Maysa Terada - Academia.edu (original) (raw)

Papers by Maysa Terada

Surface and Interface Analysis, 2016

The International Journal of Advanced Manufacturing Technology, 2021

Friction stir welding is a solid-state joining/processing technique that offers high strength and... more Friction stir welding is a solid-state joining/processing technique that offers high strength and productivity, resulting in a microstructure similar to hot working cycles. However, high melting temperature metals such as steels cause excessive wear over welding tools, representing a significant economic issue. Most studies conducted in steels have used polycrystalline cubic boron nitride (PCBN) and W-Re composite tools, which offer a combination of high strength and hardness at high temperatures, along with hightemperature stability. However, even those tools are susceptible to tool wear. In the present study, experimental data was collected during friction stir processing of X70 grade pipeline steel plates, using W-Re and PCBN composite tools under well-controlled conditions. Profilometry and optical microscopy were used to quantify the volume loss at the welding tool due to the number of plunges and the welded distance. Torque and transverse force at the welding tool and the welded bead width were measured and related to the wear process. Tool contamination in boron-nitrogen particles and dissolved tungsten was identified at the stir and hard zones, more substantial at the latter.

CORROSION, 2019

To protect Al alloys from corrosion, standard procedures in the aerospace industry use chromium-b... more To protect Al alloys from corrosion, standard procedures in the aerospace industry use chromium-based acid anodizing with subsequent post-treatment steps also containing hexavalent chromium (Cr(VI)) ions. However, environmental and health related concerns associated with Cr(VI) have encouraged the search for new surface treatments providing effective corrosion protection without the drawback of generating toxic residues. In this investigation, a hydrothermal treatment in aqueous solution with cerium ions is proposed as a post-treatment for tartaric-sulfuric acid (TSA) anodizing, and its effects on the AA2524-T3 alloy corrosion resistance investigated. The effect of Ce on the characteristics of the surface film formed, such as morphology and corrosion resistance, is investigated by scanning electron microscopy and electrochemical impedance spectroscopy (EIS). The results show that the hydrothermal treatment in solution containing Ce(III) ions presents a less stable behavior than the treatment in boiling water. However, the results of the EIS experiments show recovery of the protective properties of the system, indicating that some self-healing properties must be imparted to the system.

Journal of Materials Research and Technology, 2019

Friction stir welding has been considered as an alternative to fusion welding processes of stainl... more Friction stir welding has been considered as an alternative to fusion welding processes of stainless steels. A lean duplex stainless steel, grade UNS S82441, has been recently developed and is prone to localized corrosion, such as pitting when exposed to harsh conditions during use. However, pitting resistance of UNS S82441 has not been previously investigated. In this study, UNS S82441 lean duplex stainless steel was friction stir welded, and its microstructure and localized corrosion resistance were investigated by phase volumetric fraction, scanning electron microscopy, transmission electron microscopy and electrochemical tests. The pitting resistance of each zone was investigated by polarization tests and by determining the critical pitting temperature. The results indicated that microstructural changes promoted by friction stir welding affected the pitting resistance of the lean duplex stainless steel.

Surface and Interface Analysis, 2019

In the aircraft industry, anodizing and posttreatment steps use Cr (VI) compounds, which, despite... more In the aircraft industry, anodizing and posttreatment steps use Cr (VI) compounds, which, despite offering good corrosion resistance and self-healing properties, are highly toxic and carcinogenic. Ce compounds are recognized as efficient corrosion inhibitors for Al alloys, and several works report self-healing ability for these chemicals. In this investigation, the corrosion resistance of Alclad AA2024-T3 alloy anodized in tartaric-sulphuric acid (TSA) bath and posttreated in a solution comprising cerium nitrate without and with hydrogen peroxide was evaluated. The purpose is to investigate the potentiality of using hydrothermal treatment in Ce nitrate solution as candidate to replace Cr (VI) posttreatment. The aim is to provide a posttreatment step which, while improving the corrosion resistance, does not plug the mouths of the pores maintaining the adhesion properties of the porous anodic layer. Microstructural characterization was carried out by SEM-EDS whereas corrosion resistance was evaluated by EIS. The surface analysis showed that the posttreatments, all performed at 50°C, kept the open structure of the pores. EIS analysis showed that the posttreatments performed in the H 2 O 2 solution for short immersion times were the most effective in improving the corrosion resistance of the samples, whereas electrical equivalent circuit (EEC) fitting of the data indicated sealing of the porous layer during the immersion of the different samples in the test solution. SEM-EDS analysis of the samples posttreated in the H 2 O 2 containing solution, prior and after the corrosion test, showed the presence of Ce oxy-hydroxide randomly deposited on the sample surface, indicating that Ce could be incorporated/stored in the anodic layer.

