机械类外文翻译【FY084】等径角挤压的织构演变【PDF+WORD】【中文7000字】
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Materials Science and Engineering A 372 (2004) 235244Texture evolution during equal channel angular extrusion (ECAE)Part II. An effect of post-deformation annealingS. Ferrasse, V.M. Segal, F. AlfordHoneywell Electronic Materials, 15128 East Euclid Avenue, Spokane, WA 99216, USAReceived 4 November 2002; received in revised form 21 December 2003AbstractThe influence of annealing on texture after ECAE of Al0.5Cu alloy is described. It is shown that annealing presents multiple opportunitiesto control texture, which are correlated with the transformations of microstructures created during various ECAE strain paths. Up to thetemperature of primary recrystallization, two domains are distinguishable. Before four passes, large modifications in texture strength and/ororientation are obtained. After four passes, except in some cases for route C, rather limited changes in texture strength and orientationsare observed. Annealing at higher temperatures decreases texture strength in both domains. Route C exhibits a specific behavior showingsignificant changes even after four passes. 2004 Elsevier B.V. All rights reserved.Keywords: Texture evolution; Equal channel angular extrusion (ECAE); Post-deformation annealing1. IntroductionCurrent studies concerning texture evolution during an-nealing reveals many complex and not yet fully understoodphenomena. One of the most remarkable results is that ini-tial deformation textures can be completely modified by re-crystallization 15. Three main types of evolution havebeen reported upon recrystallization 3: (i) the deformationtexture retains essentially its main features upon annealing;(ii) there is a clear randomization; (iii) a component that isonly negligible in the deformed condition can become dom-inant resulting in a strong recrystallized texture. Theoreticalefforts have tried to explain the origin of texture modifica-tion by using the models of oriented nucleation and orientedgrowth. Most of this work has focused on conventional pro-cesses, in particular rolling.The intent of this paper is to investigate the effect of an-nealing after equal channel angular extrusion (ECAE) 69.This process based on simple shear has been proven veryefficient to produce sub-micron-grained (SMG) microstruc-tures by severe plastic deformation 919. Textures pro-duced by ECAE are also increasingly studied 2041. Part Iof this study 26 revealed that two ECAE parameters are theCorresponding author.E-mail address: stephane.ferrasse (S. Ferrasse).most effective to control texture: route and number of passes.Annealing is expected to be a third controlling factor. In thispaper, three annealing treatments are performed to allow thefollowing basic phenomena to occur: recovery, full comple-tion of static recrystallization and secondary recrystalliza-tion. Several cases with specific ECAE route and number ofpasses are investigated. This study provides a description ofthe influence of post-ECAE annealing on texture.2. Experimental procedureECAE experiments including materials selection and pro-cessing were described in Part I 26. Each Al0.5Cu spec-imen was subjected to three different annealing treatments.The first one consists of annealing at 150C, 1 h and resultsin recovery, the second one at 225C, 1 h provides earlystage of static recrystallization and the third one at 300C,1 h promotes grain growth after full static recrystallization.In the case of six passes via route D, the typical structures af-ter the aforementioned annealing treatments showed an aver-age grain size of 0.5H9262m (both for as deformed and recoveredstates), 12 and 25H9262m, respectively (Fig. 1). Measurement ofcrystallographic textures 4244 and their definitions werealso described in Part I 26. The extrusion direction of thelast ECAE pass in all cases refers to the horizontal axis of0921-5093/$ see front matter 2004 Elsevier B.V. All rights reserved.doi:10.1016/j.msea.2003.12.043nts236 S. Ferrasse et al. / Materials Science and Engineering A 372 (2004) 235244Fig. 1. TEM (a); (b) and optical (c); (d) structures of Al0.5Cu after six passes via route D in the as deformed state (a) and after further annealing at150C, 1 h (b); 225C, 1 h (c) and 300C, 1 h (d).ODF 26. Similarly to Part I 26, main orientations arecharacterized both by the ideal representation xyzuvwand Euler angles , , (Roe/Matthies convention) and cor-responding fibers are noted