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The second phases in Ti40 burn resistant alloy after high temperature exposure for a long time
Journal of Alloys and Compounds 333 (2002) 165–169
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The second phases in Ti40 burn resistant alloy after high temperature exposure for a long time Y.Q. Zhao*, H.L. Qu, K.Y. Zhu, H. Wu, C.L. Liu, L. Zhou Northwest Institute for Nonferrous Metal Research, PO Box 51, Xi’ an, Shaanxi 710016, PR China Received 21 February 2001; accepted 8 June 2001
Abstract The Ti40 (Ti–25V–15Cr–0.2Si) alloy is a burn resistant b titanium alloy. Second phase precipitation after high temperature exposure for a long time has been studied. The second phases, i.e. Ti 5 Si 3 and a, precipitate from the b matrix after the Ti40 alloy has been exposed at high temperature for a long time. The Ti 5 Si 3 phase distributes discontinuously along the grain boundary if the exposure temperature is below 5408C. Exposed at 7008C for 100 h, the coarse Ti 5 Si 3 phase rapidly grows, its tensile properties obviously reducing after thermal exposure when conventionally forged. Coarse Ti 5 Si 3 and a phases form after exposure at 5408C for 100 h, which leads to serious decrease of tensile properties after thermal exposure for isothermally forged alloys. Ti 5 Si 3 precipitates distribute discontinuously along grain boundary in the conventionally forged alloys after creep exposure. There are also many coarse rod-like a phases in isothermally forged alloys after creep exposure. 2002 Elsevier Science B.V. All rights reserved. Keywords: Transition metal alloys; Transmission electron microscopy (TEM); Oxidation; Metallography
1. Introduction Although b titanium alloys have been studied for more than 40 years, practical applications of b-Ti alloys are limited. These alloys account for only 1% of the total Ti market [1]. However, excellent cold workability and good combinations of strength and fracture resistance have resulted in continued development of b-Ti alloys. For example, the metastable b-Ti alloys, such as b21s and SP700, were designed in the early 1990s and have been put to practical applications [2]. Further use of conventional titanium alloys is inhibited by the mechanical properties, oxidation resistance and the risk of titanium-related fire. The research on stable b-Ti alloys is driven by the requirement that high performance gas turbines not only need their excellent mechanical properties but also require burn resistance for some key parts. For example, Alloy C (Ti–35V–15Cr) [3,4] developed in USA in the early 1990s, is a stable burn resistant b titanium alloy; it has replaced Ni super-alloy in the F119 engines that power F22 USAF jet fighters [5,6]. In Alloy C, a phase precipitates precipitate after exposure at 5408C for a long time [7]. A new stable burn resistant b titanium alloy, i.e. Ti40 *Corresponding author. E-mail address: [email protected] (Y.Q. Zhao).
(Ti–25V–15Cr–0.2Si) [8–11], has been studied by the present authors since the early 1990s. Compared with Alloy C, Ti40 alloy has 10% less V (wt.%), and the alloying elemental Si is added. It should be recognized that Si is seldom added to b titanium alloys except for b 21s . This element is mainly added to a and a1b alloys, especially a alloys, which can improve the creep strength. However, second phases, i.e. a and Ti 5 Si 3 , have been observed in Ti40 alloy at RT or after exposure at 5408C for 100 h [12]. The objective of the present paper was to study the size and distribution of the second phases after Ti40 alloy exposure at T 8C (T5400 and 7008C) for 100 h and creep exposure at 5408C, 250 MPa for 100 h.
2. Experimental procedures A 5-kg Ti40 alloy ingot (90 mm in diameter and 125 mm in height) was used in this study. Its chemical composition was Ti–24.6V–14.6Cr–0.33Si–0.15O. The ingot breakdown was conducted in two ways. Condition A was obtained by conventional forging at 10008C (with 60% of deformation amount) to a 25-mm-thick pancake and condition B was obtained by isothermal forging at 10008C (with 60% of deformation amount) to a 25-mm-thick pancake. After solution treating at 8208C for 30 min and
0925-8388 / 02 / $ – see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388( 01 )01710-8
Y.Q. Zhao et al. / Journal of Alloys and Compounds 333 (2002) 165 – 169
166
Fig. 1. TEM image of Ti40 alloy by conventional forging (A).
aging at 6008C for 5 h, condition A has a fine equiaxed b structure and condition B has a coarse b structure. H-600 transmission electron microscopy (TEM) was use for microstructure determination.
