Free surface of polycrystalline metal becomes roughened after plastic deformation. The surface roughening is closely related to the inhomogeneity of polycrystalline metals, that is, to the inhomogeneous plastic deformation of respective grains. In the present study, inhomogeneous deformation on the free surface of polycrystalline aluminum specimen during uniaxial tension is studied. The inhomogeneous deformation of grains in the central area of the free surface of specimen is observed by the laser scanning microscope, while the inhomogeneous deformation perpendicular to the surface is studied by the laser scanning microscope as well as the stylus measuring instrument. It is shown that the surface roughness and the strain of respective grains increase with the applied strain. Discussions are made on the change in the surface roughness, the strain in each grain and the slip-line angles with the applied strain

Abe, Takeji

Akagi, Yasuo

Hualin, Song

Shimizu, Ichiro

English

Okayama University Scientific Achievement Repository

Memoirs of the Faculty of Engineering, Okayama University, Vo1.35, Nos.1&2, pp.1-8, March 2001Microscopic Observation of Plastic DeformationofPolycrystalline Aluminumby Laser Scanning MicroscopeTakeji ABE', SONG Hualin", Yasuo AKAGI"'and Ichiro SHIMIZU"(Received December 14, 2000)Free surface of polycrystalline metal becomes roughened after plastic deformation. Thesurface roughening is closely related to the inhomogeneity of polycrystalline metals, that is,to the inhomogeneous plastic deformation of respective grains. In the present study,inhomogeneous deformation on the free surface of polycrystalline aluminum specimen duringuniaxial tension is studied. The inhomogeneous deformation of grains in the central area ofthe free surface of specimen is observed by the laser scanning microscope, while theinhomogeneous deformation perpendicular to the surface is studied by the laser scanningmicroscope as well as the stylus measuring instrument.It is shown that the surface roughness and the strain of respective grains increase withthe applied strain. Discussions are made on the change in the surface roughness, the strainin each grain and the slip-line angles with the applied strain.1. INTRODUCTIONFree surface of polycrystalline metal becomes roughened after plastic deformation. The surface roughening isimportant for the finishing of surface during plastic working. It is known that the surface roughening is closelyrelated to the inhomogeneity of polycrystalline metals, that is, to the inhomogeneous plastic deformation of respectivegrains [1'8]. Then, the experimental study of the surface roughening is also important for the understanding ofmicroscopic deformation behavior of polycrystalline metals. In the present study, inhomogeneous deformation on thefree surface of polycrystalline aluminum specimen during uniaxial tension is studied. The inhomogeneousdeformation of grains in the central area of the free surface of specimen is observed by a laser scanning microscope,while the inhomogeneous deformation perpendicular to the surface is studied by the laser scanning microscope as wellas the stylus measuring instrument. The relation between the strain in respective grains, the shape of free surfaceroughness curve and the applied strain is investigated. Discussions are also made on the relation among thevariations of strain in each grain, profile wavelength, slip'line angles and the surface roughness due to the appliedstrain.* Graduate School of Natural Science and Engineering and Cooperative Research Center,Okayama University, Tsushima-Naka 3'1'1, Okayama, 700-8530, Japan.** Graduate School of Natural Science and Engineering, Okayama University.