IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 39, NO. 11, NOVEMBER 2011 3061 Surface Corrosion of Ti–16Si–4B Powder Alloy Implanted With Nitrogen by Plasma-Based Technique Bruno Bacci Fernandes, Mario Ueda, Graziela da Silva Savonov, Carlos de Moura Neto, and Alfeu Saraiva Ramos Abstract—Titanium materials with a new ternary phase, Ti6 Si2 B, can be manufactured by high-energy ball milling and further sintering of titanium, silicon, and boron powders. In this paper, hot pressing was chosen to compact the granules and then prevent high porosity and grain coarsening during sintering. Subsequently, the surface of the Ti–16Si–4B (at.%) alloy was modified by nitrogen ion implantation using a plasma immersion technique. The marine corrosion behavior of this powder alloy was studied in this paper. Scanning electron microscopy and X-ray diffraction analyses were performed on the powders and alloys in order to observe phase compositions and morphologies. The morphology of sample surfaces was also observed by utilizing an atomic force microscope. The concentration profile of the detected elements has been investigated using Auger electron spectroscopy depth profiling. The results show that a shallow nitrogen-rich layer was obtained after implantation treatment. Potentiodynamic analyses showed that, with the nitrogen insertion, there is a significant reduction of the anodic current in almost the whole potential spam explored, meaning that the corrosion rate decreases when ion implantation is performed. Index Terms—Corrosion, plasma applications, surface treatment, titanium alloys. I. I NTRODUCTION MPROVEMENTS OF aircraft and spacecraft necessitate the use of high specific-strength low-density materials [1], [2]. With such property and also excellent corrosion resistance, titanium alloys are potential candidates for widespread applications in these vehicles. However, it is necessary to prevent oxygen diffusion into these alloys if they are intended to be used at elevated temperatures. Working temperatures up to 1000 ◦ C can be achieved in alloys by intermetallic matrix and intermetallic dispersion strengthening. Silicon addition, for I Manuscript received January 28, 2011; revised March 23, 2011 and April 28, 2011; accepted June 1, 2011. Date of publication July 14, 2011; date of current version November 9, 2011. This work was supported in part by the Research Funding of São Paulo State (FAPESP) and National Council of Research and Development (CNPq) funding agencies. B. Bacci Fernandes, M. Ueda, and G. da Silva Savonov are with the National Institute for Space Research (INPE), 12227-010 São José dos Campos, Brazil (e-mail: brunobacci@yahoo.com.br; ueda@plasma.inpe.br; grazielads@ig.com.br). C. de Moura Neto is with the Department of Mechanical Engineering, Technological Institute of Aeronautics (ITA), 12228-900 São José dos Campos, Brazil (e-mail: mneto@ita.br). A. Saraiva Ramos is with the Materials Department, São Paulo State University (UNESP), 12516-410 Guaratinguetá, Brazil (e-mail: alfeu@hotmail.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPS.2011.2159031 example, increases corrosion and creep resistance of titanium and some of its alloys [3]. Ion implantation has been utilized as an effective method for improving the oxidation behavior of titanium alloys [4], [5]. TiN coatings obtained by plasma immersion ion implantation (PIII) increase the wear and corrosion resistances when adopted in pure titanium substrates [6], [7]. However, silicon-containing films showed significantly better oxidation resistance compared to that of TiN. Ti–B–N films are also attracting much attention due to the combination of high hardness and wear/corrosion resistance. However, oxidation resistance of Ti–B–N films was shown to be much lower than that of Ti–Si–N nanocomposite films. Ti–Cr–B–N films also show good values of hardness and wear