3. Results and discussion
3.1. The second phases after exposure at different temperatures The TEM image of condition A is shown in Fig. 1. It is an equiaxed b grain structure. Although a precipitates were not observed, some Ti 5 Si 3 phases are found within grains. Fig. 2 shows TEM image of condition A after exposure at 4008C for 100 h. Ti 5 Si 3 particles are in grains 0.2 mm long30.3 mm wide, and small Ti 5 Si 3 phases are on grain boundaries with discontinuous distribution. The TEM observation of condition A exposed at 5408C for 100 h revealed that the Ti 5 Si 3 phases within grains became coarse, 0.430.5 mm in size, and Ti 5 Si 3 precipitates on grain boundaries were still discontinuous [12].
Fig. 2. TEM image of A after exposure at 4008C for 100 h. Ti 5 Si 3 precipitates are as shown by arrow.
Fig. 3. TEM image of A after exposure at 7008C for 100 h. Ti 5 Si 3 precipitates are as shown by arrow.
Fig. 3 shows the TEM image of condition A after exposure at 7008C for 100 h. The Ti 5 Si 3 precipitates within grains or on grain boundaries become coarser, 0.5330.6 mm in size, and their volume fraction increases greatly. However, a precipitates are not found. The coarse Ti 5 Si 3 particle is thought to greatly decrease the tensile properties after thermal exposure. Fig. 4 is the TEM image of condition B after exposure at 5408C for 100 h. There are different kinds of Ti 5 Si 3 and a precipitates whose volume fraction is high. The a phase is present in two forms. One is blocky a (0.3230.3 mm in size) within grain, as shown in Fig. 4a; there is almost no dislocation within blocky a, however, the dislocation density around it is very high. The other form is long rod-like a (0.2532.53 mm in size), as shown in Fig. 4c; there are dislocations within rod-like a and high dislocation density exists around it. The Ti 5 Si 3 precipitates are mainly present in lenticular type, as shown in Fig. 4e. Table 1 lists the tensile properties after Ti40 alloy exposure at different conditions. With increasing exposure temperature, the tensile properties decrease. The main factors influencing the loss of strength and ductility are the surface and microstructural stability. Previous results revealed that Ti40 alloy possesses good oxidation resistance below 6508C [13]. If the temperature is above 6508C, oxidation mass gain increases gradually with increase of temperature [14,15]. Therefore, it is proposed that the decrease of tensile properties upon exposure at 400 and 5408C is mainly controlled by the change of microstructure, especially at 5408C, where Ti 5 Si 3 within grain and on grain boundary become coarse and a phase precipitates within grains leading to increase of brittleness. The obvious decrease of the tensile properties of condition A at 7008C is caused by the interaction of decomposition of microstructure and obvious surface oxidation. Exposed at 7008C for 100 h, Ti 5 Si 3 phases within grain and on grain boundary become coarse, which results in increase of brittleness. In addition, the surface oxidation (surface
Y.Q. Zhao et al. / Journal of Alloys and Compounds 333 (2002) 165 – 169
167
Fig. 4. TEM image of B after exposure at 5408C for 100 h. (a) Blocky a (as shown by arrows); (b) SAD of blocky a; (c) rod-like a (as shown by arrows); (d) SAD of rod-like a; (e) lenticular Ti 5 Si 3 (as shown by arrows); (f) SAD of lenticular Ti 5 Si 3 .
oxygen content is 65% if oxidation at 7008C for 50 h) causes the thickness of brittle layer to increase. As a result, cracks initiate on the brittle surface, which decreases plasticity. The tensile properties of condition B at RT are lower than those of A, which mainly corresponds with the
original coarse b microstructure by the isothermal forging. The obvious decrease of the loss of tensile properties after exposure at 5408C is mainly controlled by the change of microstructure, i.e. a lot of coarse Ti 5 Si 3 and a phases precipitate.
