《金属材料强韧化与组织调控》教学资源（参考文献）Constrained groove pressing and its application to grain refinement of aluminum

MATERIALS SGIENGE& EMGINEERING ELSEVIER Materials Science and Engineering A328 (2002)98-103 www.elsevier.com/locate/msea Constrained groove pressing and its application to grain refinement of aluminum Dong Hyuk Shin .*Jong-Jin Parkb,Yong-Seog Kim,Kyung-Tae Park d Department of Metallurgy and Materials Science.Hanyang University,Ansan,Kyunggi-Do 425-791,South Korea bDepartment of Mechanical Engineering,Hongik University,Seoul 121-791.South Korea Department of Metallurgy and Materials Science,Hongik University,Seoul 121-791,South Korea a Division of Advanced Materials Science and Engineering,Hanbat National University,Taejon 305-719.South Korea Received 19 March 2001;received in revised form 4 June 2001 Abstract The new intense plastic straining technique,named 'constrained groove pressing'(CGP).was developed for fabrication of plate-shaped ultrafined grained metallic materials without changing their initial dimensions.The principle of CGP is that a material is subjected to the repetitive shear deformation under the plane strain deformation condition by utilizing alternate pressing with the asymmetrically grooved die and flat die constrained tightly by the cylinder wall.A submicrometer order grain structure was obtained in pure aluminum by utilizing this technique.The grain refinement sequences during pressing were examined by transmission electron microscopy.The enhancement of the mechanical properties of submicrometer order grained pure aluminum fabricated by this technique was comparable to that produced by other intense plastic straining techniques at the similar accumulated strains.2002 Elsevier Science B.V.All rights reserved. Keywords:Grain refinement;Aluminum;Transmission electron microscopy;Mechanical properties 1.Introduction ultrafine grained materials was developed and applied to pure Al to examine its feasibility for grain Recently,a considerable effort has been made to refinement. produce ultrafine grained bulk materials without poros- ity by imposing severe plastic straining such as equal channel angular pressing (ECAP),accumulative roll 2.Experimental procedures bonding (ARB),and severe torsional straining (STS) [1].However,the existing techniques using severe plas- 2.1.CGP tic straining seem to be impractical for manufacturing plate-shaped ultrafine grained materials.Although an A schematic illustration of a CGP process is pre- ARB process is designed to make plate-shaped ultrafine sented in Fig.1.At first,a set of asymmetrically grained materials,it involves a repeated bonding be- grooved dies tightly constrained by cylinder wall is tween two rolled plates [2-4].If a perfect bonding is prepared.As groove pressing is carried out such that a not achieved between the plates during ARB,the exis- gap between the upper die and the lower die is same tence of the bonding interface may degrade the me- with the sample thickness,the inclined region of the chanical properties of ARB processed materials.In this sample (single hatched area in Fig.1(b))is subjected to study,a new process,named 'constrained groove press- pure shear deformation under plane strain deformation ing (CGP)',having a potential to produce plate-shaped condition.However,no deformation is induced in the flat region (unhatched area in Fig.1(b)).For the Corresponding author.Tel.:+82-345-400-5224;fax:+82-345- present die design with the groove angle (of 45,a 417-3701. single pressing yields a shear strain of I at deformed E-mail address:dhshin@email.hanyang.ac.kr (D.H.Shin) region.This is equivalent to an effective strain,m of 0921-5093/02/S see front matter 2002 Elsevier Science B.V.All rights reserved. PΠ：S0921-5093(01)01665-3

Materials Science and Engineering A328 (2002) 98–103 Constrained groove pressing and its application to grain refinement of aluminum Dong Hyuk Shin a,*, Jong-Jin Park b , Yong-Seog Kim c , Kyung-Tae Park d a Department of Metallurgy and Materials Science, Hanyang Uni
ersity, Ansan, Kyunggi-Do 425-791, South Korea b Department of Mechanical Engineering, Hongik Uni
ersity, Seoul 121-791, South Korea c Department of Metallurgy and Materials Science, Hongik Uni
ersity, Seoul 121-791, South Korea d Di
ision of Ad
anced Materials Science and Engineering, Hanbat National Uni
