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Mechanical alloying and spark plasma sintering of the intermetallic compound Ti50Al50
Journal of Alloys and Compounds 440 (2007) 154–157
Mechanical alloying and spark plasma sintering of the intermetallic compound Ti50Al50 Yaodong Liu ∗ , Wei Liu School of Materials Science and Engineering, Changchun University of Technology, Changchun 130012, China Received 11 July 2006; received in revised form 11 September 2006; accepted 11 September 2006 Available online 19 October 2006
Abstract This study investigates the microstructures and mechanical properties of Ti50 Al50 alloys prepared via mechanical alloying (MA) starting from elemental powders. The process of the spark plasma sintering (SPS) has also been studied. It is found that the nanocrystallization process of the Ti–Al alloy proceeds and the sintering temperature can control the microstructure of alloy. The sintering of the compacts is carried out at the temperatures of 1100–1200 ◦ C with a compaction pressure of 30 MPa and a heating rate of 30 ◦ C min−1 . Specimens with high densities and approaching the equilibrium state can be obtained in short time by spark sintering than conventional sintering. Such shorter high temperature is important to prevent grain growth. © 2006 Elsevier B.V. All rights reserved. Keywords: Mechanical alloying; Spark plasma sintering; Microstructure
1. Introduction The titanium-aluminized compounds have received considerable attention recently as candidate materials for relatively high temperature uses such as turbine engine components [1–4]. The advantages of these materials include their high specific moduli and strengths, high melting temperatures and reasonable oxidation resistances. The major disadvantages are their low ductility and toughness at room temperature [5]. Mechanical alloying and sintering process have achieved considerable improvements in these properties. Because it can achieve amorphous phase, nanocrystals, reactive milling synthesis and intermetallic compounds as well as alloying at atomic level [6]. The mechanical alloying process is characterized by repeated welding and fracturing of powder particles and microstructural changes during mechanical alloying are influenced by the mechanical behavior of the powder components and process variables. A few investigations on mechanical alloying (MA) process of Ti/Al powder have been recently reported [7]. Zheng et al. [8] and Yang and Wang et al. [9,10] separately studied the
∗
Corresponding author. E-mail address: [email protected] (Y. Liu).
0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.09.060
microstructures and mechanical properties of Ti/Al alloy, show that strength and plasticity depend on compositions and process. In Zheng’ s research group a novel near net shape processing technique to manufacture TiAl has been developed [5]. However, the processing-microstructure-property relationship for Ti50 Al50 alloys in this system has not been investigated yet. In the coming years, the emphases will be put on how to further determine the relationships among the processing, microstructure and mechanical properties [6]. As a rule, several problems are involved in obtaining nanostructured material from ultrafine particles; on the one hand, in order to retain a small grain size it is necessary to minimize recrystallization processes that are initiated at high temperatures, while on the other hand the production of dense and strong material requires quite high sintering temperatures [11]. Even if the use of [12] provided a high heating rate and a relatively minor holding time, but unusually high load and a high rate of cooling is necessary [13]. Furthermore, they are too costly to be applied to commercial applications, especially to a civil application such as the automobile industry. However, spark plasma sintering (SPS) somewhere, offers many advantages over conventional systems using hot press (HP) sintering, hot isostatic pressing (HIP) [14], which enables sintering and sinter-bonding at low temperatures by charging powder particles with electrical energy and effectively applying locally high temperature at the interfaces. It is regarded as a rapid sintering
Y. Liu, W. Liu / Journal of Alloys and Compounds 440 (2007) 154–157
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process, using the self-heating action from inside the powder, similar to self-propagation high temperature synthesis (SHS) and microwave sintering. In this study, special attention is given to mechanical alloying process and the spark plasma sintering parameters, which are a very important series for application. 2. Experimental procedure Pure Ti (99.99% and size under 0.15 mm) and Al (99.99% and size under 0.18 mm) powders were used as starting materials in this study. The elemental powders were mixed as compositions Ti50 Al50 (at%) for mechanical alloying process. A stainless steel vials and balls with diameters of 10 mm was employed for milling process. The weight ratio of ball-to-powder was approximately 5:1. Milling time was 5, 10, 15 and 20 h, respectively. Acetone was added as a process control agent. The vial loaded with powders of the desired composition was sealed in a glove box under an argon atmosphere. After mechanical alloying, the spark plasma sintering was carried out in 10 mm diameter graphite dies in vacuum (0.1 Torr) with compaction pressures of up to 30 MPa. Pressing temperatures ranged between 1100 and 1200 ◦ C with a heating rate equal to 30 ◦ C min−1 . The microstructure of specimens was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray diffraction (XRD) was performed using Cu K␣-radiation at 30 KV(Rich–Seifert). The densities of specimens were measured by means the Archimedean principle. The HXD-1000 micro-hardness instrument was used to show the micro-hardness of the sintered specimens.