Table 1 Tensile properties of Ti40 alloy after selected thermal exposure Exposure condition
UTS (MPa)
YS (MPa)
El (%)
DEl (%)
RA (%)
DRA (%)
A
4008C / 100 h 5008C / 100 h 7008C / 100 h No exposure
915 1077 855 979
905 1007 854 960
13 9.4 2.5 18
28 48 86
22 17 – 30
27 43 .90
B
4008C / 100 h No exposure
917 984
914
0.2 3.5
94
– –
–
–
DEl 5 (El 2 El 0 ) /El 0 , DRA 5 (RA 2 RA 0 ) /RA 0 , where El 0 and RA 0 are the elongation and reduction in area before exposure.
Y.Q. Zhao et al. / Journal of Alloys and Compounds 333 (2002) 165 – 169
168
Fig. 5. TEM image of A after creep exposure at 5408C, 250 MPa for 100 h. (a) Ti 5 Si 3 precipitates (as shown by arrows); (b) SAD of Ti 5 Si 3 .
Table 2 Post-creep strain of Ti40 alloy creep exposure at 5408C, 250 MPa for 100 h
A B
Heat treatment
Residual strain (%)
8208C / 30 min W.Q16008C / 5 h /A.C 7008C / 30 min W.Q16008C / 5 h A.C 8208C / 30 min W.Q16008C / 5 h /A.C
0.16 19.3 10.7
phase, as shown in Fig. 7. The unknown phase occurs at grain boundary triple points. Fig. 8 shows the TEM images of condition B after creep exposure at 5408C, 250 MPa for 100 h. There are many rod-like a precipitates, which reduces the creep resistance (as shown in Table 2).
4. Conclusions
3.2. The second phases after creep exposure Fig. 5 shows the TEM images of condition A after creep exposure at 5408C, 250 MPa for 100 h. The Ti 5 Si 3 precipitates are discontinuous along grain boundary, and there are also some a precipitates. However, there are no second phase precipitates in most zones, which guarantees good creep behavior, as shown in Table 2. There are a lot of coarse rod-like a and Ti 5 Si 3 phases (Fig. 6) and Ti 5 Si 3 precipitates near-continuously along grain boundary if the heat treatment of condition A is 7008C / 30 min W.Q16008C / 5 h /A.C, followed by creep exposure at 5408C, 250 MPa for 100 h. This type of second phases is associated with a decrease of creep resistance (Table 2). There is also an unidentified blocky
The second phases, i.e. Ti 5 Si 3 and a, precipitate from b matrix after the Ti40 alloy has been exposed at high temperatures for a long time. The Ti 5 Si 3 phase distributes discontinuously along grain boundary in conventionally forged alloys if the exposure temperature is below 5408C. Exposed at 7008C for 100 h, Ti 5 Si 3 phase grows greatly, which obviously reduces the tensile properties. There are coarse Ti 5 Si 3 and a phases in isothermally forged alloys annealed at 5408C for 100 h, which leads to serious decrease of tensile properties. Ti 5 Si 3 precipitates distribute discontinuously along grain boundary in conventionally forged alloys after creep exposure. Many coarse rod-like Ti 5 Si 3 and a phases precipitate, and Ti 5 Si 3 distributes near-continuously along
Fig. 6. TEM image of A after creep exposure at 5408C, 250 MPa for 100 h with heat treatment of 7008C / 30 min W.Q16008C / 5 h A.C. (a) Rod-like a and Ti 5 Si 3 phases on grain boundary are as shown by arrows; (b) SAD of rod-like a.
Y.Q. Zhao et al. / Journal of Alloys and Compounds 333 (2002) 165 – 169
169
Fig. 7. Uncertain phase (a) in TEM images and its SAD (b).
Fig. 8. TEM images of B after creep exposure at 5408C, 250 MPa for 100 h. (a) Rod-like a phase (as shown by arrow); (b) SAD of a.
grain boundary if the heat treatment temperature is lower than 7008C followed by creep exposure. Many rod-like a phases precipitate within grains for condition B after creep exposure.
