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Effect of 60 keV nitrogen ion implantation on oxidation resistance of IMI 834 titanium alloy
Surface & Coatings Technology 203 (2009) 2605–2607
Contents lists available at ScienceDirect
Surface & Coatings Technology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / s u r f c o a t
Effect of 60 keV nitrogen ion implantation on oxidation resistance of IMI 834 titanium alloy A.K. Lal a,⁎, S.K. Sinha a, P.K. Barhai a, K.G.M. Nair b, S. Kalavathy b, D.C. Kothari c a b c
Department of Applied Physics, Birla Institute of Technology, Mesra, Ranchi-835215, Jharkhand, India Material Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamilnadu, India Department of Physics, University of Mumbai, Vidyanagri, Santacruz (E), Mumbai 400 098, India
a r t i c l e
i n f o
Available online 3 March 2009 Keywords: Surface morphology Oxidation resistance Compound formation
a b s t r a c t IMI 834 titanium alloy has been proved to be beneficial for aerospace application because of its light weight and high strength. The poor oxidation property at high temperature however produces a bottleneck for using these alloys in aero engines. Ion implantation is a proved technique to improve the surface property without changing its bulk properties. N+ ion is implanted at 60 keV with varying ion doses ranging from 5 × 1015 to 1 × 1017 ions/cm2. Atomic Force Microscopy (AFM) has been used to study surface morphology showing evidence of compound formation. TiN compound formation is confirmed using Glancing Incidence X-ray Diffraction (GIXRD) technique. Oxidation resistance is studied at 700 °C and 800 °C. The change in oxidation resistance with the change in ion dose is described in this paper. © 2009 Elsevier B.V. All rights reserved.
1. Introduction For the betterment of efficiency and performance of aero gas turbine engines, it is necessary to use high specific strength, lowdensity materials. This has resulted in the development of a wide range of titanium alloys like IMI 834 (Ti–5.8Al–4Sn–3.5Zr–0.7Nb– 0.5Mo–0.35Si). It is the most recently developed near-alpha type titanium alloy for high-temperature application up to 873 K. It possesses a good combination of creep and fatigue resistance at elevated temperature, in properly heat-treated condition, and has a fine bimodal microstructure, consisting of a small volume fraction of equiaxed alpha in a fine-grained matrix of lamellar transformed beta [1]. With their high specific strength and excellent corrosion resistance, titanium alloys are potential candidates for the component of aerospace application and widespread other non-aerospace applications as well. These alloys save the order of 50% of component weight over super alloy and steels and, are virtually immune to the highly corrosive environment like acidic, marine and industrial environment by forming a protective oxide scale at lower temperature [2]. But the poor oxidation resistance of titanium and its alloys at higher temperature (N500 °C) produces a bottleneck to use these alloys at elevated temperatures like compressor section of modern gas turbine engine. At elevated temperature titanium alloys readily absorb oxygen that leads to oxidation and α case formation [3]. It has been
⁎ Corresponding author. 0257-8972/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2009.02.053
shown that corrosion rate increases five times if we increase the temperature two times in acidic and industrial environment and increases two times in marine environment [2]. At higher temperature in marine and industrial environment the alloy is susceptible to both pitting and crevice corrosion. Systematic studies on the titanium alloy IMI834 at various elevated temperature revealed that the thickness of oxide scale and the depth of the oxygen-dissolved region are dependent upon the oxidation temperature. Oxygen dissolution is significantly high at elevated temperature [4] and the α case formation is significantly enhanced at and above 800 °C [3]. The thickness of the oxide scale and the depth of α case are proportional to the exposed temperature [3]. Therefore it is necessary to prevent oxygen diffusion into the titanium base alloys if they are intended to be used at elevated temperature. To improve the high-temperature oxidation resistance surface treatment of the substrate is a good idea. Ion implantations have been utilized as effective method for improving the oxidation behavior of titanium alloy [5]. Ion implantation is a novel surface modification technology that enhances the mechanical, chemical and electrical properties of substrate's surface using accelerated ions [6]. It is one of the promising techniques of material surface treatment aimed at changing the specific characteristics of materials i.e. increase of fatigue limit, thermal stability, corrosion resistance, wear, etc. [7]. The nitrogen ion implanted titanium showed marked changes in the corrosion resistance with various doses. It was reported that nitrides of titanium were formed at various doses of implanted nitrogen [4]. It is known that titanium nitrides exhibit better oxidation resistance than titanium alloy itself [8,9]. Therefore ion implantation of nitrogen on IMI 834 is a promising way to improve there oxidation resistance.
