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Study on the microstructure and formability of commercially pure titanium in two-temperature deep drawing
Journal of Materials Processing Technology 95 (1999) 65±70
Study on the microstructure and formability of commercially pure titanium in two-temperature deep drawing Jaan-Ming Liu*, Sheh-Shon Chou Department of Materials Science and Engineering(22), National Cheng Kung University, Tainan 70101, Taiwan Received 16 March 1998
Abstract From recent research, it has been found that deep drawing at two temperatures can make SUS304 exhibit deep drawability, the present investigation testing materials with other structures by the process. Commercially pure titanium (CP Ti)(a-Ti) exhibits almost twice the deep drawability when the temperature is increased from room temperature to 4008C. The process can make the deep drawability of a-Ti much more effective. The breaking point of titanium sheet is in the direction perpendicular to the rolling direction because of the effect from two different directions due to the anisotropy of the material. A suitable blank-holding force (BHF) can help to reach a limited drawing depth, the required force decreasing when the operating temperature increases. From X-ray and TEM identi®cation the process can drive more slip systems to relax strain energy to obtain good deep drawability by virtue of better ductility. # 1999 Elsevier Science S.A. All rights reserved. Keywords: Two-temperature deep drawing; Commercially pure titanium
1. Introduction The deep drawing process is used widely with press equipment and molds to form seamless vessels of different shells from metal sheets. The metal sheets are heated by a heater in the mold plate and cooled by an iced water ¯ow in the punch during the two-temperature deep drawing process, which increases deep drawability and results in a product with a more uniform wall thickness. By research, the process has been con®rmed to be able to improve the deep drawability of stainless steel SUS304 [1±3]. The microstructure of the deformation was also explored. SUS304 is of f.c.c. structure, so there is doubt as to whether the process can also promote material of other structures. Titanium, with c.p.h. structure at room temperature and b.c.c. structure at high temperature, has been chosen as the test material. 2. Theory Titanium is either a-Ti(c.p.h.), ab-Ti(h.c.p.b.c.c.) or b-Ti(b.c.c.), according to the temperature, the alloy compo*Corresponding author. E-mail address: [email protected] (J.-M. Liu)
sition and the stress condition. The plastic deformation model is generally either slip deformation or twin deformation. Compared with f.c.c. and b.c.c. structure, metals and alloys with c.p.h. structure would be more complex. When c/ a<1.594, slip occurs on the metal prismatic plane f0 1 1 0g; whilst when c/a>1.614, slip occurs on the metal basel plane {0 0 0 1} [4]. Thus the active slip system is relative to the c/a value of titanium of 1.587, the main slip system being f1 1 0 0gh1 1 2 0i, and when it moves on f0 0 0 1gh1 1 2 0i. The a-dislocation [5] forms on the basic plane in the slip plane and slip direction with no strain along the c axis. Twin deformation occurs in single crystal titanium, whilst twin deformation and slip deformation occur in polycrystal titanium. Ductility can be extended because of the satisfying of von Mises' condition. The slip of titanium occurs on f1 0 1 0g; 0 0 0 1, and f1 0 1 1g along h1 1 2 0i by 1=3h1 1 2 0i dislocation at room temperature or lower [6]. The change along the c axis does not only need h1 1 2 0i slip, but also slip beyond the basic plane. It was observed in commercially pure titanium and Ti±Al alloy by reason of 1=3h1 1 2 3i movement or ca dislocation, but not yet in high-purity titanium [7,8]. The slip along h1 1 2 3i was observed in Cd and Zr at room temperature [9] and in Be at high temperature [10±12].