References [1] P.J. Bania, in: D. Eylon, R.R. Boyer, D.A. Koss (Eds.), Beta Titanium Alloys in the 90s, TMS Publications, Warrendale, PA, 1993, p. 3. [2] R. Boyer, G. Welsch, E.W. Collings (Eds.), Materials Properties Handbook — Titanium Alloys, The Materials Information Society, USA, 1994, p. 685. [3] UK Patent Application, 2 238057, 1987. [4] K. Giary, Adv. Mater. Processes 9 (1993) 7. [5] S.R. Seagle, Mater. Sci. Eng. A213 (1996) 1. [6] R.R. Boyer, Mater. Sci. Eng. A213 (1996) 103.
[7] D.W. Anderson, A.F. Condliff, in: Processing of the Technical Program from the 1994 International Conference, USA, 1994, p. 91. [8] Y.Q. Zhao, K.Y. Zhu, H.L. Qu, H. Wu, Mater. Sci. Technol. 16 (9) (2000) 1073. [9] Y.Q. Zhao, K.Y. Zhu, H.L. Qu, H. Wu, Mater. Sci. Eng. A282 (2000) 153. [10] Y.Q. Zhao, L. Zhou, J. Deng, Mater. Sci. Eng. A267 (2000) 167. [11] Y.Q. Zhao, L. Zhou, J. Deng, Rare Metal Mater. Eng. 28 (3) (1999) 77. [12] Y.Q. Zhao, K.Y. Zhu, H.L. Qu, J. Mater. Sci. 2001 (in press). [13] H. Wu, Q. Zhao, H.L. Qu, K.Y. Zhu, in: J. Song, R. Yin (Eds.), Proceedings of the International Conference on Engineering and Technological Science 2000, New World Press, Beijing, 2000, p. 407. [14] Y.Q. Zhao, L. Zhou, H.L. Qu, K.Y. Zhu, in: Titanium Alloys at Elevated Temperature: Structural Development and Service Behaviour, UK, 2001, p. 123. [15] Y.Q. Zhao, H.L. Zhu, H. Wu, Rare Metal Mater. Eng. 29 (6) (2000) 403.
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The second phases in Ti40 burn resistant alloy after high temperature exposure for a long time Y.Q. Zhao*, H.L. Qu, K.Y. Zhu, H. Wu, C.L. Liu, L. Zhou Northwest Institute for Nonferrous Metal Research, PO Box 51, Xi’ an, Shaanxi 710016, PR China Received 21 February 2001; accepted 8 June 2001
Abstract The Ti40 (Ti–25V–15Cr–0.2Si) alloy is a burn resistant b titanium alloy. Second phase precipitation after high temperature exposure for a long time has been studied. The second phases, i.e. Ti 5 Si 3 and a, precipitate from the b matrix after the Ti40 alloy has been exposed at high temperature for a long time. The Ti 5 Si 3 phase distributes discontinuously along the grain boundary if the exposure temperature is below 5408C. Exposed at 7008C for 100 h, the coarse Ti 5 Si 3 phase rapidly grows, its tensile properties obviously reducing after thermal exposure when conventionally forged. Coarse Ti 5 Si 3 and a phases form after exposure at 5408C for 100 h, which leads to serious decrease of tensile properties after thermal exposure for isothermally forged alloys. Ti 5 Si 3 precipitates distribute discontinuously along grain boundary in the conventionally forged alloys after creep exposure. There are also many coarse rod-like a phases in isothermally forged alloys after creep exposure. 2002 Elsevier Science B.V. All rights reserved. Keywords: Transition metal alloys; Transmission electron microscopy (TEM); Oxidation; Metallography
1. Introduction Although b titanium alloys have been studied for more than 40 years, practical applications of b-Ti alloys are limited. These alloys account for only 1% of the total Ti market [1]. However, excellent cold workability and good combinations of strength and fracture resistance have resulted in continued development of b-Ti alloys. For example, the metastable b-Ti alloys, such as b21s and SP700, were designed in the early 1990s and have been put to practical applications [2]. Further use of conventional titanium alloys is inhibited by the mechanical properties, oxidation resistance and the risk of titanium-related fire. The research on stable b-Ti alloys is driven by the requirement that high performance gas turbines not only need their excellent mechanical properties but also require burn resistance for some key parts. For example, Alloy C (Ti–35V–15Cr) [3,4] developed in USA in the early 1990s, is a stable burn resistant b titanium alloy; it has replaced Ni super-alloy in the F119 engines that power F22 USAF jet fighters [5,6]. In Alloy C, a phase precipitates precipitate after exposure at 5408C for a long time [7]. A new stable burn resistant b titanium alloy, i.e. Ti40 *Corresponding author. E-mail address: [email protected] (Y.Q. Zhao).