3. Results and discussion 3.1. Characterization of MAed Ti50 Al50 powder Fig. 1 shows the TEM image of Ti50 Al50 powder prepared by high-energy ball milling at different times. The mean particle size of Ti50 Al50 powder decreased significantly to 100 nm after milling for 15 h, with further ball milling to 20 h. Fig. 1(c) shows that particle size decreased rapidly to 10 nm until amorphous formation. The XRD patterns of the Ti50 Al50 powder mixture milled for different times are presented in Fig. 2. It can be seen that Ti and Al peaks are sharp (5 h) and then the position of Al and Ti peaks tend to the middle of the two peaks during the MA process. This implies that the mechanically alloyed powders possess essentially a crystal structure of alpha Ti, that is, during the mechanical
Fig. 2. SEM micrograph of Ti50 Al50 composite powder milled for 20 h (720 rpm) at sintered at different temperatures for 3 min.
alloying process the Ti structure is maintained while the Al dissolved into the Ti structure, in a non-equilibrium state, which was also reported in the literature [15]. Considering the smaller size of the Al atom of 0.286 nm compared with the Ti atom size of 0.291 nm, the lattice parameter and hence the inter-panar spacing d in the Ti crystal structure is reduced due to the replacement of Al atom for Ti and therefore the diffraction angle 2θ is increased according to Bragg’s law of 2d sinθ = λ,where λ is the X-ray wave length. Intensities of the Ti and Al peaks decreased with increasing milling time (10, 15 and 20 h). Mechanical alloying often results in extended solid solubility of the soluble elements [4–7]. Fig. 2 show that solid solution Ti (Al) present in powder milled for 15 h and formation of the intermetallic Ti3 Al. It has been established that Ti3 Al enriched with aluminum forms first at the interface. This has the lowest heat of formation of all phases that can be present in the alloys of this system [16]. In this case the diffusion coefficient DTi DAl . The initial formation of Ti3 Al has also been established for heated mixtures of titanium and aluminum [17].
Fig. 1. TEM image of Ti50 Al50 composite powder (720 rpm) milled for (a) 5 h, (b) 15 h and (c) 20 h.
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Y. Liu, W. Liu / Journal of Alloys and Compounds 440 (2007) 154–157
Fig. 3. X-ray diffraction patterns of Ti50 Al50 composite powder milled for different times (5, 10, 15 and 20 h) at 720 rpm (a) 1100 ◦ C, (b) 1150 ◦ C and (c) 1200 ◦ C.
