- Email: [email protected]
Metal vapour vacuum arc ion implantation facility in Turkey
Surface & Coatings Technology 196 (2005) 327 – 332 www.elsevier.com/locate/surfcoat
Metal vapour vacuum arc ion implantation facility in Turkey ¨ ztarhana,*, I. Brownb, C. Bakkalogluc, G. Wattd, P. Evansd, E. Okse, A. O A. Nikolaeve, Z. Tekf a Ege University, Bio Engineering Department, 35100 Izmir, Turkey Lawrence Berkeley National Laboratory, University of California, CA 94720, USA c ELTASS , AOSB, 35200 C¸ig˘li, I˙zmV r, Turkey d Australian Nuclear Science and Techonology Organization Menai, NSW 2234, Australia e High Current Electronics Institute, Tomsk, Russia f Celal Bayar U¨niversitesi Fen EdebiyetFaku¨ltesi Fizik Bo¨lu¨mu¨ 45040 Muradiye/Manisa, Turkey b
Available online 2 October 2004
Abstract A vacuum arc ion source based metal ion implantation facility is built and in operation at TUBITAK (The Scientific and Technical Research Council of Turkey), Izmir, Turkey and a surface modification research and development program is being carried out here. The system is similar to the one in Lawrence Berkeley Laboratory, which was first built and developed by Brown et al. The broad-beam ion source can be repetitively pulsed at rates up to ~50 pulses per second and the extracted ion beam current can be up to ~1 A peak or ~10 mA time averaged. The ion source extraction voltage can be increased up to 110 kV. Additionally, mixed metal and gas ion beams were generated by a magnetic field, which was obtained through a magnet coil located in front of anode plate and by adding gas in the discharge region. This modified system was used to form buried layers of mixed metal–gas species such as Ti+N (on 316 SS and Ti alloy samples) and Zr and W (316 SS and Ti alloy samples, respectively) of which their hardness, coefficient of friction and wear volumes were measured and their RBS results were obtained. The anodic electrochemical tests showed that the corrosion resistance of Ti implanted 304 SS samples was increased with the dose. Micro structures of Ti implanted surfaces of 304 SS samples were examined with SEM before and after the corrosion tests and the results showed that the pittings were formed mostly in the areas where implanted Ti concentration was less. Recently, the system is equipped with TOF for measuring the charge state distribution of ions. R&D work is planned for the purpose of forming tribologically enhanced materials for industrial applications by using ion implantation, PVD coating, plasma nitriding and their combinations. The results showed that the hardness and performance of ion implanted (with various metals and N) PVD coated cutting inserts increased remarkably. The use of ion implantation techniques in modifying the properties of textile and other materials and optimising the performance of textile and other industrial machine parts and tools is also being investigated and some of the results are presented in this work. D 2004 Elsevier B.V. All rights reserved. Keywords: Ion implantation; Surface Modification; Ion Beams; Duplex treatment; Tribology; Surface treatment
1. Introduction Early studies on the implantation of metal ions were not as numerous as their gaseous counterparts. This may have been partly due to the relative superiority, at the time, of ion sources that generated ions from stable gases. In contrast, many metal ion sources of that period employed either * Corresponding author. Tel.: +90 232 323 30 34; fax: +90 232 374 42 84. ¨ ztarhan). E-mail address: [email protected] (A. O 0257-8972/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2004.08.178
reactive gases, or solid or liquid feed materials. Decomposition and ionisation of these materials often caused accelerated degradation of ion source components, which shortened operational life. The ion beam currents generated by many of these sources were also comparatively low which extended the time required for high dose implants. These limitations have (to a large degree) been overcome during the past 20 years, with the development of new types of metal ion sources [1], and improvements to existing types; the metal vapour vacuum arc (MEVVA) ion source falls into the former category.
328
A. O¨ztarhan et al. / Surface & Coatings Technology 196 (2005) 327–332
Invented by Brown et al. [2] at Lawrence Berkeley National Laboratory, the MEVVA ion source utilises a vacuum arc plasma as the source of metal ions which are subsequently extracted and accelerated by three beam formation electrodes. The simplicity of MEVVA sources combined with their ability to produce ions of most metals have become an established tool for ion implantation research. Currently, a number of laboratories worldwide have MEVVA systems from which a substantial number of publications have resulted. Tu¨bitak Textile Research Center in Izmir is a recent addition to the list of organisations operating this type of facility. The present report describes briefly the MEVVA ion implanter recently installed there. The MEVVA ion implanter has been employed in generating high current metal ion beams which are used for ion implantation to modify the composition of the near surface region of materials. Usually the vacuum arc ion sources can generate only metal ion beams, but for many metallurgical and other surface modification appplications it is necessary to form the buried layers of mixed gas–metal species. It was shown earlier by Efim et al. [3] that a certain amount of gas ions can be produced in a vacuum arc ion source if a magnetic field was applied in the anode chamber by a magnetic coil fed by the discharge current of about 100 A, which is induced by the power supply of the vacuum arc. It was reported that mean charge states of ions and their energies can be increased with magnetic field [4]. We upgraded our MEVVA multi cathode ion source in this way and used this technique for hybrid co-implantation of nitrogen with various metals to modify some materials surfaces including textiles. Furthermore, our MEVVA ion implanter system was recently equipped with the Time of Flight mass spectrometer (HCEI-TOMSK) to measure the charge state distribution of the beam generated by the source.
