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Surface plasma chromized burn-resistant titanium alloy
Surface & Coatings Technology 201 (2007) 4884 – 4887 www.elsevier.com/locate/surfcoat
Surface plasma chromized burn-resistant titanium alloy Pingze Zhang a , Zhong Xu a,b,⁎, Gaohui Zhang b , Zhiyong He b a
School of Material Science and Technology, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street. Nanjing, 210016, China b Institute of Surface Engineering, Taiyuan University of Technology, 79 Yingze Str.,Taiyuan, 030024, China Available online 27 September 2006
Abstract Conventional titanium alloy may be ignited and burnt under high temperature, high pressure and high gas flow velocity conditions. In order to avoid this problem, a new kind of burn-resistant titanium alloy—double glow plasma surface alloying burn-resistant titanium alloy has been developed. Alloying element Cr is induced into the Ti-6.5Al-0.3Mo-1.5Zr-0.25Si substrate according to double glow discharge phenomenon, Ti– Cr burn-resistant alloy layer is formed on the surface of Ti–6.5Al–0.3Mo–1.5Zr–0.25Si alloy. The depth of the surface burn-resistant alloy layer can reach to above 200 μm and alloying element concentration can reach 90%. Burn-resistant property experiments reveal that if Cr concentration is above 14% in the alloying layer, ignition and burn of titanium alloy can be effectively avoided. © 2006 Elsevier B.V. All rights reserved. PACS: 81.65.Lp; 81.15.Rs; 81.15.-z Keywords: Surface alloying; Burn-resistant titanium alloy; Plasma chromizing; Double glow plasma surface alloying
1. Introduction Titanium and its alloys have been extensively used in aeronautics and astronautics industries because of their low specific gravities, high strength, stiffness, good toughness and high corrosion resistance. However, conventional titanium alloys may be ignited and burnt under high temperature, high pressure and high gas flow velocity conditions. Titanium fire took place several times in engines [1–4]. This shortcoming limits application of titanium alloys. In order to avoid this technical problem, Ti–Cr–V, Ti–Cu–Al and Ti–Nb series burnresistant titanium alloys have been invented since 1990s. For security reason, detailed references about burn-resistant titanium alloys are lacked. From little information we can find that typical burn-resistant titanium include Alloy C (Ti–35V–15Cr), Ti–45Nb (USA) [5–7], BTT-1 (Ti–13Cu–4Al–4Mo–2Zr) (Russia) [8], recently invited Ti–25V–15Cr–2Al–0.2C (Great Britain) [9–12]] and Ti-40 (China) [13–16]. Though these alloys have obvious burn-resistant property, their limitations are also evident. Main limitation of current burn-resistant titanium ⁎ Corresponding author. School of Material Science and Technology, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street. Nanjing,210016, China. Tel.: +86 25 52112904 83132. E-mail address: [email protected] (Z. Xu). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.07.078
is lower strength-gravity ratio induced by adding large amount of heavy alloying elements into titanium alloys. In order to solve this problem, surface burn-resistant titanium alloys have been proposed in this paper. Using Double Glow Plasma Surface Alloying Technology (DG Technology). Cr element has been introduced into the surface of Ti–6.5Al–0.3Mo–1.5Zr– 0.25Si alloy and Ti–Cr burn-resistant alloy layer is formed on the surface of this conventional titanium alloy. For the surface burn-resistant titanium alloy, loads are endured by substrate and surface alloyed layer fulfills the function of burn-resistance. 2. Description of DG technology The Double Glow Plasma Surface Alloying Technology has been developed by utilizing double glow discharge phenomenon [17] to introduce metallic alloying elements into a conductive material substrate. The process is a unique hybrid plasma surface metallurgy technique, which has evolved from both ion nitriding and sputtering technique. Fig. 1 shows a simplified schematic of a typical DG surface alloying installation. In a vacuum chamber there are three electrodes: the anode and negatively charged cathode (work piece) and source electrode. The source electrode is made of the desired alloying elements which are introduced into the surface of the work piece to form a surface alloy layer. The work piece
P. Zhang et al. / Surface & Coatings Technology 201 (2007) 4884–4887
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Fig. 1. Simple schematics of double glow plasma surface alloying installation.
