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Equal channel angular pressing technique for the formation of ultra-fine grained structures
Kazeem O. Sanusi,Oluwole D. Makinde,Graeme J. Oliver
South African Journal of Science , 2012,
Abstract: Equal channel angular pressing is one of the techniques in metal forming processes in which an ultra-large plastic strain is imposed on a bulk material in order to make ultra-fine grained and nanocrystalline metals and alloys. The technique is a viable forming procedure to extrude materials by use of specially designed channel dies without substantially changing the geometry by imposing severe plastic deformation. This technique has the potential for high strain rate superplasticity by effective grain refinement to the level of the submicron-scale or nanoscale. Wereview recent work on new trends in equal channel angular pressing techniques and the manufacturing of die-sets used for the processing of metals and alloys. We also experimented on a copper alloy using the equal channel angular pressing technique to examine the microstructural, mechanical and hardness properties of the ultra-fine grained and nanocrystalline materials produced. After deformation, all samples were subjected to a hardness test and the results showed improved mechanical behaviour of the ultra-fine grained copper alloy that was developed. This research provides an opportunity to examine the significance of the equal channel angular pressing process for metals and alloys. That is, these ultra-fine grained materials can be used in the manufacturing of semi-finished products used in the power, aerospace, medical and automotive industries.
EVOLUTION OF MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ULTRA-FINE-GRAINED INTERSTITIAL-FREE STEEL PROCESSED BY EQUAL CHANNEL ANGULAR PRESSING
Tomá? Krajňák,Kristián Máthis
Materials Engineering , 2013,
Abstract: Equal channel angular pressing (ECAP) is one of the severe plastic deformation techniques which is widely used for producing metals with ultra- ne-grained microstructures. In the present work the influence of number of pressing by route BC on grain size, evolution of microstructure and mechanical properties of interstitial-free (IF) steel has been investigated by means of optical microscopy, electron back-scattering diffraction (EBSD) and tensile tests. It has been found, that the grain size decreases with increasing number of passes. Simultaneously tensile strength increases. The thermal stability of ECAP-processed microstructures has been also examined. It was found that the degradation of mechanical properties occurs only above 600 C and 700 C.
Texture analysis in ultrafine grained coppers processed by equal channel angular pressing
Higuera, Oscar Fabián;Cabrera, J. M.;
Materials Research , 2013, DOI: 10.1590/S1516-14392013005000032
Abstract: electrolytic tough pitch (etp) and fire refined high conductivity (frhc) copper samples were severely deformed at room temperature by equal channel angular pressing (ecap) up to 16 passes (ε ~ 1 per pass), following route bc. the effect of the initial texture on the evolution of texture after the ecap process for both materials was analyzed. the annealed materials present a marked anisotropy, with a texture controlled by the <110> fiber. according to the orientation distribution function (odf), this initial behavior allows the presence of a strong c ({001} <110>) component after the first two ecap passes in both coppers. however in the second pass the c component significantly increases in the frhc copper, whereas the etp copper presents a much more balanced behavior of the a1* (111)[ 2]and a2* (111)[11 ]components. the textures obtained for both coppers after each ecap pass exhibit predominant orientations with continuous distributions along the orientation fiber with simple shear texture.
Microstructural evolution of fine-grained ZA27 alloy during partial remelting  [PDF]
Chen Tijun,Fu Mingfeng,Hao Yuan
China Foundry , 2010,
Abstract: The microstructural evolution process of fined-grained ZA27 alloy during partial remelting has been investigated. The relationship between the as-cast and semi-solid microstructures has been discussed in particular. The results indicate that a semi-solid microstructure with small and spheroidal primary particles can be obtained when the ZA27 alloy is partially remelted. The microstructural evolution can be divided into four stages, the initial coarsening of the dendrites due to coalescence of dendrite arms, structural separation resulted from the melting of residual interdendritic eutectic, spheroidization due to the partial melting of solid particles and final coarsening attributed to the coalescence and Ostwald ripening. An equiaxed dendrite in the as-cast microstructure may evolve into one spheroidal particle in the semi-solid microsturucture after being partially remelted. The more equiaxed the dendrites in an as-cast microstructure are, the more spheroidal the solid particles in the semi-solid microstructure will be. Finer primary particles could be obtained if the alloy with finer as-cast microstructure was partially remelted. However, due to the coalescence effect, their sizes cannot be reduced further if the refined as-cast microstructure reached a certain extent.
