure in the one-pass sample, comprising equiaxed grains of several micrometers in size with ultrafine grains of the order of 100 nm uniformly distributed at the triple grain junctions. Most grains had high-angle grain boundaries with some boundaries exhibiting non-equilibrium characteristics. Upon further BP-ECA processing to three passes, the micrometer-sized grains were refined down to the ultrafine level and copious nanoscale deformation twins were introduced by severe plastic strain into those ultrafine grains of the order of 100 nm. As a result of high interstitial contents and refined grains, the sample after processing for 3 passes exhibited remarkably enhanced true yield and ultimate strengths of 1510 and 2050 MPa, respectively. Significantly, a noticeable compressive ductility was simultaneously attained despite such a high interstitial content, thanks probably to the non-equilibrium grain boundaries, bimodal grain structure and the occurrence of deformation twinning.

Regularities of Deformation and Fracture of Steels Subjected to Equal Channel Angular Pressing and Thermal Processing

The article deals with the problems of strengthening and cold resistance increase of steels through combining equal channel angular pressing (ECAP) with thermal processing (TP). Dependence of cold resistance on the state of the material structure determined by regimes of equal channel angular pressing and thermal processing is shown. Dependence of specific work of plastic deformations, stored and dissipated energy of steel on its plasticity is stated.

On the Cyclic Stability and Fatigue Performance of Ultrafine-Grained Interstitial-Free Steel under Mean Stress

This paper reports on the fatigue performance of an ultrafine-grained (UFG) interstitialfree (IF) steel deformed at various mean stress levels. The UFG microstructure was achieved using equal channel angular extrusion processing at room temperature (RT) and along an “efficient” route, giving way to the formation of high angle grain boundaries (HAGBs) with a high volume fraction. The current study not only confirms the previous finding that a high volume fraction of HAGBs promotes cyclic stability, but also inquires into the role of mean stress level on the cyclic stability. It is shown that the UFG IF steel exhibits a stable cyclic deformation response in the lowcycle fatigue regime within the medium applied mean stress range of -75 to 75 MPa. The corresponding fatigue lives can still be predicted with the Smith-Watson-Topper approach within this range. Furthermore, the present study demonstrates that the evolution of mean strains with cyclic deformation can be linked to the evolution of mean stresses in strain-controlled loading.

Magnesium Powder Metallurgy: Process and Materials Opportunities

The major efforts in magnesium alloy development for automotive applications have concentrated on creep resistant alloys produced by permanent mould and high-pressure die casting routes. While large components, such as crankcases, will never be produced by powder metallurgy, there are smaller components in and around the powertrain which could be fabricated from powder precursors. This article will explore the potential of some of the more recent powder compaction developments, and discuss the alloy development strategies that emerge for magnesium-based components as a consequence of these process developments. In particular, the viability of direct powder extrusion of semi-finished product, using conventional extrusion or equal channel angular processing, combined with T6 heat treatments, will be considered.

Ultrafine-grained titanium of high interstitial contents with a good combination of strength and ductility

A dehydrided Ti powder of very high oxygen content was successfully consolidated using back pressure equal channel angular processing into a fully dense bulk ultrafine-grained Ti showing apparent compressive ductility as well as high true yield and ultimate strengths of 1350 and 1780MPa, respectively. Interstitial solid solution strengthening contributed to the majority of the increase in strength with additional contribution from ultrafine grains. Significantly, the material also exhibited much improved ductility for such a high interstitial content, thanks probably to the nonequilibrium grain boundaries and bimodal grain structure introduced during severe plastic deformation.

Grain Boundary Sliding in a Superplastic Zinc-Aluminum Alloy Processed Using Severe Plastic Deformation

A Zn-22% Al eutectoid alloy was processed by Equal-Channel Angular Processing (ECAP) to produce a grain size of ?0.8 ?m. Tensile testing at 473 K gave a maximum elongation of ?2230% at a strain rate of 1.0 × 10-2 s-1. The significance of grain boundary sliding was evaluated by taking measurements of offsets in surface marker lines at an elongation of 30%. The highest sliding contribution was recorded under testing conditions corresponding to the maximum superplastic elongation. Detailed measurements showed that relatively large offsets occurred at the Zn-Zn and Zn-Al interfaces but there were smaller offsets at the Al-Al interfaces. It is concluded that grain boundary sliding is the dominant flow process during superplastic deformation.

Grain size and grain boundary character distribution in ultra-fine grained (ECAP) nickel

Microstructures of the Ultra-fine grained (UFG) nickel produced through equal channel angular processing (ECAP), pressed 12 times through the B C route to impart a strain of ∼12, were investigated using transmission electron microscopy (TEM) and electron back-scattering diffraction (EBSD). The average grain size obtained from orientation imaging microscopy (OIM) was 0.23 μm, for a tolerance angle of 5° and 0.24 μm from TEM investigations. The microstructure of ECAP nickel was not homogeneous. The grain refinement was more extensive after 12 passes as in the present investigation than 8 passes (studied earlier), when processing in both the cases was through ECAP using route B C. The grain boundary character distribution (GBCD) was determined in the 12-pass ECAP Nickel. The details changed depending on whether the cut-off angle was 5° or 2°. In the present investigation we found that a 5° cut-off gave physically more meaningful results. The Vickers micro-hardness depended on the location in the extruded sample and varied between 1.56 GPa and 2.47 GPa, for an applied load of 25 g. When the load was increased to 50 g, it ranged between 1.6 GPa and 2.3 GPa.

Effects of equal channel angular extrusion and subsequent heat treatment on tribological properties of TiNi alloy

The friction and wear properties of TiNi alloy processed by equal channel angular extrusion (ECAE) and subsequent heat treatment processing under dry sliding condition were evaluated on a block on ring M-2000 tribometer. The effects of ECAE and heat treatment on the tribological properties of TiNi alloy were investigated. The worn surface morphologies of TiNi alloy were examined by scanning electron microscopy (SEM) and the wear mechanisms were discussed. The results showed that ECAE and heat treatment contributed to improve the friction and wear behaviours of TiNi alloy remarkably. The friction coefficient and wear loss of TiNi alloy decreased after ECAE and heat treatment. The maximum wear reduction was obtained when the heat treatment temperature after ECAE was 773 K. Adhesion wear and delamination were notable for the initial TiNi alloy. The material delamination was greatly abated when the heat treatment temperature of TiNi alloy processed by ECAE was 773 K.