(Ti–25V–15Cr–0.2Si) [8–11], has been studied by the present authors since the early 1990s. Compared with Alloy C, Ti40 alloy has 10% less V (wt.%), and the alloying elemental Si is added. It should be recognized that Si is seldom added to b titanium alloys except for b 21s . This element is mainly added to a and a1b alloys, especially a alloys, which can improve the creep strength. However, second phases, i.e. a and Ti 5 Si 3 , have been observed in Ti40 alloy at RT or after exposure at 5408C for 100 h [12]. The objective of the present paper was to study the size and distribution of the second phases after Ti40 alloy exposure at T 8C (T5400 and 7008C) for 100 h and creep exposure at 5408C, 250 MPa for 100 h.
2. Experimental procedures A 5-kg Ti40 alloy ingot (90 mm in diameter and 125 mm in height) was used in this study. Its chemical composition was Ti–24.6V–14.6Cr–0.33Si–0.15O. The ingot breakdown was conducted in two ways. Condition A was obtained by conventional forging at 10008C (with 60% of deformation amount) to a 25-mm-thick pancake and condition B was obtained by isothermal forging at 10008C (with 60% of deformation amount) to a 25-mm-thick pancake. After solution treating at 8208C for 30 min and
0925-8388 / 02 / $ – see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388( 01 )01710-8
Y.Q. Zhao et al. / Journal of Alloys and Compounds 333 (2002) 165 – 169
166
Fig. 1. TEM image of Ti40 alloy by conventional forging (A).
aging at 6008C for 5 h, condition A has a fine equiaxed b structure and condition B has a coarse b structure. H-600 transmission electron microscopy (TEM) was use for microstructure determination.
3. Results and discussion
3.1. The second phases after exposure at different temperatures The TEM image of condition A is shown in Fig. 1. It is an equiaxed b grain structure. Although a precipitates were not observed, some Ti 5 Si 3 phases are found within grains. Fig. 2 shows TEM image of condition A after exposure at 4008C for 100 h. Ti 5 Si 3 particles are in grains 0.2 mm long30.3 mm wide, and small Ti 5 Si 3 phases are on grain boundaries with discontinuous distribution. The TEM observation of condition A exposed at 5408C for 100 h revealed that the Ti 5 Si 3 phases within grains became coarse, 0.430.5 mm in size, and Ti 5 Si 3 precipitates on grain boundaries were still discontinuous [12].
Fig. 2. TEM image of A after exposure at 4008C for 100 h. Ti 5 Si 3 precipitates are as shown by arrow.
Fig. 3. TEM image of A after exposure at 7008C for 100 h. Ti 5 Si 3 precipitates are as shown by arrow.