ersity, Taejon 305-719, South Korea Received 19 March 2001; received in revised form 4 June 2001 Abstract The new intense plastic straining technique, named ‘constrained groove pressing’ (CGP), was developed for fabrication of plate-shaped ultrafined grained metallic materials without changing their initial dimensions. The principle of CGP is that a material is subjected to the repetitive shear deformation under the plane strain deformation condition by utilizing alternate pressing with the asymmetrically grooved die and flat die constrained tightly by the cylinder wall. A submicrometer order grain structure was obtained in pure aluminum by utilizing this technique. The grain refinement sequences during pressing were examined by transmission electron microscopy. The enhancement of the mechanical properties of submicrometer order grained pure aluminum fabricated by this technique was comparable to that produced by other intense plastic straining techniques at the similar accumulated strains. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Grain refinement; Aluminum; Transmission electron microscopy; Mechanical properties www.elsevier.com/locate/msea 1. Introduction Recently, a considerable effort has been made to produce ultrafine grained bulk materials without poros￾ity by imposing severe plastic straining such as equal channel angular pressing (ECAP), accumulative roll bonding (ARB), and severe torsional straining (STS) [1]. However, the existing techniques using severe plas￾tic straining seem to be impractical for manufacturing plate-shaped ultrafine grained materials. Although an ARB process is designed to make plate-shaped ultrafine grained materials, it involves a repeated bonding be￾tween two rolled plates [2–4]. If a perfect bonding is not achieved between the plates during ARB, the exis￾tence of the bonding interface may degrade the me￾chanical properties of ARB processed materials. In this study, a new process, named ‘constrained groove press￾ing (CGP)’, having a potential to produce plate-shaped ultrafine grained materials was developed and applied to pure Al to examine its feasibility for grain refinement. 2. Experimental procedures 2.1. CGP A schematic illustration of a CGP process is pre￾sented in Fig. 1. At first, a set of asymmetrically grooved dies tightly constrained by cylinder wall is prepared. As groove pressing is carried out such that a gap between the upper die and the lower die is same with the sample thickness, the inclined region of the sample (single hatched area in Fig. 1(b)) is subjected to pure shear deformation under plane strain deformation condition. However, no deformation is induced in the flat region (unhatched area in Fig. 1(b)). For the present die design with the groove angle (
) of 45°, a single pressing yields a shear strain of 1 at deformed region. This is equivalent to an effective strain, eff, of * Corresponding author. Tel.: +82-345-400-5224; fax: +82-345- 417-3701. E-mail address: dhshin@email.hanyang.ac.kr (D.H. Shin). 0921-5093/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 5 0 9 3 ( 0 1 ) 0 1 6 6 5 - 3

D.H.Shin et al.Materials Science and Engineering A328 (2002)98-103 99 (a) (b) (c) 曲田曲由曲田田 sample (thickness:t) (d) (e) ( ☐no deformation ☐eem0.58 田eel.16 Fig.1.A schematic illustration of the sequences of the constrained groove pressing (CGP)technique. 0.58.The second pressing is performed with a set of flat ples was examined by utilizing a JEOL 2010 transmis- dies (Fig.1(c)).By flat pressing under the constrained sion electron microscope (TEM)operating at 200 kV. condition,the previous deformed region is subjected to The pieces of the sample for thin foil preparation were the reverse shear deformation while the previous unde- taken from the central part of the CGPed plate.Thin formed region remains undeformed.The cumulative foils for TEM observation were prepared by twin-jet strain,fem in the deformed region following the second polishing using a mixture of 20%perchloric acid and pressing becomes 1.16 (double hatched area in Fig. 80%methanol at an applied potential of 40 V and at 1(c)).After the second pressing,the sample is rotated 233 K.In order to examine the homogeneity of defor- by 180(Fig.I(d)).This allows the undeformed region mation,the Vickers microhardness was measured along to be deformed by further pressings due to the asymme- the central line of the transverse cross-section by apply- try of the grooved die.Then,the successive pressings ing 100 g load for 15 s.The tensile testing specimens with a grooved die (Fig.1(e))and a flat die (Fig.1(f)) with the gage length dimension of25.4×6×2mm3 result in a homogeneous effective strain of 1.16 were machined such that the gage length was aligned throughout the sample.By repeating a CGP process, along the longitudinal direction of the pressed plate. very large amount of plastic strain can be accumulated Room temperature tensile testing was carried out on an in the sample without changing its initial dimensions Instron machine operating at an initial strain rate of and,resultantly,an ultrafine grained structure can be 1×10-3s-. obtained 2.2.Material,microstructural examination and 3.Results and