2. Description of the facility The MEVVA Ion Implantation System was first installed in 1997 in Dokuz Eylul University and was dismantled and set up again at TUBITAK Textile Research Center and equipped with TOF in 2003. The ion source is built to the MEVVA-V design of Dr. Ian Brown. This family of ion sources has been evolving since MEVVA I, which was built in 1982. The main elements of MEVVA ion source are shown in picture [1], which is a more recent 18-cathode design and the essential electrical elements of a MEVVA ion source are shown in Fig. 1. The major functional components of the ion implanter are as follows: (1) Vacuum system and sample processing chamber, (2) 0 to 100 kV DC extractor power supply (current output 0 to 10 mA),
Fig. 1. Essential electrical elements of a MEVVA ion source.
(3) Ion source assembly, (4) 220 V to 220 V mains voltage isolation transformer (not shown) which powers: 4(a) Trigger voltage generator (10 kV/30 A, pulsed), 4(b) Arc current power supply (0 to 700 V/0 to 500 A, pulsed), (5) Common electronic measurement instruments (Oscilloscope, Pulse Generator), (6) Second-grid power supply (0 to 2 kV DC/0 to 10 mA), (7) Protective enclosure (faraday cage)to contain the high-voltage and to provide radiation shielding. The sample processing chamber was fabricated from 316 stainless steel and it has an internal diameter of 480 mm, 4150 mm diameter sample access ports and a pressure measurement port, and is equipped with an Alcatel maglevATP1500 turbopump-based vacuum system for clean vacuum. Ion source, turbo pump and one of the sample access ports have VAT gate valves. The extractor power supply is powered from the 220 V mains by means of a 0–220 V, 20 A variable autotransformer. The high-voltage output is controlled by manually varying the auto-transformer output voltage setting. 220 V–220 V Mains Voltage Isolation Transformer is rated at 6 kVA and provides 220 V AC power for the electronics in the arc and trigger power supplies. These power supplies operate at the extractor voltage potential, up to 100 kV above ground. Therefore the isolation transformer must provide a very high degree of electrical isolation between primary and secondary windings, and was constructed so that the risk of high-voltage breakdown (and electrical leakage) on the secondary winding is minimal. This has been achieved by bringing the load terminals out by means of a fiberglass bushing 90 mm in diameter and approximately 500 mm high. A MEVVA ion source typically operates at arc current levels up to 500 A and voltages up to 700 V. The arc current may be steady DC for the implantation period, but it is more commonly a train of square pulses. Typically, less than 0.1%
A. O¨ztarhan et al. / Surface & Coatings Technology 196 (2005) 327–332 Table 1 Mechanical characterisation tests of implanted 316 and Ti–6Al–4V sample with various ions Samples
Implanted
Hardness (Hv)
Coefficient of friction
Wear (Am2)
316 LSS 316 LSS 316 LSS Ti–6Al–4V Ti–6Al–4V Ti–6Al–4V
Unimplanted Zr Ti+N Unimplanted Ti+N W
350 1500 2600 450 2600 1800
0.68 0.50 0.44 0.67 0.65 0.66
9.6 2.8 3.3 7.3 0.51 0.53
Each sample (30 mm dia., 4 mm thick) were polished down to 0.01 Am Ra. Samples implanted with Doses: 110e17, Extraction voltage: 50 kV. Hardness measured with CSEM Nano Indenter, Load: 10 mN. Wear tracks and friction coefficents were obtained by CSEM Tribotester. Wear values were calculated from the wear track profiles obtained with Mahr profilometer.
of the arc current flows to the target—the remaining 99.9% flows to the ion source bgroundQ and performs no useful function. The arc current pulse duty cycle (bonQ time/boffQ time) is typically less than 1%, and this pulsed mode is very convenient because: ! it results in minimal heating (and distortion) of the ion source and target, ! the power supply may be very simple and can be easily protected against load faults, ! the power supply internal heating is low, and, ! the average currents required from the other (highvoltage) power supplies are low. The pulsed mode requires an electronic pulse generator to define the trigger rate, and a means of re-triggering the arc discharge upon receipt of every pulse. The re-triggering is performed by a btrigger power supplyQ which generates a narrow 10–30 A current pulse at a voltage of up to 11 kV. This is applied across the surface of the cathode (implanting) material. Both the arc and trigger power supplies are located in a smoothed and rounded aluminium housing. Fiber-optic cables are used to transmit the pulse generator signal to the trigger power supply, and the signals that monitor arc voltage and current are transmitted to ground potential by two more fiber-optic links. Such fiberoptic links allow signal transmission over large voltage differences in a safe, reliable, and robust manner. To summarise, the ion source power supply unit contains an arc current power supply, a trigger power supply, and fiber-optic links from the extractor potential to ground. The system derives AC power from an isolation transformer insulated to withstand high voltages. This transformer is energised by a control unit which provides: ! an input to accept a pulse generator output, ! readout meters for indicating extractor and arc voltage, ! connectors for providing waveforms to an oscilloscope, and,
329
! connections from interlock circuits, which prevent unsafe operation. The arc power supply consists of a six-stage LC transmission line with an electrical delay time of 250 As. It is charged to a DC voltage which is varied by the user by means of a variable ratio auto-transformer using an insulating perspex shaft. The arc current is directly related to the charging voltage. The second grid of the ion source is normally operated at a negative bias voltage in order to suppress electrons; this voltage is not critical. We modified our ion source by introducing a magnetic coil and the gas inlet into the anode region as described by Efim et al. [3] to obtain mixed ion beams of metal and gas ion species to form the buried layers of mixed metal–gas species with regulated ratios [5]. The system was also equipped with Time Of Flight (picture [2]) to measure the mean charge state of ions.