*** NEC Hiroshima, Ltd., Higashi·Hiroshima.12 Takeji ABE, SONG Hualin, Yasuo AKAGI and Ichiro SHIMIZU2. EXPERIMENTAL METHOD2. 1 SpecimenThe material used is polycrystalline pure aluminum for industrial use (99.5wt%). The shape of tensile specimen isshown in Fig. 1. The central surface of the specimen was finished with abrasive papers and diamond paste until itscenter-line average roughness becomes below Ra = O.l,urn. Then, the specimen was annealed for 1hr at 400°C forSpecimen A, while for 24hr at 600°C for Specimen B, and then cooled in the furnace. The surface of the specimen waselectropolished and chemically etched in order to distinguish the grain boundary. The averaged grain sizes are35-40,urn and 70-80,urn, respectively for Specimen A and B.~--> ~"I./_~ Ir---l- - -- - ----C'J ---~l~~ --- ---- - --/' j,'"Area Of:/ ~measurement 140x--Fig. 1 Tensile specimen2. 2 Surface Roughness Measurements and Observation of Microscopic DeformationThe specimen was taken out from the tensile testing machine after a certain fixed amount of strain. Andmicroscopic deformation on the surface, that is, the surface roughening and the strain of grains were observed with thelaser scanning microscope (Keyence, VF-7500). The operating principle of the laser scanning microscope is shown inFig. 2.The average surface roughness was also measured eight lines for the central area of 8 X 8mm2 on the specimensurface, by the use of the stylus surface roughness measurement apparatus.l\IJi.rrorObjective lensx· y. z· () stageFig. 2 Principle of Laser Scanning MicroscopeFig. 3 Optical micrograph taken by laser scanning microscope and composed with personal computer ( &x = 0.17)Loading direction3::()'"'oI/>()o'0()ocrI/>ro<;:;.o':Jo::2.,~.()oro0'...,3;:;.o:Jw4 Takeji ABE. SO!\G Hualin, Yasuo AKAGI and Ichiro SHIMIZU2. 3 Measurement of Strain in Grains and Angle of Slip LinesThe strains of grains in the axial and in the perpendicular direction were measured for the area 0.7 x 0.6mm2 atthe central area of Specimen B. The total number of grains used for the measurement was about 80.The angle of slip lines was also measured on the display of the laser scanning microscope3. EXPERIMENTAL RESULTS AND DISCUSSION3. 1 Deformation and Surface Roughness of Respective GrainsAt first, deformation and surface roughness for respective grains are observed with laser scanning microscope.Figures 3 and 4 show examples of surface observation. Figure 3 is the micrograph taken by the CCD camera andcomposed with the personal computer, which shows the grain deformation and the slip lines in respective grains.Five different grains (Grain 1-5) were chosen respectively for Specimen B-1 and Specimen B-2 as shown in Figs. 5(a) and (b), respectively. Figs. 4 (a) and (b) show of the photographs at the applied strain E, = 0.10 for Grain 1 andfor Grain 2, respectively. Figs. 6 (a) and (b) show the corresponding surface roughness profiles for Grain 1 and Grain2, respectively.Fig. 7 shows the change in the average surface roughness measured for the five grains shown in Fig. 5 with theapplied strain. Fig. 8 shows the change in the strain of grain for the five grains shown in Fig. 5 with the appliedstrains. It is seen from Fig. 7 and 8 that there are large variety of the deformation mode in respective grains(a) Grain 1 of Specimen B-1 (b) Grain 2 of Specimen B-1Fig. 4 Examples of surface photograph taken by laser scanning microscope (x 1250)o 100 (J,I m)L-..I(a) Specimen B-1o 100 (p m)~(b) Specimen B-2Fig. 5 Distribution of grains for Specimen B-1 and Specimens B-2Microscopic Observation of Plastic Deformation 5100 200Measured distance (p m)(b) Grain 2o100 200Measured distance (p m)(a) Grain 1E Ra(pm) E Ra(pm)a 0.00 0.260 4 a 0.00 0.3554 b 0.05 0.523b 0.05 0.416 c 0.10 0.735c 0.10 0.708 d 0.15 0.769d 0.15 0.781 E e 0.20 1.305E e 0.20 1.533 :::t~ ~a E.....2> 0.s:: bCl Q)~O :I:Fig. 6 Observation with laser scanning microscope along center line of grains (Specimen B-1)Grain No. e Grain No.0 1 ~ 1.5 0 1 iiiEE 1.5 • 2 D :::t • 2 iii lIDa lID 3 0 lU @ 3lU iii D a:: 0a:: 4 mI In iii 4 eIn e 5 III 1.0 e 5In ~l!! 1.0 c::.s:: iii.s:: Cl•Cl ::J::I e f1jl ~ e •e Q) BQ) ClCl f!