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Transverse kinking of BCC fibers in drawn FCC(matrix)-BCC(dispersoid) in situ composites
Scripta METALLURGICA
Vol. 23, pp. 141-145, 1989 Printed in the U.S.A.
Pergamon Press plc
TRANSVERSE KINKING OF BCC FIBERS IN DRAWN FCC(MATRIX)-BCC(DISPERSOID) IN SITU COMPOSITES J. C. Malzalm Kampe* and T. H. Courtuey** *Naval Research Laboratory Washington, DC 20375
**University of Virginia Charlottesville, Va 22901
( R e c e i v e d O c t o b e r 13, 1988) ( R e v i s e d O c t o b e r 31, 1988) Introduction Deformation processing of mechanically compatible two-phase alloys produces in situ composite materials which can be made to manifest exceptional strengths (1-8). Of the many composites so fabricated, fcc(matrix)-bcc (dispersoid) systems appear to offer the greatest strengthening potential. These systems have been typically processed via wire drawing, which produces a fibrous composite structure. Because the strength of these materials is inevitably linked to their structure, efforts to understand microstructural development with processing are underway. The bcc fibers produced during the wire drawing of fcc(matrix)-bcc (dispersoid) systems possess two notable features. The fLrst of these is a ribbon morphology, as opposed to the cylindrical shape expected from an axially symmetric deformation mode. This is evident in transverse cross sections, as shown in Fig. 1 for a drawn Cu-14 vol.% Fe composite. The ribbon morphology is attributable to the <110> drawing texture that develops in the bcc phase, and the plane strain deformation that subsequently ensues. This explanation stems from Hosford's analysis (9) of Peck and Thomas' observations (10) of ribboned grains in drawn bcc polycrystals. The second feature of bcc fibers, also apparent in Fig. 1, is their kinked, or chevron, cross sections. Such transverse bcc kinking has been noted by several investigators (2-7), and is somewhat similar in appearance to the transverse curling of grain cross sections in drawn polycrystalline bcc wires (10-12)*. The characteristic kinking of bcc ribboned fibers has been explained in terms of compatibility requirements (2, 3, 6, 7). This also stems from the work of Peck and Thomas (10) and Hosford (9), who proposed that the grains in drawn bcc polycrystals curl and bend around each other in order to maintain microstructural integrity after plane strain deformation begins. Such mutual conformity is certainly important when all the grains of the bcc aggregate favor plane strain elongation and the overall deformation mode is axially symmetric (wire drawing). However, it is expected, as will be discussed later, that compatibility requirements are relaxed for bcc crystals embedded in a softer fcc matrix which can deform axially symmetrically**. The purpose of this communication is to describe an additional factor which contributes to transverse bec kinking, particularly in the fcc-bcc systems. The mechanism presented here has been linked to the development of deformation bands within the bcc crystals (17). Deformation Band~ and Transverse BCC Kinking The plastic deformation of a metallic crystal often does not proceed in a macroscopically homogeneous fashion, particularly when the deformation mode induces strong texture development. Rather, upon straining, the crystal divides itself into several regions called deformation bands. Such crystal division is due to variations, between neighboring regions, in the set of slip systems activated (18-23)***. That is, as the nature and sense of lattice rotation with deformation is governed by the combination of slip systems operating, variations in the activated slip system sets induce crystal division by causing neighboring regions to rotate in different directions, * Drawn pearlite also exhibits a transverse curving of eutectoid lamellae (13-16). ** The fcc drawing texture, a mixture of <111> and <100>, allows axially symmetric flow to occur since these orientations have, respectively, three and four slip directions arranged symmetrically about the wire axis (9). *** The motivation for slip to occur on different systems and system combinations in different portions of the crystal may derive from 1) the statistical nature of slip, 2) variations in external constraints, or 3) certain initial symmetrical orientations of the parent crystal (24). Also, it should be noted that the means of band formation presented here do not pertain to the "kink" bands observed in hcp crystals (23). 141 0036-9748/89 $3.00 + .00