3. Results Over the past 15 years, MEVVA ion sources have contributed significantly to the field of metal ion implantation. They have been used to implant a wide range of materials with mostly beneficial results [6]. Even a brief review of the latter is beyond the scope of the present report. However, several representative results will be briefly described in order to illustrate the sorts of improvements that were achieved. 3.1. Increased hardness and reduced wear The modification of metal surfaces for increased hardness and reduced wear has been a particular focus of MEVVA ion implantation research to date. Some of the mechanical characterisation tests of implanted 316 L Stainles Steel and Ti–6Al–4V are shown in Table 1. All
Fig. 2. RBS result of Zr implanted on 316.
A. O¨ztarhan et al. / Surface & Coatings Technology 196 (2005) 327–332
330
Fig. 3. RBS result of W implanted on 316.
samples were implanted with a dose of 11017 ions/cm2, and extracted voltage of 50 kV. For wear tracks, and measurement of coefficient of friction, CSEM Tribotester with 6 mm diameter Alumina ball was used on 30 mm diameter and 4 mm thick disk samples. Wear areas were estimated from the measured profiles across the wear tracks with Mahr profilometer. Hardnesses of samples were measured with CSEM nano indenter with a load of 10 mN. RBS results of Zr and W implanted on 316 are shown in Figs. 2 and 3, respectively. The hardness of Zr implanted 316 SS sample increased by a factor of 4 and increased by a factor of 7 for Ti+N hybrid ion implanted 316 SS sample compared to unimplanted 316 SS samples. In both cases the coefficient of friction decreased approximately by 30%, wear rates decreased approximately by factor of 3. However, coefficient of friction of W and Ti+N hybrid ion implanted Ti–6Al–4V samples did not change but their hardnesses increased by a factor of 4 and 5.5, respectively, compared to unimplanted ones. Wear rates of W implanted and Ti+N hybrid ion implanted Ti–6Al–4V samples decreased by a factor of 18. Hardnesses of some PVD coated inserts which were implanted with various metal ions were measured and the results are shown in Table 2. The hardness of samples was measured by CSEM Nano indenter tester with 10 mN load. The results show that the hardness of PVD TiN coated insert increased most when implanted with W ions with a dose 11017 ions/cm2 and at an extraction voltage 50 kV.
Table 2 Hardness values of ion implanted PVD coated cutting inserts Hardness of cutting inserts (Hv)
Before implantation After implantation
Al implanted PVD TiCN coated inserts
Al implanted PVD TiN coated inserts
Al+W implanted PVD TiN coated inserts
W implanted PVD TiN coated inserts
3000 3930
2200 2920
2200 3280
2200 3330
Fig. 4. Anodic polarisation curves of unimplanted and Ti implanted 304 SS samples with doses of 11016 and 11017 (at an extraction voltage of 50 kV), and pure Ti samples.
3.2. Corrosion behaviour of Ti implanted 304 SS samples Corrosion behaviour of 304 SS samples were observed by performing the electrochemical corrosion tests in a 3.5% NaCl solution. Samples were unimplanted 304SS, pure Ti, and Ti+ implanted 304 SS samples with doses of 11016 and 11017 ions/cm2 at 50 kV extraction voltage. Measurements were taken in 15 mV/min steps. Anodic polarisation curves obtained together with pure Ti sample are shown in Fig. 4. The results showed that the corrosion resistance of 304 SS samples increased with Ti ion implantation and was better with a higher dose. Pictures (3) and (4) show SEM micrographs of pittings and elemental line distribution of Ti after and before the corrosion tests, respectively. Pictures show that Ti depleted regions coincide with places where pittings occurred and their sizes were the same indicating that after the Ti ion implantation, Ti rich regions may inhibit corrosion with the formation of TiO2.
Table 3 Flame retardancy of cotton fabric implanted with various ions NO
Fiber
CO8 CO9 CO10
Cotton Cotton Cotton Cotton
Ion implantation
Extraction voltage and dose
Results (s)
Ti+Al+N Cr+N W+C
20 kV 11016 20 kV 11016 20 kV 11016
12.8 13.5 12.4 46
A. O¨ztarhan et al. / Surface & Coatings Technology 196 (2005) 327–332
331
Table 4 Hydophility and flame retardancy of PES fabrics implanted with C ions
Table 6 Wear tests of cotton and polyester fabrics implanted with various ions
Fabric
Ion implantation
Energy and dose
Results
Samples
Ion implantation
Break off at no. of revolution
Weight loss (%)
PES
–
–
10 kV, 11015 cm 10 kV, 21015 cm 10 kV, 11016 cm
– Ti+Al+N Cr+N W+C – Ti+N Ti+Al+N W+C Ti+N
12.9 13.89 13.8
C
Unimplanted cotton CO8 CO9 CO10 Unimplanted PES PES16 PES19 PES20 PES21
19,000 18,000 20,000
PES
Hydrophility (min) 13.11 2.93
PES PES
C C
Flame retardancy (s) 10 10
2
4.96
There is no flame 24
2
7.5 2
a
3.3. Changing the properties of some textile materials by ion implantation An attempt was made to change the properties of some textile materials by ion implantation of various ions without changing their bulk properties. Flame retardancy, hydrophility, hydrophobity, pilling and abrasion resistance properties of ion implanted Cotton and Polyester fabrics were measured and the results are given in Tables 3–6. Flame retardancy was measured with CFR1610, hydrophility and hydrophobity were measured with TS866(1985) standards. Resistance to pilling and change of appearance of fabrics were determined by modified Martindale method (ISO/D15, 12945-2). Abrasion resistance of textile fabrics was determined by Martindale method TS EN ISO12947-2, and the bursting properties of fabrics were determined by BSEN ISO13938-2 standard.
