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On the origin of cube texture in face-centered cubic metals
Scripta METALLURGICA
Vol. 23, pp. 881-884, 1989 Printed in the U.S.A.
Pergamon Press plc All rights reserved
ON THE ORIGIN OF CUBE TEXTURE IN FACE-CENTERED CUBIC METALS Hsun Hu Department of Materials Science and Engineering University of Pittsburgh Pittsburgh, PA 15261
(Received February 15, 1989) (Revised March 17, 1989) Introduction The formation of a strong cube texture upon recrystallization of a heavily rolled polycrystalline fec metal has been a subject of great interest for decades. The origin of cube-oriented grains and their subsequent growth during recrystallization have attracted particular attention. In a recent review (i) of this research topic, the historical background of cube texture formation and the early theories on the mechanism of its formation - the oriented nucleation versus oriented growth - were revisited briefly. The more recent developments, in theory and in experiments, were critically examined. A new approach for further studies of the problem was also suggested. It was emphasized that, since the strong cube texture can only form in those fce metals that develop the copper-type rolling texture (2,3) of which the presence of the {112}<111> component is a main characteristic feature, the formation of the cube-oriented grains would likely be related to this texture component through some transition bands. A valid theory for cube texture formation should, therefore, be connected in some way with this texture component. Accumulated information relevant to the formation of cube texture in pure copper or aluminum has provided us further evidence in that the use of {112}<111> orientation for the study of cubegrain nucleation is a fruitful approach. A re-examination of the now available information in connection with cube texture formation has given us new ideas for critical experiments for determining the true origin of the cube-oriented grains. The present communication is intended to help accomplish this purpose. The Importance of Orientation Spread In an attempt to test his "inverse Rowland" hypothesis for cube grain nucleation, Verbraak (4) had conducted a series of experiments with heavily rolled single crystals of copper that developed a double {112} <111> components of the deformation texture. When the orientation spread was nearly as extensive as that in the polycrystalline copper-type rolling texture, the recrystallized cube texture (with minor twin orientations) was almost as strong as that observed from the heavily rolled polycrystalline copper after recrystallization. On the other hand, when the deformation texture of a heavily rolled single crystal was a double {112}<111> texture but with rather limited orientation spread, the recrystallization texture was actually composed of equally strong cube and twin texture components plus some other minor orientations. These results indicate the importance of orientation spread in the nucleation of cube grains. It is known that the orientation spread between the prominent deformation texture components corresponds to the microband or transition band region where nucleation of recrystallized grain occurs(5). Comparison of Textures between Rolled and Channel-Die Compressed Specimens It has been taken for granted that rolling and plane-strain deformations are considered completely equivalent. To see whether this is true particularly at high degrees of reduction, the deformation and reerystallization textures of electrolytic copper, deformed by roiling and by channel-die compression up to 95% reduction were compared (6). It was found that noticeable differences, in both the deformation and the recrystallized cube textures, were observed by comparing the pole figures of corresponding specimens. For the deformation textures, slightly stronger brass components, { 110} <112>, was produced in the channel-die compressed strip, but the copper component, {112}<111>, the S component, {123}<412> or {123}<634>, and the Goss component, {110}<001>, all appeared slightly weaker in the channel-die compressed strip in comparison with the rolled strip. Also, at high reductions, the rolled strip showed more orientation spreads. For the recrystallized specimens, the cube texture formed in the rolled strip was stronger
881 0036-9748/89 $3.00 + .00 Copyright (c) 1989 Pergamon Press plc
882
CUBE TEXTURE
Vol.