Fxy 26, where a letter x showsECAE route and a number y relates to sets of Euler angles , at the considered ODF cross-sections. This notation waschosen because, on the one hand, each ECAE route selectsspecific fibers and, on the other hand, there is some resem-blance in the definition of these fibers (especially , angles)due to simple shear deformation mode at each ECAE pass.3. Results3.1. Textures after ECAE and recovery annealing at(150C, 1 h)Textures after recovery annealing are compared to the asdeformed textures described in Part I (see Tables 15 in26). Principal results are summarized below.First, a large variety of asymmetric textures are foundafter recovery annealing (Figs. 27) because characteristicdeformation textures of each ECAE route 26 are clearlypresent. The main deformation fibers are still visible afterrecovery including FA3 for route A, FD1 for route D, FC1and FC3 for route C, and FB3 and FB1 for route B.Second, for most routes, annealing at 150C, 1 h affectsdeformation textures in two different ways.Before four passes, there are obvious transformations intexture strength and orientation during recovery annealing(Figs. 25 and 8). These changes are linked to variations inthe strength and main orientations of each fiber. The mostradical modifications take place at two passes via routes C,B and D (Figs. 3(a), and 8(b) and (d), and at three andfour passes via route A (Figs. 2(d) and 8(a). For route A,the (7 2 10) and (2 1 2) planes are chosen after three passesinstead of the initial (1 0 2) plane (Fig. 2(d), and the (1 0 2)and (2 1 2) planes are selected after four passes instead ofinitial (2 1 3) plane 26. For two passes via route C, there isa sharp diminution in OD index by a factor 12 (Fig. 8(c).After more than four passes, for all routes except route Cat odd passes (Figs. 7 and 8(c), recovered textures remainquite similar to deformation textures. Routes D (see ODFin Fig. 7) and B are the most stable. In route D, the FD1fiber associated with the (1 0 3)(1 0 2) major planes is pre-dominant and its strength is slightly reinforced (Figs. 7 andntsS. Ferrasse et al. / Materials Science and Engineering A 372 (2004) 235244 237Fig. 2. Inverse pole figures for two passes (a, b and c) and three passes (d, e and f) via route A after annealing at: 150C, 1 h (a and d); 225C, 1 h (band e) and 300C, 1 h (c and f).8(d). For route B, limited texture weakening is observed(Fig. 8(b). For route A, textures remain weak and max-ima in each fiber possess less than 5% of total orientations(Fig. 8(a). For route C with four, six and eight passes, tex-ture strength in deformed and recovered samples remainsidentical while orientations shift slightly from the (2 2 0)plane to near (4 1 4) plane with the addition of a weak (2 0 0)component.Third, contrary to other investigated routes, route C ex-hibits a special behavior (Figs. 5 and 8(c). Even after fiveand seven passes, significant changes are observed duringrecovery in both texture strength and orientation (Fig. 8(c).Strong textures are created at one, three, five and sevenpasses, whereas mediumstrong ones are produced at two,four, six and eight passes. In addition, texture orientationsfor four, six and eight passes are concentrated around planes(2 2 0)(4 1 4) and (2 0 0) (Fig. 5(a) and (c), whereas for fiveFig. 3. Inverse pole figures for two passes via route B (or D) after annealing at: 150C, 1 h (a); 225C, 1 h (b) and 300C, 1 h (c).and seven passes, a single main orientation is observed nearthe (2 1 3)(7 2 10) planes (Fig. 5(b) and (d). Textural cy-cles were also found for route C in the as deformed state forroute C and attributed to the inversion of simple shear direc-tion at each pass combined with hysteresis 26. However,in recovered specimens, the amplitude of cycles is exactlyinverted to the deformed case (Fig. 8(c). ODF analysis ofthe two major fibers for route C, namely FC1 and FC3 26,shows that, while FC1 stays relatively stable, the FC3 fiberalternates at each pass but in a reverse manner compared tothe as deformed condition.3.2. First stage of static recrystallization (primaryrecrystallization)The textures presented in this chapter are comparedto those in the recovered state to assess the influence ofnts238 S. Ferrasse et al. / Materials Science and Engineering A 372 (2004) 235244Fig. 4. Inverse pole figures for three passes via route B (a, b and c) and D (d, e and f) after annealing at: 150C, 1 h (a and d); 225C, 1 h (b and e)and 300C, 1 h (c and