Table 5 Hydrophility and pilling tests of implanted cotton fabrics with various ions NO
Fabric
Implantation Experimental Results conditions Pilling Hydrophility (s)
CO1
Unimplanted – cotton cotton C
CO2
cotton
C
CO3
cotton
C
CO4
cotton
Cr
CO5
cotton
Cr
CO6
cotton
Cr
CO7
cotton
Cr
CO8
cotton
Ti+Al+N
CO9
cotton
Cr+N
CO10 cotton
W+C
–
1–2
0.3
20 kV, 21015, 908 10 kV, 21015, 308 15 kV, 11016, 908 15 kV, 21015, 908 20 kV, 11015, 908 25 kV, 51015, 458 20 kV, 11016, 458 20 kV, 11016 20 kV, 11016 20 kV, 11016
2.5
41.6
2
44
3
96
2
7
1–2
4.2
3–4
–
–
111
–
59
4.35a 3.64a 1.36a 1.2 0.9
Weight loss at number of 24,000 revolution.
The results showed that best flame retardancy of cotton was obtained when it was implanted with W+C ions at extraction voltage of 20 kV and at 11016 ions/cm2 dose, whereas the best flame retardancy of Polyester(PES) was obtained (infact there was no flame) when it was implanted with C ions at an extraction voltage of 10 kV and at 21015 ions/cm2 dose. Hydrophility of PES was better found with low doses of C. The results in Table 5 show that Cotton fabric became hydrophob and its hydrophility decreased by a factor of 900 when implanted with W+C ions at an extraction voltage of 20 kV and 11016 ions/cm2 dose. Best pilling conditions of cotton fabric was found when it was implanted with Cr ions at an angle of 458 and at an extraction voltage of 25 kV and 11016 dose. Table 6 gives the results of abrasion resistance of cotton and PES fabrics. Because of wiry nature of cotton fibers as seen in picture [5] the abrasion resistance of cotton fabric cannot be improved by ion implantation as fibers break off easily. However, abrasion resistance of PES fabric increased by ion implantation and the best result was obtained with the implantation of Ti+Al+N ions (at an extraction voltage of 25 kV, 11016 dose). As compared to cotton fibers, PES filaments are smooth and regular as shown in picture.6, thus PES fabric has an advantage of utilising ion implantation.
1.5
2.3
–
24.000 28,000 28,000 11,000 10,000
268.25 Fig. 5. Charge state distribution of Ti+N ions.
332
A. O¨ztarhan et al. / Surface & Coatings Technology 196 (2005) 327–332
so novel. From this work have emerged many possibilities, which may become successful applications in the future. It is the exploration of these many possibilities over several decades which has provided the wealth of information currently available on the modification of surface properties by ion implantation. Systems like the MEVVA ion implanter described above have made a significant contribution to this process and it is expected that this contribution will continue into the foreseeable future.
Acknowledgements
Fig. 6. Charge distribution of Cr+N ions.
To obtain Ti+Al+N ion implantation, Al ion implantation was done after the Ti+N metal gas hybrid ion implantation. Ion charge state distribution of Ti+ N and Cr+ N, which were obtained with TOF, are shown in Figs. 5 and 6, respectively. It was also observed that implanting both sides of PES fabrics by Cu ions at an extraction voltage of 25 kV and 11016 ions/cm2 dose, prevented static electricification of PES fabric.
4. Summary In this report, we have briefly described a typical MEVVA ion implanter with reference to the system currently operating at Tubitak Textile Research Center. In addition, several applications including textile fabrics of metal ion implantation and metal–gas hybrid ion implantation have been presented. The preliminary results show that the utilisation of ion implantation in textiles especially in technical textiles looks (might be) very promising as it’s
The MEVVA Ion Implantation System was built with a fund from the bScientific and Technical Research Council of Turkey (TUBITAK) Q under project no. MISAG 43. Coauthor’s; I. Brown, C. Bakkalog˘lu, G. Watt, P. Evans, E. Oks and A. Nikolaev were involved with MEVVA Ion Implanter. The author thanks TUBITAK Textile Research Center for supporting the work with the textiles and I. ¨ ktem, E. O ¨ zdog˘an, A. Karaaslan and S. Tarakc¸Vog˘lu, T. O NamlVgo¨z for their work related to some of the characterisation tests with textiles.
References [1] I.G. Brown, The Physics and Technology of Ion Sources, Wiley, New York, 1989. [2] I.G. Brown, J.E. Galvin, B.F. Gavin, R.A. MacGill, Rev. Sci. Instrum. 57 (1986) 1069. [3] E. Oks, P. Spadtke, H. Emig, B.H. Wolf, Rev. Sci. Instrum. 65 (1994) 3109. [4] E.M. Oks, A. Anders, I.G. Brown, M.R. Dickinson, R.A. MacGill, Nucl. Instrum. Methods, B 127/128 (1997) 779. [5] E.M. OksG.Yu. Yushkov, P.J. Evans, A. Oztarhan, I.G. Brown, M.R. Dickinson, F. Liu, in: R.A. MacGill, O.R. Monteiro, Z. Wang (Eds.), Hybrid GasMetal Co-Implantation with a Modified Vacuum Arc Iyon Source, Nucl. Instrum. Methods, B, vol. 127/128, p. 782. [6] G. Dearnaley, Surf. Coat. Technol. 65 (1994) 1.
