Different materials processed by Equal Channel Angular Sheet Extrusion (ECASE): Microstructure and Texture EvolutionDifferent materials processed by Equal Channel Angular Sheet Extrusion (ECASE): Microstructure and Texture Evolution

BOLMARO, RAÚL; TARTALINI, VANINA; ÁVALOS, MARTINA; MUÑOZ, JAIRO; RISSO, PABLO

La Falda

Congreso; 5º Congreso Argentino de Microscopía; 2018

Sociedad Argentina de Microscopía

p { margin-bottom: 0.1in; direction: ltr; line-height: 120%; text-align: left; }p.western { font-family: "Calibri",serif; }p.cjk { font-family: "Calibri"; }p.ctl { font-family: "Times New Roman"; }a:link { }Severeplastic deformation leads to an increase in the strength of themetallic materials but at the same time also reduces the homogeneousdeformation zone leading to lower ductility. Because of the reductionin the strain hardening capacity of the material as a consequence ofdepletion in dislocations accumulation. Another issue related withthe production of UFG materials is the productivity of SPDtechniques, since the processing requirements (pressure, friction,and tools processing strength) are highly demanding, particularlywhen increasing the dimensions of the processed material. To solvethis problem some new SPD techniques, based on the originalprinciples of shear strain, have been proposed. Equal Channel AngularRolling (ECAR) [CITATION Han04 l 11274 ]and Equal Channel Angular SheetExtrusion (ECASE) [CITATION Zis06 l 11274 ]are some of these Equal Channel Angular Pressing (ECAP) modifiedtechniques. Theyhave been both proposed with the main purpose of using alreadyaccepted production techniques, like rolling, with minimummodifications on the technical characteristics to minimize industrialadoption resistance. Theaim of this work is the study of the microstructure and textureevolution of metallic materials processed by ECASE at differentnumber of passes via ElectronBackscattered Diffraction (EBSD)and X-ray diffraction. Twomaterials (AA6063T6 and stainless steel 304L) were received in theform of sheets of 38mm width and 3 mm thickness. The sheets weredivided into billets, and subject to severe plastic deformation byECASE at room temperature. ECASEwas carried out using two parts die with an inner angle of Ф = 150º(see Figure 1), resulting in a strain of ~0.31per pass according with Zisman et al. [CITATION Zis06 l 11274 ].Themicrostructure and local texture of the samples were characterized byEBSD. For this purpose, specimens were cut from the TD plane of theECASE samples (see Error: Reference source not foundb) andmechanically polished to 2500 grit finishing with colloidal silica(0.05µm) in a vibratory polisher for 2 hours. Kikuchi patterns wereacquired by using a TSL EDAX system mounted on a FEG-SEM (Quanta 200- FEI). TheX-ray diffraction measurements (overall texture measure) of thesamples were carried out on a Philips X pert Pro MPD diffractometerwith a Cu-Kα radiation. Thespecimens were mechanically polished to 1000 grit and then etchedwith Kellers solution.Theinitial data was corrected for defocusing and further analyzed byWXpopLA. InFigure 2itcanbe observed the different EBSD microstructures (Inverse Pole Figures(IPF) maps) for both materials processed at different number of ECASEpasses. It is seen how there is a progressive change in themicrostructure morphology (grain size) and internal statisticparameters (average misorientation) as the deformation increases.Both materials showed textures changes with respect to theunprocessed condition especially near to the sheet edges. Indicatingthe higher material hardening in the edges than in the center of thesheets. Thetwo materials, one with high Stacking Fault Energy (SFE) (Al) and thesecond with low SFE (Stainless steel) were processed by ECASE at roomtemperature. Both materials showed microstructure changes such as thereduction in the grain size and the average misorientation. Differentstrengthening mechanisms were identified. In the case of the AA6063the main contributions were coming from the precipitation anddislocation effect. On the other hand, the steel 304L presentedcontribution from dislocations, twins and from phase transformations.