f).recrystallization. Many of the major trends observedduring recovery are still valid at the recrystallizationstage.First, the same set of fibers can be identified.Fig. 5. Inverse pole figures for four ECAE passes (a); five ECAE passes (b); six ECAE passes (c) and seven ECAE passes (d) via route C after annealingat 150C, 1 h.Second, the same areas for strains are discernable in termof texture evolution.Before four passes, textures can be significantly modified,especially at two passes (Figs. 24 and 6). For example, afterntsS. Ferrasse et al. / Materials Science and Engineering A 372 (2004) 235244 239Fig. 6. Inverse pole figure for six ECAE passes (a) and seven ECAE passes (b) via route C after annealing at 225C, 1 h.two passes via route A (Fig. 2(b), the OD index increasesfrom5to19t.r.(Fig. 8(a). For routes B or D, the OD indexis reduced from 32 to 13 t.r. and the (1 1 1) and (2 0 3) planesare preferred in contrast to plane (2 1 6) for the recoveredstate (Fig. 3(b), and 8(b) and (d). Also for route C at twopasses (Fig. 6(a), texture gets stronger compared to therecovered state due to the FC3 fiber, which contains up to21% of the grains and is associated with the (1 0 1) plane(Fig. 8(c). However, textures at three and four passes viaroute A remain stable (Figs. 2(e) and 8(a).After four passes, for all routes and even in a lesser extentfor route C, textures conserve most of the features alreadyFig. 7. ODF sections for = 0, 15, 30 and 45for eight passes via route D after ECAE (a) and following annealing at: 150C, 1 h (b); 225C, 1 h(c) and 300C, 1 h (d).presented in the recovered state (Figs. 7 and 8). Route D isthe most stable with FD1 as the major fiber (Figs. 7 and 8(d).In route B, there is a strengthening of the FB1 fiber at six andeight passes up to 1012% while (1 0 4)(1 0 3) and (7 2 10)orientations are maintained. In route A, texture strength staysunchanged in the weak or medium range (Fig. 8(a) and,after six passes, orientations vary insignificantly. For routeC, in contrast to the deformed and recovery cases, there ismore continuity between the recovered and recrystallizedtextures after three passes. The main changes consist in aglobal decrease in texture strength linked with the weakeningof the principal fiber FC3 (Fig. 8(c). In parallel, the cyclicnts240 S. Ferrasse et al. / Materials Science and Engineering A 372 (2004) 235244texture evolution typical for route C is still observed butat lower amplitude and without inversion of the strengthmaxima and minima between recovered and recrystallizedconditions. Main orientations, which have migrated towardthe (2 2 0) plane, remain nearly the same as in the recoveredstate (Fig. 6(a) and (b). In a sense, there is less effect ofhysteresis on texture for recrystallized samples.3.3. Extended stage of static recrystallization (secondaryrecrystallization)First, the most common effect of annealing at 300C, 1 hin comparison to annealing at 225C, 1 h is a global decreasein texture strength (Fig. 8). This effect is especially clearbefore four passes and for routes A and C because of veryFig. 8. Texture strength (OD index) in function of total number of passes and annealing for route A (a); route B (b); route C (c) and route D (d).strong recrystallized textures after annealing at 225C, 1 h.The only case where texture strength remains quite stable istwo passes via routes B and D (Fig. 8(b) and (d).Second, there is a trend toward (1 0 0) orientations formost routes, especially before four passes (Figs. 24). Ma-jor planes approach the areas extending from (1 0 0)(1 0 4)to approximately (1 1 9)(1 1 5), which are within less than15of the (1 0 0) pole. Main deformation fibers are still vis-ible but become weaker and reach the level of minor fibers.The shift toward the (1 0 0) pole corresponds to lower val-ues of Euler angle within a fiber. It is particularly evi-dent for textures obtained before four passes, which showsthe widest variations in orientation. Sufficiently strong near(1 0 0) textures are obtained for routes A and B (or D) attwo passes (Figs. 3(c) and 4(c). Other (1 0 0)-like texturesntsS. Ferrasse et al. / Materials Science and Engineering A 372 (2004) 235244 241Fig. 8. (Continued ).are rather weak or medium (Figs. 3(f) and 5(f). The cubeorientation found in recrystallized rolled samples is presentbut not predominant. For example, at two passes, the cubecomponent is minor compared to 108010 for route Aor 102221 for routes B or D. Also, some textures arenot close