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Synthesis of Ti3Si0.8Al0.4C1.8 solid solution from Ti–Si–Al–C powder mixture
Materials Letters 61 (2007) 3575 – 3577 www.elsevier.com/locate/matlet
Synthesis of Ti3Si0.8Al0.4C1.8 solid solution from Ti–Si–Al–C powder mixture Cuiwei Li ⁎, Hongxiang Zhai, Yan Ding, Yang Zhou, Shibo Li, Zhili Zhang The School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, People's Republic of China Received 13 October 2006; accepted 25 November 2006 Available online 14 December 2006
Abstract In this study, free Ti/Si/Al/C powder mixtures with molar ratios of 3:0.8:0.4:1.8 were heated in argon with various schedules, in order to reveal the possibility for the synthesis of high Ti3Si0.8Al0.4C1.8 content powder. X-ray diffraction (XRD) was used for the evaluation of phase identities of the powder after different treatments. Scanning electron microscopy (SEM) was used to observe the morphology of the Ti3Si0.8Al0.4C1.8 solid solution. XRD results showed that predominantly single phase samples of Ti3Si0.8Al0.4C1.8 were prepared after heating at 1450 °C for 5 min in argon and the lattice parameters of Ti3Si0.8Al0.4C1.8 lay between those of Ti3SiC2 and Ti3AlC2. SEM observation showed that the grains of Ti3Si0.8Al0.4C1.8 solid solution exhibited a lamellar shape, which is a characteristic feature of Ti3SiC2 and Ti3AlC2. © 2006 Elsevier B.V. All rights reserved. Keywords: Solid solution; Ti3SiC2; Lattice parameter; Heat treatment; Microstructure
1. Introduction The ternary compounds, with the formula Mn + 1AXn, where n = 1 to 3, M is an early transition metal, A is an A-group (mostly IIIA and IVA) element, and X is either C and/or N, are studied widely because of their astonishing properties [1–3]. The best properties mainly derive from the special structure of the compounds. As a class, the compounds are best described as polycrystalline nanolaminates. In these near closed packed layers of transition metal carbide and/or nitride layers are interleaved with layers of pure A-group elements. In the M3AX2 phases, every fourth layer is an A-group element. Among the family of the layered ternary compounds Mn + 1AXn, only three are M3AX2: Ti3SiC2, Ti3AlC2 and Ti3GeC2 [1]. Ti3SiC2 was first synthesized by Jeitschko and Nowotny as far back as 1967 [4], while Ti3AlC2 was first synthesized by Pietzka and Schuster in the early 90s [5]. Ti3SiC2 and Ti3AlC2 are isostructure compounds, in which two edgy-shared layers of Ti6C octahedral groups were linked by two-dimensional closed packed Si or Al atomic layers. Both Ti3SiC2 and Ti3AlC2 have astonishing properties. For Ti3SiC2, it has the density of Ti, but is roughly three times as stiff and yet is most readily machinable ⁎ Corresponding author. Tel./fax: +86 10 51685554. E-mail address: [email protected] (C. Li). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.11.126
(even by manual hacksaw). It is stable at inert atmospheres to temperatures up to 2200 °C. It is fatigue and thermal shock resistant, as well as relatively tough. It is more than twice as conductive as Ti metal, both electrically and thermally. For Ti3AlC2, it is readily machinable and relatively soft (Vickers hardness 3.5 GPa). Its electrical conductivity at room temperature is identical to that of Ti3SiC2. Compared to the comprehensive knowledge on the properties of stoichiometric layered Ti3SiC2 and Ti3AlC2, less information is available for the solid solution counterparts. Zhu [6] and Zhou [7] reported that 10 at.% Al could substitute Si to form Ti3Si0.9Al0.1C2 solid solution with improved oxidation resistance. Wang [8] demonstrated that the solid solution with the composition of Ti3Si0.75Al0.25C2 was stable through the first principles calculations. As far as we are aware this is the first report on the synthesis and characteristics of Ti3Si0.8Al0.4C1.8 solid solution. The purpose of this paper is to report on the processing parameters for synthesizing predominantly single phase Ti3Si0.8Al0.4C1.8 solid solution from Ti–Si–Al–C powder mixture. 2. Experimental details Powders of Ti (200 mesh in average size, 99.9% in purity), Si (200 mesh in average size, 99.9% in purity), Al (200 mesh in