0924-0136/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved. PII: S 0 9 2 4 - 0 1 3 6 ( 9 9 ) 0 0 1 0 8 - 9
66
J.-M. Liu, S.-S. Chou / Journal of Materials Processing Technology 95 (1999) 65±70
The change along c axis can also work by twin deformation. For titanium f1 0 1 2g; f1 1 2 1g and f1 1 2 3g , twins occur in extension along the c axis; and f1 1 2 2g; f1 1 2 4g [13,14], and f1 0 1 1g [15] twins in compression along the c axis. When the temperature increases, twin deformation becomes less important generally. Rosi et al. [13] did not ®nd twins of any type at 8008C, but McHargue and Hammond [16] found less f1 1 2 2g and f1 1 2 1g twins at 8158C. Paton and Backfen [17] revealed that the compression of single-crystal Ti from 258C to 8008C, to about 5% strain along the c axis, was accommodated entirely by f1 1 2 2g twins from 258C to 3008C, and by a combination of f1 0 1 1g twins from 4008C to 8008C. Reduction normal to the c axis deformed by a combination of f1 0 1 2g twins and prism slip at 258C, and by prism slip alone above 5008C. Although ca slip is not responsible for a signi®cation amount of strain below 3008C, it is important in accommodating the shear ahead of a propagating f1 1 2 2g twin [17]. 3. Experiments The experiments use an electric wire to heat the mold and the specimen before pressing. When the specimen reaches the selected temperature, the deep drawing process is executed with a cooling effect in punch. The press equipment is an Amino universal forming test machine, the test being similar to the SUS304 test [1±3]. The selected material, listed in Table 1, is commercially pure titanium sheet (AMS 4901 grade 4). The mold shoulder radius is 8 mm, there is a coating of TiC on the mold surface, lubrication with graphite for high temperature, and the punch speed is 4 mm/s. The results are measured for changing BHF load under spring strain, for changing operating temperature by means of a heat controller with thermal couple and a heating wire, and for different sheet size. The sheet was cut to the selected size and a grid etched upon it. When the mold was heated to the operating temperature, graphite was applied to the surface of the specimen and BHF applied. Then the specimen was caused to ¯ow into mold cavity hole by the cooled punch after it had been heated to the selected temperature. The best deep-drawing conditions and the forming limit were found by changing the experiment variables in accordance with wrinkling or fracture of the drawn cups. The cups with best operating
condition were tested by X-ray and TEM identi®cation to explore the deformed microstructure and the reason for the increased forming limit. 4. Results and discussion The relationship between the appearances of the drawn cups and the drawing conditions is shown in Fig. 1. 4.1. Operating temperature The height of the drawn cups for different operating temperatures is shown in Fig. 2. The forming limit increases from room temperature to elevated temperature: at 4008C the height of the drawn cup increases to twice the height of a cup drawn at 258C. The material deforms more easily as the temperature increases due to the strength decreasing, and the ¯owability becomes better as work hardening becomes milder than at room temperature. The cooling effect from the punch makes material ¯ow into the mold cavity easily by raising the strength of cup wall. Differing from stainless steel SUS304, the breakage point of CP Ti is in the cup wall normal to the rolling direction, not at the edge of the cup bottom as with SUS304, as due to anisotropy [18,19]. CP Ti is tensioned non-uniformly on the cup wall, but thinned by tension more easily normal to the rolling direction causing fracture by necking. 4.2. Blank-holding force Illustrated in Fig. 2 is the best BHF for different operating temperatures. The degrees of work hardening decreases when the temperature increases, and large BHF advances the fracture time of the cup. The BHF needs to be raised at a lower temperature to avoid wrinkling and reach limit drawn height. 4.3. X-ray test of the cup-bottom material 2 can determine the crystal plane from diffraction analysis data. TCh k i l [20] (texture coef®cient) is given by TCh k i l
Ih k i l =Ih0 k i l P 1=n Ih k i l =Ih0 k i l
Wt%
Ti
C
Fe
O
N
H
a-Ti
Bal.
0.01
0.12
0.34
0.011
0.0026
and can be counted by the integral intensity to determine the preferred orientation [20]. Fig. 3 shows the dependence of the calculated TC values on operating temperature. TC1 1 2 2 increased at 2008C but then decreased with further increase in temperature, TC0 1 1 2 increased when the temperature increased and reached the highest value at 4008C.
G A (mm)
4.4. TEM identification of the fracture point
0.88
The TEM microstructures of CP Ti at the symmetric position of the fracture point are shown in Figs. 4±7: before
Table 1 The chemical composition and properties of CP Ti (1 ksi0.89 kN)
YS (ksi)
US (ksi)
El. (%)
L
T
L
T
L
T
81.1
87.6
102.7
102.9
21
25
J.-M. Liu, S.-S. Chou / Journal of Materials Processing Technology 95 (1999) 65±70
67
Fig. 1. Appearance of the drawn cups.