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creating a misorientation between these regions. The misorientation generated can be quite substantial (15 ° or greater (25-26)), depending on initial crystal orientation and the amount and mode of deformation. Deformation bands are separated by very narrow "transition" or "micro-" bands, so called because these boundaries often consist of a series of parallel sub-boundaries across which the lattice misorientation between the neighboring deformation bands is apportioned (27-28). Consider a bcc crystal embedded in a fcc matrix. Upon drawing, the bec crystal breaks up into deformation bands. It is likely that this crystal division produces parallel lamellar deformation bands, such as those observed within the grains of drawn bec polycrystals by Barrett and Levenson (25), and illustrated schematically in Fig. 2a. Initially (as in the grains of bcc polycrystalline wires), the bands lie at some angle to the wire axis, and with continued drawing rotate to become parallel to the wire axis (Fig. 2b). Within each band, the lattice rotates in its own manner to align a < l l 0 > direction with the wire axis (25), and once the crystal portions attain stable < l l 0 > end orientations they deform under plane strain conditions. With only {1l0 } slip systems operating, the crystal portions then thin in a <001> direction, bringing a {001 } plane coincident with the broad face of the ribbon that forms. However, as the orientations of neighboring crystal regions differ, owing to their differing lattice rotation paths, the {001 } face plane of a given portion will be inclined to those of its neighbors. Hence, in cross section, the bcc ribbon will possess kinks where the crystal portions meet, and the kinks denote the location of deformation band boundaries that lie parallel to the wire axis (Fig. 2c). The extent of kinking induced by deformation banding depends on the initial orientation of the bcc crystal, which largely determines the propensity of the crystal to divide. The severity of a given kink increases with plane strain deformation to a maximum which is dictated by the misorientation established between neighboring crystal portions with attainment of stable <110> end orientations. Perhaps it should be emphasized that banding alone does not produce transverse kinking; it is the combination of lamellar banding and development of a drawing texture which favors plane stiain deformation (i.e., thinning in a preferred crystallographic direction) that yields a kinked bec cross section. Discussion Direct evidence of the presence of bcc deformation bands in drawn fcc(matrix)-bec(dispersoid) systems has not yet been obtained. However, strong indications of banding are cited in the work of Peltun, et al. (7). These investigators extracted bib fibers from a Cu-20 vol.% Nb composite drawn to a reduction ratio (11= In (Ao/A)) of 7. LongitudinalTEM examination showed that the Nb filaments were divided into several parallel (to the fiber length) regions which were separated by distinct dislocation boundaries. The misorientation between neighboring regions was reported to range from <2° to ~35° about a common <110> direction. These investigators also determined that the contrast variation between regions was due both to differences in diffraction conditions (crystallographic misorientation) and in projected thickness. Thus, the bends or kinks responsible for differences in projected fiber thickness have been linked to the positions of longitudinal boundaries by Pelton and his coworkers. These investigators (7), however, did not emphasize this link, or make a connection between the d e v e l o p m e n t of the kinked morphology and the presence of the longitudinal boundaries. They attributed kinking to the plane strain deformation which produces the ribbon morphology and referenced Hosford's (9) work. The presence of longitudinalboundaries, and their position association with kinks, is easily understood in terms of the kinking mechanism presented above. The misorientation between neighboring deformation bands, which is established with attainment of the <110> texture, manifests itself in the form of a kink at the boundary between bands as plane strain deformation ensues. The severity of the kink, however, is governed by the misorientation established between regions, and, ff this is small (e.g., on the low side of the range observed by Peltun et al. (7), 2°-35°), the "kink" may not be discernible though its associated boundary is apparent. Due to this, the observation (29) of boundaries without kinks also seems compatible with the kinking mechanism described here. It is interesting to note that Pelton, et al. (7) also detected longitudinalparallel dislocation boundaries in the Cu matrix of heavily worked (ln(Ao/A) = 12) composite wires. This is not surprising, as matrix grains should also develop deformation bands which rotate to align with the wire axis. Banding in the fcc matrix, though, does not lead to transverse kinking because that phase continues to deform axially symmetrically after attaining stable <111> or <100> end orientations. Again, it is the combination of banding and thinning in a preferred crystallographic direction that produces kinked bec cross sections upon wire drawing. Longitudinal boundaries are also found within the bcc fibers of drawn and annealed Cu-14 vol.% Fe composites (8). These boundaries become evident in the initial stages of heat treatment, and induce longitudinal fiber splitting during continued elevated temperature exposure. As it is difficult to comprehend or envision a motivating force for which recovery or recrystallization alone would produce longitudinal boundaries that apparently extend over the entire fiber length, it is reasonable to expect that such boundaries derive from deformation band boundaries which are produced and aligned during wire drawing.