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average size, 99.9% in purity) and graphite (200 mesh in average size, 99.9% in purity) were used as starting powders in the present study. They were blended in molar composition of 3Ti/1.2Si/1.8C, 3Ti/0.8Si/0.4Al/1.8C and 3Ti/1.2Al/1.8C to synthesize Ti3SiC2, Ti3Si0.8Al0.4C1.8 and Ti3AlC2 respectively. The mixtures were ball milled in ethanol for 12 h and agate balls were used. The obtained slurry was dried and then uniaxially die pressed under 10 MPa into compact with dimensions of ∅ 10 mm. The green compact was placed into a graphite crucible and sintering was conducted in argon with four conditions: (1) at 1400 °C for 5 min, (2) at 1450 °C for 5 min, (3) at 1500 °C for 5 min, and (4) at 1450 °C for 30 min. In order to investigate the change of lattice parameters, pure Ti3SiC2 and Ti3AlC2 were synthesized at 1500 °C and 1400 °C for 5 min in Ar respectively. The sintered compacts were pulverized and grind into powders for X-ray diffraction (RIGAKU D/MAXØB) with Cu Kα radiation at 40 kV and 30 mA. Scans were made with Cu Kα radiation (40 kV and 30 mA) at a rate of 4° (2θ) min− 1 . Pure chromium powder was added as an internal standard. Phases were identified according to the data in the ICCD Powder Diffraction File, card no. 40-1132 for Ti3SiC2, and no. 73-0472 for TiC. Ti3AlC2 was identified according to powder data in Ref. [9]. The fracture surface of a sample was microstructurally characterized using a scanning electronic microscope (JSM-6460). 3. Results and discussion
Fig. 2. This figure shows the indexed XRD pattern of Ti3Si0.8Al0.4C1.8 compared with those of Ti3SiC2 and Ti3AlC2.
1450 °C and 5 min may be proper for the synthesis of predominately single phase Ti3Si0.8Al0.4C1.8. Fig. 2 shows the XRD pattern of 3Ti/0.8Si/0.4Al/1.8C powder mixture after heating at 1450 °C for 5 min in argon compared with those of TI3SIC2 and TI3AIC2. From Fig. 2, no impurity phases like TiC, SiC and Al4C3 were detected within the resolution of the XRD for Ti3SiC2 and Ti3AlC2. The main peaks of Ti3Si0.8Al0.4C1.8 were in between those of Ti3SiC2 and Ti3AlC2, which could be indexed using the structure of Ti3SiC2 or Ti3AlC2. Thus, Ti3Si0.8Al0.4C1.8 was a solid solution between Ti3SiC2 and Ti3AlC2, which is consistent with the results of Wang [8] who indicated that Ti3Si1 − xAlxC2 solid solutions were stable through first ab initio calculations. A careful analysis of XRD patterns showed that all peaks of the Ti3Si0.8Al0.4C1.8 solid solution shifted to the low angle
Fig. 1 shows the XRD patterns of 3Ti/0.8Si/0.4Al/1.8C powder mixture after heating at the four conditions. Except those peaks from Ti3Si0.8Al0.4C1.8, peaks of TiC and Ti5Si3 were also detected in the samples after heat treatment at 1400 °C. After heating at 1450 °C, the peaks of Ti5Si3 were too weak to be detected, indicating its low content in the synthesized powder. In this process, the diffraction line intensities of TiC decreased greatly, indicating its relatively low content. After heating at 1500 °C, the diffraction line intensities of TiC increased again, indicating that the content of TiC increased again as temperature increased. After heating at 1450 °C for 30 min, the diffraction line intensities of TiC increased greatly and the peaks of Ti3Si0.8Al0.4C1.8 were obviously broadened, which indicated that Ti3Si0.8Al0.4C1.8 began to decompose after a long holding time. So
Fig. 1. XRD patterns of 3Ti/0.8Si/0.4Al/1.8C powder mixture after heating at 1400–1500 °C for 5 min and at 1450 °C for 30 min in argon.