resistance, aside from a thermal stability of up to 1000 ◦ C and an oxidation resistance of up to 900 ◦ C [8]. It is possible to form titanium oxynitrides that are promising as functional coatings on titanium alloys [9]. All these examples show different variables, as methods, parameters, and materials, and it is more adequate that their property data be corroborated by other researchers. Mechanical alloying uses high-energy ball milling for obtaining new synthetic powders through a self-reacting process, which allows a subsequent production of nanomaterials starting from mixed elemental powders [10]–[15]. High-energy ball milling is a cost-effective method to achieve ultrafinegrained and dispersion-strengthened microstructure from powder mixtures. Interesting results are obtained with coarse grains (above 500 nm) embedded in a matrix of smaller grains (below 500 nm) [16], [17]. Owing to the formation of reinforcements within the matrix during fabrication, there are several potential advantages associated with in situ composites [2], [18]. Material scientists demonstrated the good fatigue properties of in situ Ti–6Al–4V (wt%) composites with TiB reinforcements [19]. Additions of several elements and also excess of silicon can increase the stability of Ti5 Si3 and reduce its thermal expansion anisotropy [20]–[22]. In this paper, a multiphase structure with a significant contamination is characterized to aid these improvement trials. In the marine environment, the corrosion rate is almost doubled compared with acidic and industrial environments [23]. The corrosion of DLC-coated metallic substrates is thought to occur at flaws or pores of the films; then, the use of techniques that reduce the porosity could promote further improvement on the corrosion protection ability [24]. The alpha titanium alloys are commonly used in applications where corrosion resistance 0093-3813/$26.00 © 2011 IEEE 3062 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 39, NO. 11, NOVEMBER 2011 is a primary concern. The corrosion potential of IMI-834 alloy in 3.5% NaCl is about −400 mV, and its corrosion current is 169 µA/cm2 [23]. Commercial pure titanium after oxynitriding shows a corrosion potential of 360 mV and a corrosion current of about 10−4 µA/cm2 in 3% NaCl solution. Such good corrosion resistance is due the higher nitrogen content of the oxynitrides; however, the test parameters were not described in this paper [9]. Corrosion resistance and hardness of Ti–6Al–4V alloy were improved by high-temperature PIII [25]. Ti–Si–B materials can be applied as sputtering targets in vacuum arc and magnetron synthesis of thin films and coatings [26]–[28]. When pressureless sintering is adopted for Ti–Si materials, there is a temperature limit that the liquid temperature is exceeded by a thermal explosion. Such phenomenon causes shrinkage of the sintered specimens, maybe under surface tension force. Ti–15Si and Ti–20Si (at.%) sintered samples present a maximum density of around 3.9 g/cm3 [28]. Moreover, the Ti5 Si3 phase is a material of considerable technological importance [29], and titanium borides exhibit an excellent combination of properties [30], [31]. In this paper, we present current knowledge on surface modification of new Ti–16Si–4B alloy using nitrogen PIII at moderate temperature, including phase formation, surface morphology, and corrosion properties of the resulting surface layer. II. E XPERIMENTAL Titanium powder (99.9 wt%, particle sizes < 110 µm, spherical particle shape) was used as the matrix material. The alloying elements were silicon (99.999 wt%, particle sizes < 43 µm, irregular particle shape) and boron (99.5 wt%, particle sizes < 43 µm, angular particle shape) powders. The powder mixtures were prepared by mixing the components in a planetary ball mill for 1 h in a dry medium. Milling and handling of the powders were done under argon