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A.K. Lal et al. / Surface & Coatings Technology 203 (2009) 2605–2607
The paper describes the effect of 60 keV nitrogen ion implantation with various ion doses ranging from 5 × 1015 to 1 × 1017 on oxidation behavior of titanium alloy. 2. Experimental The alloy IMI834 has been procured from Defense Metallurgical Research Lab, Hyderabad in the form of rod of 24 mm diameter. The discs of 0.5 mm thickness have been sliced from the rod with the help of wire Electric Discharge Machine (EDM) cutter (Electra maxi cut 734). These discs were further divided in four equal parts. We have used each of these equal parts as our samples for implantation of nitrogen ion. These samples are polished manually by different no. of emery papers, starting from 80 to 1200, followed by buffing cloth polishing. After that these were cleaned with organic solvents in ultrasonic bath for 30 min. After cleaning the samples, N+ ions were implanted at Material Science Division (MSD), Indira Gandhi Centre for Atomic Research (IGCAR) Kalpakkam with the help of 150 keV particle accelerator, TAM SAMES, model J15, made by Sames company of Grenoble, France. The beam current was kept below 2 μA to maintain the sample temperature below 40 °C. During ion implantation, the vacuum at the target chamber was maintained around 1 × 10− 7 mbar. For implantation, the sample was pasted using silver paste on a rectangular block of copper and thus continuity was maintained between the top of the sample surface and sample holder. The ion doses were varied from 5 × 1015 ions/cm2 to 1 × 1017 ions/cm2. The nitrogen ion range was theoretically investigated with the software, the Stopping and Ranges of Ion in Matter (SRIM) [10]. The mean ion range of nitrogen ions in IMI 834 is 116 nm as determined from SRIM.
Fig. 1. (a). AFM micrograph of unimplanted IMI 834. (b). AFM micrograph of 60 keV nitrogen implanted IMI 834 with ion dose 5 × 1015 ions/cm2.
Fig. 2. GIXRD pattern of the implanted Ti-alloy with nitrogen ion doses showing compound formation of TiN after ion implantation.
As the implantation is in shallow region, GXRD was used to determine compound formation. STOE Powder Diffraction System was used for GXRD which is located at MSD, IGCAR, Kalpakkam. It was used in θ–2θ scan mode, having reflection of 0.3°. The source was Cu Kα radiation, having wavelength 1.54060 Å. Collection steps were kept at 15.0 s/0.100°. Microstructural analysis is studied using AFM of NDMDT SOLVER PRO. For all the samples, AFM was operated in semi contact mode. The feedback mechanism is employed to adjust the tipto-sample distance to keep the force between the tip and the sample constant. SPM-controller PCI interface Window compatible software is used for the AFM data analysis. Oxidation resistance study was carried out at atmospheric pressure in air at two different temperatures i.e. 700 °C and 800 °C. Samples were loaded in alumina boat and kept inside a furnace at desired temperature under atmospheric condition. Furnace Electroheat NASKAR & Co., Model No. EN 345T located at BIT, Mesra, Ranchi was used. Change in weight was measured using a discontinuous mode by interrupting the experiment. Microbalance of Mettler, Toledo
Fig. 3. Oxidation curve of unimplanted and nitrogen implanted IMI 834 at 60 keV with varying ion dose studied at 700 °C showing the variation of weight gain with time of oxidation.