discussion mechanical testing 3.I.Microstructure In the present study,a plate of pure Al(99.99%)with the dimension of 70 x 70 x 6 mm was pressed by apply- The linear intercept grain size of annealed pure Al ing the CGP technique described above.Before press- was about 1.2 mm.As shown in Fig.2,the substructure ing,the plate of pure Al was annealed at 773 K for 4 h. of annealed pure Al consisted of dislocation cells with Pressing was conducted up to a total of 16 pressings on an average diameter of about 3 um.In Fig.3,the a 200 ton hydraulic pressing machine operating at a microstructural changes during CGP are shown in or- constant press speed of 0.2 mm s-at room tempera- der to understand the grain refinement sequences.A ture.Since each series of four pressings yields a homo- single pressing (e=0.58,the single hatched area in Fig. geneous effective strain of 1.16 throughout the sample, 1(b))resulted in a non-uniform microstructure consist- 16 pressings are expected to accumulate an effective ing of both equiaxed and elongated dislocation cells,as strain of 4.64.The microstructure of the pressed sam- shown in Fig.3(a).However,the cell refinement follow-

D.H. Shin et al. / Materials Science and Engineering A328 (2002) 98–103 99 Fig. 1. A schematic illustration of the sequences of the constrained groove pressing (CGP) technique. 0.58. The second pressing is performed with a set of flat dies (Fig. 1(c)). By flat pressing under the constrained condition, the previous deformed region is subjected to the reverse shear deformation while the previous unde￾formed region remains undeformed. The cumulative strain, eff, in the deformed region following the second pressing becomes 1.16 (double hatched area in Fig. 1(c)). After the second pressing, the sample is rotated by 180° (Fig. 1(d)). This allows the undeformed region to be deformed by further pressings due to the asymme￾try of the grooved die. Then, the successive pressings with a grooved die (Fig. 1(e)) and a flat die (Fig. 1(f)) result in a homogeneous effective strain of 1.16 throughout the sample. By repeating a CGP process, very large amount of plastic strain can be accumulated in the sample without changing its initial dimensions and, resultantly, an ultrafine grained structure can be obtained. 2.2. Material, microstructural examination and mechanical testing In the present study, a plate of pure Al (99.99%) with the dimension of 70×70×6 mm was pressed by apply￾ing the CGP technique described above. Before press￾ing, the plate of pure Al was annealed at 773 K for 4 h. Pressing was conducted up to a total of 16 pressings on a 200 ton hydraulic pressing machine operating at a constant press speed of 0.2 mm s−1 at room tempera￾ture. Since each series of four pressings yields a homo￾geneous effective strain of 1.16 throughout the sample, 16 pressings are expected to accumulate an effective strain of 4.64. The microstructure of the pressed sam￾ples was examined by utilizing a JEOL 2010 transmis￾sion electron microscope (TEM) operating at 200 kV. The pieces of the sample for thin foil preparation were taken from the central part of the CGPed plate. Thin foils for TEM observation were prepared by twin-jet polishing using a mixture of 20% perchloric acid and 80% methanol at an applied potential of 40 V and at 233 K. In order to examine the homogeneity of defor￾mation, the Vickers microhardness was measured along the central line of the transverse cross-section by apply￾ing 100 g load for 15 s. The tensile testing specimens with the gage length dimension of 25.4×6×2 mm3 were machined such that the gage length was aligned along the longitudinal direction of the pressed plate. Room temperature tensile testing was carried out on an Instron machine operating at an initial strain rate of 1×10−3 s−1 . 3. Results and discussion 3.1. Microstructure The linear intercept grain size of annealed pure Al was about 1.2 mm. As shown in Fig. 2, the substructure of annealed pure Al consisted of dislocation cells with an average diameter of about 3
m. In Fig. 3, the microstructural changes during CGP are shown in or￾der to understand the grain refinement sequences. A single pressing (=0.58, the single hatched area in Fig. 1(b)) resulted in a non-uniform microstructure consist￾ing of both equiaxed and elongated dislocation cells, as shown in Fig. 3(a). However, the cell refinement follow-