deformation; deformed at room temperature; and deformed at 2008C and 4008C, respectively. Listed in Table 2 is the slip system and twinning observed at different operating temperatures. In CP Ti sheet there is only dislocation tangle at room temperature (Fig. 4). f0 1 1 1g1 2 1 3 slip (Fig. 5) was
Fig. 2. Height of the drawn cups and the best BHF for different operating temperatures.
observed at 258C; f0 1 1 0g0 0 0 1 slip, f1 1 0 1g0 1 1 1 slip, f1 1 2 0g0 0 0 1 slip (Fig. 6), f1 1 2 1g1 2 1 3 slip, f1 2 1 2g1 2 1 3 slip and f0 1 1 1g0 1 1 2 twin at 2008C; and f0 1 1 1g1 2 1 3 slip, f2 1 1 0g0 0 0 1 slip, f2 1 1 0g0 1 1 1 slip, f0 1 1 1g0 1 1 2 twin (Fig. 7) and f0 1 1 2g0 1 1 1 twin at 4008C. Among these, f0 1 1 1g1 2 1 3 pyramidal slip system [21] with c a
Fig. 3. TCh k i l at different operating temperatures.
68
J.-M. Liu, S.-S. Chou / Journal of Materials Processing Technology 95 (1999) 65±70 Table 2 The slip system and twinning observed at different operating temperatures
f0 11 0g f0 11 1g
Fig. 4. TEM photograph before deformation at room temperature.
dislocation is found both at 258C and 4008C; f1 1 2 0g0 0 0 1 pyramidal slip system with c dislocation and f0 1 1 1g0 1 1 2 tension twinning [5] are found both at 2008C and 4008C. Comparing with 258C, f0 1 1 0g0 0 0 1 prismatic slip system [21] with c dislocation, f1 1 2 0g0 0 0 1 pyramidal slip system with c dislocation, f1 1 2 1g1 2 1 3 and f1 2 1 2g1 2 1 3 pyramidal slip system with c a dislocation, and f0 1 1 1g0 1 1 2 tension twinning are found at 2008C; whilst comparing with 2008C, f0 1 1 2g0 1 1 1 compression twinning [5] is found at 4008C. When the operating temperature is increased, CRSS (critical resolved shear stress) for slip system and twinning decreased [22]. Accordingly it was deduced that at 2008C, slip system with c or c a dislocation can make CP Ti more
RT
2008C
0 1 1 11 2 1 3
0 1 1 00 0 0 1 1 1 0 10 1 1 1 0 1 1 10 1 1 2
f0 1 1 2g f1 1 2 0g
1 1 2 00 0 0 1
f1 1 2 1g f1 1 2 2g
1 1 2 11 2 1 3 1 2 1 21 2 1 3
4008C 0 1 1 11 2 1 3 0 1 1 10 1 1 2 1 1 0 11 2 1 3 0 1 1 20 1 1 1 2 1 1 00 0 0 1 1 2 1 00 0 0 1 2 1 1 00 1 1 1
ductile, with CP Ti being accommodated by f1 0 1 1g tension twinning; and at 4008C, CP Ti is more ductile being accommodated by f0 1 1 2g compression twinning. Thus it shows that CP Ti relaxes more strain energy at elevated temperatures by a more active slip system to obtain better formability. 5. Conclusion 1. Deep drawing at two temperatures can raise formability of commercially pure titanium effectively. The deep drawability of CP Ti at 4008C is almost twice that at room temperature. 2. The breakage point of commercially pure titanium is in the cup wall normal to the rolling direction due to anisotropy. 3. Appropriate blank-holding force can make CP Ti reach a limiting drawn height, the required BHF decreasing when the operating temperature increases.
Fig. 5. TEM photograph after deformation at room temperature.
J.-M. Liu, S.-S. Chou / Journal of Materials Processing Technology 95 (1999) 65±70
69
Fig. 6. TEM photograph after deformation at 2008C.
Fig. 7. TEM photograph after deformation at 4008C.
4. X-ray tests and TEM identification have established that CP Ti relaxes more strain energy at elevated temperature by a more active slip system to obtain better formability. Acknowledgements The authors are grateful to the Metal Industry Development Center for supplying equipment during this deep drawing study. The experiments were sponsored by the National Science Council of China (NSC 85-2216-E006016).