to (1 0 0) as, for example one pass route A andthree passes route B (Fig. 4(c). Above four passes, route Cexhibits the most obvious migration towards the (1 0 0) areafor all passes.Third, after four passes, textures are more stable as exem-plified by routes D (Figs. 7 and 8(d) and B despite somelimited strengthening at eight passes (Fig. 8(b). Route Ais subjected to limited but continuous changes (Fig. 8(a).Route C is still the most variable upon secondary recrystal-lization but with the absence of cyclic evolution (Fig. 8(c).4. DiscussionPrevious papers 2040 and Part I 26 have alreadydemonstrated the multiple advantages offered by ECAE toobtain controllable structures and textures. Two efficientECAE parameters, the number of passes and route, wereidentified 26. Post-deformation annealing at various tem-peratures and times constitutes a third technological param-eter.Thermal treatment after ECAE exerts a significant butcomplex influence on both texture strength and orientationwith three notable features: (i) characteristic deformationfibers of each ECAE route are still maintained but modi-fied even up to annealing at (300C, 1 h); (ii) two regionsfor texture evolution are identified: prior to four passes, thents242 S. Ferrasse et al. / Materials Science and Engineering A 372 (2004) 235244largest variations in texture development are found, whereasafter four passes textures are stable or exhibit a continuousevolution; (iii) after annealing at (300C, 1 h), a global tex-ture weakening is observed with, for some cases, a migra-tion towards (1 0 0)-like orientation. These features can beunderstood by the evolution during annealing of the variousmicrostructures created for each ECAE route, either beforeor after four passes.ECAE between one and four passes corresponds to a truestrain range between 1.16 and 4.64, which is equivalent torolling reduction from 50 to 99%. This deformation range istypical of rolled aluminum alloys, where most research ontexture has been concentrated 15,45,46. ECAE materialsbefore four passes are similar to what is usually termed asheavily deformed metals and one can suppose some close re-lation in operating structural mechanisms at different stagesof annealing. ECAE structures at one pass contain numerousdefects like dislocations arrays and cell substructures withsome micro-bands and shear bands, as reported in previousTEM investigations 1018. After two and three passes,subgrains with low angle boundaries are formed 14. Ex-cept for the high angle boundaries corresponding to longlamellae and shear bands, most of these structural featuresare not stable during recovery annealing 1,3,45. Even highangle boundaries are in a non-equilibrium state. In partic-ular, dislocations can be removed or rearranged and somesubgrain growth and coalescence can be observed. All thesephenomena affect textures in a complex way as shown by themultiple textural modifications observed prior to four passes3,45,46. However, these changes are not radical enough toeliminate original deformation fibers.Further annealing up to 225C, 1 h results in static re-crystallization (or primary recrystallization) in ECAE pro-cessed Al0.5Cu. Observations by optical microscopy showthat recrystallization is fully completed for microstructuresdeformed via three passes or more, whereas for one andtwo passes only partial recrystallization is observed. Duringthis process, many complex structural and textural changesoccur by formation of new nuclei and grains due to grainboundary migration 15,43. However, remarkably, themain deformation fibers are still identifiable. According to3,4550, during the first stage of static recrystallization inpolycrystals, new grains are formed from recovered regionsof the original deformed microstructure, cells or sub-grainsrather than by nucleation of new crystals with totally neworientations. Therefore, new grains have orientations simi-lar to those of deformed and recovered regions of originalstructure. This explains the presence of ECAE deformationfibers even after annealing at 225C, 1 h. At later stagesof recrystallization, the new grains start to grow at variousrates and compete as explained in various proposed mecha-nisms of oriented growth and nucleation found in literature15,4550. The important result is that the main orien-tation within a fiber change. In some cases, modificationin orientations can be radical like for two passes route C
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