- Email: [email protected]
Synthesis and high-pressure electrical resistivity studies of Ti3Al
Journal of Alloys and Compounds 392 (2005) 24–26
Synthesis and high-pressure electrical resistivity studies of Ti3Al R. Selva Vennila∗ , E. Elamurugu Porchelvi, K.M. Freny Joy, T.K. Jaya Arun, N. Victor Jaya Department of Physics, Anna University, Chennai 600025, India Received 31 August 2004; accepted 13 September 2004 Available online 30 October 2004
Abstract Titanium aluminide (Ti3 Al) has been synthesized by a powder metallurgical method. X-ray diffraction studies show the formation of a single phase with hexagonal structure. Electrical resistivity studies were carried out by a four-probe technique both at high pressure and high temperature using a Bridgman Opposed Anvil High Pressure Device (OAHPD). The sample was studied up to a pressure and temperature of 10 GPa and 250 ◦ C, respectively. The electrical resistivity is found to decrease with increasing pressure. The temperature effect causes an upward shift in the electrical resistivity in the range of pressure considered. © 2004 Elsevier B.V. All rights reserved. Keywords: Intermetallics; Powder metallurgy; X-ray diffraction; High temperature alloys; Strain; High-pressure
1. Introduction Ordered intermetallic compounds based on aluminides such as Ti3 Al, TiAl, Ni3 Al are emerging as attractive materials for high-temperature applications. They are commonly utilized in aerospace, space vehicles and in the petroleum and chemical industries. In particular, the phase Ti3 Al (Ni3 Sn-type structure) exhibits low density and good high-temperature strength and was therefore chosen for the development of aircraft engine materials [1]. In addition, their application to nuclear materials has been recently noticed because the alloys have good devoted temperature strength, corrosion resistance and low neutron induced radioactivity compared with those of conventional nuclear materials like the austenitic stainless steels. Ti3 Al-based intermetallic alloys are candidate materials for aerospace applications because of their balance of ductility at room temperature and high strength at elevated temperatures. They have been proposed as matrix alloys for intermetallic composites [2]. Experimental high-pressure studies of titanium aluminide (Ti3 Al) have been carried out under quasihydrostatic and non∗
Corresponding author. Tel.: +91 44 2220 3148; fax: +91 44 2235 2161. E-mail address: [email protected] (R.S. Vennila).
0925-8388/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2004.09.004
hydrostatic conditions up to a pressure of 25 GPa using an in situ powder X-ray diffraction technique by Dubrovinskaia et al. [3]. These authors did not observe the occurrence of a phase transition up to 25 GPa. The only changes in the diffraction patterns of Ti3 Al on compression are the disappearance of some superlattice reflections, (1 0 1), (1 1 0) and (2 1 1) and (0 0 2), (2 0 2), at pressures above 20 GPa. Furthermore, the studies showed a decrease in the a and c unit cell parameters with increasing Al content, which are in concord with the smaller radius of Al when compared to Ti. To illustrate the reliability of the combined experimental and theoretical approach (by modern ab initio calculations), the unit cell parameters, molar volumes and other parameters such as bulk modulus and its derivatives are available in the literature and can be reviewed for a comparison [5,6]. Sahu et al. fitted the experimental equation of state for Ti3 Al and the obtained parameters show good agreement with the theoretical results [4]. In their study, Dubrovinskaia et al. reported that experimentally nor theoretically there is not any pressure-induced structural phase transition in the pressure range studied. It was reported that the phase transition from the DO19 (Ni3 Sn type) structure of Ti3 Al to the DO24 (Ni3 Ti type) structure, which was reported earlier by Sahu et al. was not confirmed. In this present study, the electrical resis-
R.S. Vennila et al. / Journal of Alloys and Compounds 392 (2005) 24–26
25
Fig. 1. Powder XRD pattern of Ti3 Al.
tivity of Ti3 Al is measured at various pressures and temperatures in order to explore the possibility of a phase transition.
2. Experimental details
Fig. 2. Pressure vs. resistivity of Ti3 Al at room temperature.