100 D.H.Shin et al.Materials Science and Engineering A328 (2002)98-103 ing a single pressing was not significant:the equiaxed mation on the portion deformed at the first pressing cell size and the width of elongated cells were about I so that the total accumulated strain becomes 1.74 in um.Dislocations consisting the cell boundary exhib- this portion.Fig.3(c)presents the microstructure of ited more tangled configuration compared to those in the deformed portion with s=1.74.The microstruc- the as-annealed sample.After two pressings (s=1.16, ture is characterized by the elongated subgrains with a the double hatched area in Fig.I(c)),the microstruc- width of ~0.5 um which is comparable to the diame- ture was relatively homogeneous with the equiaxed ter of the equiaxed cells formed at s=1.16.In addi- cells of ~0.5 um (Fig.3(b)).Although most cell tion,the dislocation density is high and the dense boundaries consist of severely tangled dislocations, dislocation debris is observed inside the grain interior. well-defined and sharp sub-boundaries began to ap- The micrograph of the sample after six pressings (8= pear.In addition,the partitioning of a relatively 2.32)shown in Fig.3(d)exhibits the typical mi- coarse cell into the smaller cells was evident.The spot crostructural characteristics of ultrafine grained pattern of selected area diffraction (SAD)is clear at metallic materials fabricated by intense plastic strain- this stage,indicating the same crystallographic orien- ing:high dislocation density,ill-defined boundaries tation between cells.Due to 180 rotation of the and extensive extinction contour in the vicinity of the sample at every other pressing step,four pressings boundary,etc.The more diffused spots of the SAD yield the total strain of 1.16 throughout the whole pattern in Fig.3(d)than those observed in the sample portion of the sample as illustrated in Fig.1.There- after two pressings (Fig.3(b))indicated that the mis- fore,the entire microstructure of the sample after four orientation angle between adjacent subgrains in- pressings is expected to be similar to that shown in creased.The grain size after six pressings was slightly Fig.3(b).It is noted that,up to four pressings ( smaller than the cell size of the sample after two pressings (s=1.16)shown in Fig.3(b).This finding is 1.16),dislocations were hardly observed at the cell consistent with the general fact that the grain refine- interior.This finding would be attributed to easy dis- ment is the most significant at the initial stage of location glide inside a cell in which no obstacles for intense plastic straining and becomes saturated with dislocation motion existed as shown in Fig.2.The increasing strain.By the same argument described microstructural evolution sequences during CGP up to above,the microstructure after six pressings would four pressings are similar to those reported in ECAP represent the entire microstructure of the sample after with route C in that the formation of elongated cells eight pressings.As shown in Fig.3(e),the microstruc- or grains and the restoration of equiaxed cells or ture of the sample after 16 pressings (s=4.64)consists grains occur alternately due to repetitive reverse shear- of the polygonized dislocation-free grains with well- ing on the same plane of the segment [5].In ECAP defined boundaries.The grain size after 16 pressings, with route C,the sample is rotated 180 around its ~0.8 um,is coarser than that measured on the sam- longitudinal axis between passages and,resultantly,re- ple after six pressings.The formation of polygonized verse shearing occurs repeatedly on the same plane dislocation-free grains and grain coarsening with in- [6-8].The fifth pressing imposes the repetitive defor- creasing strain is commonly observed in pure Al dur- ing intense plastic straining [5,7,9-11].At this stage, the spots in the SAD pattern became more diffused than those of the previous samples,indicating an increase in the proportion of high-angle boundaries. In order to examine this trend,the SAD pattern of individual grains in Fig.3(e)was compared with those of the adjacent grains.As shown in Fig.4,the SAD patterns of grains 1,2 and 3 exhibit the spot patterns with the different zone axes;the zone axes are [100],[110]and [112],respectively.This in- dicates that the misorientation angles between adja- cent grains are fairly high.The existence of the Kikuchi lines in these SAD patterns is often observed when the grain is not perfectly aligned with respect to the zone axis,typically less that 3-4.Several dif- 0.5m ferent areas of the sample after 16 pressings were examined by the same procedure and the similar re- sults were obtained.This confirms that some portion Fig.2.TEM micrograph showing dislocation cell structure in the of low-angled subboundary converted to high-angled present pure Al annealed at 773 K for 4 h. boundary in the course of the present CGP process

100 D.H. Shin et al. / Materials Science and Engineering A328 (2002) 98–103 ing a single pressing was not significant: the equiaxed cell size and the width of elongated cells were about 1