Corrosion Science, 2018

The corrosion behaviour of AA2198-T851 alloy has been investigated using a combination of immersi... more The corrosion behaviour of AA2198-T851 alloy has been investigated using a combination of immersion tests and different microscopy techniques. Results showed that severe localized corrosion initiated within 1 h of corrosion immersion test in 0.01 mol L −1 NaCl solution. The corrosion mechanism in this alloy is intragranular and it propagates crystallographically. The propagation occurs through grain orientation dependent bands and it can be likened to the movement of dislocation through slip planes. Corrosion rings around stable pits result from pH variations. Secondary pits form around primary pits within corrosion rings and are preceded by hydrogen evolution.

Surface and Interface Analysis, 2016

In this investigation, the corrosion behavior of AA2198–T851 was compared to AA2024–T3 by electro... more In this investigation, the corrosion behavior of AA2198–T851 was compared to AA2024–T3 by electrochemical impedance spectroscopy and the surface of both alloys was analyzed by Field Emission Gun (FEG) scanning electron microscopy (SEM) and X‐ray energy dispersive analysis (EDX). Electrochemical impedance spectroscopy (EIS) results for the uncoated surface of both alloys showed higher pitting susceptibility associated to the AA2198–T851 alloy comparatively to the AA2024–T3. In order to improve the corrosion resistance of both alloys, tartaric sulphuric acid anodising (TSA) was carried out with both alloys followed by primer application. The corrosion resistance of the anodized and primer coated samples was also evaluated by CASS salt spray test followed by EIS tests at increasing periods of exposure to the CASS test. The results showed larger amounts of corrosion products associated to the primer coated AA2198–T851 alloy comparatively to the AA2024–T3 alloy. Diffusion was only indicated in the EIS results of the AA2198–T851 samples likely because of large amounts of porous corrosion products on the exposed surface of this alloy to the corrosive environment. Copyright © 2016 John Wiley & Sons, Ltd.

Matéria (Rio de Janeiro), 2015

Matéria (Rio de Janeiro), 2014

A new coating made of niobium pentoxide, obtained through the sol-gel process, was developed for ... more A new coating made of niobium pentoxide, obtained through the sol-gel process, was developed for the carbon steel (SAE 1010). The corrosion protection provided by this coating was evaluated through electrochemical tests such as: open circuit potential, electrochemical impedance spectroscopy and anodic potentiodynamic polarization in NaCl 0,5 mol L-1 solution. The morphology and composition of the coatings were analyzed using scanning electronic microscopy, energy dispersive spectroscopy and X-ray diffractions. A zinc phosphate coating was used as standard test for comparison of results. The electrochemical measurements revealed that: (1) The Nb 2 O 5 coating dislocates the corrosion potential towards more positive values; (2) higher impedance values were found for the Nb 2 O 5 coated samples; and (3) lower current density values were found for these samples. The electronic micrograph revealed that there was alteration in the morphology of the carbon steel surface due to the Nb 2 O 5 deposition. The EDS spectra confirmed the niobium coating deposition, as a peak regarding this element was obtained in the spectra. The X-ray diffractograms confirmed the presence of the phases in the Nb 2 O 5 coating. This new coating increases protection of the carbon steel against corrosion and presents an alternative to replace phosphating.

The ferromagnetic property of ferritic stainless steels makes them potential materials for use as... more The ferromagnetic property of ferritic stainless steels makes them potential materials for use as implantable dental devices with magnetic connections. In this work, the corrosion resistance and cytotoxicity of the AISI 444 ferritic stainless steel (SS) was evaluated in a phosphate buffer solution (PBS) and compared with two materials used for fabrication of implantable materials, specifically, NeoM (a ferritic type of SS) and ISO 5832-1 (an austenitic type of SS). All tested materials showed passivity in the PBS electrolyte used. Susceptibility to pitting corrosion in the test solution used however was only associated to the NeoM steel, that has been used in commercial dental implant devices. A large concentration of precipitates/inclusions of complex nature was found in the microstructure of this steel and it is the probable reason for its low resistance to localized corrosion, much lower than that of the AISI 444 SS used in this study. The AISI 444 stainless steel tested is a Nb and Ti stabilized steel and it presented mainly Nb and Ti rich types precipitates in its microstructure. No pits were seen at the surface of this last steel after polarization tests. The pitting resistance of the AISI 444 steel was compared to that of the ISO 5832-1 austenitic and it was found similar to this last steel that is well known for its good corrosion resistance performance. The results suggested that the AISI 444 steel is a potential candidate for replacement of the commercial ferromagnetic alloys currently used in dental prosthesis.