2.1. Synthesis of Ti3 Al Ti3 Al was synthesized by a powder metallurgical method. High purity fine powders of metallic aluminum and titanium were mixed well in the ratio 1:8. The pellets of the mixture were kept in an alumina crucible and heated in the furnace at a temperature of 1100 ◦ C for 10 h. The samples were annealed at a temperature of 700 ◦ C for 3 h and finally cooled to room temperature. An X-ray powder diffraction pattern was recorded using Cu K␣ radiation. The powder X-ray diffraction pattern (Fig. 1) shows the formation of single-phase Ti3 Al. The X-ray pattern was indexed and the crystal structure was found to be hexagonal.
perimental arrangements were discussed elsewhere [8]. The measurements were carried out for various pressures up to 10 GPa at 100, 200 and 250 ◦ C. Plots of the electrical resistivity versus pressure at various temperatures are shown in Fig. 3.
2.2. High-pressure electrical resistivity set-up The high-pressure electrical resistivity measurement was done using a Bridgman opposed anvil apparatus [7]. The cell assembly consists of the pressure medium, gasket and sample placed in between a pair of tapered cylinders. Pyrophyllite of thickness 0.5 mm, inner diameter of 2 mm and outer diameter 10 mm was used as the gasket material. Steatite was used for hydrostatic pressure generation over the sample. Bismuth was used as the pressure calibrant. Electrical contact on the sample was made using copper wires of 0.1 mm diameter. The electrical resistivity measurement was done using a four-probe technique. Trivial measurements were carried out for loading and unloading pressures. The variation of the electrical resistivity measured at various pressures up to 10 GPa at room temperature is shown in Fig. 2. High-temperature measurements up to 250 ◦ C were done using a heating coil arrangement. The details of the ex-
Fig. 3. Pressure vs. resistivity of Ti3 Al at different temperatures.
26
R.S. Vennila et al. / Journal of Alloys and Compounds 392 (2005) 24–26
3. Results and discussion
Acknowledgement
The X-ray diffraction pattern of Ti3 Al shows the formation of single phase. It is found to be crystallised in a hexagonal structure with the lattice parameters a = 5.58(1) and c = 4.57(1). The lattice parameters obtained are in good agreement with literature data [3]. The electrical resistivity behaviour with pressure is shown in Fig. 2. It is observed that at room temperature as the pressure increases, the resistivity decreases rapidly up to around 1.1 GPa, above which the resistivity is nearly constant up to 10 GPa. It can be seen from Fig. 2, the unloading curve show slightly lower values of ρ when compared to the loading curve. From this we can conclude that the decrease in ρ is mainly caused as an effect of pressure on the sample. The effect of temperature on the sample causes an upward shift of the electrical resistivity behaviour and is shown in Fig. 3. Thus, Ti3 Al shows improved electrical properties under pressure and temperature up to a maximum of 10 GPa and 250 ◦ C, respectively. The electrical resistivity studies show the absence of a phase transition in the pressure range studied up to a maximum temperature of 250 ◦ C.
The authors thank University Grants Commission and Department of Science and Technology, Govt. of India, for financial support.
References [1] F. Habashi (Ed.), Alloys: Preparation, Properties, Applications, Wiley, Weinheim, 1998. [2] W. Cai, M.S. Thesis, University of Virginia, 1993. [3] N.A. Dubrovinskaia, M. Vennstrom, I.A. Abrikosov, R. Ahuja, P. Ravindran, Y. Andersson, O. Eriksson, V. Dmitriev, L.S. Dubrovinsky, Phys. Rev. B 63 (2000) 024106. [4] P.Ch. Sahu, N.V. Chandra Shekar, M. Yousuf, K. Govindarajan, Phys. Rev. Lett. 78 (1997) 1054. [5] E. Enc, B. Margolin, J. Met. 9 (1957) 484. [6] B. Goldak, B. Parr, Trans. Am. Inst. Min. Metall. Pet. Eng. 221 (1961) 639. [7] N.V. Jaya, Ph.D. Thesis, Anna University, India, 1988. [8] R.S. Vennila, N.V. Jaya, Mater. Chem. Phys. 89 (2005) 85.