~ 0.5 ~ iii g! 0.5 I!~ « ~" iii iii iii••0 0.1 0.2 0 0.1 0.2Applied strain c x Applied strain c x(a) Specimen B-1 (b) Specimen B-2Fig. 7 Change in average surface roughness measured for the grains shown in Fig. 4 with applied strain.40..------------------, 40Grain No.~ 30 0 1 @c:: • 2.~@ 3iii @ @c:: @ 4.n;0 5 @a 20 0Q) 0Cle ® Q£ 010 •@~@00 0.1 0.2Applied strain ex(b) Specimen B-2Fig. 8 Change in strain of five grains with applied strain6 Takeji ABE, SONG Hualin, Yasuo AKAGI and Ichiro SHIMIZU3. 2 Change in Surface Roughness of SpecimenFigure 9 shows an example of the surface roughness curve with laser scanning microscope along the same selectedline on the specimen surface, for different applied strain. Fig. 9 shows the change in the surface profiles for the fixeddifferent applied strain with respect to the initial length. The figure is processed and combined from severalroughness measurements in a personal computer.The wavelength of the free surface profile increases with the applied tensile strain. The mountains and valleysproduced at the early stage remain their shape, though their heights increase. In some area of grains, thedeformation in the normal z'direction is large; while it is small in the other parts of grains.10E:::l.~Q)0c: 0~~-100 200 400Measurement distance (fJ. m)EO x = 0.088EO x = 0.207EO x = 0.288600Fig. 9 Example of surface profile processed and combined in personal computerChanges in the average surface roughness measured in the axial and the perpendicular directions of Specimen Awith the stylus measurement apparatus are shown in Fig. lO(a). Similar results for Specimen B are shown in Fig.10(b). In the figures, a is the angle between the specimen axis and the rolling direction of the original aluminumplate. It is seen that little effect ofa is observed on the changes ofthe surface roughness.0.2 0.4Applied strain EO x(b) Specimen B0.2 0.4Applied strain EO x(a) Specimen AE--0-- a=O° :::t ~ a=O°E---0-- a =45° a =45°2,4 m ---0----b- a=90° lY 4ltl III --I::r- a =90°0::: / IIIIII / Q)III / c:Q) / , , .c:c: / , , , C>.c / 0 , ::::l01:;) g. /0 0e 9,.00 ....I>. Q)~2 I>. ,19'0 0 ~2~ {}: m.[] ....Q) , D' ~~ , ,,0Fig. 10 Change in average roughness measured in loading and transverse direction with applied strain forSpecimen A and BMicroscopic Observation of Plastic Deformation 73. 3 Strain Distribution of Gr!linsFigure 11 (a) and (b) show the strain of respective grains in the axial (x-) direction and in the perpendicular (y-)direction, respectively, where the distribution of strain is shown with ratio of the strain Eg< or E gy and the appliedstrain Ex • The data are obtained from the measurements for about 70 grains of Specimen B. It is seen that theshapes of the distribution are almost the same, irrespective of the applied strain Ex, which implies that the deviationof the strain of respective grains also increases with the applied strain.0.4r----------------.0.4IIIc:.~Cl'0o:; 0.2a::o--0-- E x=0.088---.-- E x=0.169-~-E x=0.207--~--E x=0.2881 2Strain ratio IE gx I E xl(a) Loading directionIIIc:.~Cl'0o 0.2:aia::-0- E x=0.088---.