The effect of precipitation on the corrosion resistance of AISI 316L(N) stainless steel previousl... more The effect of precipitation on the corrosion resistance of AISI 316L(N) stainless steel previously exposed to creep tests at 600°C for periods of up to 10 years, has been studied. The corrosion resistance was investigated in 2 M H 2 SO 4 + 0.5 M NaCl + 0.01 M KSCN solution at 30°C by electrochemical methods. The results showed that the susceptibility to intergranular corrosion was highly affected by aging at 600°C and creep testing time. The intergranular corrosion resistance decreased by more than twenty times when the creep testing time increased from 7500 h to 85,000 h. The tendency to passivation decreased and less protective films were formed on the creep tested samples. All tested samples also showed susceptibility to pitting. Grain boundary M 23 C 6 carbides were not found after longterm exposure at 600°C and the corrosion behavior of the creep tested samples was attributed to intermetallic phases (mainly sigma phase) precipitation.

Toxicology in Vitro, 2014

Titanium is one of the most used materials in implants and changes in its surface can modify the ... more Titanium is one of the most used materials in implants and changes in its surface can modify the cellular functional response to better implant fixation. An argon plasma treatment generates a surface with improved mechanical proprieties without modifying its chemical composition. Oxidative stress induced by biomaterials is considered one of the major causes of implant failure and studies in this field are fundamental to evaluate the biocompatibility of a new material. Therefore, in this work, induction of oxidative stress by titanium surfaces subjected to plasma treatment (PTTS) was evaluated. The viability of CHO-k1 cells was higher on PTTS discs. Cells grown on titanium surfaces are subjected to intracellular oxidative stress. Titanium discs subjected to the plasma treatment induced less oxidative stress than the untreated ones, which resulted in improved cellular survival. These were associated with improved cellular antioxidant response in Plasma Treated Titanium Surface (PTTS). Furthermore, a decrease in protein and DNA oxidative damage was observed on cells grown on the roughed surface when compared to the smooth one. In conclusion, our data suggest that the treatment of titanium with argon plasma may improve its biocompatible, thus improving its performance as implants or as a scaffold in tissue engineering.

Materials Science Forum, 2006

The use of AISI 316L stainless steels for biomedical applications as implants is widespread due t... more The use of AISI 316L stainless steels for biomedical applications as implants is widespread due to a combination of low cost and easy formability. However, wrought 316L steel is prone to localized corrosion. Coating deposition is commonly used to overcome this problem. Ceramic hard coatings, like titanium nitride, are used to improve both corrosion and wear resistance of stainless steels. Powder injection moulding (PIM) is an attractive method to manufacture complex, near net-shape components. Stainless steels obtained from this route have shown mechanical and corrosion properties similar to wrought materials. The literature on the use of PIM 316L steel, either coated or not, as implants is still very scarce. The aim of the present work was to study the corrosion behaviour of PIM 316L in two conditions: TiN-coated and bare. Electrochemical investigations were performed using EIS and potentiodynamic polarization techniques.

Surface and Coatings Technology, 2010

ABSTRACT This study evaluates the possibility of replacing the hexavalent chromium passivation tr... more ABSTRACT This study evaluates the possibility of replacing the hexavalent chromium passivation treatment used as a sealer after phosphating of carbon steel (SAE 1010) by a treatment with niobium ammonium oxalate (Ox). Samples of carbon steel (SAE 1010) after being phosphated in a zinc phosphate bath (PZn+Ni) were immersed in solution of niobium ammonium oxalate (250mg L−1 of Nb) either at pH 3.0 or pH 8.0. A passivation treatment with a solution with CrO3 (200mg L−1 of Cr6+) was also used for reference.The corrosion resistance of the phosphated samples after passivation treatments was analyzed in a NaCl 0.5mol L−1 solution using electrochemical impedance spectroscopy (EIS) and anodic polarization curves. Salt spray tests were also performed to evaluate their corrosion resistance. The results showed that the highest corrosion resistance was obtained by passivation in a solution with (250mg L−1 of Nb) at pH 8.0.

Materials Research, 2006

The resistance to localised corrosion of the full austenitic 15%Cr-15%Ni-1.2%Mo titanium stabiliz... more The resistance to localised corrosion of the full austenitic 15%Cr-15%Ni-1.2%Mo titanium stabilized stainless steel (DIN W. Nr. 1.4970) was investigated by electrochemical methods including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and potentiostatic polarization measurements in a phosphatebuffered solution (PBS). The low carbon and non-stabilized austenitic stainless steel, AISI 316L (ASTM F-138), widely used for surgical implants, was also tested for comparison. The tests were conducted at room temperature after a stable potential had been reached. After the electrochemical measurements, the surfaces of the specimens were observed using SEM to evaluate the presence of pits. Potentiodynamic polarization results showed that both steels are prone to localized corrosion. Larger pits were found on the surface of AISI 316L specimens after the electrochemical tests. EIS response has indicated the duplex structure of the passive oxides. The results showed that the electrochemical behaviour of the DIN W. Nr. 1.4970 is better than of AISI 316L steel. Therefore, their application as an implant material may be considered.