Microstructural Development of Fe-20mass%Cr Alloys and Pure Copper Processed by Equal-Channel Angular Pressing  [PDF]
Muhammad Rifai, Ryosuke Haga, Hiroyuki Miyamoto, Hiroshi Fujiwara
Materials Sciences and Applications (MSA) , 2013, DOI: 10.4236/msa.2013.44031
Abstract:

Microstructural development of ultra low C, N, Fe-Cr alloy and pure copper processed by equal-channel angular pressing (ECAP) have been examined focusing on the initial stage of the formation of ultrafine grain structure. Fe-Cr alloys were pressed at 423 K while pure copper at room temperature for 1 to 3 passes via the route Bc to compare at the equivalent homologous temperature. Microstructural evolutions were characterized by electron backscatter diffraction (EBSD) image and transmission electron microscopy (TEM). It was found that deformation structures were mostly deformation-induced subboundaries in both the materials after one pass, but the fraction of high-angle grain boundary became higher in the Fe-Cr alloys than in pure copper in subsequent passes by increasing misorientation of the boundaries. The more enhanced formation of high angle boundaries in Fe-Cr alloys was discussed in terms of the nature of crystal slip of FCC and BCC structures.

Microstructural Evolution of Ultra Fine Grained C-Mn Steel Warm Rolling and Intercritical Annea
Brzuszek, R.K.;Rodrigues, P.C.M.;Motta, L.S.;Santos, D.B.;
Materials Research , 2002, DOI: 10.1590/S1516-14392002000300020
Abstract: the attainment of finer ferrite grain structure in low carbon is object of interest because significantly higher yield strengths and lower ductile-brittle transition temperatures can be predicted at the same time with ultra-fine grain sizes. this work verified the microstructural evolution of a low carbon 0.15%c-1.39%mn steel after an ice brine quenching from 1200 °c followed by warm rolling and intercritical annealing at 800 °c at different times. to compare the final microstructure, a first group of specimens were heated at temperatures in the range from 660 °c to 800 °c during 30 min and quenching in ice brine. after quenching from 1200 °c, a second group of specimens were laboratory warm rolled at 700 °c and annealed at 800 °c, for 1, 60, 120 and 180 min, following air cooling or quenching. the final microstructure of all specimens was analyzed by quantitative metallography using optical and scanning electron microscopy. the initial steel grain size condition was 120 μm. the specimens, after the whole processing cycle achieved a microstructure with ferrite grain size between 1 μm and 1.5 μm. the ferrite grain size values changed until 50% for samples warm rolled and heat treated between the first and last annealing time.
Microstructural Evolution of Ultra Fine Grained C-Mn Steel Warm Rolling and Intercritical Annea
Brzuszek R.K.,Rodrigues P.C.M.,Motta L.S.,Santos D.B.
Materials Research , 2002,
Abstract: The attainment of finer ferrite grain structure in low carbon is object of interest because significantly higher yield strengths and lower ductile-brittle transition temperatures can be predicted at the same time with ultra-fine grain sizes. This work verified the microstructural evolution of a low carbon 0.15%C-1.39%Mn steel after an ice brine quenching from 1200 °C followed by warm rolling and intercritical annealing at 800 °C at different times. To compare the final microstructure, a first group of specimens were heated at temperatures in the range from 660 °C to 800 °C during 30 min and quenching in ice brine. After quenching from 1200 °C, a second group of specimens were laboratory warm rolled at 700 °C and annealed at 800 °C, for 1, 60, 120 and 180 min, following air cooling or quenching. The final microstructure of all specimens was analyzed by quantitative metallography using optical and scanning electron microscopy. The initial steel grain size condition was 120 μm. The specimens, after the whole processing cycle achieved a microstructure with ferrite grain size between 1 μm and 1.5 μm. The ferrite grain size values changed until 50% for samples warm rolled and heat treated between the first and last annealing time.