m. Dislocations consisting the cell boundary exhib￾ited more tangled configuration compared to those in the as-annealed sample. After two pressings (=1.16, the double hatched area in Fig. 1(c)), the microstruc￾ture was relatively homogeneous with the equiaxed cells of
0.5
m (Fig. 3(b)). Although most cell boundaries consist of severely tangled dislocations, well-defined and sharp sub-boundaries began to ap￾pear. In addition, the partitioning of a relatively coarse cell into the smaller cells was evident. The spot pattern of selected area diffraction (SAD) is clear at this stage, indicating the same crystallographic orien￾tation between cells. Due to 180° rotation of the sample at every other pressing step, four pressings yield the total strain of 1.16 throughout the whole portion of the sample as illustrated in Fig. 1. There￾fore, the entire microstructure of the sample after four pressings is expected to be similar to that shown in Fig. 3(b). It is noted that, up to four pressings (= 1.16), dislocations were hardly observed at the cell interior. This finding would be attributed to easy dis￾location glide inside a cell in which no obstacles for dislocation motion existed as shown in Fig. 2. The microstructural evolution sequences during CGP up to four pressings are similar to those reported in ECAP with route C in that the formation of elongated cells or grains and the restoration of equiaxed cells or grains occur alternately due to repetitive reverse shear￾ing on the same plane of the segment [5]. In ECAP with route C, the sample is rotated 180° around its longitudinal axis between passages and, resultantly, re￾verse shearing occurs repeatedly on the same plane [6–8]. The fifth pressing imposes the repetitive defor￾mation on the portion deformed at the first pressing so that the total accumulated strain becomes 1.74 in this portion. Fig. 3(c) presents the microstructure of the deformed portion with =1.74. The microstruc￾ture is characterized by the elongated subgrains with a width of
0.5
m which is comparable to the diame￾ter of the equiaxed cells formed at =1.16. In addi￾tion, the dislocation density is high and the dense dislocation debris is observed inside the grain interior. The micrograph of the sample after six pressings (= 2.32) shown in Fig. 3(d) exhibits the typical mi￾crostructural characteristics of ultrafine grained metallic materials fabricated by intense plastic strain￾ing: high dislocation density, ill-defined boundaries and extensive extinction contour in the vicinity of the boundary, etc. The more diffused spots of the SAD pattern in Fig. 3(d) than those observed in the sample after two pressings (Fig. 3(b)) indicated that the mis￾orientation angle between adjacent subgrains in￾creased. The grain size after six pressings was slightly smaller than the cell size of the sample after two pressings (=1.16) shown in Fig. 3(b). This finding is consistent with the general fact that the grain refine￾ment is the most significant at the initial stage of intense plastic straining and becomes saturated with increasing strain. By the same argument described above, the microstructure after six pressings would represent the entire microstructure of the sample after eight pressings. As shown in Fig. 3(e), the microstruc￾ture of the sample after 16 pressings (=4.64) consists of the polygonized dislocation-free grains with well￾defined boundaries. The grain size after 16 pressings,
0.8
m, is coarser than that measured on the sam￾ple after six pressings. The formation of polygonized dislocation-free grains and grain coarsening with in￾creasing strain is commonly observed in pure Al dur￾ing intense plastic straining [5,7,9–11]. At this stage, the spots in the SAD pattern became more diffused than those of the previous samples, indicating an increase in the proportion of high-angle boundaries. In order to examine this trend, the SAD pattern of individual grains in Fig. 3(e) was compared with those of the adjacent grains. As shown in Fig. 4, the SAD patterns of grains 1, 2 and 3 exhibit the spot patterns with the different zone axes; the zone axes are [100], [110] and [112], respectively. This in￾dicates that the misorientation angles between adja￾cent grains are fairly high. The existence of the Kikuchi lines in these SAD patterns is often observed when the grain is not perfectly aligned with respect to the zone axis, typically less that 3–4°. Several dif￾ferent areas of the sample after 16 pressings were examined by the same procedure and the similar re￾sults were obtained. This confirms that some portion of low-angled subboundary converted to high-angled boundary in the course of the present CGP process. Fig. 2. TEM micrograph showing dislocation cell structure in the present pure Al annealed at 773 K for 4 h.