Materials Research, 2010

Austenitic stainless steels, titanium and cobalt alloys are widely used as biomaterials. However,... more Austenitic stainless steels, titanium and cobalt alloys are widely used as biomaterials. However, new medical devices require innovative materials with specific properties, depending on their application. The magnetic properties are among the properties of interest for some biomedical applications. However, due to the interaction of magnetic materials with Magnetic Resonance Image equipments they might used only as not fixed implants or for medical devices. The ferromagnetic superalloys, Incoloy MA 956 and PM 2000, produced by mechanical alloying, have similar chemical composition, high corrosion resistance and are used in high temperature applications. In this study, the corrosion resistance of these two ferritic superalloys was compared in a phosphate buffer solution. The electrochemical results showed that both superalloys are passive in this solution and the PM 2000 present a more protective passive film on it associated to higher impedances than the MA 956.

Materials and Corrosion, 2009

In order to lower the excessive costs of metallic prosthesis materials alternatives to Ti and Ti ... more In order to lower the excessive costs of metallic prosthesis materials alternatives to Ti and Ti alloys have been searched. In this study, the corrosion resistance of the DIN 1.4575 superferritic stainless steel, either solution annealed or solution annealed and aged at 475 8C for periods varying from 100 to 1080 h, was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization methods in Hanks' solution. The solution annealed and the aged for 1080 h samples were also tested using scanning electrochemical microscopy (SECM) in a 0.1 mol/L NaCl solution at 25 8C. The EIS results showed that the corrosion resistance of the DIN 1.4575 steel decreases with heat treatment time at 475 8C probably due to alpha prime formation. Besides the diminution of the overall impedance values, the low frequency limit of the Nyquist diagrams show a progressive change from an almost capacitive response to a resistive behavior as the heat treatment time increases. Pitting corrosion resistance also decreased with aging time at 475 8C.

Materials and Corrosion, 2011

Ferromagnetic stainless steels (SSs) have been investigated as potential candidates for dental pr... more Ferromagnetic stainless steels (SSs) have been investigated as potential candidates for dental prosthesis applications in replacement of magnetic attachments made of noble and expensive alloys. In order to be used as biomaterials, their corrosion resistance has to be appropriate. The corrosion resistance of passive materials is related to the characteristics of the passive film formed and their properties might be investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, and Mott-Schottky approach. The corrosion resistance and the capacitance of the passive films formed on PM2000, DIN 1.4575, and 17-4 PH advanced SSs during 2 days of immersion in a phosphate buffered saline solution (PBS), at 25 8C and pH 7.0 were studied by electrochemical techniques. A commercial alloy Dyna EFM was also analyzed for comparison reasons. The results showed that films on tested materials behave as both n-type and p-type semiconductors and the PM2000 presented the highest corrosion resistance among all of them.

Journal of Materials Science, 2007

The 475°C embrittlement in stainless steels is a well-known phenomenon associated to alpha prime ... more The 475°C embrittlement in stainless steels is a well-known phenomenon associated to alpha prime (a 0) formed by precipitation or spinodal decomposition. Many doubts still remain on the mechanism of a 0 formation and its consequence on deformation and fracture mechanisms and corrosion resistance. In this investigation, the fracture behavior and corrosion resistance of two high performance ferritic stainless steels were investigated: a superferritic DIN 1.4575 and MA 956 superalloy were evaluated. Samples of both stainless steels (SS) were aged at 475°C for periods varying from 1 to 1,080 h. Their fracture surfaces were observed using scanning electron microscopy (SEM) and the cleavage planes were determined by electron backscattering diffraction (EBSD). Some samples were tested for corrosion resistance using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. Brittle and ductile fractures were observed in both ferritic stainless steels after aging at 475°C. For aging periods longer than 500 h, the ductile fracture regions completely disappeared. The cleavage plane in the DIN 1.4575 samples aged at 475°C for 1,080 h was mainly {110}, however the {102}, {314}, and {131} families of planes were also detected. The pitting corrosion resistance decreased with aging at 475°C. The effect of alpha prime on the corrosion resistance was more significant in the DIN 1.4575 SS comparatively to the Incoloy MA 956.