atmosphere. Stainless steel vials and balls, a rotary speed of 300 r/min, and a ball-topowder weight ratio of 10:1 were used. The Ti–16Si–4B powders were hot pressed at 1030 ◦ C and 1060 ◦ C, with 30 MPa and a 20-min dwell time. According to the Ti–Si–B isothermal section at 1250 ◦ C [32], the adopted composition forms a three-phase alloy composed only by α-titanium, Ti5 Si3 , and Ti6 Si2 B phases. The specimens were polished with silicon carbide papers and cloth, the latter with silica colloidal suspension. They were ultrasonically washed in isopropyl alcohol for 10 min. To calculate the density of the samples, they were weighted, and their sizes were measured. Samples of Ti–16Si–4B alloy (10-mm diameter and 2–4 mm thick) with polished surface were assembled onto a sample holder. The experimental setup for the present nitrogen PIII processing of Ti–16Si–4B alloys is shown elsewhere [33]. For nitrogen implantation into Ti–16Si–4B, a dc glow discharge plasma with a density of 1010 cm−3 was produced in a 5-mtorr nitrogen gas pressure, and high voltage pulses of 14-kV amplitude, 40-µs duration, and 300-Hz repetition frequency were applied to the stainless steel sample holder for 120 min. The process temperature of around 300 ◦ C was measured by an optical pyrometer. The crystal lattice of the alloys was studied by means of X-ray diffraction (XRD) using a Philips (model X’Pert MRD) and a Shimadzu (model XRD6000) diffractometers with Cu Kα radiation. The former equipment was operated in BraggBrentano and glancing incidence modes. The morphology and the chemistry of the powder and bulk materials were analyzed by scanning electron microscopy (SEM) using a LEO 440 system, equipped with an energy-dispersive spectrometer (EDS). Surface morphology of the bulk samples was analyzed by atomic force microscopy (AFM) operating the Shimadzu SPM-9500J3 nanoindenter in the dynamic mode. AES depth profiling (Auger electron spectrometer Microlab 310-F) was used in order to get the depth dependence of the chemical composition of the surface region. AES profiles were obtained by using argon ions for sputter etching. Potentiodynamic polarization versus current density technique was used to study the corrosion characteristics. The corrosion resistance of Ti–16Si–4B was tested in a 3.5 wt% NaCl medium, with pH = 6. The tests were carried out by utilizing an Autolab PGSTAT302N potentiostat/galvanostat. A conventional electrolitic cell with three electrodes, consisting of one working electrode of Ti–16Si–4B alloy untreated or treated by a PIII sample, a Ag/AgCl reference electrode, and a platinum wire as a counter electrode, was used to perform the polarization experiments. A potential range from −1.0 up to 1.5 V was applied with the sweep rate of 1.0 mV/s. Three specimens were tested for each condition. In order to confirm the degradation mechanism, the corroded specimens were observed by means of a SEM. A Ti–6Al–4V sample without PIII treatment was also polished and subsequently submitted to the same corrosion test for comparison with the Ti–16Si–4B alloys produced by this research. III. R ESULTS AND D ISCUSSION The Ti–16Si–4B specimens present a density of around 4.3 g/cm3 after hot pressing (HP) and polishing. This value confirms the densification efficiency of the HP technique even with the use of coarse powders and lower temperature/time [34]. After PIII treatment, the surface of the samples presented a gold color, despite no formation of new nitrided phases has been observed by XRD. Fig. 1 presents XRD results obtained for Ti–16Si–4B powder alloy treated by PIII after corrosion tests. These XRD patterns present the microstructure of the surfaces of the Ti–16Si–4B alloy, which were measured in different diffractometers. XRD analyses before corrosion tests show similar microstructures for the untreated and treated Ti–16Si–4B samples [34]. The use of the