A.K. Lal et al. / Surface & Coatings Technology 203 (2009) 2605–2607
2607
lower than the unimplanted specimen. In fact if we have a closer look over the curves corresponding different doses we can clearly observe that the doses play a significant role over this improvement. The rate of weight gain decreases with the increase in the ion dose. This behavior is observed at both the temperatures 700 °C and 800 °C. For the unimplanted IMI 834 sample, the oxidation rate increases with increasing oxidation time as well as with increasing temperature and the α case formation is significantly enhanced at and above 800 °C. Thus for 800 °C the mass gain per unit area is more than that of 700 °C but weight gain tendency decreases with increasing ion dose. So the samples implanted with higher ion dose of nitrogen exhibit higher oxidation resistance. This betterment in oxidation resistance could be a result of the formation of oxidation resistant TiN layer at the surface which is shown in the GXRD. 4. Conclusions
Fig. 4. Oxidation curve of unimplanted and nitrogen implanted IMI 834 at 60 keV with varying ion dose studied at 800 °C showing the variation of weight gain with time of oxidation.
(Germany) was used to weigh the sample which is located at BIT Mesra, Ranchi.
IMI834 is implanted with 60 keV nitrogen ions at various ion doses ranging from 5 × 1015 ions/cm2 to 1 × 1017 ions/cm2. Microstructure is studied using AFM technique. Compound formation of TiN on the surface is confirmed using GXRD. Oxidation resistance improves after nitrogen ion implantation due to compound formation of TiN. Oxidation behavior also depends upon the ion dose. The rate of mass gain decreases significantly with increase in ion dose at both the temperature 700 °C and 800 °C. Oxidation resistance is best at 1 × 1017 ions/cm2 for the ion dose studied over here.
3. Results and discussions Acknowledgement Before oxidation studies, microstructural changes were studied using AFM and GXRD. The GIXRD data of the implanted sample is presented in Fig. 1(a) shows AFM micrograph of unimplanted sample and Fig. 1(b) shows the AFM micrograph of the 60 keV nitrogen ion implanted sample with the ion dose 5 × 1015 ions/cm2. Unimplanted sample is smooth whereas microstructural changes are observed on the surface of the implanted sample. This is attributed as compound formation which is conformed with GXRD. Fig. 2 shows the GXRD pattern of the 60 keV nitrogen implanted samples with varying ion dose. Clearly for 1 × 1017 ions/cm2 ion dose new peaks are developed at 2θ = 36.9, 42.47, 61.7 and 74.5°. These peaks correspond to facecentered cubic structure TiN (titanium nitride). However the signature of a new peak formation at 36.9° is already seen in the XRD data of 5 × 1016 ions/cm2 implanted sample where the bottom of the peak of Ti (002) gets broadened signifying the emergence of a new peak. But the peak is more significant at the dose 1 × 1017 ions/cm2. Oxidation behaviour of the unimplanted and implanted samples at 700 °C and 800 °C is shown in Figs. 3 and 4. Oxidation curve clearly shows that the rate of weight gain in nitrogen-implanted specimens is
Authors thank AR & DB, Ministry of defense, Government of India for providing the financial support to carry out this work. References [1] [2] [3] [4] [5]
[6] [7] [8] [9] [10]
P. Pototzky, H.J. Maier, H.J. Christ, Metall. Mater. Trans., A 29A (1998) 2995. I. Gurrappa, D. Venugopal Reddy, J. Alloys Compd. 390 (2005) 270. I. Gurrappa, A.K. Gogia, Surf. Coat. Technol. 139 (2001) 216. I. Gurrappa, Corros. Prev. Control 49 (2002) 79. T. Ishii, K. Murakami, K. Fujita, Y. Hibino, High temperature oxidation resistance of Ti Alloys by Plasma based Ion Implantation, IEEE conference record, 30th International Conference on Plasma Science, ICOPS 2003, 2-5 June 2003, 194. Hyuk-Jin Kang1, Sung-Hoon Ahn1, Jae-Sang Lee, Jae-Hyung Lee, Int. J. Prec. Eng. Manuf. 7 (1) (Jan 2006). A.V. Zhikharev, S.G. Bystrov, P.V. Bykov, A.Yu. Drozdov, V.Ya. Bayankin, SPM Proc. (2002) 160. C. Leyens, M. Schmidt, M. Peters, W.A. Keysser, Mater. Sci. Eng., A Struct. Mater.: Prop. Miscrostruct. Process. 239 (1997) 680. B. Cockeram, R.A. Rapp, Oxid. Met. 28 (1996) 427. J.F. Ziegler and J.P. Biersack, SRIM.com (2003).