Surface and Interface Analysis, 2016

The International Journal of Advanced Manufacturing Technology, 2021

Friction stir welding is a solid-state joining/processing technique that offers high strength and... more Friction stir welding is a solid-state joining/processing technique that offers high strength and productivity, resulting in a microstructure similar to hot working cycles. However, high melting temperature metals such as steels cause excessive wear over welding tools, representing a significant economic issue. Most studies conducted in steels have used polycrystalline cubic boron nitride (PCBN) and W-Re composite tools, which offer a combination of high strength and hardness at high temperatures, along with hightemperature stability. However, even those tools are susceptible to tool wear. In the present study, experimental data was collected during friction stir processing of X70 grade pipeline steel plates, using W-Re and PCBN composite tools under well-controlled conditions. Profilometry and optical microscopy were used to quantify the volume loss at the welding tool due to the number of plunges and the welded distance. Torque and transverse force at the welding tool and the welded bead width were measured and related to the wear process. Tool contamination in boron-nitrogen particles and dissolved tungsten was identified at the stir and hard zones, more substantial at the latter.

CORROSION, 2019

To protect Al alloys from corrosion, standard procedures in the aerospace industry use chromium-b... more To protect Al alloys from corrosion, standard procedures in the aerospace industry use chromium-based acid anodizing with subsequent post-treatment steps also containing hexavalent chromium (Cr(VI)) ions. However, environmental and health related concerns associated with Cr(VI) have encouraged the search for new surface treatments providing effective corrosion protection without the drawback of generating toxic residues. In this investigation, a hydrothermal treatment in aqueous solution with cerium ions is proposed as a post-treatment for tartaric-sulfuric acid (TSA) anodizing, and its effects on the AA2524-T3 alloy corrosion resistance investigated. The effect of Ce on the characteristics of the surface film formed, such as morphology and corrosion resistance, is investigated by scanning electron microscopy and electrochemical impedance spectroscopy (EIS). The results show that the hydrothermal treatment in solution containing Ce(III) ions presents a less stable behavior than the treatment in boiling water. However, the results of the EIS experiments show recovery of the protective properties of the system, indicating that some self-healing properties must be imparted to the system.

Journal of Materials Research and Technology, 2019

Friction stir welding has been considered as an alternative to fusion welding processes of stainl... more Friction stir welding has been considered as an alternative to fusion welding processes of stainless steels. A lean duplex stainless steel, grade UNS S82441, has been recently developed and is prone to localized corrosion, such as pitting when exposed to harsh conditions during use. However, pitting resistance of UNS S82441 has not been previously investigated. In this study, UNS S82441 lean duplex stainless steel was friction stir welded, and its microstructure and localized corrosion resistance were investigated by phase volumetric fraction, scanning electron microscopy, transmission electron microscopy and electrochemical tests. The pitting resistance of each zone was investigated by polarization tests and by determining the critical pitting temperature. The results indicated that microstructural changes promoted by friction stir welding affected the pitting resistance of the lean duplex stainless steel.

Surface and Interface Analysis, 2019

In the aircraft industry, anodizing and posttreatment steps use Cr (VI) compounds, which, despite... more In the aircraft industry, anodizing and posttreatment steps use Cr (VI) compounds, which, despite offering good corrosion resistance and self-healing properties, are highly toxic and carcinogenic. Ce compounds are recognized as efficient corrosion inhibitors for Al alloys, and several works report self-healing ability for these chemicals. In this investigation, the corrosion resistance of Alclad AA2024-T3 alloy anodized in tartaric-sulphuric acid (TSA) bath and posttreated in a solution comprising cerium nitrate without and with hydrogen peroxide was evaluated. The purpose is to investigate the potentiality of using hydrothermal treatment in Ce nitrate solution as candidate to replace Cr (VI) posttreatment. The aim is to provide a posttreatment step which, while improving the corrosion resistance, does not plug the mouths of the pores maintaining the adhesion properties of the porous anodic layer. Microstructural characterization was carried out by SEM-EDS whereas corrosion resistance was evaluated by EIS. The surface analysis showed that the posttreatments, all performed at 50°C, kept the open structure of the pores. EIS analysis showed that the posttreatments performed in the H 2 O 2 solution for short immersion times were the most effective in improving the corrosion resistance of the samples, whereas electrical equivalent circuit (EEC) fitting of the data indicated sealing of the porous layer during the immersion of the different samples in the test solution. SEM-EDS analysis of the samples posttreated in the H 2 O 2 containing solution, prior and after the corrosion test, showed the presence of Ce oxy-hydroxide randomly deposited on the sample surface, indicating that Ce could be incorporated/stored in the anodic layer.