Fig. 3. Micrographs for 3Ti/0.8Si/0.4Al/1.8C powder mixture after heating at 1450 °C for 5 min in argon.
C. Li et al. / Materials Letters 61 (2007) 3575–3577
direction compared with those of Ti3SiC2, but to high angle contrarily compared to the peaks of Ti3AlC2. The main peak of (104) changed from 2θ = 39.63° for pure Ti3SiC2 and 2θ = 38.79° for pure Ti3AlC2 to 2θ = 39.45° for Ti3Si0.8Al0.4C1.8 solid solution. The shift of peaks indicates the change of lattice parameters. According to the XRD diffraction data, lattice parameters were calculated according to the following equation: 1 4 h2 þ hk þ k 2 l2 þ 2: ¼ ð1Þ 2 2 a c d 3 Where h, k and l are Miller indices, d is interplanar distance, a and c are the lattice parameters. The lattice parameters of Ti3SiC2 and Ti3AlC2 samples were calculated to be a = 0.3068 nm, c = 1.7662 nm and a = 0.3076 nm, c = 1.8560 nm, respectively, which agreed with JCPDS 40-1132 for Ti3SiC2 and Ref. [9] for Ti3AlC2 well. For Ti3Si0.8Al0.4C1.8 solid solution, the calculated values of a = 0.3069 nm and c = 1.7710 nm lay in between those of Ti3SiC2 and Ti3AlC2. The overall morphology of the predominantly single phase Ti3Si0.8Al0.4C1.8 solid solution is shown in Fig. 3. The lamellar shape of Ti3Si0.8Al0.4C1.8 solid solution is clearly seen from Fig. 3(a), which is a characteristic feature of Ti3SiC2 and Ti3AlC2. A layer-bylayer growth feature is clearly shown in Fig. 3(b). This feature is a typical spiral growth, in which screw dislocations provide a continuous source of new steps. For Ti3SiC2, the top face is (0001), which is the only closed packed face or singular interface. Hence, the spiral layers arise from dislocation outcrops on the (0001) growing face.
4. Conclusions Predominantly single phase Ti3Si0.8Al0.4C1.8 solid solution was synthesized after heating at 1450 °C for a shorter time of 5 min in argon using Ti–Si–Al–C powder as raw material. The
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lattice parameters of Ti3Si0.8Al0.4C1.8 solid solution lie between those of Ti3SiC2 and Ti3AlC2. The grains of Ti3Si0.8Al0.4C1.8 solid solution exhibit a lamellar shape, which is a characteristic feature of Ti3SiC2 and Ti3AlC2. Acknowledgements This work was supported by the National Science Foundation of China (NSFC) under Grant No. 50472045, and the Science Developing Foundation of Beijing Jiaotong University. References [1] M.W. Barsoum, Prog. Solid State Chem. 28 (2000) 201. [2] M.W. Barsoum, T. El-Raghy, Metal. Mater. Trans. 30A (1999) 363. [3] M.W. Barsoum, L. Farber, T. El-Raghy, Metall. Mater. Trans. 30A (1999) 1727. [4] W. Jeitschko, H. Nowotny, Monatsh. Chem. 98 (1967) 1953. [5] M.A. Pietzka, J.C. Schuster, J. Phase Equilib. 15 (1994) 392. [6] B.C. Mei, X.W. Xu, J.Q. Zhu, J. Liu, Rare Met. Mater. Eng. 34 (2005) 895–898. [7] H.B. Zhang, Y.C. Zhou, Y.W. Bao, M.S. Li, Acta Mater. 52 (2004) 3631. [8] J.Y. Wang, Y.C. Zhou, J. Phys., Condens. Matter 15 (2003) 5959. [9] N.V. Tzenov, M.W. Barsoum, J. Am. Ceram. Soc. 83 (2000) 825.