Contents lists available at ScienceDirect
Surface & Coatings Technology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / s u r f c o a t
Effect of 60 keV nitrogen ion implantation on oxidation resistance of IMI 834 titanium alloy A.K. Lal a,⁎, S.K. Sinha a, P.K. Barhai a, K.G.M. Nair b, S. Kalavathy b, D.C. Kothari c a b c
Department of Applied Physics, Birla Institute of Technology, Mesra, Ranchi-835215, Jharkhand, India Material Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamilnadu, India Department of Physics, University of Mumbai, Vidyanagri, Santacruz (E), Mumbai 400 098, India
a r t i c l e
i n f o
Available online 3 March 2009 Keywords: Surface morphology Oxidation resistance Compound formation
a b s t r a c t IMI 834 titanium alloy has been proved to be beneficial for aerospace application because of its light weight and high strength. The poor oxidation property at high temperature however produces a bottleneck for using these alloys in aero engines. Ion implantation is a proved technique to improve the surface property without changing its bulk properties. N+ ion is implanted at 60 keV with varying ion doses ranging from 5 × 1015 to 1 × 1017 ions/cm2. Atomic Force Microscopy (AFM) has been used to study surface morphology showing evidence of compound formation. TiN compound formation is confirmed using Glancing Incidence X-ray Diffraction (GIXRD) technique. Oxidation resistance is studied at 700 °C and 800 °C. The change in oxidation resistance with the change in ion dose is described in this paper. © 2009 Elsevier B.V. All rights reserved.
1. Introduction For the betterment of efficiency and performance of aero gas turbine engines, it is necessary to use high specific strength, lowdensity materials. This has resulted in the development of a wide range of titanium alloys like IMI 834 (Ti–5.8Al–4Sn–3.5Zr–0.7Nb– 0.5Mo–0.35Si). It is the most recently developed near-alpha type titanium alloy for high-temperature application up to 873 K. It possesses a good combination of creep and fatigue resistance at elevated temperature, in properly heat-treated condition, and has a fine bimodal microstructure, consisting of a small volume fraction of equiaxed alpha in a fine-grained matrix of lamellar transformed beta [1]. With their high specific strength and excellent corrosion resistance, titanium alloys are potential candidates for the component of aerospace application and widespread other non-aerospace applications as well. These alloys save the order of 50% of component weight over super alloy and steels and, are virtually immune to the highly corrosive environment like acidic, marine and industrial environment by forming a protective oxide scale at lower temperature [2]. But the poor oxidation resistance of titanium and its alloys at higher temperature (N500 °C) produces a bottleneck to use these alloys at elevated temperatures like compressor section of modern gas turbine engine. At elevated temperature titanium alloys readily absorb oxygen that leads to oxidation and α case formation [3]. It has been
⁎ Corresponding author. 0257-8972/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2009.02.053
shown that corrosion rate increases five times if we increase the temperature two times in acidic and industrial environment and increases two times in marine environment [2]. At higher temperature in marine and industrial environment the alloy is susceptible to both pitting and crevice corrosion. Systematic studies on the titanium alloy IMI834 at various elevated temperature revealed that the thickness of oxide scale and the depth of the oxygen-dissolved region are dependent upon the oxidation temperature. Oxygen dissolution is significantly high at elevated temperature [4] and the α case formation is significantly enhanced at and above 800 °C [3]. The thickness of the oxide scale and the depth of α case are proportional to the exposed temperature [3]. Therefore it is necessary to prevent oxygen diffusion into the titanium base alloys if they are intended to be used at elevated temperature. To improve the high-temperature oxidation resistance surface treatment of the substrate is a good idea. Ion implantations have been utilized as effective method for improving the oxidation behavior of titanium alloy [5]. Ion implantation is a novel surface modification technology that enhances the mechanical, chemical and electrical properties of substrate's surface using accelerated ions [6]. It is one of the promising techniques of material surface treatment aimed at changing the specific characteristics of materials i.e. increase of fatigue limit, thermal stability, corrosion resistance, wear, etc. [7]. The nitrogen ion implanted titanium showed marked changes in the corrosion resistance with various doses. It was reported that nitrides of titanium were formed at various doses of implanted nitrogen [4]. It is known that titanium nitrides exhibit better oxidation resistance than titanium alloy itself [8,9]. Therefore ion implantation of nitrogen on IMI 834 is a promising way to improve there oxidation resistance.