Corrosion Science, 2018

The corrosion behaviour of AA2198-T851 alloy has been investigated using a combination of immersi... more The corrosion behaviour of AA2198-T851 alloy has been investigated using a combination of immersion tests and different microscopy techniques. Results showed that severe localized corrosion initiated within 1 h of corrosion immersion test in 0.01 mol L −1 NaCl solution. The corrosion mechanism in this alloy is intragranular and it propagates crystallographically. The propagation occurs through grain orientation dependent bands and it can be likened to the movement of dislocation through slip planes. Corrosion rings around stable pits result from pH variations. Secondary pits form around primary pits within corrosion rings and are preceded by hydrogen evolution.

Surface and Interface Analysis, 2016

In this investigation, the corrosion behavior of AA2198–T851 was compared to AA2024–T3 by electro... more In this investigation, the corrosion behavior of AA2198–T851 was compared to AA2024–T3 by electrochemical impedance spectroscopy and the surface of both alloys was analyzed by Field Emission Gun (FEG) scanning electron microscopy (SEM) and X‐ray energy dispersive analysis (EDX). Electrochemical impedance spectroscopy (EIS) results for the uncoated surface of both alloys showed higher pitting susceptibility associated to the AA2198–T851 alloy comparatively to the AA2024–T3. In order to improve the corrosion resistance of both alloys, tartaric sulphuric acid anodising (TSA) was carried out with both alloys followed by primer application. The corrosion resistance of the anodized and primer coated samples was also evaluated by CASS salt spray test followed by EIS tests at increasing periods of exposure to the CASS test. The results showed larger amounts of corrosion products associated to the primer coated AA2198–T851 alloy comparatively to the AA2024–T3 alloy. Diffusion was only indicated in the EIS results of the AA2198–T851 samples likely because of large amounts of porous corrosion products on the exposed surface of this alloy to the corrosive environment. Copyright © 2016 John Wiley & Sons, Ltd.

Matéria (Rio de Janeiro), 2015

Matéria (Rio de Janeiro), 2014

A new coating made of niobium pentoxide, obtained through the sol-gel process, was developed for ... more A new coating made of niobium pentoxide, obtained through the sol-gel process, was developed for the carbon steel (SAE 1010). The corrosion protection provided by this coating was evaluated through electrochemical tests such as: open circuit potential, electrochemical impedance spectroscopy and anodic potentiodynamic polarization in NaCl 0,5 mol L-1 solution. The morphology and composition of the coatings were analyzed using scanning electronic microscopy, energy dispersive spectroscopy and X-ray diffractions. A zinc phosphate coating was used as standard test for comparison of results. The electrochemical measurements revealed that: (1) The Nb 2 O 5 coating dislocates the corrosion potential towards more positive values; (2) higher impedance values were found for the Nb 2 O 5 coated samples; and (3) lower current density values were found for these samples. The electronic micrograph revealed that there was alteration in the morphology of the carbon steel surface due to the Nb 2 O 5 deposition. The EDS spectra confirmed the niobium coating deposition, as a peak regarding this element was obtained in the spectra. The X-ray diffractograms confirmed the presence of the phases in the Nb 2 O 5 coating. This new coating increases protection of the carbon steel against corrosion and presents an alternative to replace phosphating.

The ferromagnetic property of ferritic stainless steels makes them potential materials for use as... more The ferromagnetic property of ferritic stainless steels makes them potential materials for use as implantable dental devices with magnetic connections. In this work, the corrosion resistance and cytotoxicity of the AISI 444 ferritic stainless steel (SS) was evaluated in a phosphate buffer solution (PBS) and compared with two materials used for fabrication of implantable materials, specifically, NeoM (a ferritic type of SS) and ISO 5832-1 (an austenitic type of SS). All tested materials showed passivity in the PBS electrolyte used. Susceptibility to pitting corrosion in the test solution used however was only associated to the NeoM steel, that has been used in commercial dental implant devices. A large concentration of precipitates/inclusions of complex nature was found in the microstructure of this steel and it is the probable reason for its low resistance to localized corrosion, much lower than that of the AISI 444 SS used in this study. The AISI 444 stainless steel tested is a Nb and Ti stabilized steel and it presented mainly Nb and Ti rich types precipitates in its microstructure. No pits were seen at the surface of this last steel after polarization tests. The pitting resistance of the AISI 444 steel was compared to that of the ISO 5832-1 austenitic and it was found similar to this last steel that is well known for its good corrosion resistance performance. The results suggested that the AISI 444 steel is a potential candidate for replacement of the commercial ferromagnetic alloys currently used in dental prosthesis.