Metal vapour vacuum arc ion implantation facility in Turkey ¨ ztarhana,*, I. Brownb, C. Bakkalogluc, G. Wattd, P. Evansd, E. Okse, A. O A. Nikolaeve, Z. Tekf a Ege University, Bio Engineering Department, 35100 Izmir, Turkey Lawrence Berkeley National Laboratory, University of California, CA 94720, USA c ELTASS , AOSB, 35200 C¸ig˘li, I˙zmV r, Turkey d Australian Nuclear Science and Techonology Organization Menai, NSW 2234, Australia e High Current Electronics Institute, Tomsk, Russia f Celal Bayar U¨niversitesi Fen EdebiyetFaku¨ltesi Fizik Bo¨lu¨mu¨ 45040 Muradiye/Manisa, Turkey b
Available online 2 October 2004
Abstract A vacuum arc ion source based metal ion implantation facility is built and in operation at TUBITAK (The Scientific and Technical Research Council of Turkey), Izmir, Turkey and a surface modification research and development program is being carried out here. The system is similar to the one in Lawrence Berkeley Laboratory, which was first built and developed by Brown et al. The broad-beam ion source can be repetitively pulsed at rates up to ~50 pulses per second and the extracted ion beam current can be up to ~1 A peak or ~10 mA time averaged. The ion source extraction voltage can be increased up to 110 kV. Additionally, mixed metal and gas ion beams were generated by a magnetic field, which was obtained through a magnet coil located in front of anode plate and by adding gas in the discharge region. This modified system was used to form buried layers of mixed metal–gas species such as Ti+N (on 316 SS and Ti alloy samples) and Zr and W (316 SS and Ti alloy samples, respectively) of which their hardness, coefficient of friction and wear volumes were measured and their RBS results were obtained. The anodic electrochemical tests showed that the corrosion resistance of Ti implanted 304 SS samples was increased with the dose. Micro structures of Ti implanted surfaces of 304 SS samples were examined with SEM before and after the corrosion tests and the results showed that the pittings were formed mostly in the areas where implanted Ti concentration was less. Recently, the system is equipped with TOF for measuring the charge state distribution of ions. R&D work is planned for the purpose of forming tribologically enhanced materials for industrial applications by using ion implantation, PVD coating, plasma nitriding and their combinations. The results showed that the hardness and performance of ion implanted (with various metals and N) PVD coated cutting inserts increased remarkably. The use of ion implantation techniques in modifying the properties of textile and other materials and optimising the performance of textile and other industrial machine parts and tools is also being investigated and some of the results are presented in this work. D 2004 Elsevier B.V. All rights reserved. Keywords: Ion implantation; Surface Modification; Ion Beams; Duplex treatment; Tribology; Surface treatment
1. Introduction Early studies on the implantation of metal ions were not as numerous as their gaseous counterparts. This may have been partly due to the relative superiority, at the time, of ion sources that generated ions from stable gases. In contrast, many metal ion sources of that period employed either * Corresponding author. Tel.: +90 232 323 30 34; fax: +90 232 374 42 84. ¨ ztarhan). E-mail address: [email protected] (A. O 0257-8972/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2004.08.178
reactive gases, or solid or liquid feed materials. Decomposition and ionisation of these materials often caused accelerated degradation of ion source components, which shortened operational life. The ion beam currents generated by many of these sources were also comparatively low which extended the time required for high dose implants. These limitations have (to a large degree) been overcome during the past 20 years, with the development of new types of metal ion sources [1], and improvements to existing types; the metal vapour vacuum arc (MEVVA) ion source falls into the former category.
328
A. O¨ztarhan et al. / Surface & Coatings Technology 196 (2005) 327–332
Invented by Brown et al. [2] at Lawrence Berkeley National Laboratory, the MEVVA ion source utilises a vacuum arc plasma as the source of metal ions which are subsequently extracted and accelerated by three beam formation electrodes. The simplicity of MEVVA sources combined with their ability to produce ions of most metals have become an established tool for ion implantation research. Currently, a number of laboratories worldwide have MEVVA systems from which a substantial number of publications have resulted. Tu¨bitak Textile Research Center in Izmir is a recent addition to the list of organisations operating this type of facility. The present report describes briefly the MEVVA ion implanter recently installed there. The MEVVA ion implanter has been employed in generating high current metal ion beams which are used for ion implantation to modify the composition of the near surface region of materials. Usually the vacuum arc ion sources can generate only metal ion beams, but for many metallurgical and other surface modification appplications it is necessary to form the buried layers of mixed gas–metal species. It was shown earlier by Efim et al. [3] that a certain amount of gas ions can be produced in a vacuum arc ion source if a magnetic field was applied in the anode chamber by a magnetic coil fed by the discharge current of about 100 A, which is induced by the power supply of the vacuum arc. It was reported that mean charge states of ions and their energies can be increased with magnetic field [4]. We upgraded our MEVVA multi cathode ion source in this way and used this technique for hybrid co-implantation of nitrogen with various metals to modify some materials surfaces including textiles. Furthermore, our MEVVA ion implanter system was recently equipped with the Time of Flight mass spectrometer (HCEI-TOMSK) to measure the charge state distribution of the beam generated by the source.