3.2. Microstructure characterization of sintered alloys SEM micrographs of the powders mechanically alloyed for 20 h then sintered at different temperature for 3 min are shown in Fig. 3. For specimens sintered at 1100 ◦ C, the microstructure consists of amount of residual porosity and inclusion, however, the densification behavior of the Ti50 Al50 alloy changes significantly when sintering temperature increases to 1150 ◦ C. Density varies not very much from 1150 to 1200 ◦ C, even has slightly decreases due to shrinkage freeze again at a higher sintering temperature. From Fig. 3(c), a discernable grain size increase and a number of residual porosity are observed. Fig. 4 shows XRD patterns of compacts sintered from the mechanically alloyed powder Ti/Al system by SPS process. No change of phase was found at all sintering temperature from 1100 to 1200 ◦ C, the gamma phase TiAl and alpha Ti3 Al are the dominant phase in sintered alloys and little Al2 O3 also formed. In areas of local contact the temperature can rise to values close to the melting point of aluminum, which undoubtedly accelerates the transport of Al atoms across the interface and reaction with titanium atoms. The formation of Al2 O3 in the sintered alloy could be due to content of the gas elements in the starting titanium powder [5]. On the other hand, during the powder handling, like filling into molds before sintering, particle surfaces are most likely to absorb
air, though the powders are usually stored in Ar atmosphere or in vacuum before the sintering operation. Actually the existence of Al2 O3 on the Ti3 Al grain boundary suppresses its grain growth [18]. Al, Ti and Al2 O3 were finely mixed with increasing MA time. While lamellar structures of fine Al and Ti were convoluted during MA, brittle Al2 O3 particles were fractured and were distributed homogeneously in the lamellar matrix. Some authors have reported that Al2 O3 particles increase the MA efficiency [19]. The results of hardness and density tests are shown in Fig. 5, we found the hardness of specimen sintered at 1150 ◦ C is up to 710.6 Hv, furthermore, density reach a maximum. When sintering temperature is relatively lower (1100 ◦ C), incompletely densification occur, the specimen contains a large number of residual porosity lead to lower hardness and density, however, sintering at a higher temperature (1200 ◦ C) is not advantageous to retain nanostructures, Because the powder mixture is milled for a long time, a large amount of internal strain and dislocations may be stored, leading to destabilization and dilation of lattice [20]. The density of the sample decreased due to the generation of various defects [21]. Furthermore during MA process which involves welding, fracturing and rewelding of constituent elements [22], micro pores can be entrapped and remain closed inside MA Ti50 Al50 powder in steady state. As a result, in addition to defects such as stored internal
Fig. 4. X-ray diffraction patterns of Ti50 Al50 sintered at 1150 ◦ C for 3 min.
Fig. 5. Vickers hardness and density of Ti50 Al50 at different sintering temperatures for 3 min.
Y. Liu, W. Liu / Journal of Alloys and Compounds 440 (2007) 154–157
strain and stored dislocation, closed micro pores formed during milling seemed to cause an increase of grains after sintered. Mean that liquid phase sintering of Ti50 Al50 powder should be carried out at low temperature as possible to obtain fine grains. 4. Conclusion Ti50 Al50 powders were mechanically alloyed by ball mill in argon at a pressure of 0.1 MPa for different times. The mechanical alloying process and the phase variations after sintering at different temperature were investigated. The results obtained were summarized as follows: (a) The atomic diffusion of aluminum in titanium leads to the formation of the TiAl and Ti3 Al after Ti50 Al50 composite powder milled for 15 h. Ti3 Al enriched with aluminum forms first at the interface. This has the lowest heat of formation of all phases that can be present in the alloys of this system. (b) The spark plasma sintering (SPS) of Ti50 Al50 at 1150 ◦ C leads to the obtainment of low-porosity specimens. SPS somewhere is a newly synthesis and processing technique compared with other technologies of compaction, in particular, HIP. References [1] Y.-W. Kim, JOM 46 (1994) 30–39. [2] C.-q. Peng, B.-y. Huang, Y.-h. He, Chin. J. Nonferr. Metal. 11 (2001) 527–540 (in Chinese). [3] M.M. Keller, P.E. Jones, W.J. Porter, et al., JOM 49 (1997) 42–44.