high-resolution (HR) equipment aspires to identify phases with lower elemental or compound contents, whose peaks are not detected by the common diffractometer. It may be noted that TiB peaks are present in Ti–16Si–4B alloy, beyond the desired phases (Ti, Ti6 Si2 B, and Ti5 Si3 ). The additional peaks present in this diffractogram could be attributed to reflections of several phases, e.g., Ti3 Si, Ti4 N3 B2 , TiB0.024 O2 , and Ti3 SiC2 . As visualized by the HR diffactometer in the Bragg-Brentano mode, the new peaks may be attributed to the TiH phase BACCI FERNANDES et al.: SURFACE CORROSION OF Ti–16Si–4B POWDER ALLOY 3063 TABLE I F OUR S TRONGEST XRD R EFLECTIONS OF THE α-Ti, TiB, TiH, Ti5 Si3 , Ti3 Si, AND Ti6 Si2 B P HASES Fig. 1. XRD results of treated Ti–16Si–4B alloys after corrosion tests. (a) Shimadzu diffractometer. (b) Philips diffractometer. that was formed by the hydrogen reactions in the corrosion solution. Table I lists the XRD positions of phases found in the Ti–16Si–4B powder alloy at different conditions. Subsequent research regarding composition and morphology of the unknown phases must be done by transmission electron microscopy to improve the understanding of their effects in the Ti–16Si–4B alloy. Through the AFM technique, it was verified that the surface is covered by almost fully developed 3-D islands [see Fig. 2(b)]. This result is quite different from the unimplanted sample which shows a more flattened structure as shown in the image of Fig. 2(a). The roughness out of areas with porosity was increased from 0.4 to 7.6 nm. Such value rises to around 740 nm at porous regions. As measured by AES (see Fig. 3), the nitrogen penetration depth in the treated sample is about 30 nm with a maximum concentration of about 35 at.% at a depth of about 18 nm. Oxygen up to 10 at.% was also found in both the untreated and treated alloys until a depth of 25 nm. Titanium has high reactivity with oxygen when exposed to air; hence, such an element appears in both alloys at former layers. SEM analyses of the Ti–16Si–4B surface [34] reveal a microstructure mainly comprising the Ti5 Si3 , Ti6 Si2 B, and α-Ti phases uniformly distributed, with a maximum phase size of 100 µm. The conclusions regarding the composition are based on the XRD data, the average atomic number dependence of the SEM image, and the EDS microanalysis. Generally, TiB grows in specific crystallographic directions [30], but it is noteworthy from recent works that lower sintering temperatures produce equiaxial borides [13], [34]. Glancing measurements were done adopting omega up to 1◦ , and they show the same diffraction peaks but with a very noisy background. This happens due to the relatively high roughness of the analyzed samples (larger than 60 nm). As the XRD results, no difference was observed between the treated and untreated samples measured by the EDS [34]. The SEM experiments also reveal residual porosity below 70 µm and some unreacted boron particles. The use of powders processed with short milling time has disadvantages such as relative high crystallite size and coarse grains, but it has advantages such as high powder yield (100%) and lower contamination. EDS spot analysis shows a silicon solubility in the alpha titanium phase of 2.9 at.%, and in the iron-rich titanium phase, this solubility increases to 4.2 at.%. The iron content in this latter phase is of 6.9 at.%, chromium of 1.5 at.%, and nickel of 0.1 at.%. The Ti5 Si3 phase also dissolves 0.3 at.% of iron and 1.7 at.% of nickel. Sodium (maximum of 1.6 at.