2606
A.K. Lal et al. / Surface & Coatings Technology 203 (2009) 2605–2607
The paper describes the effect of 60 keV nitrogen ion implantation with various ion doses ranging from 5 × 1015 to 1 × 1017 on oxidation behavior of titanium alloy. 2. Experimental The alloy IMI834 has been procured from Defense Metallurgical Research Lab, Hyderabad in the form of rod of 24 mm diameter. The discs of 0.5 mm thickness have been sliced from the rod with the help of wire Electric Discharge Machine (EDM) cutter (Electra maxi cut 734). These discs were further divided in four equal parts. We have used each of these equal parts as our samples for implantation of nitrogen ion. These samples are polished manually by different no. of emery papers, starting from 80 to 1200, followed by buffing cloth polishing. After that these were cleaned with organic solvents in ultrasonic bath for 30 min. After cleaning the samples, N+ ions were implanted at Material Science Division (MSD), Indira Gandhi Centre for Atomic Research (IGCAR) Kalpakkam with the help of 150 keV particle accelerator, TAM SAMES, model J15, made by Sames company of Grenoble, France. The beam current was kept below 2 μA to maintain the sample temperature below 40 °C. During ion implantation, the vacuum at the target chamber was maintained around 1 × 10− 7 mbar. For implantation, the sample was pasted using silver paste on a rectangular block of copper and thus continuity was maintained between the top of the sample surface and sample holder. The ion doses were varied from 5 × 1015 ions/cm2 to 1 × 1017 ions/cm2. The nitrogen ion range was theoretically investigated with the software, the Stopping and Ranges of Ion in Matter (SRIM) [10]. The mean ion range of nitrogen ions in IMI 834 is 116 nm as determined from SRIM.
Fig. 1. (a). AFM micrograph of unimplanted IMI 834. (b). AFM micrograph of 60 keV nitrogen implanted IMI 834 with ion dose 5 × 1015 ions/cm2.
Fig. 2. GIXRD pattern of the implanted Ti-alloy with nitrogen ion doses showing compound formation of TiN after ion implantation.
As the implantation is in shallow region, GXRD was used to determine compound formation. STOE Powder Diffraction System was used for GXRD which is located at MSD, IGCAR, Kalpakkam. It was used in θ–2θ scan mode, having reflection of 0.3°. The source was Cu Kα radiation, having wavelength 1.54060 Å. Collection steps were kept at 15.0 s/0.100°. Microstructural analysis is studied using AFM of NDMDT SOLVER PRO. For all the samples, AFM was operated in semi contact mode. The feedback mechanism is employed to adjust the tipto-sample distance to keep the force between the tip and the sample constant. SPM-controller PCI interface Window compatible software is used for the AFM data analysis. Oxidation resistance study was carried out at atmospheric pressure in air at two different temperatures i.e. 700 °C and 800 °C. Samples were loaded in alumina boat and kept inside a furnace at desired temperature under atmospheric condition. Furnace Electroheat NASKAR & Co., Model No. EN 345T located at BIT, Mesra, Ranchi was used. Change in weight was measured using a discontinuous mode by interrupting the experiment. Microbalance of Mettler, Toledo
Fig. 3. Oxidation curve of unimplanted and nitrogen implanted IMI 834 at 60 keV with varying ion dose studied at 700 °C showing the variation of weight gain with time of oxidation.