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The usual explanation of kinked bcc cross sections in drawn fcc-bcC systems is based on compatibility requirements (2, 3, 6, 7). Such reasoning is essentially an extrapolation of ideas presented by Peck and Thomas (10) and Hosford (9) concerning the curled grain cross sections of drawn bcc polycrystals. Within bcc aggregates, after attainment of the < ! i 1)> texture, compatibility constraints are quite severe. This can be appreciated by noting that each grain in the aggregate favors plane strain elongation, and yet the work piece as a whole must accommodate an axially symmetric shape change. Further, the textured orientations of neighboring grains are not necessarily suited to allow unconstrained thinning in the same (i.e., equivalent) crystallographic direction in each grain, and to also maintain the microstructural integrity of the work piece. Clearly, as Hosford (9) and Peck and Thomas (10) have reasoned, the constraints of required mutual conformity must be the dominant motivation for transverse bending and curling of the bcc grains about one another. While deformation banding will also contribute to this curving via the kinking mechanism described above, it is expected that the more relevant banding influence for bcc polycrystals is the modification of compatibility requirements which must accompany such grain "fragmentation". The drawing compatibility comtraints imposed on a bec crystal embedded in a softer fcc matrix are considerably reduced from those on a grain within a bcc polycrystal. This is expected as the fcc phase has a lower flow stress and should thus be more accommodating to harder constituent phases. Additionally, even in the textured state, the fcc matrix is able to deform axially symmetrically, and can continue to accommodate both the limited means of textured bcc dispersoid deformation (plane strain "elongation") and the overall deformation mode (axially symmetric drawing). Contrary (perhaps) to first thought, the softer fcc matrix does not impose axially symmetric deformation on the developing bcc fibers simply because it is able to deform in that manner. Rather, because it remains the accommodating phase, the matrix in extreme proximity to a fiber is probably constrained to deform under near plane strain conditions. It may also be that, due to accommodation of the bcc phase, dynamic recovery/recrystallization in the fcc matrix occurs at a much lower macroscopic strain than expected based on single phase fcc deformation. At any rate, evidence of accommodation constraints being weighted more heavily toward the fcc matrix in fcc-bcc systems is found in the drawing texture studies of Wassermann and his coworkers (3032). These investigators determined that Cu and Ag texture development was inhibited by the presence of a harder, yet deformable, bcc Fe phase. Alternatively, the Fe texture developed in the presence of Cu was much sharper than that for a single phase Fe wire with the same processing history. While other factors (e.g., grain size, phase purity, etc.) must also be considered in the explicit interpretation of these results, a reduction in bcc compatibility constraints in fcc-bcc systems is strongly indicated. Yet comparing bcc cross sections of fcc-bcc composite wires to those of drawn bcc polycrystals, sharp, distinct kinks in the bcc fibers contrast the much more smoothly curved grains of the bcc polycrystals (9-10). It is felt that this results from the reduction in compatibility constraints for bcc crystals embedded in a softer fcc matrix, which allows the geometric aspects of deformation band kinking to prevail in the composite systems. Stanmarv The transverse kinking of bcc ribboned fibers in drawn fcc(matrix)-bcc(dispersoid) systems has been attributed to the development of deformation bands within the bcc crystals during the initial stages of drawing and the subsequent plane strain deformation which ensues after attainment of stable <110> end orientations. Though compatibility constraints do cause some transverse curving, as in the grains of bec aggregates, their contribution is less dominant when bcc crystals are embedded in a softer, more compliant fcc matrix. Acknowledgements The financial support of these efforts provided by the Army Research Office (#BAAG-29-84-K-0047; Dr. Andrew Crowson, contract monitor) and DARPA (#5529; Dr. Philip A. Parrish, contract monitor) is gratefully acknowledged. Referenc~ 1. 2. 3. 4. 5. 6. 7. 8. 9. I0. 11. 12.