is supported on a hearth support inside a double walled, water cooled vacuum chamber, connected to a vacuum pump system and a gas supply. The tank is evacuated to a pressure of about 5 × 10− 2 Pa and then filled with argon to 20–50 Pa. Two high voltage DC power supplies are used for generation of glow discharges. One is connected between anode and cathode and another between anode and source electrode. With the two power supplies turned on both cathode and source electrode are surrounded by glow discharge. One glow discharge heats the work piece and second glow strikes the source electrode. The desired alloying elements sputtered from the source electrode by bombardment of the ions produced in second glow discharge travel and diffuse into the surface of the work piece to form a surface alloy layer on the surface of work piece. Elements such as chromium, nickel, molybdenum, tungsten, tantalum, aluminum and their combination can be utilized to produce a wide variety of alloys. The depth of the surface alloy layer may vary from several microns up to 500 μm with alloying element in a concentration of several percent to 90% or above. The negative potentials of the cathode and the source electrode can be same or not same. In the same potential operation only one power supply is needed. There are three modes of double glow discharge in the DG process operation as follows: independent discharge, hollow cathode discharge and pulse discharge. The primary parameters of the process include: pressure of argon gas, voltage of the cathode, voltage of the source electrode, distance between the substrate and the source electrode, and processing temperature [18].
Fig. 3. X-ray diffraction pattern of chromized layer.
between 800–1000 °C for various times (1–6 h), at 20–50 Pa total pressure under pure argon plasma. The negative voltage of the cathode is distributed from 300 V to 600 V and that of the source electrode from 800 V to 1300 V. Orthogonal experiments indicate that optimized technique parameters are: negative voltage is 450 V, source electrode voltage is 950 V, working argon gas pressure is 25 Pa, and temperature is 890 °C. Working time can be selected according to the required thickness of alloyed layer, alloyed layer can reach to 50 μm in 4 h. Compositions and distributions of the alloying elements in the surface alloy layers produced by DG technology are analyzed by GDS (Glow Discharge Spectroscopy). 3.1. Microstructure and concentration The microstructure along case depth in the alloyed layer is illustrated in Fig. 2. The outer layer are deposition layer made of
3. Experiments and results Ti–6.5Al–0.3Mo–1.5Zr–0.25Si is selected as an experimental substrate material. It was DG technology alloyed
Fig. 2. Microstructure characteristics along case depth 1. Deposition layer(Cr) 2. Compound layer (Cr2Ti) 3. Diffusion layer 4. Substrate.
Fig. 4. Microstructure of Ti–6.5Al–0.3Mo–1.5Zr–0.25Si alloy after surface chromizing.
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P. Zhang et al. / Surface & Coatings Technology 201 (2007) 4884–4887
Fig. 7. Schematic diagram of the burn resistance testing device.
3.3. Burn-resistance experiments
Fig. 5. Chromium concentration in the chromized layer.
Cr which width is 1–2 μm, beneath the deposition layer are compound layers, X-ray diffraction analysis (see Fig. 3) and phase diagram analysis show that it consists of α + β substrate microstructure plus little dispersed Cr2Ti intermetallic. Most of Cr elements are solutioned to β phase, little occur as Cr2Ti intermetallic. Under the compound layer is Cr diffusion layer in substrate. Typical microstructure of cross section is shown in Fig. 4. Fig. 5 shows the distribution of chromium in the Cr-alloyed layer. Reference document [16] indicates that, when the Cr concentration reach to 14%, Ti–Cr binary alloy can be act as burn-resistant titanium alloy. 3.2. Hardness Gradually distributed micro-hardness in alloyed layer is shown in Fig. 6. On the surface it reaches to 600 (Hv0.5). In whole the alloyed layer hardness is above that in substrate. Solutioned alloying elements increase the hardness in alloyed layer.