D.H.Shin et al.Materials Science and Engineering A328 (2002)98-103 101 (a) (b) 0.5um ● 0.5m 0.5μm 0.5μm (e) 0.5um Fig.3.TEM micrographs showing microstructure of pure Al subjected to constrained groove pressing(CGP).(a)One pressing(e=0.58);(b)two pressings (=1.16);(c)five pressings (e=1.74):(d)six pressings (=2.32);(e)16 pressings (e=4.64) 3.2.Mechanical properties hardness is ascribed to the coarser grain size and near dislocation-free nature of the grains formed after 16 In order to examine the hardening behavior of pure pressings,as shown in Fig.3(e).The hardness did not Al with the CGP strain and its mechanical homogeneity vary significantly along the transverse cross-section af- throughout the sample,the Vickers microhardness ter every four pressings that yields an equal amount of value was plotted against the transverse distance of the strain in the whole sample.It implies that deformation sample in Fig.5.The average hardness of the samples induced by the present CGP with a die shown in Fig.I after four pressings(8=1.16)and after eight pressings is quite uniform throughout the sample,ensuring good (8=2.32)increased almost twice relative to that of the mechanical homogeneity.Fig.6 shows the comparison as-annealed sample.After 16 pressings (s=4.64),how- of the hardness variation with strain in pure Al between ever,the hardness decreased by ~10%compared to the present CGP and ECAP which is the most fre- that of the previous samples.The decrease of the quently used intense plastic straining technique.Con-

D.H. Shin et al. / Materials Science and Engineering A328 (2002) 98–103 101 Fig. 3. TEM micrographs showing microstructure of pure Al subjected to constrained groove pressing (CGP). (a) One pressing (=0.58); (b) two pressings (=1.16); (c) five pressings (=1.74); (d) six pressings (=2.32); (e) 16 pressings (=4.64). hardness is ascribed to the coarser grain size and near dislocation-free nature of the grains formed after 16 pressings, as shown in Fig. 3(e). The hardness did not vary significantly along the transverse cross-section af￾ter every four pressings that yields an equal amount of strain in the whole sample. It implies that deformation induced by the present CGP with a die shown in Fig. 1 is quite uniform throughout the sample, ensuring good mechanical homogeneity. Fig. 6 shows the comparison of the hardness variation with strain in pure Al between the present CGP and ECAP which is the most fre￾quently used intense plastic straining technique. Con- 3.2. Mechanical properties In order to examine the hardening behavior of pure Al with the CGP strain and its mechanical homogeneity throughout the sample, the Vickers microhardness value was plotted against the transverse distance of the sample in Fig. 5. The average hardness of the samples after four pressings (=1.16) and after eight pressings (=2.32) increased almost twice relative to that of the as-annealed sample. After 16 pressings (=4.64), how￾ever, the hardness decreased by
10% compared to that of the previous samples. The decrease of the

