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Pedro A.p. Nascente - One of the best experts on this subject based on the ideXlab platform.
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ion Nitriding of a superaustenitic stainless steel wear and corrosion characterization
Surface & Coatings Technology, 2010Co-Authors: Frederico Augusto Pires Fernandes, Pedro A.p. Nascente, S C Heck, Ricardo Gomes Pereira, Carlos Alberto Picon, Luiz Carlos CastelettiAbstract:Abstract The superiority of superaustenitic stainless steel (SASS) lies in its good weldability and great resistance to stress corrosion and pitting, because of its higher chromium, molybdenum, and nitrogen contents, when compared to general stainless steels. However, some of its applications are limited by very poor wear behavior. Plasma-Nitriding is a very effective treatment for producing wear resistant and hard surface layers on stainless steels without compromising the corrosion resistance. In this work, UNS S31254 SASS samples were plasma-nitrided at three different Temperatures (400, 450, and 500 °C), under a pressure of 500 Pa, for 5 h, in order to verify the influence of the Temperature on the morphology, wear, and corrosion behavior of the modified surface layers. The plasma-nitrided samples were analyzed by means of optical microscopy, micro-hardness, X-ray diffraction, wear, and corrosion tests. Wear tests were conducted in a fixed ball micro-wear machine and corrosion behavior was carried out in natural sea water by means of potentiodynamic polarization curves. For the sample which was plasma-nitrided at 400 °C, only the expanded austenite phase was observed, and for the treatments performed at 450 and 500 °C, chromium nitrides (CrN and Cr 2 N) were formed in addition to the expanded austenite. Wear volume and Knoop surface hardness increased as the plasma-Nitriding Temperature increased. Higher wear rates were observed at high Temperatures, probably due to the increment on layer fragility. The sample modified at 400 °C exhibited the best corrosion behavior among all the plasma-Nitriding conditions.
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x ray diffraction characterisation of expanded austenite and ferrite in plasma nitrided stainless steels
Surface Engineering, 2010Co-Authors: L C Gontijo, R Machado, Luiz Carlos Casteletti, Sebastião Elias Kuri, Pedro A.p. NascenteAbstract:AbstractThe S phase, known as expanded austenite, is formed on the surfaces of austenitic stainless steels that are nitrided under low Temperature plasma. A similar phase was observed for nitrided ferritic stainless steels and was designed as expanded ferrite or ferritic S phase. The authors treated samples of austenitic AISI 304L and AISI 316L and ferritic AISI 409 stainless steels by plasma Nitriding at different Temperatures and then studied the structural, morphological, chemical and corrosion characteristics of the modified layers by X-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy and electrochemical tests. For both austenitic AISI 304L and AISI 316L stainless steels, the results showed that a hard S phase layer was formed on the surfaces, promoting an anodic polarisation curve displacement to higher current density values that depend on the plasma Nitriding Temperature. A layer having a high amount of nitrogen was formed on the ferritic AISI 409 stainless steel. X-ray ...
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corrosion resistance of the layers formed on the surface of plasma nitrided aisi 304l steel
Thin Solid Films, 2006Co-Authors: Leonardo Cabral Gontijo, R Machado, Luiz Carlos Casteletti, S E Kuri, Pedro A.p. NascenteAbstract:Austenitic stainless steels have good corrosion resistance, but their low hardness and low wear resistance limit their use whenever surface hardness is required. Nitriding treatments have been successfully applied to stainless steels to improve their mechanical and tribological properties; however, at Temperatures above 723 K, gas or salt bath Nitriding processes decrease the corrosion resistance due to the formation of CrN and other phases within the modified layer. Chromium compounds draw chromium and nitrogen from the adjacent regions, degrading the corrosion resistance. The plasma Nitriding technique permits the use of treatment Temperatures as low as 623 K without promoting degradation in the corrosion resistance of stainless steel. In this work, the pulsed glow discharge (PGD) technique was used for Nitriding steel (AISI304L) in order to investigate the effect of the Temperature of this treatment in the morphology and, as a consequence, in the anodic behavior of the formed layers, in solution with and without chloride ions. Four different Temperatures were employed (623, 673, 723, and 773 K). The samples were characterized by optical microscopy (OM), scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), microhardness measurements, and electrochemical tests with potentiodynamic anodic polarization curves. The Nitriding Temperature alters the anodic behavior due to a displacement of the polarization curve towards higher currents, in a solution free of chloride ions. In a chloride solution, the Nitriding Temperature increases the pitting potential up to the oxygen evolution region.