2. Description of the facility The MEVVA Ion Implantation System was first installed in 1997 in Dokuz Eylul University and was dismantled and set up again at TUBITAK Textile Research Center and equipped with TOF in 2003. The ion source is built to the MEVVA-V design of Dr. Ian Brown. This family of ion sources has been evolving since MEVVA I, which was built in 1982. The main elements of MEVVA ion source are shown in picture [1], which is a more recent 18-cathode design and the essential electrical elements of a MEVVA ion source are shown in Fig. 1. The major functional components of the ion implanter are as follows: (1) Vacuum system and sample processing chamber, (2) 0 to 100 kV DC extractor power supply (current output 0 to 10 mA),
Fig. 1. Essential electrical elements of a MEVVA ion source.
(3) Ion source assembly, (4) 220 V to 220 V mains voltage isolation transformer (not shown) which powers: 4(a) Trigger voltage generator (10 kV/30 A, pulsed), 4(b) Arc current power supply (0 to 700 V/0 to 500 A, pulsed), (5) Common electronic measurement instruments (Oscilloscope, Pulse Generator), (6) Second-grid power supply (0 to 2 kV DC/0 to 10 mA), (7) Protective enclosure (faraday cage)to contain the high-voltage and to provide radiation shielding. The sample processing chamber was fabricated from 316 stainless steel and it has an internal diameter of 480 mm, 4150 mm diameter sample access ports and a pressure measurement port, and is equipped with an Alcatel maglevATP1500 turbopump-based vacuum system for clean vacuum. Ion source, turbo pump and one of the sample access ports have VAT gate valves. The extractor power supply is powered from the 220 V mains by means of a 0–220 V, 20 A variable autotransformer. The high-voltage output is controlled by manually varying the auto-transformer output voltage setting. 220 V–220 V Mains Voltage Isolation Transformer is rated at 6 kVA and provides 220 V AC power for the electronics in the arc and trigger power supplies. These power supplies operate at the extractor voltage potential, up to 100 kV above ground. Therefore the isolation transformer must provide a very high degree of electrical isolation between primary and secondary windings, and was constructed so that the risk of high-voltage breakdown (and electrical leakage) on the secondary winding is minimal. This has been achieved by bringing the load terminals out by means of a fiberglass bushing 90 mm in diameter and approximately 500 mm high. A MEVVA ion source typically operates at arc current levels up to 500 A and voltages up to 700 V. The arc current may be steady DC for the implantation period, but it is more commonly a train of square pulses. Typically, less than 0.1%
A. O¨ztarhan et al. / Surface & Coatings Technology 196 (2005) 327–332 Table 1 Mechanical characterisation tests of implanted 316 and Ti–6Al–4V sample with various ions Samples
Implanted
Hardness (Hv)
Coefficient of friction
Wear (Am2)
316 LSS 316 LSS 316 LSS Ti–6Al–4V Ti–6Al–4V Ti–6Al–4V
Unimplanted Zr Ti+N Unimplanted Ti+N W
350 1500 2600 450 2600 1800
0.68 0.50 0.44 0.67 0.65 0.66
9.6 2.8 3.3 7.3 0.51 0.53
Each sample (30 mm dia., 4 mm thick) were polished down to 0.01 Am Ra. Samples implanted with Doses: 110e17, Extraction voltage: 50 kV. Hardness measured with CSEM Nano Indenter, Load: 10 mN. Wear tracks and friction coefficents were obtained by CSEM Tribotester. Wear values were calculated from the wear track profiles obtained with Mahr profilometer.
of the arc current flows to the target—the remaining 99.9% flows to the ion source bgroundQ and performs no useful function. The arc current pulse duty cycle (bonQ time/boffQ time) is typically less than 1%, and this pulsed mode is very convenient because: ! it results in minimal heating (and distortion) of the ion source and target, ! the power supply may be very simple and can be easily protected against load faults, ! the power supply internal heating is low, and, ! the average currents required from the other (highvoltage) power supplies are low. The pulsed mode requires an electronic pulse generator to define the trigger rate, and a means of re-triggering the arc discharge upon receipt of every pulse. The re-triggering is performed by a btrigger power supplyQ which generates a narrow 10–30 A current pulse at a voltage of up to 11 kV. This is applied across the surface of the cathode (implanting) material. Both the arc and trigger power supplies are located in a smoothed and rounded aluminium housing. Fiber-optic cables are used to transmit the pulse generator signal to the trigger power supply, and the signals that monitor arc voltage and current are transmitted to ground potential by two more fiber-optic links. Such fiberoptic links allow signal transmission over large voltage differences in a safe, reliable, and robust manner. To summarise, the ion source power supply unit contains an arc current power supply, a trigger power supply, and fiber-optic links from the extractor potential to ground. The system derives AC power from an isolation transformer insulated to withstand high voltages. This transformer is energised by a control unit which provides: ! an input to accept a pulse generator output, ! readout meters for indicating extractor and arc voltage, ! connectors for providing waveforms to an oscilloscope, and,
329
! connections from interlock circuits, which prevent unsafe operation. The arc power supply consists of a six-stage LC transmission line with an electrical delay time of 250 As. It is charged to a DC voltage which is varied by the user by means of a variable ratio auto-transformer using an insulating perspex shaft. The arc current is directly related to the charging voltage. The second grid of the ion source is normally operated at a negative bias voltage in order to suppress electrons; this voltage is not critical. We modified our ion source by introducing a magnetic coil and the gas inlet into the anode region as described by Efim et al. [3] to obtain mixed ion beams of metal and gas ion species to form the buried layers of mixed metal–gas species with regulated ratios [5]. The system was also equipped with Time Of Flight (picture [2]) to measure the mean charge state of ions.