Synthesis and high-pressure electrical resistivity studies of Ti3Al R. Selva Vennila∗ , E. Elamurugu Porchelvi, K.M. Freny Joy, T.K. Jaya Arun, N. Victor Jaya Department of Physics, Anna University, Chennai 600025, India Received 31 August 2004; accepted 13 September 2004 Available online 30 October 2004
Abstract Titanium aluminide (Ti3 Al) has been synthesized by a powder metallurgical method. X-ray diffraction studies show the formation of a single phase with hexagonal structure. Electrical resistivity studies were carried out by a four-probe technique both at high pressure and high temperature using a Bridgman Opposed Anvil High Pressure Device (OAHPD). The sample was studied up to a pressure and temperature of 10 GPa and 250 ◦ C, respectively. The electrical resistivity is found to decrease with increasing pressure. The temperature effect causes an upward shift in the electrical resistivity in the range of pressure considered. © 2004 Elsevier B.V. All rights reserved. Keywords: Intermetallics; Powder metallurgy; X-ray diffraction; High temperature alloys; Strain; High-pressure
1. Introduction Ordered intermetallic compounds based on aluminides such as Ti3 Al, TiAl, Ni3 Al are emerging as attractive materials for high-temperature applications. They are commonly utilized in aerospace, space vehicles and in the petroleum and chemical industries. In particular, the phase Ti3 Al (Ni3 Sn-type structure) exhibits low density and good high-temperature strength and was therefore chosen for the development of aircraft engine materials [1]. In addition, their application to nuclear materials has been recently noticed because the alloys have good devoted temperature strength, corrosion resistance and low neutron induced radioactivity compared with those of conventional nuclear materials like the austenitic stainless steels. Ti3 Al-based intermetallic alloys are candidate materials for aerospace applications because of their balance of ductility at room temperature and high strength at elevated temperatures. They have been proposed as matrix alloys for intermetallic composites [2]. Experimental high-pressure studies of titanium aluminide (Ti3 Al) have been carried out under quasihydrostatic and non∗
Corresponding author. Tel.: +91 44 2220 3148; fax: +91 44 2235 2161. E-mail address: [email protected] (R.S. Vennila).
0925-8388/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2004.09.004
hydrostatic conditions up to a pressure of 25 GPa using an in situ powder X-ray diffraction technique by Dubrovinskaia et al. [3]. These authors did not observe the occurrence of a phase transition up to 25 GPa. The only changes in the diffraction patterns of Ti3 Al on compression are the disappearance of some superlattice reflections, (1 0 1), (1 1 0) and (2 1 1) and (0 0 2), (2 0 2), at pressures above 20 GPa. Furthermore, the studies showed a decrease in the a and c unit cell parameters with increasing Al content, which are in concord with the smaller radius of Al when compared to Ti. To illustrate the reliability of the combined experimental and theoretical approach (by modern ab initio calculations), the unit cell parameters, molar volumes and other parameters such as bulk modulus and its derivatives are available in the literature and can be reviewed for a comparison [5,6]. Sahu et al. fitted the experimental equation of state for Ti3 Al and the obtained parameters show good agreement with the theoretical results [4]. In their study, Dubrovinskaia et al. reported that experimentally nor theoretically there is not any pressure-induced structural phase transition in the pressure range studied. It was reported that the phase transition from the DO19 (Ni3 Sn type) structure of Ti3 Al to the DO24 (Ni3 Ti type) structure, which was reported earlier by Sahu et al. was not confirmed. In this present study, the electrical resis-
R.S. Vennila et al. / Journal of Alloys and Compounds 392 (2005) 24–26
25
Fig. 1. Powder XRD pattern of Ti3 Al.
tivity of Ti3 Al is measured at various pressures and temperatures in order to explore the possibility of a phase transition.
2. Experimental details
Fig. 2. Pressure vs. resistivity of Ti3 Al at room temperature.