Synthesis of Ti3Si0.8Al0.4C1.8 solid solution from Ti–Si–Al–C powder mixture Cuiwei Li ⁎, Hongxiang Zhai, Yan Ding, Yang Zhou, Shibo Li, Zhili Zhang The School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, People's Republic of China Received 13 October 2006; accepted 25 November 2006 Available online 14 December 2006
Abstract In this study, free Ti/Si/Al/C powder mixtures with molar ratios of 3:0.8:0.4:1.8 were heated in argon with various schedules, in order to reveal the possibility for the synthesis of high Ti3Si0.8Al0.4C1.8 content powder. X-ray diffraction (XRD) was used for the evaluation of phase identities of the powder after different treatments. Scanning electron microscopy (SEM) was used to observe the morphology of the Ti3Si0.8Al0.4C1.8 solid solution. XRD results showed that predominantly single phase samples of Ti3Si0.8Al0.4C1.8 were prepared after heating at 1450 °C for 5 min in argon and the lattice parameters of Ti3Si0.8Al0.4C1.8 lay between those of Ti3SiC2 and Ti3AlC2. SEM observation showed that the grains of Ti3Si0.8Al0.4C1.8 solid solution exhibited a lamellar shape, which is a characteristic feature of Ti3SiC2 and Ti3AlC2. © 2006 Elsevier B.V. All rights reserved. Keywords: Solid solution; Ti3SiC2; Lattice parameter; Heat treatment; Microstructure
1. Introduction The ternary compounds, with the formula Mn + 1AXn, where n = 1 to 3, M is an early transition metal, A is an A-group (mostly IIIA and IVA) element, and X is either C and/or N, are studied widely because of their astonishing properties [1–3]. The best properties mainly derive from the special structure of the compounds. As a class, the compounds are best described as polycrystalline nanolaminates. In these near closed packed layers of transition metal carbide and/or nitride layers are interleaved with layers of pure A-group elements. In the M3AX2 phases, every fourth layer is an A-group element. Among the family of the layered ternary compounds Mn + 1AXn, only three are M3AX2: Ti3SiC2, Ti3AlC2 and Ti3GeC2 [1]. Ti3SiC2 was first synthesized by Jeitschko and Nowotny as far back as 1967 [4], while Ti3AlC2 was first synthesized by Pietzka and Schuster in the early 90s [5]. Ti3SiC2 and Ti3AlC2 are isostructure compounds, in which two edgy-shared layers of Ti6C octahedral groups were linked by two-dimensional closed packed Si or Al atomic layers. Both Ti3SiC2 and Ti3AlC2 have astonishing properties. For Ti3SiC2, it has the density of Ti, but is roughly three times as stiff and yet is most readily machinable ⁎ Corresponding author. Tel./fax: +86 10 51685554. E-mail address: [email protected] (C. Li). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.11.126
(even by manual hacksaw). It is stable at inert atmospheres to temperatures up to 2200 °C. It is fatigue and thermal shock resistant, as well as relatively tough. It is more than twice as conductive as Ti metal, both electrically and thermally. For Ti3AlC2, it is readily machinable and relatively soft (Vickers hardness 3.5 GPa). Its electrical conductivity at room temperature is identical to that of Ti3SiC2. Compared to the comprehensive knowledge on the properties of stoichiometric layered Ti3SiC2 and Ti3AlC2, less information is available for the solid solution counterparts. Zhu [6] and Zhou [7] reported that 10 at.% Al could substitute Si to form Ti3Si0.9Al0.1C2 solid solution with improved oxidation resistance. Wang [8] demonstrated that the solid solution with the composition of Ti3Si0.75Al0.25C2 was stable through the first principles calculations. As far as we are aware this is the first report on the synthesis and characteristics of Ti3Si0.8Al0.4C1.8 solid solution. The purpose of this paper is to report on the processing parameters for synthesizing predominantly single phase Ti3Si0.8Al0.4C1.8 solid solution from Ti–Si–Al–C powder mixture. 2. Experimental details Powders of Ti (200 mesh in average size, 99.9% in purity), Si (200 mesh in average size, 99.9% in purity), Al (200 mesh in