The effect of precipitation on the corrosion resistance of AISI 316L(N) stainless steel previousl... more The effect of precipitation on the corrosion resistance of AISI 316L(N) stainless steel previously exposed to creep tests at 600°C for periods of up to 10 years, has been studied. The corrosion resistance was investigated in 2 M H 2 SO 4 + 0.5 M NaCl + 0.01 M KSCN solution at 30°C by electrochemical methods. The results showed that the susceptibility to intergranular corrosion was highly affected by aging at 600°C and creep testing time. The intergranular corrosion resistance decreased by more than twenty times when the creep testing time increased from 7500 h to 85,000 h. The tendency to passivation decreased and less protective films were formed on the creep tested samples. All tested samples also showed susceptibility to pitting. Grain boundary M 23 C 6 carbides were not found after longterm exposure at 600°C and the corrosion behavior of the creep tested samples was attributed to intermetallic phases (mainly sigma phase) precipitation.

Toxicology in Vitro, 2014

Titanium is one of the most used materials in implants and changes in its surface can modify the ... more Titanium is one of the most used materials in implants and changes in its surface can modify the cellular functional response to better implant fixation. An argon plasma treatment generates a surface with improved mechanical proprieties without modifying its chemical composition. Oxidative stress induced by biomaterials is considered one of the major causes of implant failure and studies in this field are fundamental to evaluate the biocompatibility of a new material. Therefore, in this work, induction of oxidative stress by titanium surfaces subjected to plasma treatment (PTTS) was evaluated. The viability of CHO-k1 cells was higher on PTTS discs. Cells grown on titanium surfaces are subjected to intracellular oxidative stress. Titanium discs subjected to the plasma treatment induced less oxidative stress than the untreated ones, which resulted in improved cellular survival. These were associated with improved cellular antioxidant response in Plasma Treated Titanium Surface (PTTS). Furthermore, a decrease in protein and DNA oxidative damage was observed on cells grown on the roughed surface when compared to the smooth one. In conclusion, our data suggest that the treatment of titanium with argon plasma may improve its biocompatible, thus improving its performance as implants or as a scaffold in tissue engineering.

Materials Science Forum, 2006

The use of AISI 316L stainless steels for biomedical applications as implants is widespread due t... more The use of AISI 316L stainless steels for biomedical applications as implants is widespread due to a combination of low cost and easy formability. However, wrought 316L steel is prone to localized corrosion. Coating deposition is commonly used to overcome this problem. Ceramic hard coatings, like titanium nitride, are used to improve both corrosion and wear resistance of stainless steels. Powder injection moulding (PIM) is an attractive method to manufacture complex, near net-shape components. Stainless steels obtained from this route have shown mechanical and corrosion properties similar to wrought materials. The literature on the use of PIM 316L steel, either coated or not, as implants is still very scarce. The aim of the present work was to study the corrosion behaviour of PIM 316L in two conditions: TiN-coated and bare. Electrochemical investigations were performed using EIS and potentiodynamic polarization techniques.

Surface and Coatings Technology, 2010

ABSTRACT This study evaluates the possibility of replacing the hexavalent chromium passivation tr... more ABSTRACT This study evaluates the possibility of replacing the hexavalent chromium passivation treatment used as a sealer after phosphating of carbon steel (SAE 1010) by a treatment with niobium ammonium oxalate (Ox). Samples of carbon steel (SAE 1010) after being phosphated in a zinc phosphate bath (PZn+Ni) were immersed in solution of niobium ammonium oxalate (250mg L−1 of Nb) either at pH 3.0 or pH 8.0. A passivation treatment with a solution with CrO3 (200mg L−1 of Cr6+) was also used for reference.The corrosion resistance of the phosphated samples after passivation treatments was analyzed in a NaCl 0.5mol L−1 solution using electrochemical impedance spectroscopy (EIS) and anodic polarization curves. Salt spray tests were also performed to evaluate their corrosion resistance. The results showed that the highest corrosion resistance was obtained by passivation in a solution with (250mg L−1 of Nb) at pH 8.0.

Materials Research, 2006

The resistance to localised corrosion of the full austenitic 15%Cr-15%Ni-1.2%Mo titanium stabiliz... more The resistance to localised corrosion of the full austenitic 15%Cr-15%Ni-1.2%Mo titanium stabilized stainless steel (DIN W. Nr. 1.4970) was investigated by electrochemical methods including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and potentiostatic polarization measurements in a phosphatebuffered solution (PBS). The low carbon and non-stabilized austenitic stainless steel, AISI 316L (ASTM F-138), widely used for surgical implants, was also tested for comparison. The tests were conducted at room temperature after a stable potential had been reached. After the electrochemical measurements, the surfaces of the specimens were observed using SEM to evaluate the presence of pits. Potentiodynamic polarization results showed that both steels are prone to localized corrosion. Larger pits were found on the surface of AISI 316L specimens after the electrochemical tests. EIS response has indicated the duplex structure of the passive oxides. The results showed that the electrochemical behaviour of the DIN W. Nr. 1.4970 is better than of AISI 316L steel. Therefore, their application as an implant material may be considered.