References [1] J.S. Chang, S.S. Chou, Scripta Metall. Mater. 31 (1994) 1291. [2] J.S. Chang, S.S. Chou, J. Mater. Eng. Perform., ASM Int. 3 (1994) 551. [3] J.S. Chang, S.S. Chou, J. Mater. Sci. 30 (1995) 2706. [4] I.P. Jones, W.B. Hutchison, Acta Metall. 29 (1981) 951. [5] M.H. Yoo, Metall. Trans. A 12 (1981) 409. [6] A.T. Churchman, Proc. Roy. Soc. A 226 (1954) 216. [7] J.C. Williams, M.J. Blackburn, Phys. Stat. Sol. 25 (1968) K1. [8] T.R. Cass, The Science Technology and Application of Titanium, Pergamon Press, New York, 1970, p. 459. [9] P.B. Price, Electron Microscopy and Strength of Crystals, Interscience, New York, 1970, p. 41.
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J.-M. Liu, S.-S. Chou / Journal of Materials Processing Technology 95 (1999) 65±70
[10] V.V. Damiano, G.J. London, H. Conrad, Trans. TMS-AIME 242 (1968) 987. [11] W. Taylor, A. Moore, J. Nucl. Mater. 13 (1964) 13. [12] V.D. Scott, H.M. Lindsay, J. Nucl. Mater. 18 (1966) 176. [13] F.D. Rosi, F.C. Perkins, L.L. Seigle, AIME Trans. 206 (1956) 115. [14] H.S. Rosenbaum, Deformation Twinning, Gordon and Breach, New York, 1964, p. 43. [15] N.E. Paton, W.A. Backofen, Trans. TMS-AIME 245 (1969) 1369.
[16] [17] [18] [19] [20]
C.J. McHargue, J.P. Hammond, Acta Met. 6 (1953) 700. N.E. Paton, W.A. Backfen, Metall. Trans. 1 (1970) 2839. Y. Lii, V.R. Chandran, R.E. Reed-Hill, Metall. Trans. 1 (1970) 447. M.H. Shipton, W.T. Roberts, Mater. Sci. Technol. 7(6) (1991) 537. C.S. Barrett, T.B. Massalski, Structure of Metals, Pergamon, Oxford, 1980, p. 204. [21] G.W. Hutchinson, Proc. R. Soc. London A 348 (1976) 101. [22] M.P. Biget, G. Saada, Phil. Mag. 59 (1989) 747.
Study on the microstructure and formability of commercially pure titanium in two-temperature deep drawing Jaan-Ming Liu*, Sheh-Shon Chou Department of Materials Science and Engineering(22), National Cheng Kung University, Tainan 70101, Taiwan Received 16 March 1998
Abstract From recent research, it has been found that deep drawing at two temperatures can make SUS304 exhibit deep drawability, the present investigation testing materials with other structures by the process. Commercially pure titanium (CP Ti)(a-Ti) exhibits almost twice the deep drawability when the temperature is increased from room temperature to 4008C. The process can make the deep drawability of a-Ti much more effective. The breaking point of titanium sheet is in the direction perpendicular to the rolling direction because of the effect from two different directions due to the anisotropy of the material. A suitable blank-holding force (BHF) can help to reach a limited drawing depth, the required force decreasing when the operating temperature increases. From X-ray and TEM identi®cation the process can drive more slip systems to relax strain energy to obtain good deep drawability by virtue of better ductility. # 1999 Elsevier Science S.A. All rights reserved. Keywords: Two-temperature deep drawing; Commercially pure titanium
1. Introduction The deep drawing process is used widely with press equipment and molds to form seamless vessels of different shells from metal sheets. The metal sheets are heated by a heater in the mold plate and cooled by an iced water ¯ow in the punch during the two-temperature deep drawing process, which increases deep drawability and results in a product with a more uniform wall thickness. By research, the process has been con®rmed to be able to improve the deep drawability of stainless steel SUS304 [1±3]. The microstructure of the deformation was also explored. SUS304 is of f.c.c. structure, so there is doubt as to whether the process can also promote material of other structures. Titanium, with c.p.h. structure at room temperature and b.c.c. structure at high temperature, has been chosen as the test material. 2. Theory Titanium is either a-Ti(c.p.h.), ab-Ti(h.c.p.b.c.c.) or b-Ti(b.c.c.), according to the temperature, the alloy compo*Corresponding author. E-mail address: [email protected] (J.-M. Liu)
sition and the stress condition. The plastic deformation model is generally either slip deformation or twin deformation. Compared with f.c.c. and b.c.c. structure, metals and alloys with c.p.h. structure would be more complex. When c/ a<1.594, slip occurs on the metal prismatic plane f0 1 1 0g; whilst when c/a>1.614, slip occurs on the metal basel plane {0 0 0 1} [4]. Thus the active slip system is relative to the c/a value of titanium of 1.587, the main slip system being f1 1 0 0gh1 1 2 0i, and when it moves on f0 0 0 1gh1 1 2 0i. The a-dislocation [5] forms on the basic plane in the slip plane and slip direction with no strain along the c axis. Twin deformation occurs in single crystal titanium, whilst twin deformation and slip deformation occur in polycrystal titanium. Ductility can be extended because of the satisfying of von Mises' condition. The slip of titanium occurs on f1 0 1 0g; 0 0 0 1, and f1 0 1 1g along h1 1 2 0i by 1=3h1 1 2 0i dislocation at room temperature or lower [6]. The change along the c axis does not only need h1 1 2 0i slip, but also slip beyond the basic plane. It was observed in commercially pure titanium and Ti±Al alloy by reason of 1=3h1 1 2 3i movement or ca dislocation, but not yet in high-purity titanium [7,8]. The slip along h1 1 2 3i was observed in Cd and Zr at room temperature [9] and in Be at high temperature [10±12].