A.K. Lal et al. / Surface & Coatings Technology 203 (2009) 2605–2607
2607
lower than the unimplanted specimen. In fact if we have a closer look over the curves corresponding different doses we can clearly observe that the doses play a significant role over this improvement. The rate of weight gain decreases with the increase in the ion dose. This behavior is observed at both the temperatures 700 °C and 800 °C. For the unimplanted IMI 834 sample, the oxidation rate increases with increasing oxidation time as well as with increasing temperature and the α case formation is significantly enhanced at and above 800 °C. Thus for 800 °C the mass gain per unit area is more than that of 700 °C but weight gain tendency decreases with increasing ion dose. So the samples implanted with higher ion dose of nitrogen exhibit higher oxidation resistance. This betterment in oxidation resistance could be a result of the formation of oxidation resistant TiN layer at the surface which is shown in the GXRD. 4. Conclusions
Fig. 4. Oxidation curve of unimplanted and nitrogen implanted IMI 834 at 60 keV with varying ion dose studied at 800 °C showing the variation of weight gain with time of oxidation.
(Germany) was used to weigh the sample which is located at BIT Mesra, Ranchi.
IMI834 is implanted with 60 keV nitrogen ions at various ion doses ranging from 5 × 1015 ions/cm2 to 1 × 1017 ions/cm2. Microstructure is studied using AFM technique. Compound formation of TiN on the surface is confirmed using GXRD. Oxidation resistance improves after nitrogen ion implantation due to compound formation of TiN. Oxidation behavior also depends upon the ion dose. The rate of mass gain decreases significantly with increase in ion dose at both the temperature 700 °C and 800 °C. Oxidation resistance is best at 1 × 1017 ions/cm2 for the ion dose studied over here.
3. Results and discussions Acknowledgement Before oxidation studies, microstructural changes were studied using AFM and GXRD. The GIXRD data of the implanted sample is presented in Fig. 1(a) shows AFM micrograph of unimplanted sample and Fig. 1(b) shows the AFM micrograph of the 60 keV nitrogen ion implanted sample with the ion dose 5 × 1015 ions/cm2. Unimplanted sample is smooth whereas microstructural changes are observed on the surface of the implanted sample. This is attributed as compound formation which is conformed with GXRD. Fig. 2 shows the GXRD pattern of the 60 keV nitrogen implanted samples with varying ion dose. Clearly for 1 × 1017 ions/cm2 ion dose new peaks are developed at 2θ = 36.9, 42.47, 61.7 and 74.5°. These peaks correspond to facecentered cubic structure TiN (titanium nitride). However the signature of a new peak formation at 36.9° is already seen in the XRD data of 5 × 1016 ions/cm2 implanted sample where the bottom of the peak of Ti (002) gets broadened signifying the emergence of a new peak. But the peak is more significant at the dose 1 × 1017 ions/cm2. Oxidation behaviour of the unimplanted and implanted samples at 700 °C and 800 °C is shown in Figs. 3 and 4. Oxidation curve clearly shows that the rate of weight gain in nitrogen-implanted specimens is
Authors thank AR & DB, Ministry of defense, Government of India for providing the financial support to carry out this work. References [1] [2] [3] [4] [5]
[6] [7] [8] [9] [10]
P. Pototzky, H.J. Maier, H.J. Christ, Metall. Mater. Trans., A 29A (1998) 2995. I. Gurrappa, D. Venugopal Reddy, J. Alloys Compd. 390 (2005) 270. I. Gurrappa, A.K. Gogia, Surf. Coat. Technol. 139 (2001) 216. I. Gurrappa, Corros. Prev. Control 49 (2002) 79. T. Ishii, K. Murakami, K. Fujita, Y. Hibino, High temperature oxidation resistance of Ti Alloys by Plasma based Ion Implantation, IEEE conference record, 30th International Conference on Plasma Science, ICOPS 2003, 2-5 June 2003, 194. Hyuk-Jin Kang1, Sung-Hoon Ahn1, Jae-Sang Lee, Jae-Hyung Lee, Int. J. Prec. Eng. Manuf. 7 (1) (Jan 2006). A.V. Zhikharev, S.G. Bystrov, P.V. Bykov, A.Yu. Drozdov, V.Ya. Bayankin, SPM Proc. (2002) 160. C. Leyens, M. Schmidt, M. Peters, W.A. Keysser, Mater. Sci. Eng., A Struct. Mater.: Prop. Miscrostruct. Process. 239 (1997) 680. B. Cockeram, R.A. Rapp, Oxid. Met. 28 (1996) 427. J.F. Ziegler and J.P. Biersack, SRIM.com (2003).