Materials Research, 2010

Austenitic stainless steels, titanium and cobalt alloys are widely used as biomaterials. However,... more Austenitic stainless steels, titanium and cobalt alloys are widely used as biomaterials. However, new medical devices require innovative materials with specific properties, depending on their application. The magnetic properties are among the properties of interest for some biomedical applications. However, due to the interaction of magnetic materials with Magnetic Resonance Image equipments they might used only as not fixed implants or for medical devices. The ferromagnetic superalloys, Incoloy MA 956 and PM 2000, produced by mechanical alloying, have similar chemical composition, high corrosion resistance and are used in high temperature applications. In this study, the corrosion resistance of these two ferritic superalloys was compared in a phosphate buffer solution. The electrochemical results showed that both superalloys are passive in this solution and the PM 2000 present a more protective passive film on it associated to higher impedances than the MA 956.

Materials and Corrosion, 2009

In order to lower the excessive costs of metallic prosthesis materials alternatives to Ti and Ti ... more In order to lower the excessive costs of metallic prosthesis materials alternatives to Ti and Ti alloys have been searched. In this study, the corrosion resistance of the DIN 1.4575 superferritic stainless steel, either solution annealed or solution annealed and aged at 475 8C for periods varying from 100 to 1080 h, was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization methods in Hanks' solution. The solution annealed and the aged for 1080 h samples were also tested using scanning electrochemical microscopy (SECM) in a 0.1 mol/L NaCl solution at 25 8C. The EIS results showed that the corrosion resistance of the DIN 1.4575 steel decreases with heat treatment time at 475 8C probably due to alpha prime formation. Besides the diminution of the overall impedance values, the low frequency limit of the Nyquist diagrams show a progressive change from an almost capacitive response to a resistive behavior as the heat treatment time increases. Pitting corrosion resistance also decreased with aging time at 475 8C.

Materials and Corrosion, 2011

Ferromagnetic stainless steels (SSs) have been investigated as potential candidates for dental pr... more Ferromagnetic stainless steels (SSs) have been investigated as potential candidates for dental prosthesis applications in replacement of magnetic attachments made of noble and expensive alloys. In order to be used as biomaterials, their corrosion resistance has to be appropriate. The corrosion resistance of passive materials is related to the characteristics of the passive film formed and their properties might be investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, and Mott-Schottky approach. The corrosion resistance and the capacitance of the passive films formed on PM2000, DIN 1.4575, and 17-4 PH advanced SSs during 2 days of immersion in a phosphate buffered saline solution (PBS), at 25 8C and pH 7.0 were studied by electrochemical techniques. A commercial alloy Dyna EFM was also analyzed for comparison reasons. The results showed that films on tested materials behave as both n-type and p-type semiconductors and the PM2000 presented the highest corrosion resistance among all of them.

Journal of Materials Science, 2007

The 475°C embrittlement in stainless steels is a well-known phenomenon associated to alpha prime ... more The 475°C embrittlement in stainless steels is a well-known phenomenon associated to alpha prime (a 0) formed by precipitation or spinodal decomposition. Many doubts still remain on the mechanism of a 0 formation and its consequence on deformation and fracture mechanisms and corrosion resistance. In this investigation, the fracture behavior and corrosion resistance of two high performance ferritic stainless steels were investigated: a superferritic DIN 1.4575 and MA 956 superalloy were evaluated. Samples of both stainless steels (SS) were aged at 475°C for periods varying from 1 to 1,080 h. Their fracture surfaces were observed using scanning electron microscopy (SEM) and the cleavage planes were determined by electron backscattering diffraction (EBSD). Some samples were tested for corrosion resistance using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. Brittle and ductile fractures were observed in both ferritic stainless steels after aging at 475°C. For aging periods longer than 500 h, the ductile fracture regions completely disappeared. The cleavage plane in the DIN 1.4575 samples aged at 475°C for 1,080 h was mainly {110}, however the {102}, {314}, and {131} families of planes were also detected. The pitting corrosion resistance decreased with aging at 475°C. The effect of alpha prime on the corrosion resistance was more significant in the DIN 1.4575 SS comparatively to the Incoloy MA 956.