0924-0136/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved. PII: S 0 9 2 4 - 0 1 3 6 ( 9 9 ) 0 0 1 0 8 - 9
66
J.-M. Liu, S.-S. Chou / Journal of Materials Processing Technology 95 (1999) 65±70
The change along c axis can also work by twin deformation. For titanium f1 0 1 2g; f1 1 2 1g and f1 1 2 3g , twins occur in extension along the c axis; and f1 1 2 2g; f1 1 2 4g [13,14], and f1 0 1 1g [15] twins in compression along the c axis. When the temperature increases, twin deformation becomes less important generally. Rosi et al. [13] did not ®nd twins of any type at 8008C, but McHargue and Hammond [16] found less f1 1 2 2g and f1 1 2 1g twins at 8158C. Paton and Backfen [17] revealed that the compression of single-crystal Ti from 258C to 8008C, to about 5% strain along the c axis, was accommodated entirely by f1 1 2 2g twins from 258C to 3008C, and by a combination of f1 0 1 1g twins from 4008C to 8008C. Reduction normal to the c axis deformed by a combination of f1 0 1 2g twins and prism slip at 258C, and by prism slip alone above 5008C. Although ca slip is not responsible for a signi®cation amount of strain below 3008C, it is important in accommodating the shear ahead of a propagating f1 1 2 2g twin [17]. 3. Experiments The experiments use an electric wire to heat the mold and the specimen before pressing. When the specimen reaches the selected temperature, the deep drawing process is executed with a cooling effect in punch. The press equipment is an Amino universal forming test machine, the test being similar to the SUS304 test [1±3]. The selected material, listed in Table 1, is commercially pure titanium sheet (AMS 4901 grade 4). The mold shoulder radius is 8 mm, there is a coating of TiC on the mold surface, lubrication with graphite for high temperature, and the punch speed is 4 mm/s. The results are measured for changing BHF load under spring strain, for changing operating temperature by means of a heat controller with thermal couple and a heating wire, and for different sheet size. The sheet was cut to the selected size and a grid etched upon it. When the mold was heated to the operating temperature, graphite was applied to the surface of the specimen and BHF applied. Then the specimen was caused to ¯ow into mold cavity hole by the cooled punch after it had been heated to the selected temperature. The best deep-drawing conditions and the forming limit were found by changing the experiment variables in accordance with wrinkling or fracture of the drawn cups. The cups with best operating
condition were tested by X-ray and TEM identi®cation to explore the deformed microstructure and the reason for the increased forming limit. 4. Results and discussion The relationship between the appearances of the drawn cups and the drawing conditions is shown in Fig. 1. 4.1. Operating temperature The height of the drawn cups for different operating temperatures is shown in Fig. 2. The forming limit increases from room temperature to elevated temperature: at 4008C the height of the drawn cup increases to twice the height of a cup drawn at 258C. The material deforms more easily as the temperature increases due to the strength decreasing, and the ¯owability becomes better as work hardening becomes milder than at room temperature. The cooling effect from the punch makes material ¯ow into the mold cavity easily by raising the strength of cup wall. Differing from stainless steel SUS304, the breakage point of CP Ti is in the cup wall normal to the rolling direction, not at the edge of the cup bottom as with SUS304, as due to anisotropy [18,19]. CP Ti is tensioned non-uniformly on the cup wall, but thinned by tension more easily normal to the rolling direction causing fracture by necking. 4.2. Blank-holding force Illustrated in Fig. 2 is the best BHF for different operating temperatures. The degrees of work hardening decreases when the temperature increases, and large BHF advances the fracture time of the cup. The BHF needs to be raised at a lower temperature to avoid wrinkling and reach limit drawn height. 4.3. X-ray test of the cup-bottom material 2 can determine the crystal plane from diffraction analysis data. TCh k i l [20] (texture coef®cient) is given by TCh k i l
Ih k i l =Ih0 k i l P 1=n Ih k i l =Ih0 k i l
Wt%
Ti
C
Fe
O
N
H
a-Ti
Bal.