G. Frommeyer and G. Wassermann, Acta Met., 23, 1353 (1975). J . P . Harbison and J. Bevk, J. Appl. Phys., 48, 5180 (1977). J. Bevk, J. P. Harbison, and J. L. Bell, J. Appl. Phys.,49, 6031 (1978). P . D . Funkenbusch and T. H. Courmey, Scripta Met., 15, 1349 (1981). J . D . Verhoeven in In Situ Composites IV, F. D. Lemkey, H. E. Cline, and M. McLean, eds., p. 267, Elsevier Science Publishing Co., Inc., New York (1982). W . A . Spitzig, A. R. Pelton, and F. C. Laabs, Acta Met., 35, 2427 (1987). A . R . Pelton, F. C. Laabs, W. A. Spitzig, and C. C. Cheng, Ultramicroscopy, 22,251 (1987). J.C. Malzahn Kampe, T. H. Courtney, and Y. Leng, submitted to Acta Met. (1988). W . F . Hosford, Jr., Trans. TMS AIME, 230, 12 (1964). J. F. Peck and D. A. Thomas, Trans. TMS A1ME, 221, 1240 (1961). G. Langford and M. Cohen, Trans. ASM, 62,623 (1969). G. Langford and M. Cohen, Met. Trans. A, 6A, 901 (1975).
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M. A. P. Dewey and G. W. Briers, J. Iron atutSteellnst.,204, 102 (1966). J. D. Embury and R. M. Fisher, Acta Met., 14, 147 (1966). G. Langford, Met. Trans., 1,465 (1970). G. Langford, Met. Trans. A, 8A, 861 (1977). J. C. Malzahn Kampe, Ph.D. Thesis, Michigan Technological University, Houghton, MI (1987). L. B. Pfeil, Carnegie Scholarship Memoirs, 15,319 (1926). L. B. Pfeil, Carnegie Scholarship Memoirs, 16, 153 (1927). H. Hu, R. S. Cline, and S. R. Goodman in Recrystallization, Grain Growth and Textures, p. 295, ASM, Metals Park, OH (1966). C. S. Barrett, Structure of Metals, 2nd Edition, p. 372, McGraw-HiU Book Company, New York (1952). G. Y. Chin in The lnhomogeneity of Piastic Deformation, p. 83, ASM, Metals Park, OH (1973). G. E. Dieter, Mechanical Metallurgy, p. 534, McGraw-Hill Book Company, New York (1986). G. Y. Chin and B. C. Wonsiewicz, Trans. TMS AIME, 245, 871 (1969). C. S. Barrett and L H. Levenson, Trans. AIME, 135, 327 (1939). R. D. Doherty, Metal Sci., 8, 132 (1974). H. Hu in Recovery andRecrystallization of Metals, L. I-limmel, ed., p.311, Interscience Publishers, New York (1963). J. L. Walter in Recovery and Recrystullization of Metals, L. Himmel, ed., p.364, Interscience Publishers, New York (1963). J. D. Verhoeven and W. A. Spitzig, Private communication, July, 1988. G. Wassermann, Z. Metalikunde, 64, 844 (1973). H. P. Wahl and G. Wassermann, Z. Metallkunde, 61,326 (1970). C. Liesner and G. Wassermann, Metall., 23,414 (1969).