Burn-resistance experiments are performed using self-made testing device, its schematics is shown in Fig. 7. Highly rotated cone-shaped sample made by Ti–6Al–4V alloy frictionizes with round sample which is surface alloyed. High-pressure air is heated to 600 °C by furnace and flows to samples. In high speed, high temperature air condition and wear condition, burn phenomena don't occur in all samples which Cr concentration is above 14%. Until their alloyed layer is worn off. When burnresistant alloying layer is destroyed, the samples ignite and burn swiftly. The experiments show that if the alloyed layer on the surface of conventional titanium alloy has necessary thickness and alloying element concentrations, it can fulfill the burnresistant function. 4. Summary Burn-resistant titanium alloys have been successfully created by the DG plasma surface alloying technology upon the surface of conventional titanium alloys. This unique technology is a very powerful means of transforming the ordinary material surface into an exotic alloy layer. The surface alloy produced by this process is a gradient material. Composition in the alloyed surface layer gradually changes in the depth direction of the substrate. Therefore, there exists no distinct boundary between the surface alloy and matrix and risk of delamination is greatly reduced. Main advantage of the surface burn-resistant titanium alloys is that loads are endured by substrate and surface alloyed layer fulfills the function of burn-resistance. Acknowledgements The authors acknowledge the financial support of the National Science Foundation of China (NSFC). (Grant Number 50271045) References
Fig. 6. Micro-hardness distribution along the cross section.
[1] Mohan V. Gunaji, Sircar Subhasish, Harold D. Beeson, Proceedings of the Symposium on Flammability and Sensitivity of Materials in OxygenEnriched Atmospheres, Denver, USA, 1995. [2] Wilson D. Bruce, Joel M. Stoltzfus, Proceedings of the 1997 8th International Symposium on Flammability and Sensitivity of Materials in Oxygen-Enriched Environments, San Diego, USA, 1997. [3] V.I. Bolobov, Combust. Explos. Shock Waves 38 (2002) 635. [4] V. Rosenband, Combust. Flame 137 (2004) 366.
P. Zhang et al. / Surface & Coatings Technology 201 (2007) 4884–4887 [5] UK Patent Application 2,238,057,1987. [6] D. Eylon, J. Mater. 6 (1994) 14. [7] D.W. Anderson, A.F. Condliff, International Conference on Titanium Products and Applications,Titanium Development Association, 1994, p. 91. [8] J.O. Hansen, D. Novotnak, M.F. Welter, J.R. Wood, Titanium' 95: Science and technology, 1995, p. 675. [9] Y.G. Li, P.A. Blenkinsop, M.H. Loretto, D. Rugg, W. Voice, Acta Mater. 47 (1999) 2889. [10] Y.G. Li, M.H. Loretto, D. Rugg, W. Voice, Acta Mater. 49 (2001) 3011. [11] X. Wu, R. Sharman, J. Mei, W. Voice, Mater. Des. 23 (2002) 239. [12] X. Wu, R. Sharman, J. Mei, W. Voice, Mater. Des. 25 (2004) 103. [13] Yongqing Zhao, Lian Zhou, Ju Deng, J. Alloys Compd. 284 (1999) 190.
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[14] K.Y. Zhu, Y.Q. Zhhao, H.L. Qu, Z.L. Wu, X.M. Zhao, J. Mater. Sci. 35 (2000) 5609. [15] Y.Q. Zhao, W.L. Wu, X.D. Ma, et al., Mater. Sci. Eng., A Struct. Mater.: Prop. Microstruct. Process. 373 (2004) 315. [16] Y.Q. Zhao, H.L. Qu, M.M. Wang, H. Wu, K.Y. Zhu, J. Alloys Compd. 407 (2006) 118. [17] Zhong Xu, US Patent 4,520,268 and 4,731,539, UK Patent 2,150,602, Austria Patent 580,734, Canada Patent 1,212,486, Sweden Patent 8500364-8. [18] Zhong Xu, Yuan Gao, Zhiyong He, Zaifeng Xu, Yongan Su, J. Adv. Mater. 34 (2002) 32.