Fig. 3 shows the TEM image of condition A after exposure at 7008C for 100 h. The Ti 5 Si 3 precipitates within grains or on grain boundaries become coarser, 0.5330.6 mm in size, and their volume fraction increases greatly. However, a precipitates are not found. The coarse Ti 5 Si 3 particle is thought to greatly decrease the tensile properties after thermal exposure. Fig. 4 is the TEM image of condition B after exposure at 5408C for 100 h. There are different kinds of Ti 5 Si 3 and a precipitates whose volume fraction is high. The a phase is present in two forms. One is blocky a (0.3230.3 mm in size) within grain, as shown in Fig. 4a; there is almost no dislocation within blocky a, however, the dislocation density around it is very high. The other form is long rod-like a (0.2532.53 mm in size), as shown in Fig. 4c; there are dislocations within rod-like a and high dislocation density exists around it. The Ti 5 Si 3 precipitates are mainly present in lenticular type, as shown in Fig. 4e. Table 1 lists the tensile properties after Ti40 alloy exposure at different conditions. With increasing exposure temperature, the tensile properties decrease. The main factors influencing the loss of strength and ductility are the surface and microstructural stability. Previous results revealed that Ti40 alloy possesses good oxidation resistance below 6508C [13]. If the temperature is above 6508C, oxidation mass gain increases gradually with increase of temperature [14,15]. Therefore, it is proposed that the decrease of tensile properties upon exposure at 400 and 5408C is mainly controlled by the change of microstructure, especially at 5408C, where Ti 5 Si 3 within grain and on grain boundary become coarse and a phase precipitates within grains leading to increase of brittleness. The obvious decrease of the tensile properties of condition A at 7008C is caused by the interaction of decomposition of microstructure and obvious surface oxidation. Exposed at 7008C for 100 h, Ti 5 Si 3 phases within grain and on grain boundary become coarse, which results in increase of brittleness. In addition, the surface oxidation (surface
Y.Q. Zhao et al. / Journal of Alloys and Compounds 333 (2002) 165 – 169
167
Fig. 4. TEM image of B after exposure at 5408C for 100 h. (a) Blocky a (as shown by arrows); (b) SAD of blocky a; (c) rod-like a (as shown by arrows); (d) SAD of rod-like a; (e) lenticular Ti 5 Si 3 (as shown by arrows); (f) SAD of lenticular Ti 5 Si 3 .
oxygen content is 65% if oxidation at 7008C for 50 h) causes the thickness of brittle layer to increase. As a result, cracks initiate on the brittle surface, which decreases plasticity. The tensile properties of condition B at RT are lower than those of A, which mainly corresponds with the
original coarse b microstructure by the isothermal forging. The obvious decrease of the loss of tensile properties after exposure at 5408C is mainly controlled by the change of microstructure, i.e. a lot of coarse Ti 5 Si 3 and a phases precipitate.
Table 1 Tensile properties of Ti40 alloy after selected thermal exposure Exposure condition
UTS (MPa)
YS (MPa)
El (%)
DEl (%)
RA (%)
DRA (%)
A
4008C / 100 h 5008C / 100 h 7008C / 100 h No exposure
915 1077 855 979
905 1007 854 960
13 9.4 2.5 18
28 48 86
22 17 – 30
27 43 .90
B
4008C / 100 h No exposure
917 984
914
0.2 3.5
94
– –
–
–
DEl 5 (El 2 El 0 ) /El 0 , DRA 5 (RA 2 RA 0 ) /RA 0 , where El 0 and RA 0 are the elongation and reduction in area before exposure.
Y.Q. Zhao et al. / Journal of Alloys and Compounds 333 (2002) 165 – 169
168
Fig. 5. TEM image of A after creep exposure at 5408C, 250 MPa for 100 h. (a) Ti 5 Si 3 precipitates (as shown by arrows); (b) SAD of Ti 5 Si 3 .
Table 2 Post-creep strain of Ti40 alloy creep exposure at 5408C, 250 MPa for 100 h
A B
Heat treatment
Residual strain (%)
8208C / 30 min W.Q16008C / 5 h /A.C 7008C / 30 min W.Q16008C / 5 h A.C 8208C / 30 min W.Q16008C / 5 h /A.C
0.16 19.3 10.7
phase, as shown in Fig. 7. The unknown phase occurs at grain boundary triple points. Fig. 8 shows the TEM images of condition B after creep exposure at 5408C, 250 MPa for 100 h. There are many rod-like a precipitates, which reduces the creep resistance (as shown in Table 2).