25, No. 6
and the twin orientations were weaker than those in the channel-die compressed strip. A more careful and detailed study of these phenomena was later conducted jointly at Aachen (7) by ODF techniques, using high purity copper. The results were essentially similar to those lust described in the above. In both these two series of experiments, the textures were examined on the midthickness plane of the strip. To see whether the observed difference in texture can still be recognized in the overall texture of the entire thickness of the strip, the textures of the high purity copper specimens were examined by neutron diffraction at Riso National Laboratory. The neutron diffraction results indicated that the overall texture of the full thickness of the strip showed some minor discrepancies, in comparison with that of the midthickness plane determined by X-ray diffraction, but the main difference in the deformation texture and in the recrystallized cube texture of the rolled and of the channel-die compressed strips appeared still persisting (8). In other words, for the deformation texture, the S component is stronger in the rolled strip than in the channel-die compressed strip, whereas for the other texture components, the reverse is indicated. And, for the recrystallization texture, the cube orientation is stronger and the twin orientation weaker, in the rolled strip than in the channel-die compressed strip. Being similar to the features observed from the midthickness plane of the strips, these differences are particularly prominent in the heavily deformed specimens. The reason for these observed differences in texture between the rolled and the channel-die compressed is not clear at present. It is apparent that the deformation rate of channel-die compression was substantially lower than that of roiling in our processing experiments. An estimate of the difference in strain rate between rolling and channel-die compression was 3 to 4 orders of magnitude maximum. However, as shown many years ago by Leffers (9), the higher rate of rolling would influence the texture in the direction from the copper type towards the brass type. Our results indicated the opposite, and should, therefore, unlikely be a consequence of the starin-rate difference. A possible explanation of the observed difference in the deformation textures of rolled and channel-die compressed copper may be contemplated by the shape change of the work piece produced by these two deformation methods. Even with our carefully controlled experiments, it was found that appreciable widening of the work piece was always observed in the rolled strip, despite the precaustions that were taken in the preparation of the starting piece and in the rolling operations. The amount of widening was found to increase with increasing reduction of the rolled strip (6,7). For example, the widening of the rolled strip was ~ 4.2% at 80% reduction to - 12.7% at 95% reduction (7). On the other hand, the widening of the channel-die compressed strips was practically nil. Therefore, there is certainly a substantial difference in widening between the rolled and the channeldie compressed strips. A test of the possible effect of strip widening on texture, e.g., by computer simulation, would seem worthwhile. This is currently being conducted at Riso National Laboratory. Recent Developments in Cube-Grain Nucleation Studies Using the newly developed EBSP (electron back scatter pattern) technique (I0) for microtexture determination, H]elen and Nes (11) have studied the nucleation of reerystallized grains in rolled high purity aluminum specimens. They reported that cube-oriented grains were found to grow out from transition band in the { 112 } <111> deformation texture. This is a heartening evidence showing that the origin of cube texture is closely related with the copper-texture~in rolled fee metals as emphasized in the mtroductlon of the present eommunleatlon and m prevlous discussions (I). However, the initial material used by these authors was a directionally solidified high purity aluminum ingot with columnar grains having a fibre texture and a prominent cube-oriented component superimposed on the <100> fibre texture. The starting plate for cold rolling was cut in such a way that the fibre axis was parallel to the normal direction, and the cube-oriented component of the fibre texture was rolled in the cube orientation (12). Even though the deformation texture after 90% cold rolling was mainly a double (112}<111>, the possible contribution to the orientation spread by the initial cube oriented elements was an unknown quantity. .
.
.
.
.
~
°
In a more recent study on the heterogenieties in heavily roiled commercial purity aluminum, Nes and co-workers (13) postulated a mechanism for the cube-oriented elements in the transition band between the double {112}<111> textures. They described that the rotations involved starting from one of the copper components are firstly around the rolling direction, then gradually around the transverse direction through the cube orientation. Beyond that, it continues through a symmetrical
Vol.
23,
No.
6
CUBE
TEXTURE
883
path ending in a new copper-orientation which is a mirror image of the starting one. This postulation appears attractive, as it makes an important connection between the { 112 } <111> copper texture and the cube-oriented elements for the development of the cube texture upon recrystallization. Moreover, the rotations involved, first around the rolling direction then around the transverse direction, for connecting the two copper orientations {112}<111>, are consistent with the shape change observed in rolling. Suggestions for Critical Experiments To test whether the aforementioned interpretation is truly valid or not, some simple experiments may be conducted. In these experiments, some controlled widening may be applied to the channel-die compressed work piece by some additional procedures in deformation. This can be achieved by cutting out square pieces from a channel-die compressed strip, then deform each piece to controlled length in the channel-die length direction. An alternate approach of controlled widening in channel-die compression is to reduce the width of the channel-die compressed strip at suitable intermediate reductions, then apply additional reductions by channel-die compression to the full diewidth. The results of some exploratory experiments of controlled widening in channel-die compression will be reported in the near future. It is hoped that some basic information helpful for further understanding of the problem can be produced from these experiments. In conclusion, the recent findings of Nes and co-workers (11,13) are encouraging. Considering the fact that the polycrystalline texture of the copper type is highly complex, the transition band between the double {112}<111> texture components may be just one of the important sites for cube grain nucleation. The transition regions between a {112}<111> component and one of the other texture components such as the (110}<112>, {123}<412>, or {110}<001>, are largely unknown. For a complete understanding of the origin of cube grains, the characteristic feature and behavior of these transition regions should be studied systematically. Acknowledgement This idea of approach to the cube-grain nucleation studies was initiated while the writer was on a sabbatical leave at the Riso National Laboratory for three months. Stimulating and helpful discussions with N. Hansen, T. Leffers, and D. Juul-Jensen of the Riso National laboratory are sincerely acknowledged. The writer's research in this particular area has been supported by the National Science Foundation, contract number DMR-8614903. References i.