3576
C. Li et al. / Materials Letters 61 (2007) 3575–3577
average size, 99.9% in purity) and graphite (200 mesh in average size, 99.9% in purity) were used as starting powders in the present study. They were blended in molar composition of 3Ti/1.2Si/1.8C, 3Ti/0.8Si/0.4Al/1.8C and 3Ti/1.2Al/1.8C to synthesize Ti3SiC2, Ti3Si0.8Al0.4C1.8 and Ti3AlC2 respectively. The mixtures were ball milled in ethanol for 12 h and agate balls were used. The obtained slurry was dried and then uniaxially die pressed under 10 MPa into compact with dimensions of ∅ 10 mm. The green compact was placed into a graphite crucible and sintering was conducted in argon with four conditions: (1) at 1400 °C for 5 min, (2) at 1450 °C for 5 min, (3) at 1500 °C for 5 min, and (4) at 1450 °C for 30 min. In order to investigate the change of lattice parameters, pure Ti3SiC2 and Ti3AlC2 were synthesized at 1500 °C and 1400 °C for 5 min in Ar respectively. The sintered compacts were pulverized and grind into powders for X-ray diffraction (RIGAKU D/MAXØB) with Cu Kα radiation at 40 kV and 30 mA. Scans were made with Cu Kα radiation (40 kV and 30 mA) at a rate of 4° (2θ) min− 1 . Pure chromium powder was added as an internal standard. Phases were identified according to the data in the ICCD Powder Diffraction File, card no. 40-1132 for Ti3SiC2, and no. 73-0472 for TiC. Ti3AlC2 was identified according to powder data in Ref. [9]. The fracture surface of a sample was microstructurally characterized using a scanning electronic microscope (JSM-6460). 3. Results and discussion
Fig. 2. This figure shows the indexed XRD pattern of Ti3Si0.8Al0.4C1.8 compared with those of Ti3SiC2 and Ti3AlC2.
1450 °C and 5 min may be proper for the synthesis of predominately single phase Ti3Si0.8Al0.4C1.8. Fig. 2 shows the XRD pattern of 3Ti/0.8Si/0.4Al/1.8C powder mixture after heating at 1450 °C for 5 min in argon compared with those of TI3SIC2 and TI3AIC2. From Fig. 2, no impurity phases like TiC, SiC and Al4C3 were detected within the resolution of the XRD for Ti3SiC2 and Ti3AlC2. The main peaks of Ti3Si0.8Al0.4C1.8 were in between those of Ti3SiC2 and Ti3AlC2, which could be indexed using the structure of Ti3SiC2 or Ti3AlC2. Thus, Ti3Si0.8Al0.4C1.8 was a solid solution between Ti3SiC2 and Ti3AlC2, which is consistent with the results of Wang [8] who indicated that Ti3Si1 − xAlxC2 solid solutions were stable through first ab initio calculations. A careful analysis of XRD patterns showed that all peaks of the Ti3Si0.8Al0.4C1.8 solid solution shifted to the low angle
Fig. 1 shows the XRD patterns of 3Ti/0.8Si/0.4Al/1.8C powder mixture after heating at the four conditions. Except those peaks from Ti3Si0.8Al0.4C1.8, peaks of TiC and Ti5Si3 were also detected in the samples after heat treatment at 1400 °C. After heating at 1450 °C, the peaks of Ti5Si3 were too weak to be detected, indicating its low content in the synthesized powder. In this process, the diffraction line intensities of TiC decreased greatly, indicating its relatively low content. After heating at 1500 °C, the diffraction line intensities of TiC increased again, indicating that the content of TiC increased again as temperature increased. After heating at 1450 °C for 30 min, the diffraction line intensities of TiC increased greatly and the peaks of Ti3Si0.8Al0.4C1.8 were obviously broadened, which indicated that Ti3Si0.8Al0.4C1.8 began to decompose after a long holding time. So
Fig. 1. XRD patterns of 3Ti/0.8Si/0.4Al/1.8C powder mixture after heating at 1400–1500 °C for 5 min and at 1450 °C for 30 min in argon.