%) was detected on the tested samples, indicating that NaCl ions were deposited in the specimens. The observed pits (see Fig. 4) on the surface of the Ti–16Si–4B treated alloy indicate this material as susceptible to the pitting corrosion in the NaCl solution. Normally, pits initiate at imperfection sites such as surface compositional heterogeneities and porosities when these sites are exposed to a corrosive medium. The results of the potentiodynamic polarization test of titanium alloys in the NaCl solution are shown in Fig. 5. The samples are dissolved above corrosion potential when titanyl ions of tetravalent titanium pass into the solution. By comparing 3064 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 39, NO. 11, NOVEMBER 2011 Fig. 2. (a) AFM—untreated sample. (b) AFM—sample treated by PIII. region of scanned potentials, meaning that the corrosion rate decreases when such alloys are adopted. The peak presented by the untreated Ti–16Si–4B is due to a rupture of the passive film and its repassivation. With the nitrogen implantation, the rupture peak disappeared. This behavior can be attributed to the formation of a layer of higher stability. IV. C ONCLUSION Fig. 3. AES results of elemental concentration (titanium, carbon, oxygen, and nitrogen). the polarization behavior of the implanted sample, a shift in corrosion potential to more noble values was observed. Such potential of Ti–16Si–4B alloy treated by PIII is about −260 mV. The initial section of the cathodic curve is related to hydrogen release, and the other corresponds to the desorption of previously adsorbed oxygen bonded to the surface. It is observed that, in an unimplanted sample, the passive current density decreased by nitrogen implantation from 5.0 × 10−5 to 2.0 × 10−5 A/cm2 . The passive current density at 0.5 V was obtained from the potentiodynamic polarization curve. As a consequence of the silicon and boron addition, a small shift of the corrosion potential to less positive values was observed; then, these materials need less energy to corrode as compared to the Ti–6Al–4V sample. Both implanted and unimplanted alloys did not show any change in surface appearance observed with the naked eye after corrosion tests. However, it was also confirmed that there is a significant reduction of the anodic current in almost the whole This paper gives new information to the knowledge of the production of Ti–Si–B powder alloys and their corrosion properties. It corroborates with other research works [16] regarding the improvement of surface properties that makes such materials more suitable for the use as implants in the human body for example. The results obtained for HP of the coarse Ti–16Si–4B powders indicated the formation of a crystalline microstructure composed of mainly α-Ti, TiB, Ti5 Si3 , and Ti6 Si2 B. The porosity is below 70 µm, and the phase sizes are below 100 µm. Nitrogen has been implanted into the surface layer of Ti–16Si–4B alloy by a PIII technique. The penetration depth of nitrogen is approximately 30 nm formed by almost fully 3-D islands. The reactions on Ti–16Si–4B powder alloys in a NaCl solution were demonstrated based on electrochemical properties, surface composition, and morphology. These results are summarized as follows. 1) The corrosion resistance of the PIII-treated specimen in a NaCl solution increased in comparison with that of the standard specimen. 2) EDS analysis confirmed that sodium was present on titanium alloy immersed in the NaCl solution. 3) When compared to the Ti–6Al–4V alloy, the investigated Ti–Si–B alloys need less energy to corrode, but at a lower rate. Future efforts will be directed toward the evaluation of new corrosion tests of these powder alloys and the characterization of their mechanical properties, such as hardness and wear/compression resistance. BACCI FERNANDES et al.: SURFACE CORROSION OF Ti–16Si–4B POWDER ALLOY Fig. 4. 