2. 3. 4. 5. 6. 7. 8.
9. 10.
H. Hu, in Annealing Processes - Recovery t Recrystallization and Grain Growth, Eds. N. Hansen, D. Juul-Jensen, T. Leffers, and B. Ralph (Proc. 7th Riso Int. Sym., 1986, Roskilde, Denmark), p. 75. Scripta Metall. 19, 1471 (1985). P.A. Beck and H. Hu, Trans. AIME, 194, 83 (1952). H. Hu and S. R. Goodman, Trans. Metall. Soc. AIME, 227, 627 (1983). C.A. Verbraak, Aeta Metall., 6, 580 (1958). H. Hu, in Recovery. and Recrystallization of Metals t Ed. L. Himmel, (Interscience Publishers, New York, 1963) p. 311 J . F . Butler, Jr. and H. Hu, "Deformation and Annealing Textures of Copper Deformed in Plane Strain and by Rolling", Mater. Sci. and Eng. A (in press). H. Hammelrath, J. F. Butler, Jr., H. Hu, and K. Lucke, "An ODF Study of the Deformation and Recrystallization Textures of Rolled and Channel-Die Compressed High-Purity Copper", to be published. D. Juul-Jensen, T. Leffers, H. Hu, and N. Hansen, "A Study of the Deformation and Rccrystallization Textures of Channel-Die Compressed and Rolled Copper by Neutron Diffraction", to be published. T. Leffers, Scripta Metall., 2, 447 (1968). O.J. Dingley, Scanning Electron Microscopy, 2, 569 (1984).
884
11. 12. 13.
CUBE TEXTURE
Vol.
23, No.
J. Hjelen and E. Nes, in Texture of Materials ( I C O T O M 8) Ed. J. S. Kallend and G. Gottstein, (The MetaU. Soo., 1988,) p. 597. E. Nes, J. Hirsch, and K. Lueke, in Texture of Materials~ Ed. Brakman, Jongenburger and Mittemeijer (Neth. Soc. Matls. Sei., Holland, 1984), p. 663. R. Orsund, J. Hjelen and E. Nes, Scripta Metall. (in press).
6
Vol. 23, pp. 881-884, 1989 Printed in the U.S.A.
Pergamon Press plc All rights reserved
ON THE ORIGIN OF CUBE TEXTURE IN FACE-CENTERED CUBIC METALS Hsun Hu Department of Materials Science and Engineering University of Pittsburgh Pittsburgh, PA 15261
(Received February 15, 1989) (Revised March 17, 1989) Introduction The formation of a strong cube texture upon recrystallization of a heavily rolled polycrystalline fec metal has been a subject of great interest for decades. The origin of cube-oriented grains and their subsequent growth during recrystallization have attracted particular attention. In a recent review (i) of this research topic, the historical background of cube texture formation and the early theories on the mechanism of its formation - the oriented nucleation versus oriented growth - were revisited briefly. The more recent developments, in theory and in experiments, were critically examined. A new approach for further studies of the problem was also suggested. It was emphasized that, since the strong cube texture can only form in those fce metals that develop the copper-type rolling texture (2,3) of which the presence of the {112}<111> component is a main characteristic feature, the formation of the cube-oriented grains would likely be related to this texture component through some transition bands. A valid theory for cube texture formation should, therefore, be connected in some way with this texture component. Accumulated information relevant to the formation of cube texture in pure copper or aluminum has provided us further evidence in that the use of {112}<111> orientation for the study of cubegrain nucleation is a fruitful approach. A re-examination of the now available information in connection with cube texture formation has given us new ideas for critical experiments for determining the true origin of the cube-oriented grains. The present communication is intended to help accomplish this purpose. The Importance of Orientation Spread In an attempt to test his "inverse Rowland" hypothesis for cube grain nucleation, Verbraak (4) had conducted a series of experiments with heavily rolled single crystals of copper that developed a double {112} <111> components of the deformation texture. When the orientation spread was nearly as extensive as that in the polycrystalline copper-type rolling texture, the recrystallized cube texture (with minor twin orientations) was almost as strong as that observed from the heavily rolled polycrystalline copper after recrystallization. On the other hand, when the deformation texture of a heavily rolled single crystal was a double {112}<111> texture but with rather limited orientation spread, the recrystallization texture was actually composed of equally strong cube and twin texture components plus some other minor orientations. These results indicate the importance of orientation spread in the nucleation of cube grains. It is known that the orientation spread between the prominent deformation texture components corresponds to the microband or transition band region where nucleation of recrystallized grain occurs(5). Comparison of Textures between Rolled and Channel-Die Compressed Specimens It has been taken for granted that rolling and plane-strain deformations are considered completely equivalent. To see whether this is true particularly at high degrees of reduction, the deformation and reerystallization textures of electrolytic