FIG. 1. Transverse micrograph of a Cu-14 vol.% Fe deformation processed composite wire, In (Ao/A) = 5.09. The ribbon morphology of the bec Fe fibers is evidenced by the shape and aspect ratio of their cross section. The characteristic transverse kinking of bec fibers is also apparent. As discussed in the text, this latter aspect of fiber morphology is attributable to the development of deformation bands within the bcc crystal, and to subsequent texture induced plane strain deformation.
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FIG. 2. Development of a kinked ribbon bcc fiber. (a) In the early stages of drawing, the cylindrical bcc crystal divides into parallel lamellar deformation bands. As shown, the bands initially lie at some angle to the wire axis (drawing direction). (b) With continued drawing, the deformation bands rotate to align with the wire axis, and within each band, the lattice rotates in its own manner to align a <110> direction with the wire axis. The cross hatching of the bcc crystal reflects the misorientation that is established between bands with the attainment of stable <110> end orientations, and represents the transverse orientations of {001 } planes that now lie parallel to the wire axis. (c) As drawing continues, the <110> textured bcc crystal deforms under plane strain conditions, thinning along a <001> direction. This produces the ribbon morphology of the bcc fiber, and brings the {001 } planes coincident with the flat face of the ribbon. However, as indicated, the {001} face planes of a given band are transversely inclined to those of its neighbors, and thinning in a preferred crystallographic direction thus produces kinks in the banded bcc fiber. The kinks denote the location of deformation band boundaries that lie parallel to the wire axis.
Vol. 23, pp. 141-145, 1989 Printed in the U.S.A.
Pergamon Press plc
TRANSVERSE KINKING OF BCC FIBERS IN DRAWN FCC(MATRIX)-BCC(DISPERSOID) IN SITU COMPOSITES J. C. Malzalm Kampe* and T. H. Courtuey** *Naval Research Laboratory Washington, DC 20375
**University of Virginia Charlottesville, Va 22901
( R e c e i v e d O c t o b e r 13, 1988) ( R e v i s e d O c t o b e r 31, 1988) Introduction Deformation processing of mechanically compatible two-phase alloys produces in situ composite materials which can be made to manifest exceptional strengths (1-8). Of the many composites so fabricated, fcc(matrix)-bcc (dispersoid) systems appear to offer the greatest strengthening potential. These systems have been typically processed via wire drawing, which produces a fibrous composite structure. Because the strength of these materials is inevitably linked to their structure, efforts to understand microstructural development with processing are underway. The bcc fibers produced during the wire drawing of fcc(matrix)-bcc (dispersoid) systems possess two notable features. The fLrst of these is a ribbon morphology, as opposed to the cylindrical shape expected from an axially symmetric deformation mode. This is evident in transverse cross sections, as shown in Fig. 1 for a drawn Cu-14 vol.% Fe composite. The ribbon morphology is attributable to the <110> drawing texture that develops in the bcc phase, and the plane strain deformation that subsequently ensues. This explanation stems from Hosford's analysis (9) of Peck and Thomas' observations (10) of ribboned grains in drawn bcc polycrystals. The second feature of bcc fibers, also apparent in Fig. 1, is their kinked, or chevron, cross sections. Such transverse bcc kinking has been noted by several investigators (2-7), and is somewhat similar in appearance to the transverse curling of grain cross sections in drawn polycrystalline bcc wires (10-12)*. The characteristic kinking of bcc ribboned fibers has been explained in terms of compatibility requirements (2, 3, 6, 7). This also stems from the work of Peck and Thomas (10) and Hosford (9), who proposed that the grains in drawn bcc polycrystals curl and bend around each other in order to maintain microstructural integrity after plane strain deformation begins. Such mutual conformity is certainly important when all the grains of the bcc aggregate favor plane strain elongation and the overall deformation mode is axially symmetric (wire drawing). However, it is expected, as will