157
[4] T. Matsubara, T. Shibutani, K. Uenishi, K.F. Kobayashi, Intermetallics 8 (2000) 815. [5] M.S. Zheng, H. Hitoshi, Intermetallics 11 (2003) 825–834. [6] P.L. Martin, D.A. Hardwick, in: J.H. Westbrook, R.L. Fleischer (Eds.), Intermetallic Compounds, I, John, Wiley, New York, 1994, p. 637. [7] T. ItsukaiChi, K. Masuyama, M. Umemoto, I. Okane, J.G. CabanasMoreno, Mater. Res. 8 (1993) 1817. [8] C.-q. Peng, Effects of Cyclic Heat Treatment on Microstructures and Mechanical Properties of TiAl-based Alloys D, Central South University, Changsha, 2001 (in Chinese). [9] L.W. Yang, J.Y. Cheng, T. Luoh, P.L. Sun, P.W. Kao, Scripta Mater. 51 (2004) 47–51. [10] Wang Jian-nong, Key Fundamental Problems Research of High Performance Intermetallic Structural Materials, 2000-05. [11] E. Szewczak, A. Presz, A. Witek, J.W. Wyrzykowski, H. Matyja, Nanostruct. Mater. 12 (1–4) (1999) 167–170. [12] Park Y.H. et al. Microstructure and mechanical properties of HIPed compacts of mechanically alloyed Ti–Al powder. [13] V.E. Oliker, V.S. Kresanov, V.L. Sirovatka, T.Ya. Gridasova, I.I. Timofeeva, A.I. Bykov, Powder Metall. Met. Ciram. 42 (1–2) (2003) 38–49. [14] Abe, T; Hashimoto, H; Um, T; Park, Y H; Sun, Z.M. PM98: 1998 Powder Metallurgy World Congress & Exhibition; Granada; Spain; 18-22 October 1998. pp. 5.437–5.442. 1998. [15] K. Ameyama, O. Okada, M. Tokizane, K. Nakata, A. Hishinuma, Jpn. Soc. Pow. Metall. 40 (1993) 341. [16] C. Suryanarayana, Guo-Hao. Chen, A. Frefer, F.H. Froes, Mater. Sci. Eng. A 158 (1) (15 October 1992) 93–101. [17] O.M. Ivasishin, A.N. Demidik, D.G. Savvakin, Poroshk. Metall. 9–10 (1999) 632–669. [18] K. Uenishi, T. Matsubara, T. Shibutani, K.F. Kobayash, Intermetallics 10 (2002) 105–111. [19] K. Uenishi, T. Matsubara, M. Kambara, K.F. Kobayashi, Scripta. Mater. 44 (2001) 2093. [20] N.Q. Wu, G.X. Wang, W. Li, J.M. Wu, Z.Z. Li, Mater. Lett. 32 (1997) 259. [21] S.Q. Xi, X.Y. Qu, M.L. Ma, J.G. Zhou, X.L. Zheng, X.T. Wang, J. Alloy. Comp. 268 (1998) 211. [22] A. Benghalem, D.G. Morris, Acta Metall. Mater. 42 (1994) 4071.
Mechanical alloying and spark plasma sintering of the intermetallic compound Ti50Al50 Yaodong Liu ∗ , Wei Liu School of Materials Science and Engineering, Changchun University of Technology, Changchun 130012, China Received 11 July 2006; received in revised form 11 September 2006; accepted 11 September 2006 Available online 19 October 2006
Abstract This study investigates the microstructures and mechanical properties of Ti50 Al50 alloys prepared via mechanical alloying (MA) starting from elemental powders. The process of the spark plasma sintering (SPS) has also been studied. It is found that the nanocrystallization process of the Ti–Al alloy proceeds and the sintering temperature can control the microstructure of alloy. The sintering of the compacts is carried out at the temperatures of 1100–1200 ◦ C with a compaction pressure of 30 MPa and a heating rate of 30 ◦ C min−1 . Specimens with high densities and approaching the equilibrium state can be obtained in short time by spark sintering than conventional sintering. Such shorter high temperature is important to prevent grain growth. © 2006 Elsevier B.V. All rights reserved. Keywords: Mechanical alloying; Spark plasma sintering; Microstructure
1. Introduction The titanium-aluminized compounds have received considerable attention recently as candidate materials for relatively high temperature uses such as turbine engine components [1–4]. The advantages of these materials include their high specific moduli and strengths, high melting temperatures and reasonable oxidation resistances. The major disadvantages are their low ductility and toughness at room temperature [5]. Mechanical alloying and sintering process have achieved considerable improvements in these properties. Because it can achieve amorphous phase, nanocrystals, reactive milling synthesis and intermetallic compounds as well as alloying at atomic level [6]. The mechanical alloying process is characterized by repeated welding and fracturing of powder particles and microstructural changes during mechanical alloying are influenced by the mechanical behavior of the powder components and process variables. A few investigations on mechanical alloying (MA) process of Ti/Al powder have been recently reported [7]. Zheng et al. [8] and Yang and Wang et al. [9,10] separately studied the
∗
Corresponding author. E-mail address: [email protected] (Y. Liu).