copper, deformed by roiling and by channel-die compression up to 95% reduction were compared (6). It was found that noticeable differences, in both the deformation and the recrystallized cube textures, were observed by comparing the pole figures of corresponding specimens. For the deformation textures, slightly stronger brass components, { 110} <112>, was produced in the channel-die compressed strip, but the copper component, {112}<111>, the S component, {123}<412> or {123}<634>, and the Goss component, {110}<001>, all appeared slightly weaker in the channel-die compressed strip in comparison with the rolled strip. Also, at high reductions, the rolled strip showed more orientation spreads. For the recrystallized specimens, the cube texture formed in the rolled strip was stronger
881 0036-9748/89 $3.00 + .00 Copyright (c) 1989 Pergamon Press plc
882
CUBE TEXTURE
Vol.
25, No. 6
and the twin orientations were weaker than those in the channel-die compressed strip. A more careful and detailed study of these phenomena was later conducted jointly at Aachen (7) by ODF techniques, using high purity copper. The results were essentially similar to those lust described in the above. In both these two series of experiments, the textures were examined on the midthickness plane of the strip. To see whether the observed difference in texture can still be recognized in the overall texture of the entire thickness of the strip, the textures of the high purity copper specimens were examined by neutron diffraction at Riso National Laboratory. The neutron diffraction results indicated that the overall texture of the full thickness of the strip showed some minor discrepancies, in comparison with that of the midthickness plane determined by X-ray diffraction, but the main difference in the deformation texture and in the recrystallized cube texture of the rolled and of the channel-die compressed strips appeared still persisting (8). In other words, for the deformation texture, the S component is stronger in the rolled strip than in the channel-die compressed strip, whereas for the other texture components, the reverse is indicated. And, for the recrystallization texture, the cube orientation is stronger and the twin orientation weaker, in the rolled strip than in the channel-die compressed strip. Being similar to the features observed from the midthickness plane of the strips, these differences are particularly prominent in the heavily deformed specimens. The reason for these observed differences in texture between the rolled and the channel-die compressed is not clear at present. It is apparent that the deformation rate of channel-die compression was substantially lower than that of roiling in our processing experiments. An estimate of the difference in strain rate between rolling and channel-die compression was 3 to 4 orders of magnitude maximum. However, as shown many years ago by Leffers (9), the higher rate of rolling would influence the texture in the direction from the copper type towards the brass type. Our results indicated the opposite, and should, therefore, unlikely be a consequence of the starin-rate difference. A possible explanation of the observed difference in the deformation textures of rolled and channel-die compressed copper may be contemplated by the shape change of the work piece produced by these two deformation methods. Even with our carefully controlled experiments, it was found that appreciable widening of the work piece was always observed in the rolled strip, despite the precaustions that were taken in the preparation of the starting piece and in the rolling operations. The amount of widening was found to increase with increasing reduction of the rolled strip (6,7). For example, the widening of the rolled strip was ~ 4.2% at 80% reduction to - 12.7% at 95% reduction (7). On the other hand, the widening of the channel-die compressed strips was practically nil. Therefore, there is certainly a substantial difference in widening between the rolled and the channeldie compressed strips. A test of the possible effect of strip widening on texture, e.g., by computer simulation, would seem worthwhile. This is currently being conducted at Riso National Laboratory. Recent Developments in Cube-Grain Nucleation Studies Using the newly developed EBSP (electron back scatter pattern) technique (I0) for microtexture determination, H]elen and Nes (11) have studied the nucleation of reerystallized grains in rolled high purity aluminum specimens. They reported that cube-oriented grains were found to grow out from transition band in the { 112 } <111> deformation texture. This is a heartening evidence showing that the origin of cube texture is closely related with the copper-texture~in rolled fee metals as emphasized in the mtroductlon of the present eommunleatlon and m prevlous discussions (I). However, the initial material used by these authors was a directionally solidified high purity aluminum ingot with columnar grains having a
.