be discussed later, that compatibility requirements are relaxed for bcc crystals embedded in a softer fcc matrix which can deform axially symmetrically**. The purpose of this communication is to describe an additional factor which contributes to transverse bec kinking, particularly in the fcc-bcc systems. The mechanism presented here has been linked to the development of deformation bands within the bcc crystals (17). Deformation Band~ and Transverse BCC Kinking The plastic deformation of a metallic crystal often does not proceed in a macroscopically homogeneous fashion, particularly when the deformation mode induces strong texture development. Rather, upon straining, the crystal divides itself into several regions called deformation bands. Such crystal division is due to variations, between neighboring regions, in the set of slip systems activated (18-23)***. That is, as the nature and sense of lattice rotation with deformation is governed by the combination of slip systems operating, variations in the activated slip system sets induce crystal division by causing neighboring regions to rotate in different directions, * Drawn pearlite also exhibits a transverse curving of eutectoid lamellae (13-16). ** The fcc drawing texture, a mixture of <111> and <100>, allows axially symmetric flow to occur since these orientations have, respectively, three and four slip directions arranged symmetrically about the wire axis (9). *** The motivation for slip to occur on different systems and system combinations in different portions of the crystal may derive from 1) the statistical nature of slip, 2) variations in external constraints, or 3) certain initial symmetrical orientations of the parent crystal (24). Also, it should be noted that the means of band formation presented here do not pertain to the "kink" bands observed in hcp crystals (23). 141 0036-9748/89 $3.00 + .00
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creating a misorientation between these regions. The misorientation generated can be quite substantial (15 ° or greater (25-26)), depending on initial crystal orientation and the amount and mode of deformation. Deformation bands are separated by very narrow "transition" or "micro-" bands, so called because these boundaries often consist of a series of parallel sub-boundaries across which the lattice misorientation between the neighboring deformation bands is apportioned (27-28). Consider a bcc crystal embedded in a fcc matrix. Upon drawing, the bec crystal breaks up into deformation bands. It is likely that this crystal division produces parallel lamellar deformation bands, such as those observed within the grains of drawn bec polycrystals by Barrett and Levenson (25), and illustrated schematically in Fig. 2a. Initially (as in the grains of bcc polycrystalline wires), the bands lie at some angle to the wire axis, and with continued drawing rotate to become parallel to the wire axis (Fig. 2b). Within each band, the lattice rotates in its own manner to align a < l l 0 > direction with the wire axis (25), and once the crystal portions attain stable < l l 0 > end orientations they deform under plane strain conditions. With only {1l0 }
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The usual explanation of kinked bcc cross sections in drawn fcc-bcC systems is based on compatibility requirements (2, 3, 6, 7). Such reasoning is essentially an extrapolation of ideas presented by Peck and Thomas (10) and Hosford (9) concerning the curled grain cross sections of drawn bcc polycrystals. Within bcc aggregates, after attainment of the < ! i 1)> texture, compatibility constraints are quite severe. This can be appreciated by noting that each grain in the aggregate favors plane strain elongation, and yet the work piece as a whole must accommodate an axially symmetric shape change. Further, the textured orientations of neighboring grains are not necessarily suited to allow unconstrained thinning in the same (i.e., equivalent) crystallographic direction in each grain, and to also maintain the microstructural integrity of the work piece. Clearly, as Hosford (9) and Peck and Thomas (10) have reasoned, the constraints of required mutual conformity must be the dominant motivation for transverse bending and curling of the bcc grains about