Fig. 3. Micrographs for 3Ti/0.8Si/0.4Al/1.8C powder mixture after heating at 1450 °C for 5 min in argon.
C. Li et al. / Materials Letters 61 (2007) 3575–3577
direction compared with those of Ti3SiC2, but to high angle contrarily compared to the peaks of Ti3AlC2. The main peak of (104) changed from 2θ = 39.63° for pure Ti3SiC2 and 2θ = 38.79° for pure Ti3AlC2 to 2θ = 39.45° for Ti3Si0.8Al0.4C1.8 solid solution. The shift of peaks indicates the change of lattice parameters. According to the XRD diffraction data, lattice parameters were calculated according to the following equation: 1 4 h2 þ hk þ k 2 l2 þ 2: ¼ ð1Þ 2 2 a c d 3 Where h, k and l are Miller indices, d is interplanar distance, a and c are the lattice parameters. The lattice parameters of Ti3SiC2 and Ti3AlC2 samples were calculated to be a = 0.3068 nm, c = 1.7662 nm and a = 0.3076 nm, c = 1.8560 nm, respectively, which agreed with JCPDS 40-1132 for Ti3SiC2 and Ref. [9] for Ti3AlC2 well. For Ti3Si0.8Al0.4C1.8 solid solution, the calculated values of a = 0.3069 nm and c = 1.7710 nm lay in between those of Ti3SiC2 and Ti3AlC2. The overall morphology of the predominantly single phase Ti3Si0.8Al0.4C1.8 solid solution is shown in Fig. 3. The lamellar shape of Ti3Si0.8Al0.4C1.8 solid solution is clearly seen from Fig. 3(a), which is a characteristic feature of Ti3SiC2 and Ti3AlC2. A layer-bylayer growth feature is clearly shown in Fig. 3(b). This feature is a typical spiral growth, in which screw dislocations provide a continuous source of new steps. For Ti3SiC2, the top face is (0001), which is the only closed packed face or singular interface. Hence, the spiral layers arise from dislocation outcrops on the (0001) growing face.
4. Conclusions Predominantly single phase Ti3Si0.8Al0.4C1.8 solid solution was synthesized after heating at 1450 °C for a shorter time of 5 min in argon using Ti–Si–Al–C powder as raw material. The
3577
lattice parameters of Ti3Si0.8Al0.4C1.8 solid solution lie between those of Ti3SiC2 and Ti3AlC2. The grains of Ti3Si0.8Al0.4C1.8 solid solution exhibit a lamellar shape, which is a characteristic feature of Ti3SiC2 and Ti3AlC2. Acknowledgements This work was supported by the National Science Foundation of China (NSFC) under Grant No. 50472045, and the Science Developing Foundation of Beijing Jiaotong University. References [1] M.W. Barsoum, Prog. Solid State Chem. 28 (2000) 201. [2] M.W. Barsoum, T. El-Raghy, Metal. Mater. Trans. 30A (1999) 363. [3] M.W. Barsoum, L. Farber, T. El-Raghy, Metall. Mater. Trans. 30A (1999) 1727. [4] W. Jeitschko, H. Nowotny, Monatsh. Chem. 98 (1967) 1953. [5] M.A. Pietzka, J.C. Schuster, J. Phase Equilib. 15 (1994) 392. [6] B.C. Mei, X.W. Xu, J.Q. Zhu, J. Liu, Rare Met. Mater. Eng. 34 (2005) 895–898. [7] H.B. Zhang, Y.C. Zhou, Y.W. Bao, M.S. Li, Acta Mater. 52 (2004) 3631. [8] J.Y. Wang, Y.C. Zhou, J. Phys., Condens. Matter 15 (2003) 5959. [9] N.V. Tzenov, M.W. Barsoum, J. Am. Ceram. Soc. 83 (2000) 825.