2.1. Synthesis of Ti3 Al Ti3 Al was synthesized by a powder metallurgical method. High purity fine powders of metallic aluminum and titanium were mixed well in the ratio 1:8. The pellets of the mixture were kept in an alumina crucible and heated in the furnace at a temperature of 1100 ◦ C for 10 h. The samples were annealed at a temperature of 700 ◦ C for 3 h and finally cooled to room temperature. An X-ray powder diffraction pattern was recorded using Cu K␣ radiation. The powder X-ray diffraction pattern (Fig. 1) shows the formation of single-phase Ti3 Al. The X-ray pattern was indexed and the crystal structure was found to be hexagonal.
perimental arrangements were discussed elsewhere [8]. The measurements were carried out for various pressures up to 10 GPa at 100, 200 and 250 ◦ C. Plots of the electrical resistivity versus pressure at various temperatures are shown in Fig. 3.
2.2. High-pressure electrical resistivity set-up The high-pressure electrical resistivity measurement was done using a Bridgman opposed anvil apparatus [7]. The cell assembly consists of the pressure medium, gasket and sample placed in between a pair of tapered cylinders. Pyrophyllite of thickness 0.5 mm, inner diameter of 2 mm and outer diameter 10 mm was used as the gasket material. Steatite was used for hydrostatic pressure generation over the sample. Bismuth was used as the pressure calibrant. Electrical contact on the sample was made using copper wires of 0.1 mm diameter. The electrical resistivity measurement was done using a four-probe technique. Trivial measurements were carried out for loading and unloading pressures. The variation of the electrical resistivity measured at various pressures up to 10 GPa at room temperature is shown in Fig. 2. High-temperature measurements up to 250 ◦ C were done using a heating coil arrangement. The details of the ex-
Fig. 3. Pressure vs. resistivity of Ti3 Al at different temperatures.
26
R.S. Vennila et al. / Journal of Alloys and Compounds 392 (2005) 24–26
3. Results and discussion
Acknowledgement
The X-ray diffraction pattern of Ti3 Al shows the formation of single phase. It is found to be crystallised in a hexagonal structure with the lattice parameters a = 5.58(1) and c = 4.57(1). The lattice parameters obtained are in good agreement with literature data [3]. The electrical resistivity behaviour with pressure is shown in Fig. 2. It is observed that at room temperature as the pressure increases, the resistivity decreases rapidly up to around 1.1 GPa, above which the resistivity is nearly constant up to 10 GPa. It can be seen from Fig. 2, the unloading curve show slightly lower values of ρ when compared to the loading curve. From this we can conclude that the decrease in ρ is mainly caused as an effect of pressure on the sample. The effect of temperature on the sample causes an upward shift of the electrical resistivity behaviour and is shown in Fig. 3. Thus, Ti3 Al shows improved electrical properties under pressure and temperature up to a maximum of 10 GPa and 250 ◦ C, respectively. The electrical resistivity studies show the absence of a phase transition in the pressure range studied up to a maximum temperature of 250 ◦ C.
The authors thank University Grants Commission and Department of Science and Technology, Govt. of India, for financial support.
References [1] F. Habashi (Ed.), Alloys: Preparation, Properties, Applications, Wiley, Weinheim, 1998. [2] W. Cai, M.S. Thesis, University of Virginia, 1993. [3] N.A. Dubrovinskaia, M. Vennstrom, I.A. Abrikosov, R. Ahuja, P. Ravindran, Y. Andersson, O. Eriksson, V. Dmitriev, L.S. Dubrovinsky, Phys. Rev. B 63 (2000) 024106. [4] P.Ch. Sahu, N.V. Chandra Shekar, M. Yousuf, K. Govindarajan, Phys. Rev. Lett. 78 (1997) 1054. [5] E. Enc, B. Margolin, J. Met. 9 (1957) 484. [6] B. Goldak, B. Parr, Trans. Am. Inst. Min. Metall. Pet. Eng. 221 (1961) 639. [7] N.V. Jaya, Ph.D. Thesis, Anna University, India, 1988. [8] R.S. Vennila, N.V. Jaya, Mater. Chem. Phys. 89 (2005) 85.