one another. While deformation banding will also contribute to this curving via the kinking mechanism described above, it is expected that the more relevant banding influence for bcc polycrystals is the modification of compatibility requirements which must accompany such grain "fragmentation". The drawing compatibility comtraints imposed on a bec crystal embedded in a softer fcc matrix are considerably reduced from those on a grain within a bcc polycrystal. This is expected as the fcc phase has a lower flow stress and should thus be more accommodating to harder constituent phases. Additionally, even in the textured state, the fcc matrix is able to deform axially symmetrically, and can continue to accommodate both the limited means of textured bcc dispersoid deformation (plane strain "elongation") and the overall deformation mode (axially symmetric drawing). Contrary (perhaps) to first thought, the softer fcc matrix does not impose axially symmetric deformation on the developing bcc fibers simply because it is able to deform in that manner. Rather, because it remains the accommodating phase, the matrix in extreme proximity to a fiber is probably constrained to deform under near plane strain conditions. It may also be that, due to accommodation of the bcc phase, dynamic recovery/recrystallization in the fcc matrix occurs at a much lower macroscopic strain than expected based on single phase fcc deformation. At any rate, evidence of accommodation constraints being weighted more heavily toward the fcc matrix in fcc-bcc systems is found in the drawing texture studies of Wassermann and his coworkers (3032). These investigators determined that Cu and Ag texture development was inhibited by the presence of a harder, yet deformable, bcc Fe phase. Alternatively, the Fe texture developed in the presence of Cu was much sharper than that for a single phase Fe wire with the same processing history. While other factors (e.g., grain size, phase purity, etc.) must also be considered in the explicit interpretation of these results, a reduction in bcc compatibility constraints in fcc-bcc systems is strongly indicated. Yet comparing bcc cross sections of fcc-bcc composite wires to those of drawn bcc polycrystals, sharp, distinct kinks in the bcc fibers contrast the much more smoothly curved grains of the bcc polycrystals (9-10). It is felt that this results from the reduction in compatibility constraints for bcc crystals embedded in a softer fcc matrix, which allows the geometric aspects of deformation band kinking to prevail in the composite systems. Stanmarv The transverse kinking of bcc ribboned fibers in drawn fcc(matrix)-bcc(dispersoid) systems has been attributed to the development of deformation bands within the bcc crystals during the initial stages of drawing and the subsequent plane strain deformation which ensues after attainment of stable <110> end orientations. Though compatibility constraints do cause some transverse curving, as in the grains of bec aggregates, their contribution is less dominant when bcc crystals are embedded in a softer, more compliant fcc matrix. Acknowledgements The financial support of these efforts provided by the Army Research Office (#BAAG-29-84-K-0047; Dr. Andrew Crowson, contract monitor) and DARPA (#5529; Dr. Philip A. Parrish, contract monitor) is gratefully acknowledged. Referenc~ 1. 2. 3. 4. 5. 6. 7. 8. 9. I0. 11. 12.
G. Frommeyer and G. Wassermann, Acta Met., 23, 1353 (1975). J . P . Harbison and J. Bevk, J. Appl. Phys., 48, 5180 (1977). J. Bevk, J. P. Harbison, and J. L. Bell, J. Appl. Phys.,49, 6031 (1978). P . D . Funkenbusch and T. H. Courmey, Scripta Met., 15, 1349 (1981). J . D . Verhoeven in In Situ Composites IV, F. D. Lemkey, H. E. Cline, and M. McLean, eds., p. 267, Elsevier Science Publishing Co., Inc., New York (1982). W . A . Spitzig, A. R. Pelton, and F. C. Laabs, Acta Met., 35, 2427 (1987). A . R . Pelton, F. C. Laabs, W. A. Spitzig, and C. C. Cheng, Ultramicroscopy, 22,251 (1987). J.C. Malzahn Kampe, T. H. Courtney, and Y. Leng, submitted to Acta Met. (1988). W . F . Hosford, Jr., Trans. TMS AIME, 230, 12 (1964). J. F. Peck and D. A. Thomas, Trans. TMS A1ME, 221, 1240 (1961). G. Langford and M. Cohen, Trans. ASM, 62,623 (1969). G. Langford and M. Cohen, Met. Trans. A, 6A, 901 (1975).