Surface plasma chromized burn-resistant titanium alloy Pingze Zhang a , Zhong Xu a,b,⁎, Gaohui Zhang b , Zhiyong He b a
School of Material Science and Technology, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street. Nanjing, 210016, China b Institute of Surface Engineering, Taiyuan University of Technology, 79 Yingze Str.,Taiyuan, 030024, China Available online 27 September 2006
Abstract Conventional titanium alloy may be ignited and burnt under high temperature, high pressure and high gas flow velocity conditions. In order to avoid this problem, a new kind of burn-resistant titanium alloy—double glow plasma surface alloying burn-resistant titanium alloy has been developed. Alloying element Cr is induced into the Ti-6.5Al-0.3Mo-1.5Zr-0.25Si substrate according to double glow discharge phenomenon, Ti– Cr burn-resistant alloy layer is formed on the surface of Ti–6.5Al–0.3Mo–1.5Zr–0.25Si alloy. The depth of the surface burn-resistant alloy layer can reach to above 200 μm and alloying element concentration can reach 90%. Burn-resistant property experiments reveal that if Cr concentration is above 14% in the alloying layer, ignition and burn of titanium alloy can be effectively avoided. © 2006 Elsevier B.V. All rights reserved. PACS: 81.65.Lp; 81.15.Rs; 81.15.-z Keywords: Surface alloying; Burn-resistant titanium alloy; Plasma chromizing; Double glow plasma surface alloying
1. Introduction Titanium and its alloys have been extensively used in aeronautics and astronautics industries because of their low specific gravities, high strength, stiffness, good toughness and high corrosion resistance. However, conventional titanium alloys may be ignited and burnt under high temperature, high pressure and high gas flow velocity conditions. Titanium fire took place several times in engines [1–4]. This shortcoming limits application of titanium alloys. In order to avoid this technical problem, Ti–Cr–V, Ti–Cu–Al and Ti–Nb series burnresistant titanium alloys have been invented since 1990s. For security reason, detailed references about burn-resistant titanium alloys are lacked. From little information we can find that typical burn-resistant titanium include Alloy C (Ti–35V–15Cr), Ti–45Nb (USA) [5–7], BTT-1 (Ti–13Cu–4Al–4Mo–2Zr) (Russia) [8], recently invited Ti–25V–15Cr–2Al–0.2C (Great Britain) [9–12]] and Ti-40 (China) [13–16]. Though these alloys have obvious burn-resistant property, their limitations are also evident. Main limitation of current burn-resistant titanium ⁎ Corresponding author. School of Material Science and Technology, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street. Nanjing,210016, China. Tel.: +86 25 52112904 83132. E-mail address: [email protected] (Z. Xu). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.07.078
is lower strength-gravity ratio induced by adding large amount of heavy alloying elements into titanium alloys. In order to solve this problem, surface burn-resistant titanium alloys have been proposed in this paper. Using Double Glow Plasma Surface Alloying Technology (DG Technology). Cr element has been introduced into the surface of Ti–6.5Al–0.3Mo–1.5Zr– 0.25Si alloy and Ti–Cr burn-resistant alloy layer is formed on the surface of this conventional titanium alloy. For the surface burn-resistant titanium alloy, loads are endured by substrate and surface alloyed layer fulfills the function of burn-resistance. 2. Description of DG technology The Double Glow Plasma Surface Alloying Technology has been developed by utilizing double glow discharge phenomenon [17] to introduce metallic alloying elements into a conductive material substrate. The process is a unique hybrid plasma surface metallurgy technique, which has evolved from both ion nitriding and sputtering technique. Fig. 1 shows a simplified schematic of a typical DG surface alloying installation. In a vacuum chamber there are three electrodes: the anode and negatively charged cathode (work piece) and source electrode. The source electrode is made of the desired alloying elements which are introduced into the surface of the work piece to form a surface alloy layer. The work piece
P. Zhang et al. / Surface & Coatings Technology 201 (2007) 4884–4887
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Fig. 1. Simple schematics of double glow plasma surface alloying installation.