102 AD.H.Shin et al.Materials Science and Engineering A328 (2002)98-103 0.3μm 3 [110] [100 112 Fig.4.The SAD patterns of individual grains in Fig.3(e)having the different zone axis. sidering the initial hardness difference in the as-an- 4.Conclusions nealed state,CGP exhibits the equivalent hardening effect on the sample to ECAP at similar accumulated A new technique for manufacturing plate-shaped ul- strains. trafine grained materials was introduced.The principle The nominal tensile properties of the CGPed samples of the technique,named 'constrained groove pressing' are presented in Fig.7.The yield strength (YS)and (CGP),is that a material is subjected to the repetitive ultimate tensile strength (UTS)greatly increased in the shear deformation under the plane strain deformation CGPed samples,over three times compared to those of condition by utilizing alternate pressing with the asym- the as-annealed sample.Similar to hardness,the strength of the sample after 16 pressings (8=4.64)was lower than that of the CGPed samples subjected to 60 lower CGP strain.The yield ratio (YS/UTS)and an pure Al inspection of the stress-strain curves,not shown here, 50 reveal that negligible strain hardening takes place in all the CGPed samples while the as-annealed sample ex- 40 hibits the extensive strain hardening behavior that is typical in FCC pure metals.The ultrahigh strength and 全30 the absence of strain hardening with a moderate ductil- ity are typically observed in tensile deformation of 20 ultrafine grained materials.Along with the grain refine- -O-as-annealed --g1.16 (total 4 pressings) ment sequences during the present CGP described in 10 --g 2.32 (total 8 pressings) the preceding section,the enhancement of mechanical 4.64(total 16 pressings) 0 10 properties indicates that the present CGP technique is a 20 3040 506070 strong candidate for fabricating plate-shaped ultrafine Distance,mm grained metallic materials without changing their initial Fig.5.The Vickers microhardness profile along the transverse dis- dimensions. tance of the CGPed pure Al plate

102 flD.H. Shin et al. / Materials Science and Engineering A328 (2002) 98–103 Fig. 4. The SAD patterns of individual grains in Fig. 3(e) having the different zone axis. sidering the initial hardness difference in the as-an￾nealed state, CGP exhibits the equivalent hardening effect on the sample to ECAP at similar accumulated strains. The nominal tensile properties of the CGPed samples are presented in Fig. 7. The yield strength (YS) and ultimate tensile strength (UTS) greatly increased in the CGPed samples, over three times compared to those of the as-annealed sample. Similar to hardness, the strength of the sample after 16 pressings (=4.64) was lower than that of the CGPed samples subjected to lower CGP strain. The yield ratio (YS/UTS) and an inspection of the stress–strain curves, not shown here, reveal that negligible strain hardening takes place in all the CGPed samples while the as-annealed sample ex￾hibits the extensive strain hardening behavior that is typical in FCC pure metals. The ultrahigh strength and the absence of strain hardening with a moderate ductil￾ity are typically observed in tensile deformation of ultrafine grained materials. Along with the grain refine￾ment sequences during the present CGP described in the preceding section, the enhancement of mechanical properties indicates that the present CGP technique is a strong candidate for fabricating plate-shaped ultrafine grained metallic materials without changing their initial dimensions. 4. Conclusions A new technique for manufacturing plate-shaped ul￾trafine grained materials was introduced. The principle of the technique, named ‘constrained groove pressing’ (CGP), is that a material is subjected to the repetitive shear deformation under the plane strain deformation condition by utilizing alternate pressing with the asym￾Fig. 5. The Vickers microhardness profile along the transverse dis￾tance of the CGPed pure Al plate.