Microstructural evolution of equal channel angular pressed AZ91D magnesium alloy during semi-solid isothermal heat treatment  [PDF]
Chen Tijun,Lu Guoxiang,Hao Yuan
China Foundry , 2008,
Abstract: The microstructural evolution of AZ91D magnesium alloy processed by equal channel angular pressing during isothermal heat treatment at 570℃ was investigated. The results indicated that the equal channel angular pressing followed by semi-solid isothermal heat treatment was an effective method to prepare semisolid nondendritic slurry of AZ91D magnesium alloy. During this process, its microstructure change underwent four stages, the initial coarsening stage, the structure separation stage, the spheroidization stage and the final coarsening stage. The microstructural spheroidization effect was the best after being heated for 15 min for the alloy pressed for four passes, and the grain size was the smallest. With the further increase of heating time, the grain size and shape factor increased. When the heating time was kept constant, the grain size and shape factor decreased with the increase of pressing passes.
Grain refinement in AZ31 alloy processed by equal channel angular pressing  [PDF]
K. Bry?a,J. Dutkiewicz,Institute of Metallurgy and Materials Science, Polish Academy of Sciences, ul. W. Reymonta 25, 30-059 Kraków, Poland
Archives of Materials Science and Engineering , 2009,
Abstract: Purpose: of this paper was to investigate the effect of grain refinement in AZ31 magnesium alloy processed by ECAP and to study microstructure evolution and hardness response of AZ31 alloy associated with ECAP processing.Design/methodology/approach: The microstructure of AZ31 magnesium alloy after two passes of equal channel angular pressing at 150°C, 180°C and 250°C was studied by means of metallographic and transmission electron microscopy. The hardness changes after ECAP processing were determined by Vickers hardness.Findings: The grain refinement in AZ31 magnesium alloy was successfully carried out using ECAP processing at 150, 180 and 250°C. The grain size decreases nearly 10 times after 2 passes of ECAP at 150 and 180°C, but microstructure is characterized by bimodal grains structure. The rather homogenous grains were achieved after ECAP processing at 250°C. Processes of dynamic recrystallization during ECAP were observed. The hardness increase related to grain refinement proceeded by ECAP is in accordance with Hall-Petch relationship.Research limitations/implications: The ECAP processing were carried out only after 2 passes, therefore in order to describe in detail the microstructural changes connected with grain refinement, the analysis of more passes of ECAP processing should be done.Practical implications: The development of highly ductile magnesium alloys allows to apply these materials as structural materials. The grain refinement of materials leads to the significant improvement of the mechanical properties and plasticity. The present results extend the knowledge about grain refinement in AZ31 alloy proceeded by ECAP.Originality/value: The microstructural studies of AZ31 alloy after grain refining by ECAP processing performed by transmission electron microscopy were presented.
Microstructure and mechanical properties of Pb-4%Sb alloy processed by equal channel angular pressing
Figueiredo, Roberto Braga;Costa, André Luiz de Moraes;Andrade, Margareth Spangler;Aguilar, Maria Teresa Paulino;Cetlin, Paulo Roberto;
Materials Research , 2006, DOI: 10.1590/S1516-14392006000100019
Abstract: equal channel angular pressing (ecap) is the most prominent spd (severe plastic deformation) method for the production of ultrafine and nanostructured metals, and has been extensively employed and analyzed. this technique was applied to a pb-4%sb alloy at room temperature, in order to study its effect on a low melting point and multiphase metallic material. the material was subjected to effective strains higher than 9, after 8 passes of processing, where dynamic and static recrystallization are expected during and after each pass. this eliminates any grain refinement and allows the analysis only of the microstructural effects associated with second phase redistribution and eventual precipitate dissolution. ecap followed route c, which eliminates structural alignment after each even ecap pass, facilitating the study of the microstructural evolution. it is shown that three ecap passes are necessary to completely break the lamellar structure of the as cast strucure and that antimony dissolves into the lead rich matrix. dynamic recrystallization and structural changes reduce the material strength and change the flow curve format.
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