.
.
.
~
°
In a more recent study on the heterogenieties in heavily roiled commercial purity aluminum, Nes and co-workers (13) postulated a mechanism for the cube-oriented elements in the transition band between the double {112}<111> textures. They described that the rotations involved starting from one of the copper components are firstly around the rolling direction, then gradually around the transverse direction through the cube orientation. Beyond that, it continues through a symmetrical
Vol.
23,
No.
6
CUBE
TEXTURE
883
path ending in a new copper-orientation which is a mirror image of the starting one. This postulation appears attractive, as it makes an important connection between the { 112 } <111> copper texture and the cube-oriented elements for the development of the cube texture upon recrystallization. Moreover, the rotations involved, first around the rolling direction then around the transverse direction, for connecting the two copper orientations {112}<111>, are consistent with the shape change observed in rolling. Suggestions for Critical Experiments To test whether the aforementioned interpretation is truly valid or not, some simple experiments may be conducted. In these experiments, some controlled widening may be applied to the channel-die compressed work piece by some additional procedures in deformation. This can be achieved by cutting out square pieces from a channel-die compressed strip, then deform each piece to controlled length in the channel-die length direction. An alternate approach of controlled widening in channel-die compression is to reduce the width of the channel-die compressed strip at suitable intermediate reductions, then apply additional reductions by channel-die compression to the full diewidth. The results of some exploratory experiments of controlled widening in channel-die compression will be reported in the near future. It is hoped that some basic information helpful for further understanding of the problem can be produced from these experiments. In conclusion, the recent findings of Nes and co-workers (11,13) are encouraging. Considering the fact that the polycrystalline texture of the copper type is highly complex, the transition band between the double {112}<111> texture components may be just one of the important sites for cube grain nucleation. The transition regions between a {112}<111> component and one of the other texture components such as the (110}<112>, {123}<412>, or {110}<001>, are largely unknown. For a complete understanding of the origin of cube grains, the characteristic feature and behavior of these transition regions should be studied systematically. Acknowledgement This idea of approach to the cube-grain nucleation studies was initiated while the writer was on a sabbatical leave at the Riso National Laboratory for three months. Stimulating and helpful discussions with N. Hansen, T. Leffers, and D. Juul-Jensen of the Riso National laboratory are sincerely acknowledged. The writer's research in this particular area has been supported by the National Science Foundation, contract number DMR-8614903. References i.
2. 3. 4. 5. 6. 7. 8.
9. 10.
H. Hu, in Annealing Processes - Recovery t Recrystallization and Grain Growth, Eds. N. Hansen, D. Juul-Jensen, T. Leffers, and B. Ralph (Proc. 7th Riso Int. Sym., 1986, Roskilde, Denmark), p. 75. Scripta Metall. 19, 1471 (1985). P.A. Beck and H. Hu, Trans. AIME, 194, 83 (1952). H. Hu and S. R. Goodman, Trans. Metall. Soc. AIME, 227, 627 (1983). C.A. Verbraak, Aeta Metall., 6, 580 (1958). H. Hu, in Recovery. and Recrystallization of Metals t Ed. L. Himmel, (Interscience Publishers, New York, 1963) p. 311 J . F . Butler, Jr. and H. Hu, "Deformation and Annealing Textures of Copper Deformed in Plane Strain and by Rolling", Mater. Sci. and Eng. A (in press). H. Hammelrath, J. F. Butler, Jr., H. Hu, and K. Lucke, "An ODF Study of the Deformation and Recrystallization Textures of Rolled and Channel-Die Compressed High-Purity Copper", to be published. D. Juul-Jensen, T. Leffers, H. Hu, and N. Hansen, "A Study of the Deformation and Rccrystallization Textures of Channel-Die Compressed and Rolled Copper by Neutron Diffraction", to be published. T. Leffers, Scripta Metall., 2, 447 (1968). O.J. Dingley, Scanning Electron Microscopy, 2, 569 (1984).
884
11. 12. 13.
CUBE TEXTURE
Vol.
23, No.
J. Hjelen and E. Nes, in Texture of Materials ( I C O T O M 8) Ed. J. S. Kallend and G. Gottstein, (The MetaU. Soo., 1988,) p. 597. E. Nes, J. Hirsch, and K. Lueke, in Texture of Materials~ Ed. Brakman, Jongenburger and Mittemeijer (Neth. Soc. Matls. Sei., Holland, 1984), p. 663. R. Orsund, J. Hjelen and E. Nes, Scripta Metall. (in press).
6