0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.09.060
microstructures and mechanical properties of Ti/Al alloy, show that strength and plasticity depend on compositions and process. In Zheng’ s research group a novel near net shape processing technique to manufacture TiAl has been developed [5]. However, the processing-microstructure-property relationship for Ti50 Al50 alloys in this system has not been investigated yet. In the coming years, the emphases will be put on how to further determine the relationships among the processing, microstructure and mechanical properties [6]. As a rule, several problems are involved in obtaining nanostructured material from ultrafine particles; on the one hand, in order to retain a small grain size it is necessary to minimize recrystallization processes that are initiated at high temperatures, while on the other hand the production of dense and strong material requires quite high sintering temperatures [11]. Even if the use of [12] provided a high heating rate and a relatively minor holding time, but unusually high load and a high rate of cooling is necessary [13]. Furthermore, they are too costly to be applied to commercial applications, especially to a civil application such as the automobile industry. However, spark plasma sintering (SPS) somewhere, offers many advantages over conventional systems using hot press (HP) sintering, hot isostatic pressing (HIP) [14], which enables sintering and sinter-bonding at low temperatures by charging powder particles with electrical energy and effectively applying locally high temperature at the interfaces. It is regarded as a rapid sintering
Y. Liu, W. Liu / Journal of Alloys and Compounds 440 (2007) 154–157
155
process, using the self-heating action from inside the powder, similar to self-propagation high temperature synthesis (SHS) and microwave sintering. In this study, special attention is given to mechanical alloying process and the spark plasma sintering parameters, which are a very important series for application. 2. Experimental procedure Pure Ti (99.99% and size under 0.15 mm) and Al (99.99% and size under 0.18 mm) powders were used as starting materials in this study. The elemental powders were mixed as compositions Ti50 Al50 (at%) for mechanical alloying process. A stainless steel vials and balls with diameters of 10 mm was employed for milling process. The weight ratio of ball-to-powder was approximately 5:1. Milling time was 5, 10, 15 and 20 h, respectively. Acetone was added as a process control agent. The vial loaded with powders of the desired composition was sealed in a glove box under an argon atmosphere. After mechanical alloying, the spark plasma sintering was carried out in 10 mm diameter graphite dies in vacuum (0.1 Torr) with compaction pressures of up to 30 MPa. Pressing temperatures ranged between 1100 and 1200 ◦ C with a heating rate equal to 30 ◦ C min−1 . The microstructure of specimens was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray diffraction (XRD) was performed using Cu K␣-radiation at 30 KV(Rich–Seifert). The densities of specimens were measured by means the Archimedean principle. The HXD-1000 micro-hardness instrument was used to show the micro-hardness of the sintered specimens.
3. Results and discussion 3.1. Characterization of MAed Ti50 Al50 powder Fig. 1 shows the TEM image of Ti50 Al50 powder prepared by high-energy ball milling at different times. The mean particle size of Ti50 Al50 powder decreased significantly to 100 nm after milling for 15 h, with further ball milling to 20 h. Fig. 1(c) shows that particle size decreased rapidly to 10 nm until amorphous formation. The XRD patterns of the Ti50 Al50 powder mixture milled for different times are presented in Fig. 2. It can be seen that Ti and Al peaks are sharp (5 h) and then the position of Al and Ti peaks tend to the middle of the two peaks during the MA process. This implies that the mechanically alloyed powders possess essentially a crystal structure of alpha Ti, that is, during the mechanical
Fig. 2. SEM micrograph of Ti50 Al50 composite powder milled for 20 h (720 rpm) at sintered at different temperatures for 3 min.
alloying process the Ti structure is maintained while the Al dissolved into the Ti structure, in a non-equilibrium state, which was also reported in the literature [15]. Considering the smaller size of the Al atom of 0.286 nm compared with the Ti atom size of 0.291 nm, the lattice parameter and hence the inter-panar spacing d in the Ti crystal structure is reduced due to the replacement of Al atom for Ti and therefore the diffraction angle 2θ is increased according to Bragg’s law of 2d sinθ = λ,where λ is the X-ray wave length. Intensities of the Ti and Al peaks decreased with increasing milling time (10, 15 and 20 h). Mechanical alloying often results in extended solid solubility of the soluble elements [4–7]. Fig. 2 show that solid solution Ti (Al) present in powder milled for 15 h and formation of the intermetallic Ti3 Al. It has been established that Ti3 Al enriched with aluminum forms first at the interface. This has the lowest heat of formation of all phases that can be present in the alloys of this system [16]. In this case the diffusion coefficient DTi DAl . The initial formation of Ti3 Al has also been established for heated mixtures of titanium and aluminum [17].