3065 SEM micrographs of hot-pressed Ti–16Si–4B alloys after corrosion tests. (a) Secondary electron mode. (b) Backscattering electron mode. Fig. 5. Potentiodynamic polarization curves of different titanium alloys: Ti–16Si–4B standard powder alloy, Ti–16Si–4B powder alloy treated by PIII, and Ti–6Al–4V standard alloy. ACKNOWLEDGMENT The authors would like to thank Dr. F. C. L. de Melo and Dr. V. A. R. Henriques from the Aeronautics and Space Institute (IAE). The authors would also like to thank M. L. B. de Matos for the scanning electron microscopy analysis, J. Bernardes for the help with the pressing operations, Dr. H. Reuther from the Institute of Ion Beam Physics and Materials Research, Dresden, Germany, for the AES experiment, and several coworkers at ITA, IAE, USP, and INPE. R EFERENCES [1] I. Gurrappa and A. K. Gogia, “High performance coatings for titanium alloys to protect against corrosion,” Surf. Coat. Technol., vol. 139, pp. 216– 221, 2001. [2] P. Cavaliere, M. El Mehtedi, E. Evangelista, N. Kuzmenko, and O. Vasylyev, “Hot forming behaviour of Ti–Al–Zr–Si ‘in situ’ metal matrix composite by means of hot torsion tests,” Composites: Part A, vol. 37, no. 10, pp. 1514–1520, Oct. 2006. [3] M. Bulanova, Y. Podrezov, and Y. Fartushna, “Phase composition, structure and mechanical properties of Ti–Dy–Si–Sn alloys,” Intermetallics, vol. 14, no. 4, pp. 435–443, Apr. 2006. [4] A. K. Lal, S. K. Sinha, P. K. Barhai, K. G. M. Nair, S. Kalavathy, and D. C. Kothari, “Effect of 60 keV nitrogen ion implantation on oxidation resistance of IMI 834 titanium alloy,” Surf. Coat. Technol., vol. 203, no. 17/18, pp. 2605–2607, Jun. 2009. [5] Z. He, Z. Wang, W. Wang, A. Fan, and Z. Xu, “Surface modification of titanium alloy Ti6Al4V by plasma niobium alloying process,” Surf. Coat. Technol., vol. 201, no. 9–11, pp. 5705–5709, Feb. 2007. [6] J. D. Damborenea, A. Conde, C. Palacio, and R. Rodriguez, “Modification of corrosion properties of titanium by N-implantation,” Surf. Coat. Technol., vol. 91, no. 1/2, pp. 1–6, May 1997. [7] A. Anders, Handbook of Plasma Immersion Ion Implantation and Deposition. New York: Wiley, 2000, p. 555. [8] D. V. Shtansky, P. V. Kiryukhantsev-Korneev, I. A. Bashkova, A. N. Sheveiko, and E. A. Levashov, “Multicomponent nanostructured films for various tribological applications,” Int. J. Refractory Metals Hard Mater., vol. 28, no. 1, pp. 32–39, Jan. 2010. [9] I. M. Pohrelyuk, V. M. Fedirko, O. I. Yas’kiv, D.-B. Lee, and O. V. Tkachuk, “Influence of parameters of modifying oxygen-containing atmosphere on oxynitriding of titanium alloys,” Mater. Sci., vol. 45, no. 6, pp. 779–789, Nov. 2009. [10] H.-B. Lee, I.-J. Kwon, H.-J. Lee, and Y.-H. Han, “Characterization of mechanical alloying processed Ti–Si–B nanocomposite consolidated by spark plasma sintering,” J. Korean Ceram. Soc., vol. 45, no. 12, pp. 815– 820, 2008. [11] K. Niespodziana, K. Jurczyk, J. Jakubowicz, and M. Jurczyk, “Fabrication and properties of titanium–hydroxyapatite nanocomposites,” Mater. Chem. Phys., vol. 123, no. 1, pp. 160–165, Sep. 2010. [12] E. C. T. Ramos, D. R. dos Santos, C. A. A. Cairo, V. A. R. Henriques, and A. S. Ramos, “Effect of composition and milling parameters on the critical ball milling of Ti–Si–B alloys,” J. Alloys Compds., vol. 483, no. 1/2, pp. 190–194, Aug. 2009. [13] A. N. Silva, G. Silva, A. S. Ramos, A. L. Paschoal, E. C. T. Ramos, and M. Filgueira, “Preparation of Ti + Ti6 Si2 B powders by high-energy ball milling and subsequent heat treatment,” Intermetallics, vol. 14, no. 6, pp. 585–591, Jun. 2006. [14] B. B. Fernandes, A. S. Ramos, and P. A. Suzuki, “Preparation of Ti + Ti6 Si2 B + Ti5 Si3 and Ti + Ti6 Si2 B + TiB powders by high-energy ball milling and subsequent heat treatment,” J. Metastable Nanocryst. Mater., vol. 24/25, pp. 467–471, 2005. [15] B. B. Fernandes, A. S. Ramos, C. M. Neto, F. C. L. Melo, and P. B. Fernandes, “Structural characterization of Ti–18Si–6B and Ti–7.5Si–22.5B alloys processed by high-energy ball milling,” (in Portuguese), Tecnologia em Metalurgia e Materiais, vol. 4, no. 2, pp. 56–62, 2007. [16] D. Handtrack, C. Sauer, and B. Kieback, “Microstructure and properties of ultrafine-grained and dispersion-strengthened titanium materials for