3. Results Over the past 15 years, MEVVA ion sources have contributed significantly to the field of metal ion implantation. They have been used to implant a wide range of materials with mostly beneficial results [6]. Even a brief review of the latter is beyond the scope of the present report. However, several representative results will be briefly described in order to illustrate the sorts of improvements that were achieved. 3.1. Increased hardness and reduced wear The modification of metal surfaces for increased hardness and reduced wear has been a particular focus of MEVVA ion implantation research to date. Some of the mechanical characterisation tests of implanted 316 L Stainles Steel and Ti–6Al–4V are shown in Table 1. All
Fig. 2. RBS result of Zr implanted on 316.
A. O¨ztarhan et al. / Surface & Coatings Technology 196 (2005) 327–332
330
Fig. 3. RBS result of W implanted on 316.
samples were implanted with a dose of 11017 ions/cm2, and extracted voltage of 50 kV. For wear tracks, and measurement of coefficient of friction, CSEM Tribotester with 6 mm diameter Alumina ball was used on 30 mm diameter and 4 mm thick disk samples. Wear areas were estimated from the measured profiles across the wear tracks with Mahr profilometer. Hardnesses of samples were measured with CSEM nano indenter with a load of 10 mN. RBS results of Zr and W implanted on 316 are shown in Figs. 2 and 3, respectively. The hardness of Zr implanted 316 SS sample increased by a factor of 4 and increased by a factor of 7 for Ti+N hybrid ion implanted 316 SS sample compared to unimplanted 316 SS samples. In both cases the coefficient of friction decreased approximately by 30%, wear rates decreased approximately by factor of 3. However, coefficient of friction of W and Ti+N hybrid ion implanted Ti–6Al–4V samples did not change but their hardnesses increased by a factor of 4 and 5.5, respectively, compared to unimplanted ones. Wear rates of W implanted and Ti+N hybrid ion implanted Ti–6Al–4V samples decreased by a factor of 18. Hardnesses of some PVD coated inserts which were implanted with various metal ions were measured and the results are shown in Table 2. The hardness of samples was measured by CSEM Nano indenter tester with 10 mN load. The results show that the hardness of PVD TiN coated insert increased most when implanted with W ions with a dose 11017 ions/cm2 and at an extraction voltage 50 kV.
Table 2 Hardness values of ion implanted PVD coated cutting inserts Hardness of cutting inserts (Hv)
Before implantation After implantation
Al implanted PVD TiCN coated inserts
Al implanted PVD TiN coated inserts
Al+W implanted PVD TiN coated inserts
W implanted PVD TiN coated inserts
3000 3930
2200 2920
2200 3280
2200 3330
Fig. 4. Anodic polarisation curves of unimplanted and Ti implanted 304 SS samples with doses of 11016 and 11017 (at an extraction voltage of 50 kV), and pure Ti samples.
3.2. Corrosion behaviour of Ti implanted 304 SS samples Corrosion behaviour of 304 SS samples were observed by performing the electrochemical corrosion tests in a 3.5% NaCl solution. Samples were unimplanted 304SS, pure Ti, and Ti+ implanted 304 SS samples with doses of 11016 and 11017 ions/cm2 at 50 kV extraction voltage. Measurements were taken in 15 mV/min steps. Anodic polarisation curves obtained together with pure Ti sample are shown in Fig. 4. The results showed that the corrosion resistance of 304 SS samples increased with Ti ion implantation and was better with a higher dose. Pictures (3) and (4) show SEM micrographs of pittings and elemental line distribution of Ti after and before the corrosion tests, respectively. Pictures show that Ti depleted regions coincide with places where pittings occurred and their sizes were the same indicating that after the Ti ion implantation, Ti rich regions may inhibit corrosion with the formation of TiO2.
Table 3 Flame retardancy of cotton fabric implanted with various ions NO
Fiber
CO8 CO9 CO10
Cotton Cotton Cotton Cotton
Ion implantation
Extraction voltage and dose
Results (s)
Ti+Al+N Cr+N W+C
20 kV 11016 20 kV 11016 20 kV 11016
12.8 13.5 12.4 46
A. O¨ztarhan et al. / Surface & Coatings Technology 196 (2005) 327–332
331
Table 4 Hydophility and flame retardancy of PES fabrics implanted with C ions
Table 6 Wear tests of cotton and polyester fabrics implanted with various ions
Fabric
Ion implantation
Energy and dose
Results
Samples
Ion implantation
Break off at no. of revolution
Weight loss (%)
PES
–
–
10 kV, 11015 cm 10 kV, 21015 cm 10 kV, 11016 cm
– Ti+Al+N Cr+N W+C – Ti+N Ti+Al+N W+C Ti+N
12.9 13.89 13.8
C
Unimplanted cotton CO8 CO9 CO10 Unimplanted PES PES16 PES19 PES20 PES21
19,000 18,000 20,000
PES
Hydrophility (min) 13.11 2.93
PES PES
C C
Flame retardancy (s) 10 10
2
4.96
There is no flame 24
2
7.5 2
a
3.3. Changing the properties of some textile materials by ion implantation An attempt was made to change the properties of some textile materials by ion implantation of various ions without changing their bulk properties. Flame retardancy, hydrophility, hydrophobity, pilling and abrasion resistance properties of ion implanted Cotton and Polyester fabrics were measured and the results are given in Tables 3–6. Flame retardancy was measured with CFR1610, hydrophility and hydrophobity were measured with TS866(1985) standards. Resistance to pilling and change of appearance of fabrics were determined by modified Martindale method (ISO/D15, 12945-2). Abrasion resistance of textile fabrics was determined by Martindale method TS EN ISO12947-2, and the bursting properties of fabrics were determined by BSEN ISO13938-2 standard.