Fig. 1. TEM image of Ti50 Al50 composite powder (720 rpm) milled for (a) 5 h, (b) 15 h and (c) 20 h.
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Y. Liu, W. Liu / Journal of Alloys and Compounds 440 (2007) 154–157
Fig. 3. X-ray diffraction patterns of Ti50 Al50 composite powder milled for different times (5, 10, 15 and 20 h) at 720 rpm (a) 1100 ◦ C, (b) 1150 ◦ C and (c) 1200 ◦ C.
3.2. Microstructure characterization of sintered alloys SEM micrographs of the powders mechanically alloyed for 20 h then sintered at different temperature for 3 min are shown in Fig. 3. For specimens sintered at 1100 ◦ C, the microstructure consists of amount of residual porosity and inclusion, however, the densification behavior of the Ti50 Al50 alloy changes significantly when sintering temperature increases to 1150 ◦ C. Density varies not very much from 1150 to 1200 ◦ C, even has slightly decreases due to shrinkage freeze again at a higher sintering temperature. From Fig. 3(c), a discernable grain size increase and a number of residual porosity are observed. Fig. 4 shows XRD patterns of compacts sintered from the mechanically alloyed powder Ti/Al system by SPS process. No change of phase was found at all sintering temperature from 1100 to 1200 ◦ C, the gamma phase TiAl and alpha Ti3 Al are the dominant phase in sintered alloys and little Al2 O3 also formed. In areas of local contact the temperature can rise to values close to the melting point of aluminum, which undoubtedly accelerates the transport of Al atoms across the interface and reaction with titanium atoms. The formation of Al2 O3 in the sintered alloy could be due to content of the gas elements in the starting titanium powder [5]. On the other hand, during the powder handling, like filling into molds before sintering, particle surfaces are most likely to absorb
air, though the powders are usually stored in Ar atmosphere or in vacuum before the sintering operation. Actually the existence of Al2 O3 on the Ti3 Al grain boundary suppresses its grain growth [18]. Al, Ti and Al2 O3 were finely mixed with increasing MA time. While lamellar structures of fine Al and Ti were convoluted during MA, brittle Al2 O3 particles were fractured and were distributed homogeneously in the lamellar matrix. Some authors have reported that Al2 O3 particles increase the MA efficiency [19]. The results of hardness and density tests are shown in Fig. 5, we found the hardness of specimen sintered at 1150 ◦ C is up to 710.6 Hv, furthermore, density reach a maximum. When sintering temperature is relatively lower (1100 ◦ C), incompletely densification occur, the specimen contains a large number of residual porosity lead to lower hardness and density, however, sintering at a higher temperature (1200 ◦ C) is not advantageous to retain nanostructures, Because the powder mixture is milled for a long time, a large amount of internal strain and dislocations may be stored, leading to destabilization and dilation of lattice [20]. The density of the sample decreased due to the generation of various defects [21]. Furthermore during MA process which involves welding, fracturing and rewelding of constituent elements [22], micro pores can be entrapped and remain closed inside MA Ti50 Al50 powder in steady state. As a result, in addition to defects such as stored internal
Fig. 4. X-ray diffraction patterns of Ti50 Al50 sintered at 1150 ◦ C for 3 min.
Fig. 5. Vickers hardness and density of Ti50 Al50 at different sintering temperatures for 3 min.