0.01
0.12
0.34
0.011
0.0026
and can be counted by the integral intensity to determine the preferred orientation [20]. Fig. 3 shows the dependence of the calculated TC values on operating temperature. TC1 1 2 2 increased at 2008C but then decreased with further increase in temperature, TC0 1 1 2 increased when the temperature increased and reached the highest value at 4008C.
G A (mm)
4.4. TEM identification of the fracture point
0.88
The TEM microstructures of CP Ti at the symmetric position of the fracture point are shown in Figs. 4±7: before
Table 1 The chemical composition and properties of CP Ti (1 ksi0.89 kN)
YS (ksi)
US (ksi)
El. (%)
L
T
L
T
L
T
81.1
87.6
102.7
102.9
21
25
J.-M. Liu, S.-S. Chou / Journal of Materials Processing Technology 95 (1999) 65±70
67
Fig. 1. Appearance of the drawn cups.
deformation; deformed at room temperature; and deformed at 2008C and 4008C, respectively. Listed in Table 2 is the slip system and twinning observed at different operating temperatures. In CP Ti sheet there is only dislocation tangle at room temperature (Fig. 4). f0 1 1 1g1 2 1 3 slip (Fig. 5) was
Fig. 2. Height of the drawn cups and the best BHF for different operating temperatures.
observed at 258C; f0 1 1 0g0 0 0 1 slip, f1 1 0 1g0 1 1 1 slip, f1 1 2 0g0 0 0 1 slip (Fig. 6), f1 1 2 1g1 2 1 3 slip, f1 2 1 2g1 2 1 3 slip and f0 1 1 1g0 1 1 2 twin at 2008C; and f0 1 1 1g1 2 1 3 slip, f2 1 1 0g0 0 0 1 slip, f2 1 1 0g0 1 1 1 slip, f0 1 1 1g0 1 1 2 twin (Fig. 7) and f0 1 1 2g0 1 1 1 twin at 4008C. Among these, f0 1 1 1g1 2 1 3 pyramidal slip system [21] with c a
Fig. 3. TCh k i l at different operating temperatures.
68
J.-M. Liu, S.-S. Chou / Journal of Materials Processing Technology 95 (1999) 65±70 Table 2 The slip system and twinning observed at different operating temperatures
f0 11 0g f0 11 1g
Fig. 4. TEM photograph before deformation at room temperature.