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M. A. P. Dewey and G. W. Briers, J. Iron atutSteellnst.,204, 102 (1966). J. D. Embury and R. M. Fisher, Acta Met., 14, 147 (1966). G. Langford, Met. Trans., 1,465 (1970). G. Langford, Met. Trans. A, 8A, 861 (1977). J. C. Malzahn Kampe, Ph.D. Thesis, Michigan Technological University, Houghton, MI (1987). L. B. Pfeil, Carnegie Scholarship Memoirs, 15,319 (1926). L. B. Pfeil, Carnegie Scholarship Memoirs, 16, 153 (1927). H. Hu, R. S. Cline, and S. R. Goodman in Recrystallization, Grain Growth and Textures, p. 295, ASM, Metals Park, OH (1966). C. S. Barrett, Structure of Metals, 2nd Edition, p. 372, McGraw-HiU Book Company, New York (1952). G. Y. Chin in The lnhomogeneity of Piastic Deformation, p. 83, ASM, Metals Park, OH (1973). G. E. Dieter, Mechanical Metallurgy, p. 534, McGraw-Hill Book Company, New York (1986). G. Y. Chin and B. C. Wonsiewicz, Trans. TMS AIME, 245, 871 (1969). C. S. Barrett and L H. Levenson, Trans. AIME, 135, 327 (1939). R. D. Doherty, Metal Sci., 8, 132 (1974). H. Hu in Recovery andRecrystallization of Metals, L. I-limmel, ed., p.311, Interscience Publishers, New York (1963). J. L. Walter in Recovery and Recrystullization of Metals, L. Himmel, ed., p.364, Interscience Publishers, New York (1963). J. D. Verhoeven and W. A. Spitzig, Private communication, July, 1988. G. Wassermann, Z. Metalikunde, 64, 844 (1973). H. P. Wahl and G. Wassermann, Z. Metallkunde, 61,326 (1970). C. Liesner and G. Wassermann, Metall., 23,414 (1969).
FIG. 1. Transverse micrograph of a Cu-14 vol.% Fe deformation processed composite wire, In (Ao/A) = 5.09. The ribbon morphology of the bec Fe fibers is evidenced by the shape and aspect ratio of their cross section. The characteristic transverse kinking of bec fibers is also apparent. As discussed in the text, this latter aspect of fiber morphology is attributable to the development of deformation bands within the bcc crystal, and to subsequent texture induced plane strain deformation.
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fcc matrix i
FIG. 2. Development of a kinked ribbon bcc fiber. (a) In the early stages of drawing, the cylindrical bcc crystal divides into parallel lamellar deformation bands. As shown, the bands initially lie at some angle to the wire axis (drawing direction). (b) With continued drawing, the deformation bands rotate to align with the wire axis, and within each band, the lattice rotates in its own manner to align a <110> direction with the wire axis. The cross hatching of the bcc crystal reflects the misorientation that is established between bands with the attainment of stable <110> end orientations, and represents the transverse orientations of {001 } planes that now lie parallel to the wire axis. (c) As drawing continues, the <110> textured bcc crystal deforms under plane strain conditions, thinning along a <001> direction. This produces the ribbon morphology of the bcc fiber, and brings the {001 } planes coincident with the flat face of the ribbon. However, as indicated, the {001} face planes of a given band are transversely inclined to those of its neighbors, and thinning in a preferred crystallographic direction thus produces kinks in the banded bcc fiber. The kinks denote the location of deformation band boundaries that lie parallel to the wire axis.