-- E x=0.169-~-E x=0.207--6--- E x=0.288o 1Strain ratio -E 9Y I E x(b) Transverse direction2Fig. 11 Distribution of grain strain measured in loading and transverse directions3.4 Direction of Slip-lines in GrainsFigure 12(a) shows the measured angle () between the slip-lines on the surface and x-direction for respectivegrains in Specimen B. Figure 12(b) shows the change in the averaged slip-line angle if with respect to the appliedstrain. It is seen that the angle if decreases with the increase of the applied strain.Figure 13 shows the angle <iJ between two kinds of slip-lines appeared in a grain, where the angle is measured soas to the x-direction lies in between the two slip-lines. It is seen the angle <iJ between the two slip-lines alsodecreases with the applied strain.O.4r-----------------,--0-- E x=0.088-.-- E x=0.169-<>-- E x=0.207~- E x=G.2880.2 0.3Applied straine x0.130L............................................L..................................~-~50~IQ)Q)C>c:III"0Q)Cl40~~7525 50Angle B(deg)oIIIc:"i!Cl'0o 0.2~a::(a) Distribution of angle () (b) Change in averaged angle if with applied strainFig. 12 Distribution of angles between slip-line in grains and loading direction8 Takeji ABE, SONG Hualin, Yasuo AKAGI and Ichiro SHIMIZU0.3--0-- E: x=0.088-.-- E: x=0.169III.~ 0.2C!'0o:;0::0.1o 50 100Angle It> (deg)150Fig. 13 Distribution of angle ¢ between two slip-line systems in grains4. CONCLUSIONSMicroscopic deformation behavior of polycrystalline aluminum was observed with the laser scanning microscope.The surface roughening is also measured with the laser scanning microscope as well as the stylus surface roughnessmeasuring apparatus. The main conclusions are as follows.(1) The microscopic deformation behavior of respective grains in polycrystalline metal is observed successfully withlaser scanning microscope. It is applicable to clarify the deformation behavior in the plane of the specimen surfaceas well as that out of the plane of the surface.(2) It is also possible to process and combine the measured digital data of surface profile and surface photographs bythe use of personal computer. In some are in respective grains, the surface roughness increases with the appliedstrain, while in the other area the surface profile scarcely changes with the applied strain.(3) The distribution of grain strain is similar for different applied strain, if the strain of grains is expressed with theratio to the applied strain.(4) The angle between the slip lines and the tensile direction slightly decreases with the applied strain. When twopairs of the slip lines are observed in the same grain, the angle between them also decreases with the appliedstrain.The authors are indebted to the financial support of the science promotion program of the Ministry of Education[ Fundamental Research (B)(2) 11450045, 19991REFERENCES[1] T. Abe, I. Shimizu and T. Nishiyama, JSME Int. J., Ser. A, 35 (1992) 462-469.[2] I. Shimizu and T. Abe, JSME Int. J., Ser. A, 37 (1994), 403-411.[3] T. Abe, I. Shimizu, T. Nosho and S. Nagaki, AEPA'94 (1994), Eds. B. Xu and W. Yang, 191-198, Int. Acad. Pub.[4] T. Nosho, I. Shimizu, T. Abe, H. Kawanami and H. Terai, IMMM'95 (1995), Eds. B. Xu, M. Tokuda and J. Song, Int.Acad. Pub, 309-314.[5] T. Abe, Y. Tai, I. Shimizu and T. Nosho, AEPA'96 (1996), Eds. T. Abe and T. Tsuta, Pergamon, 771-776.[6] I. Shimizu, T. Nosho, T. Abe and H. Terai, AEPA'96 (1996), Eds. T. Abe and T. Tsuta, Pergamon, 277-282.[7] I. Shimizu, Y-Z Tai, T. Abe, J. Kawaguchi and T. Nosho, IMMM'97 (1997), Eds. M. Senoo, B. Xu, M. Tokuda and B.Bundara, Mie University Press, 271-278.[8] I. Shimizu, T. Abe, T. Nosho and M. Wakayama, Metals and Materials, 4 (1998), 939-943.

Microscopic Observation of Plastic Deformation of Polycrystalline Aluminum by Laser Scanning Microscope

Abstract

Similar works

Full text

Available Versions

Okayama University Scientific Achievement Repository

Okayama University Digital Information Repository