Table 5 Hydrophility and pilling tests of implanted cotton fabrics with various ions NO
Fabric
Implantation Experimental Results conditions Pilling Hydrophility (s)
CO1
Unimplanted – cotton cotton C
CO2
cotton
C
CO3
cotton
C
CO4
cotton
Cr
CO5
cotton
Cr
CO6
cotton
Cr
CO7
cotton
Cr
CO8
cotton
Ti+Al+N
CO9
cotton
Cr+N
CO10 cotton
W+C
–
1–2
0.3
20 kV, 21015, 908 10 kV, 21015, 308 15 kV, 11016, 908 15 kV, 21015, 908 20 kV, 11015, 908 25 kV, 51015, 458 20 kV, 11016, 458 20 kV, 11016 20 kV, 11016 20 kV, 11016
2.5
41.6
2
44
3
96
2
7
1–2
4.2
3–4
–
–
111
–
59
4.35a 3.64a 1.36a 1.2 0.9
Weight loss at number of 24,000 revolution.
The results showed that best flame retardancy of cotton was obtained when it was implanted with W+C ions at extraction voltage of 20 kV and at 11016 ions/cm2 dose, whereas the best flame retardancy of Polyester(PES) was obtained (infact there was no flame) when it was implanted with C ions at an extraction voltage of 10 kV and at 21015 ions/cm2 dose. Hydrophility of PES was better found with low doses of C. The results in Table 5 show that Cotton fabric became hydrophob and its hydrophility decreased by a factor of 900 when implanted with W+C ions at an extraction voltage of 20 kV and 11016 ions/cm2 dose. Best pilling conditions of cotton fabric was found when it was implanted with Cr ions at an angle of 458 and at an extraction voltage of 25 kV and 11016 dose. Table 6 gives the results of abrasion resistance of cotton and PES fabrics. Because of wiry nature of cotton fibers as seen in picture [5] the abrasion resistance of cotton fabric cannot be improved by ion implantation as fibers break off easily. However, abrasion resistance of PES fabric increased by ion implantation and the best result was obtained with the implantation of Ti+Al+N ions (at an extraction voltage of 25 kV, 11016 dose). As compared to cotton fibers, PES filaments are smooth and regular as shown in picture.6, thus PES fabric has an advantage of utilising ion implantation.
1.5
2.3
–
24.000 28,000 28,000 11,000 10,000
268.25 Fig. 5. Charge state distribution of Ti+N ions.
332
A. O¨ztarhan et al. / Surface & Coatings Technology 196 (2005) 327–332
so novel. From this work have emerged many possibilities, which may become successful applications in the future. It is the exploration of these many possibilities over several decades which has provided the wealth of information currently available on the modification of surface properties by ion implantation. Systems like the MEVVA ion implanter described above have made a significant contribution to this process and it is expected that this contribution will continue into the foreseeable future.
Acknowledgements
Fig. 6. Charge distribution of Cr+N ions.
To obtain Ti+Al+N ion implantation, Al ion implantation was done after the Ti+N metal gas hybrid ion implantation. Ion charge state distribution of Ti+ N and Cr+ N, which were obtained with TOF, are shown in Figs. 5 and 6, respectively. It was also observed that implanting both sides of PES fabrics by Cu ions at an extraction voltage of 25 kV and 11016 ions/cm2 dose, prevented static electricification of PES fabric.
4. Summary In this report, we have briefly described a typical MEVVA ion implanter with reference to the system currently operating at Tubitak Textile Research Center. In addition, several applications including textile fabrics of metal ion implantation and metal–gas hybrid ion implantation have been presented. The preliminary results show that the utilisation of ion implantation in textiles especially in technical textiles looks (might be) very promising as it’s
The MEVVA Ion Implantation System was built with a fund from the bScientific and Technical Research Council of Turkey (TUBITAK) Q under project no. MISAG 43. Coauthor’s; I. Brown, C. Bakkalog˘lu, G. Watt, P. Evans, E. Oks and A. Nikolaev were involved with MEVVA Ion Implanter. The author thanks TUBITAK Textile Research Center for supporting the work with the textiles and I. ¨ ktem, E. O ¨ zdog˘an, A. Karaaslan and S. Tarakc¸Vog˘lu, T. O NamlVgo¨z for their work related to some of the characterisation tests with textiles.
References [1] I.G. Brown, The Physics and Technology of Ion Sources, Wiley, New York, 1989. [2] I.G. Brown, J.E. Galvin, B.F. Gavin, R.A. MacGill, Rev. Sci. Instrum. 57 (1986) 1069. [3] E. Oks, P. Spadtke, H. Emig, B.H. Wolf, Rev. Sci. Instrum. 65 (1994) 3109. [4] E.M. Oks, A. Anders, I.G. Brown, M.R. Dickinson, R.A. MacGill, Nucl. Instrum. Methods, B 127/128 (1997) 779. [5] E.M. OksG.Yu. Yushkov, P.J. Evans, A. Oztarhan, I.G. Brown, M.R. Dickinson, F. Liu, in: R.A. MacGill, O.R. Monteiro, Z. Wang (Eds.), Hybrid GasMetal Co-Implantation with a Modified Vacuum Arc Iyon Source, Nucl. Instrum. Methods, B, vol. 127/128, p. 782. [6] G. Dearnaley, Surf. Coat. Technol. 65 (1994) 1.