dislocation is found both at 258C and 4008C; f1 1 2 0g0 0 0 1 pyramidal slip system with c dislocation and f0 1 1 1g0 1 1 2 tension twinning [5] are found both at 2008C and 4008C. Comparing with 258C, f0 1 1 0g0 0 0 1 prismatic slip system [21] with c dislocation, f1 1 2 0g0 0 0 1 pyramidal slip system with c dislocation, f1 1 2 1g1 2 1 3 and f1 2 1 2g1 2 1 3 pyramidal slip system with c a dislocation, and f0 1 1 1g0 1 1 2 tension twinning are found at 2008C; whilst comparing with 2008C, f0 1 1 2g0 1 1 1 compression twinning [5] is found at 4008C. When the operating temperature is increased, CRSS (critical resolved shear stress) for slip system and twinning decreased [22]. Accordingly it was deduced that at 2008C, slip system with c or c a dislocation can make CP Ti more
RT
2008C
0 1 1 11 2 1 3
0 1 1 00 0 0 1 1 1 0 10 1 1 1 0 1 1 10 1 1 2
f0 1 1 2g f1 1 2 0g
1 1 2 00 0 0 1
f1 1 2 1g f1 1 2 2g
1 1 2 11 2 1 3 1 2 1 21 2 1 3
4008C 0 1 1 11 2 1 3 0 1 1 10 1 1 2 1 1 0 11 2 1 3 0 1 1 20 1 1 1 2 1 1 00 0 0 1 1 2 1 00 0 0 1 2 1 1 00 1 1 1
ductile, with CP Ti being accommodated by f1 0 1 1g tension twinning; and at 4008C, CP Ti is more ductile being accommodated by f0 1 1 2g compression twinning. Thus it shows that CP Ti relaxes more strain energy at elevated temperatures by a more active slip system to obtain better formability. 5. Conclusion 1. Deep drawing at two temperatures can raise formability of commercially pure titanium effectively. The deep drawability of CP Ti at 4008C is almost twice that at room temperature. 2. The breakage point of commercially pure titanium is in the cup wall normal to the rolling direction due to anisotropy. 3. Appropriate blank-holding force can make CP Ti reach a limiting drawn height, the required BHF decreasing when the operating temperature increases.
Fig. 5. TEM photograph after deformation at room temperature.
J.-M. Liu, S.-S. Chou / Journal of Materials Processing Technology 95 (1999) 65±70
69
Fig. 6. TEM photograph after deformation at 2008C.
Fig. 7. TEM photograph after deformation at 4008C.
4. X-ray tests and TEM identification have established that CP Ti relaxes more strain energy at elevated temperature by a more active slip system to obtain better formability. Acknowledgements The authors are grateful to the Metal Industry Development Center for supplying equipment during this deep drawing study. The experiments were sponsored by the National Science Council of China (NSC 85-2216-E006016).
References [1] J.S. Chang, S.S. Chou, Scripta Metall. Mater. 31 (1994) 1291. [2] J.S. Chang, S.S. Chou, J. Mater. Eng. Perform., ASM Int. 3 (1994) 551. [3] J.S. Chang, S.S. Chou, J. Mater. Sci. 30 (1995) 2706. [4] I.P. Jones, W.B. Hutchison, Acta Metall. 29 (1981) 951. [5] M.H. Yoo, Metall. Trans. A 12 (1981) 409. [6] A.T. Churchman, Proc. Roy. Soc. A 226 (1954) 216. [7] J.C. Williams, M.J. Blackburn, Phys. Stat. Sol. 25 (1968) K1. [8] T.R. Cass, The Science Technology and Application of Titanium, Pergamon Press, New York, 1970, p. 459. [9] P.B. Price, Electron Microscopy and Strength of Crystals, Interscience, New York, 1970, p. 41.
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J.-M. Liu, S.-S. Chou / Journal of Materials Processing Technology 95 (1999) 65±70
[10] V.V. Damiano, G.J. London, H. Conrad, Trans. TMS-AIME 242 (1968) 987. [11] W. Taylor, A. Moore, J. Nucl. Mater. 13 (1964) 13. [12] V.D. Scott, H.M. Lindsay, J. Nucl. Mater. 18 (1966) 176. [13] F.D. Rosi, F.C. Perkins, L.L. Seigle, AIME Trans. 206 (1956) 115. [14] H.S. Rosenbaum, Deformation Twinning, Gordon and Breach, New York, 1964, p. 43. [15] N.E. Paton, W.A. Backofen, Trans. TMS-AIME 245 (1969) 1369.
[16] [17] [18] [19] [20]
C.J. McHargue, J.P. Hammond, Acta Met. 6 (1953) 700. N.E. Paton, W.A. Backfen, Metall. Trans. 1 (1970) 2839. Y. Lii, V.R. Chandran, R.E. Reed-Hill, Metall. Trans. 1 (1970) 447. M.H. Shipton, W.T. Roberts, Mater. Sci. Technol. 7(6) (1991) 537. C.S. Barrett, T.B. Massalski, Structure of Metals, Pergamon, Oxford, 1980, p. 204. [21] G.W. Hutchinson, Proc. R. Soc. London A 348 (1976) 101. [22] M.P. Biget, G. Saada, Phil. Mag. 59 (1989) 747.