implants,” J. Mater. Sci., vol. 43, no. 2, pp. 671–679, Jan. 2008. [17] A. M. Soufiani, M. H. Enayati, and F. Karimzadeh, “Mechanical alloying behavior of Ti6Al4V residual scraps with addition of Al2 O3 to produce nanostructured powder,” Mater. Des., vol. 31, no. 8, pp. 3954–3959, Sep. 2010. [18] S. O. Firstov, M. I. Kuz’menko, L. D. Kulak, A. V. Kotko, O. Y. Koval’, and I. D. Horna, “Structure and properties of high-modulus alloys of the Ti–B system,” Mater. Sci., vol. 42, no. 3, pp. 309–315, May 2006. [19] S. Dubey, Y. Li, K. Reece, W. O. Soboyejo, and R. J. Lederich, “Fatigue crack growth in an in-situ titanium matrix composite,” Mater. Sci. Eng. A, vol. 266, no. 1/2, pp. 303–309, Jun. 1999. 3066 [20] J. J. Williams, Y. Y. Ye, M. J. Kramer, K. M. Ho, L. Hong, C. L. Fu, and S. K. Malik, “Theoretical calculations and experimental measurements of the structure of Ti5 Si3 wit interstitial additions,” Intermetallics, vol. 8, no. 8, pp. 937–943, Aug. 2000. [21] Z. Tang, J. J. Williams, A. J. Thom, and M. Akinc, “High temperature oxidation behavior of Ti5 Si3 -based intermetallics,” Intermetallics, vol. 16, no. 9, pp. 1118–1124, Sep. 2008. [22] J. H. Schneibel and C. J. Rawn, “Thermal expansion anisotropy of ternary titanium silicides based on Ti5 Si3 ,” Acta Mater., vol. 52, no. 13, pp. 3843– 3848, Aug. 2004. [23] I. Gurrappa and D. V. Reddy, “Characterisation of titanium alloy, IMI-834 for corrosion resistance under different environmental conditions,” J. Alloys Compds., vol. 390, no. 1/2, pp. 270–274, Mar. 2005. [24] R. P. O. S. Nery, R. S. Bonelli, and S. S. Camargo, Jr., “Evaluation of corrosion resistance of diamond-like carbon films deposited onto AISI 4340 steel,” J. Mater. Sci., vol. 45, no. 20, pp. 5472–5477, Oct. 2010. [25] L. L. G. Silva, M. Ueda, M. M. Silva, and E. N. Codaro, “Effects of the high-temperature plasma immersion ion-implantation treatment on corrosion behavior of Ti–6Al–4V,” IEEE Trans. Plasma Sci., vol. 34, no. 4, pp. 1141–1147, Aug. 2006. [26] M. Audronis, A. Leyland, A. Matthews, F. V. Kiryukhantsev-Korneev, D. V. Shtansky, and E. A. Levashov, “The structure and mechanical properties of Ti–Si–B coatings deposited by dc and pulsed-dc unbalanced magnetron sputtering,” Plasma Process. Polym., vol. 4, pp. S687–S692, Apr. 2007. [27] D. V. Shtansky, A. N. Sheveiko, M. I. Petrzhik, F. V. KiryukhantsevKorneev, E. A. Levashov, A. Leyland, A. L. Yerokhin, and A. Matthews, “Hard tribological Ti–B–N, Ti–Cr–B–N, Ti–Si–B–N and Ti–Al–Si–B–N coatings,” Surf. Coat. Technol., vol. 200, no. 1–4, pp. 208–212, Oct. 2005. [28] E. N. Korosteleva, G. A. Pribytkov, and A. V. Gurskikh, “Bulk changes and structurization in solid-phase sintering of titanium–silicon powder mixtures,” Powder Metall. Met. Ceram., vol. 48, no. 1/2, pp. 8–12, Jan. 2009. [29] N. N. Thadhani, R. A. Graham, T. Royal, E. Dunbar, M. U. Anderson, and G. T. Holman, “Shock-induced chemical reactions in titanium–silicon powder mixtures of different morphologies: Time-resolved pressure measurements and material analysis,” J. Appl. Phys., vol. 82, no. 3, pp. 1113– 1128, Aug. 1997. [30] Z.-H. Zhang, X.-B. Shen, S. Wen, J. Luo, S.-K. Lee, and F.-C. Wang, “In situ reaction synthesis of Ti–TiB composites containing high volume fraction of TiB by spark plasma sintering process,” J. Alloys Compds., vol. 503, no. 1, pp. 145–150, Jul. 2010. [31] V. V. Patel, A. El-Desouky, J. E. Garay, and K. Morsi, “Pressure-less and current-activated pressure-assisted sintering of titanium dual matrix composites: Effect of reinforcement particle size,” Mater. Sci. Eng. A, vol. 507, no. 1/2, pp. 161–166, May 2009. [32] A. S. Ramos, C. A. Nunes, G. Rodrigues, P. A. Suzuki, G. C. Coelho, A. Grytsiv, and P. Rogl, “Ti6 Si2 B, a new ternary phase in the Ti–Si–B system,” Intermetallics, vol. 12, no. 5, pp. 487–491, May 2004. [33] M. Ueda, L. A. Berni, J. O. Rossi, J. J. Barroso, G. F. Gomes, A. F. Beloto, and