D.H.Shin et al.Materials Science and Engineering A328 (2002)98-103 103 160 140 8 pressings 色 16 pressings % 40 0 0 0 30 40 :海 20 pure Al 10 O ECAP I51 0 CGP 40 234 56 Effective strain 20 Fig.6.The comparison of the hardness variation with strain in pure Al between the present CGP and ECAP. metrically grooved die and flat die constrained tightly Strain by the cylinder wall. By applying CGP to well-annealed pure Al whose Fig.7.Room temperature tensile properties of pure Al with CGP initial grain size was ~1.2 mm,a submicrometer order strain. polygonized grain structure with the well-defined grain boundary was obtained. The results of the mechanical tests revealed the me- chanical superiority and its homogeneity of the sample fabricated by the present CGP,comparable to those of the sample prepared by other intense plastic straining [2]Y.Saito,N.Tsuji,H.Utsunomiya,T.Sakai,R.G.Hong.Scr. Mater..39(1998)1221. techniques.Accordingly,the present CGP technique is [3]N.Tsuji,Y.Saito,H.Utsunomiya,S.Tanigawa,Scr.Mater.40 a strong candidate for fabricating plate-shaped ultrafine (1999)795. grained metallic materials. [4]Y.Saito,H.Utsunomiya,N.Tsuji,T.Sakai,Acta Mater.47 (1999)579 [5]Y.Iwahashi,Z.Horita,M.Nemoto,T.G.Langdon,Acta Mater.46(1998)3317. Acknowledgements [6]V.M.Segal,Mater.Sci.Eng.A197 (1995)157. [7]M.Nemoto,Z.Horita,M.Furukawa,T.G.Langdon,Metals This work was supported by Korea Ministry of Mater.4(1998)1181. Science and Technology through '2000 National Re- [8]M.Furukawa,Y.Iwahashi,Z.Horita,M.Nemoto,T.G.Lang- search Laboratory Program'. don,Mater.Sci.Eng.A257(1998)328. [9]H.Hasegawa,S.Komura,A.Utsunomiya,Z.Horita,M.Fu- rukawa,M.Nemoto,T.G.Langdon,Mater.Sci.Eng.A265 (1999)188. References [10]P.L.Sun,P.W.Kao.C.P.Chang.Mater.Sci.Eng.A283 (2000) 82. [1]R.Z.Valiev,R.K.Islamgaliev,I.V.Alexandrov,Prog.Mater. [11]A.Yamashita,D.Yamaguchi,Z.Horita,T.G.Langdon,Mater. Sci.45(2000)103. Sci.Eng.A287(2000)100

D.H. Shin et al. / Materials Science and Engineering A328 (2002) 98–103 103 Fig. 6. The comparison of the hardness variation with strain in pure Al between the present CGP and ECAP. Fig. 7. Room temperature tensile properties of pure Al with CGP strain. metrically grooved die and flat die constrained tightly by the cylinder wall. By applying CGP to well-annealed pure Al whose initial grain size was
1.2 mm, a submicrometer order polygonized grain structure with the well-defined grain boundary was obtained. The results of the mechanical tests revealed the me￾chanical superiority and its homogeneity of the sample fabricated by the present CGP, comparable to those of the sample prepared by other intense plastic straining techniques. Accordingly, the present CGP technique is a strong candidate for fabricating plate-shaped ultrafine grained metallic materials. Acknowledgements This work was supported by Korea Ministry of Science and Technology through ‘2000 National Re￾search Laboratory Program’. References [1] R.Z. Valiev, R.K. Islamgaliev, I.V. Alexandrov, Prog. Mater. Sci. 45 (2000) 103. [2] Y. Saito, N. Tsuji, H. Utsunomiya, T. Sakai, R.G. Hong, Scr. Mater. 39 (1998) 1221. [3] N. Tsuji, Y. Saito, H. Utsunomiya, S. Tanigawa, Scr. Mater. 40 (1999) 795. [4] Y. Saito, H. Utsunomiya, N. Tsuji, T. Sakai, Acta Mater. 47 (1999) 579. [5] Y. Iwahashi, Z. Horita, M. Nemoto, T.G. Langdon, Acta Mater. 46 (1998) 3317. [6] V.M. Segal, Mater. Sci. Eng. A197 (1995) 157. [7] M. Nemoto, Z. Horita, M. Furukawa, T.G. Langdon, Metals Mater. 4 (1998) 1181. [8] M. Furukawa, Y. Iwahashi, Z. Horita, M. Nemoto, T.G. Lang￾don, Mater. Sci. Eng. A257 (1998) 328. [9] H. Hasegawa, S. Komura, A. Utsunomiya, Z. Horita, M. Fu￾rukawa, M. Nemoto, T.G. Langdon, Mater. Sci. Eng. A265 (1999) 188. [10] P.L. Sun, P.W. Kao, C.P. Chang, Mater. Sci. Eng. A283 (2000) 82. [11] A. Yamashita, D. Yamaguchi, Z. Horita, T.G. Langdon, Mater. Sci. Eng. A287 (2000) 100