4. Conclusions
3.2. The second phases after creep exposure Fig. 5 shows the TEM images of condition A after creep exposure at 5408C, 250 MPa for 100 h. The Ti 5 Si 3 precipitates are discontinuous along grain boundary, and there are also some a precipitates. However, there are no second phase precipitates in most zones, which guarantees good creep behavior, as shown in Table 2. There are a lot of coarse rod-like a and Ti 5 Si 3 phases (Fig. 6) and Ti 5 Si 3 precipitates near-continuously along grain boundary if the heat treatment of condition A is 7008C / 30 min W.Q16008C / 5 h /A.C, followed by creep exposure at 5408C, 250 MPa for 100 h. This type of second phases is associated with a decrease of creep resistance (Table 2). There is also an unidentified blocky
The second phases, i.e. Ti 5 Si 3 and a, precipitate from b matrix after the Ti40 alloy has been exposed at high temperatures for a long time. The Ti 5 Si 3 phase distributes discontinuously along grain boundary in conventionally forged alloys if the exposure temperature is below 5408C. Exposed at 7008C for 100 h, Ti 5 Si 3 phase grows greatly, which obviously reduces the tensile properties. There are coarse Ti 5 Si 3 and a phases in isothermally forged alloys annealed at 5408C for 100 h, which leads to serious decrease of tensile properties. Ti 5 Si 3 precipitates distribute discontinuously along grain boundary in conventionally forged alloys after creep exposure. Many coarse rod-like Ti 5 Si 3 and a phases precipitate, and Ti 5 Si 3 distributes near-continuously along
Fig. 6. TEM image of A after creep exposure at 5408C, 250 MPa for 100 h with heat treatment of 7008C / 30 min W.Q16008C / 5 h A.C. (a) Rod-like a and Ti 5 Si 3 phases on grain boundary are as shown by arrows; (b) SAD of rod-like a.
Y.Q. Zhao et al. / Journal of Alloys and Compounds 333 (2002) 165 – 169
169
Fig. 7. Uncertain phase (a) in TEM images and its SAD (b).
Fig. 8. TEM images of B after creep exposure at 5408C, 250 MPa for 100 h. (a) Rod-like a phase (as shown by arrow); (b) SAD of a.
grain boundary if the heat treatment temperature is lower than 7008C followed by creep exposure. Many rod-like a phases precipitate within grains for condition B after creep exposure.
References [1] P.J. Bania, in: D. Eylon, R.R. Boyer, D.A. Koss (Eds.), Beta Titanium Alloys in the 90s, TMS Publications, Warrendale, PA, 1993, p. 3. [2] R. Boyer, G. Welsch, E.W. Collings (Eds.), Materials Properties Handbook — Titanium Alloys, The Materials Information Society, USA, 1994, p. 685. [3] UK Patent Application, 2 238057, 1987. [4] K. Giary, Adv. Mater. Processes 9 (1993) 7. [5] S.R. Seagle, Mater. Sci. Eng. A213 (1996) 1. [6] R.R. Boyer, Mater. Sci. Eng. A213 (1996) 103.
[7] D.W. Anderson, A.F. Condliff, in: Processing of the Technical Program from the 1994 International Conference, USA, 1994, p. 91. [8] Y.Q. Zhao, K.Y. Zhu, H.L. Qu, H. Wu, Mater. Sci. Technol. 16 (9) (2000) 1073. [9] Y.Q. Zhao, K.Y. Zhu, H.L. Qu, H. Wu, Mater. Sci. Eng. A282 (2000) 153. [10] Y.Q. Zhao, L. Zhou, J. Deng, Mater. Sci. Eng. A267 (2000) 167. [11] Y.Q. Zhao, L. Zhou, J. Deng, Rare Metal Mater. Eng. 28 (3) (1999) 77. [12] Y.Q. Zhao, K.Y. Zhu, H.L. Qu, J. Mater. Sci. 2001 (in press). [13] H. Wu, Q. Zhao, H.L. Qu, K.Y. Zhu, in: J. Song, R. Yin (Eds.), Proceedings of the International Conference on Engineering and Technological Science 2000, New World Press, Beijing, 2000, p. 407. [14] Y.Q. Zhao, L. Zhou, H.L. Qu, K.Y. Zhu, in: Titanium Alloys at Elevated Temperature: Structural Development and Service Behaviour, UK, 2001, p. 123. [15] Y.Q. Zhao, H.L. Zhu, H. Wu, Rare Metal Mater. Eng. 29 (6) (2000) 403.