E. Abramof, “Plasma immersion ion implantation experiments at the Instituto Nacional de Pesquisas Espaciais (INPE), Brazil,” Surf. Coat. Technol., vol. 136, no. 1–3, pp. 28–31, Feb. 2001. [34] B. B. Fernandes, M. Ueda, C. B. Mello, P. B. Fernandes, H. Reuther, and A. S. Ramos, “Modification of surface properties of Ti–16Si–4B powder alloy by plasma immersion ion implantation,” Intermetallics, vol. 19, no. 5, pp. 693–697, May 2011. IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 39, NO. 11, NOVEMBER 2011 Bruno Bacci Fernandes was born in Pouso Alegre, Brazil, in 1978. He received the B.Sc. degree in mechanical engineering from the College of Industrial Engineering (nowadays ETEP College), São José dos Campos, Brazil, in 2002, the M.Sc. degree in biomedical engineering from the University of Paraíba Valley, São José dos Campos, in 2006, and the Ph.D. degree in aeronautics and mechanical engineering from the Technological Institute of Aeronautics (ITA), São José dos Campos, in 2010. From 2003 to 2010, he was engaged in M.Sc. and Ph.D. research on powder metallurgy with the Institute of Research and Development and Division of Aeronautics and Mechanical, respectively. He is currently with the National Institute for Space Research (INPE), São José dos Campos. Mario Ueda was born in São Paulo, Brazil, on August 16, 1951. He received the B.Sc. degree in physics from São Paulo University, São Paulo, in 1974, the M.Sc. degree from Nagoya University, Nagoya, Japan, in 1978, and the Ph.D. degree from Cornell University, Ithaca, NY, in 1986. During 1990–1991, he was a Visiting Scientist at the National Institute for Fusion Science, Toki, Japan. Since 1978, he has been with the National Institute for Space Research (INPE), São José dos Campos, Brazil. His current research interests include plasma immersion ion implantation, diagnostics of high- and low-temperature plasmas using a neutral lithium beam technique, high-power pulsed systems, and material processing by plasma and ion implantation. Graziela da Silva Savonov was born in São José dos Campos, Brazil. She received the B.Sc. degree in chemical engineering from the Federal University of Minas Gerais, Belo Horizonte, Brazil, in 2002. She received the M.Sc. and Ph.D. degrees in aeronautics and mechanical engineering from the Technological Institute of Aeronautics, São José dos Campos, Brazil, in 2007 and 2011, respectively. She is currently with the National Institute for Space Research (INPE), São José dos Campos. Her current research interests include surface treatment of aluminum and titanium alloys by plasma ion implantation as well as surface corrosion studies of these treated materials. Carlos de Moura Neto was born in Caçapava, Brazil, in 1945. He received the B.Sc. and M.Sc. degrees in metallurgical engineering and nuclear engineering from the Military Institute of Engineering, Rio de Janeiro, Brazil, in 1974 and 1977, respectively, and the Ph.D. degree in aeronautics and mechanical engineering from the Technological Institute of Aeronautics (ITA), São José dos Campos, Brazil, in 1987. Since 1992, he has been with ITA, where he has been involved in materials research, mainly titanium and steel alloys. Alfeu Saraiva Ramos was born in São Paulo, Brazil, in 1965. He received the B.Sc. and Ph.D. degrees in chemistry engineering and materials engineering from the Chemistry Engineering College of Lorena (nowadays, EEL USP), Lorena, Brazil, in 1992 and 2001, respectively, and the M.Sc. degree in mechanical engineering from São Paulo State University, Guaratinguetá, Brazil, in 1997. He is currently with the Materials Department, São Paulo State University. His current research interests include multiphase materials (e.g., Ti–Si–B, Ta–Si–B, Ti–Si, TiB, Nb–Si, Nb–Si–B, Ni–Ti, Ni–Ti–Nb, and Ni–Ti–Zr) processing by high-energy ball milling and their subsequent sintering.