is supported on a hearth support inside a double walled, water cooled vacuum chamber, connected to a vacuum pump system and a gas supply. The tank is evacuated to a pressure of about 5 × 10− 2 Pa and then filled with argon to 20–50 Pa. Two high voltage DC power supplies are used for generation of glow discharges. One is connected between anode and cathode and another between anode and source electrode. With the two power supplies turned on both cathode and source electrode are surrounded by glow discharge. One glow discharge heats the work piece and second glow strikes the source electrode. The desired alloying elements sputtered from the source electrode by bombardment of the ions produced in second glow discharge travel and diffuse into the surface of the work piece to form a surface alloy layer on the surface of work piece. Elements such as chromium, nickel, molybdenum, tungsten, tantalum, aluminum and their combination can be utilized to produce a wide variety of alloys. The depth of the surface alloy layer may vary from several microns up to 500 μm with alloying element in a concentration of several percent to 90% or above. The negative potentials of the cathode and the source electrode can be same or not same. In the same potential operation only one power supply is needed. There are three modes of double glow discharge in the DG process operation as follows: independent discharge, hollow cathode discharge and pulse discharge. The primary parameters of the process include: pressure of argon gas, voltage of the cathode, voltage of the source electrode, distance between the substrate and the source electrode, and processing temperature [18].
Fig. 3. X-ray diffraction pattern of chromized layer.
between 800–1000 °C for various times (1–6 h), at 20–50 Pa total pressure under pure argon plasma. The negative voltage of the cathode is distributed from 300 V to 600 V and that of the source electrode from 800 V to 1300 V. Orthogonal experiments indicate that optimized technique parameters are: negative voltage is 450 V, source electrode voltage is 950 V, working argon gas pressure is 25 Pa, and temperature is 890 °C. Working time can be selected according to the required thickness of alloyed layer, alloyed layer can reach to 50 μm in 4 h. Compositions and distributions of the alloying elements in the surface alloy layers produced by DG technology are analyzed by GDS (Glow Discharge Spectroscopy). 3.1. Microstructure and concentration The microstructure along case depth in the alloyed layer is illustrated in Fig. 2. The outer layer are deposition layer made of
3. Experiments and results Ti–6.5Al–0.3Mo–1.5Zr–0.25Si is selected as an experimental substrate material. It was DG technology alloyed
Fig. 2. Microstructure characteristics along case depth 1. Deposition layer(Cr) 2. Compound layer (Cr2Ti) 3. Diffusion layer 4. Substrate.
Fig. 4. Microstructure of Ti–6.5Al–0.3Mo–1.5Zr–0.25Si alloy after surface chromizing.
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P. Zhang et al. / Surface & Coatings Technology 201 (2007) 4884–4887
Fig. 7. Schematic diagram of the burn resistance testing device.
3.3. Burn-resistance experiments
Fig. 5. Chromium concentration in the chromized layer.
Cr which width is 1–2 μm, beneath the deposition layer are compound layers, X-ray diffraction analysis (see Fig. 3) and phase diagram analysis show that it consists of α + β substrate microstructure plus little dispersed Cr2Ti intermetallic. Most of Cr elements are solutioned to β phase, little occur as Cr2Ti intermetallic. Under the compound layer is Cr diffusion layer in substrate. Typical microstructure of cross section is shown in Fig. 4. Fig. 5 shows the distribution of chromium in the Cr-alloyed layer. Reference document [16] indicates that, when the Cr concentration reach to 14%, Ti–Cr binary alloy can be act as burn-resistant titanium alloy. 3.2. Hardness Gradually distributed micro-hardness in alloyed layer is shown in Fig. 6. On the surface it reaches to 600 (Hv0.5). In whole the alloyed layer hardness is above that in substrate. Solutioned alloying elements increase the hardness in alloyed layer.