Y. Liu, W. Liu / Journal of Alloys and Compounds 440 (2007) 154–157
strain and stored dislocation, closed micro pores formed during milling seemed to cause an increase of grains after sintered. Mean that liquid phase sintering of Ti50 Al50 powder should be carried out at low temperature as possible to obtain fine grains. 4. Conclusion Ti50 Al50 powders were mechanically alloyed by ball mill in argon at a pressure of 0.1 MPa for different times. The mechanical alloying process and the phase variations after sintering at different temperature were investigated. The results obtained were summarized as follows: (a) The atomic diffusion of aluminum in titanium leads to the formation of the TiAl and Ti3 Al after Ti50 Al50 composite powder milled for 15 h. Ti3 Al enriched with aluminum forms first at the interface. This has the lowest heat of formation of all phases that can be present in the alloys of this system. (b) The spark plasma sintering (SPS) of Ti50 Al50 at 1150 ◦ C leads to the obtainment of low-porosity specimens. SPS somewhere is a newly synthesis and processing technique compared with other technologies of compaction, in particular, HIP. References [1] Y.-W. Kim, JOM 46 (1994) 30–39. [2] C.-q. Peng, B.-y. Huang, Y.-h. He, Chin. J. Nonferr. Metal. 11 (2001) 527–540 (in Chinese). [3] M.M. Keller, P.E. Jones, W.J. Porter, et al., JOM 49 (1997) 42–44.
157
[4] T. Matsubara, T. Shibutani, K. Uenishi, K.F. Kobayashi, Intermetallics 8 (2000) 815. [5] M.S. Zheng, H. Hitoshi, Intermetallics 11 (2003) 825–834. [6] P.L. Martin, D.A. Hardwick, in: J.H. Westbrook, R.L. Fleischer (Eds.), Intermetallic Compounds, I, John, Wiley, New York, 1994, p. 637. [7] T. ItsukaiChi, K. Masuyama, M. Umemoto, I. Okane, J.G. CabanasMoreno, Mater. Res. 8 (1993) 1817. [8] C.-q. Peng, Effects of Cyclic Heat Treatment on Microstructures and Mechanical Properties of TiAl-based Alloys D, Central South University, Changsha, 2001 (in Chinese). [9] L.W. Yang, J.Y. Cheng, T. Luoh, P.L. Sun, P.W. Kao, Scripta Mater. 51 (2004) 47–51. [10] Wang Jian-nong, Key Fundamental Problems Research of High Performance Intermetallic Structural Materials, 2000-05. [11] E. Szewczak, A. Presz, A. Witek, J.W. Wyrzykowski, H. Matyja, Nanostruct. Mater. 12 (1–4) (1999) 167–170. [12] Park Y.H. et al. Microstructure and mechanical properties of HIPed compacts of mechanically alloyed Ti–Al powder. [13] V.E. Oliker, V.S. Kresanov, V.L. Sirovatka, T.Ya. Gridasova, I.I. Timofeeva, A.I. Bykov, Powder Metall. Met. Ciram. 42 (1–2) (2003) 38–49. [14] Abe, T; Hashimoto, H; Um, T; Park, Y H; Sun, Z.M. PM98: 1998 Powder Metallurgy World Congress & Exhibition; Granada; Spain; 18-22 October 1998. pp. 5.437–5.442. 1998. [15] K. Ameyama, O. Okada, M. Tokizane, K. Nakata, A. Hishinuma, Jpn. Soc. Pow. Metall. 40 (1993) 341. [16] C. Suryanarayana, Guo-Hao. Chen, A. Frefer, F.H. Froes, Mater. Sci. Eng. A 158 (1) (15 October 1992) 93–101. [17] O.M. Ivasishin, A.N. Demidik, D.G. Savvakin, Poroshk. Metall. 9–10 (1999) 632–669. [18] K. Uenishi, T. Matsubara, T. Shibutani, K.F. Kobayash, Intermetallics 10 (2002) 105–111. [19] K. Uenishi, T. Matsubara, M. Kambara, K.F. Kobayashi, Scripta. Mater. 44 (2001) 2093. [20] N.Q. Wu, G.X. Wang, W. Li, J.M. Wu, Z.Z. Li, Mater. Lett. 32 (1997) 259. [21] S.Q. Xi, X.Y. Qu, M.L. Ma, J.G. Zhou, X.L. Zheng, X.T. Wang, J. Alloy. Comp. 268 (1998) 211. [22] A. Benghalem, D.G. Morris, Acta Metall. Mater. 42 (1994) 4071.