Burn-resistance experiments are performed using self-made testing device, its schematics is shown in Fig. 7. Highly rotated cone-shaped sample made by Ti–6Al–4V alloy frictionizes with round sample which is surface alloyed. High-pressure air is heated to 600 °C by furnace and flows to samples. In high speed, high temperature air condition and wear condition, burn phenomena don't occur in all samples which Cr concentration is above 14%. Until their alloyed layer is worn off. When burnresistant alloying layer is destroyed, the samples ignite and burn swiftly. The experiments show that if the alloyed layer on the surface of conventional titanium alloy has necessary thickness and alloying element concentrations, it can fulfill the burnresistant function. 4. Summary Burn-resistant titanium alloys have been successfully created by the DG plasma surface alloying technology upon the surface of conventional titanium alloys. This unique technology is a very powerful means of transforming the ordinary material surface into an exotic alloy layer. The surface alloy produced by this process is a gradient material. Composition in the alloyed surface layer gradually changes in the depth direction of the substrate. Therefore, there exists no distinct boundary between the surface alloy and matrix and risk of delamination is greatly reduced. Main advantage of the surface burn-resistant titanium alloys is that loads are endured by substrate and surface alloyed layer fulfills the function of burn-resistance. Acknowledgements The authors acknowledge the financial support of the National Science Foundation of China (NSFC). (Grant Number 50271045) References
Fig. 6. Micro-hardness distribution along the cross section.
[1] Mohan V. Gunaji, Sircar Subhasish, Harold D. Beeson, Proceedings of the Symposium on Flammability and Sensitivity of Materials in OxygenEnriched Atmospheres, Denver, USA, 1995. [2] Wilson D. Bruce, Joel M. Stoltzfus, Proceedings of the 1997 8th International Symposium on Flammability and Sensitivity of Materials in Oxygen-Enriched Environments, San Diego, USA, 1997. [3] V.I. Bolobov, Combust. Explos. Shock Waves 38 (2002) 635. [4] V. Rosenband, Combust. Flame 137 (2004) 366.
P. Zhang et al. / Surface & Coatings Technology 201 (2007) 4884–4887 [5] UK Patent Application 2,238,057,1987. [6] D. Eylon, J. Mater. 6 (1994) 14. [7] D.W. Anderson, A.F. Condliff, International Conference on Titanium Products and Applications,Titanium Development Association, 1994, p. 91. [8] J.O. Hansen, D. Novotnak, M.F. Welter, J.R. Wood, Titanium' 95: Science and technology, 1995, p. 675. [9] Y.G. Li, P.A. Blenkinsop, M.H. Loretto, D. Rugg, W. Voice, Acta Mater. 47 (1999) 2889. [10] Y.G. Li, M.H. Loretto, D. Rugg, W. Voice, Acta Mater. 49 (2001) 3011. [11] X. Wu, R. Sharman, J. Mei, W. Voice, Mater. Des. 23 (2002) 239. [12] X. Wu, R. Sharman, J. Mei, W. Voice, Mater. Des. 25 (2004) 103. [13] Yongqing Zhao, Lian Zhou, Ju Deng, J. Alloys Compd. 284 (1999) 190.
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[14] K.Y. Zhu, Y.Q. Zhhao, H.L. Qu, Z.L. Wu, X.M. Zhao, J. Mater. Sci. 35 (2000) 5609. [15] Y.Q. Zhao, W.L. Wu, X.D. Ma, et al., Mater. Sci. Eng., A Struct. Mater.: Prop. Microstruct. Process. 373 (2004) 315. [16] Y.Q. Zhao, H.L. Qu, M.M. Wang, H. Wu, K.Y. Zhu, J. Alloys Compd. 407 (2006) 118. [17] Zhong Xu, US Patent 4,520,268 and 4,731,539, UK Patent 2,150,602, Austria Patent 580,734, Canada Patent 1,212,486, Sweden Patent 8500364-8. [18] Zhong Xu, Yuan Gao, Zhiyong He, Zaifeng Xu, Yongan Su, J. Adv. Mater. 34 (2002) 32.