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study of the s phase formed on plasma nitrided aisi 316l stainless steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006Co-Authors: L C Gontijo, R Machado, Luiz Carlos Casteletti, E J Miola, Nelson Guedes De Alcântara, Pedro A.p. NascenteAbstract:Abstract Some tribological and corrosion resistance properties of austenitic stainless steels are enhanced by the formation of the S phase, also called expanded austenite. This phase is formed on the surfaces of austenitic stainless steels nitrided under certain conditions. In this work, AISI 316L steel was plasma-nitrided at 350, 400, 450, and 500 °C, and the samples were characterized by X-ray diffraction (XRD), conversion electron Mossbauer spectroscopy (CEMS), and wavelength dispersive spectroscopy (WDS) in order to investigate the S phase. XRD analysis identified the presence of a distorted cubic structure phase. The modified layer consists of an austenitic phase with different content of nitrogen, ranging from approximately 10 to 40 at%, and also γ′-Fe4N and ɛ-Fe2–3N phases. A diminution in the S phase occurs with the increase in Nitriding Temperature, and this decrease is related to the transformation of the S phase to the γ′-Fe4N phase.
Zexuan Wang - One of the best experts on this subject based on the ideXlab platform.
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low Temperature plasma Nitriding of titanium layer on ti al clad sheet
Materials & Design, 2013Co-Authors: Weiping Tong, Zexuan WangAbstract:A nanostructured surface layer was fabricated on titanium layer of a Ti/Al clad sheet composite by means of the surface mechanical attrition treatment (SMAT). The low-Temperature plasma Nitriding treatment of the SMAT sample was investigated in comparison with the coarse-grained sample by using structural analysis (X-ray diffraction, scanning electron microscopy, and transmission electron microscopy) as well as mechanical and corrosion property measurements. Results showed that the Nitriding kinetics of the SMAT sample with the nanostructured surface layer was greatly enhanced, so that the Nitriding Temperature could be as low as 550 degrees C, which is significantly lower than the melting point of the aluminum layer on Ti/Al clad sheet (conventional Nitriding can lead to melting of the aluminum layer due to higher Temperature about 800 degrees C). The nitrided layer of the SMAT sample was composed of nanostructured epsilon-TiN and gamma-Ti2N phase with high supersaturation of nitrogen. The surface hardness and the hardened surface layer thickness as well as the wear and corrosion resistances of the nitrided SMAT sample were all substantially enhanced relative to the nitrided coarse-grained sample. (C) 2012 Elsevier Ltd. All rights reserved.
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low Temperature plasma Nitriding of titanium layer on ti al clad sheet
Materials & Design, 2013Co-Authors: Jian Sun, Weiping Tong, Liang Zuo, Zexuan WangAbstract:Abstract A nanostructured surface layer was fabricated on titanium layer of a Ti/Al clad sheet composite by means of the surface mechanical attrition treatment (SMAT). The low-Temperature plasma Nitriding treatment of the SMAT sample was investigated in comparison with the coarse-grained sample by using structural analysis (X-ray diffraction, scanning electron microscopy, and transmission electron microscopy) as well as mechanical and corrosion property measurements. Results showed that the Nitriding kinetics of the SMAT sample with the nanostructured surface layer was greatly enhanced, so that the Nitriding Temperature could be as low as 550 °C, which is significantly lower than the melting point of the aluminum layer on Ti/Al clad sheet (conventional Nitriding can lead to melting of the aluminum layer due to higher Temperature about 800 °C). The nitrided layer of the SMAT sample was composed of nanostructured e-TiN and γ-Ti2N phase with high supersaturation of nitrogen. The surface hardness and the hardened surface layer thickness as well as the wear and corrosion resistances of the nitrided SMAT sample were all substantially enhanced relative to the nitrided coarse-grained sample.
Th Czerwiec - One of the best experts on this subject based on the ideXlab platform.
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a way to decrease the Nitriding Temperature of aluminium the low pressure arc assisted Nitriding process
Surface & Coatings Technology, 1999Co-Authors: Nathalie Renevier, Th Czerwiec, Aude Billard, J Von Stebut, H. MichelAbstract:Abstract For the purpose of applications in mechanics, Nitriding of aluminium has been performed in a high-current (300 A), low-voltage (20–45 V) and low-pressure (0.8 Pa) thermionic arc. Although Nitriding of ferrous materials is efficient in this arc-assisted Nitriding process even for unbiased workpieces, an additional negative substrate bias voltage is necessary to process aluminium. Ion bombardment is necessary not only for ion cleaning in an Ar–H 2 gas mixture but also for the Nitriding treatment in Ar–N 2 . Under these conditions, a compact and continuous aluminium nitride layer with hexagonal AlN phase is formed on pure aluminium at 450°C. The kinetics of aluminium nitride formation at low Temperature (between 340 and 460 °C) is characterized by a two-stage mechanism comprising first the nucleation and growth of nodular AlN grains, followed by the formation of a continuous AlN layer. The growth rate of the aluminium nitride layer seems to be controlled by the rate of the chemical reaction to form AlN, rather than the rate of nitrogen diffusion. Some tribological tests performed on the aluminium nitride layers are also reported in order to evaluate the improvement in friction and wear behaviour.
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low Temperature Nitriding of aisi 316l stainless steel and titanium in a low pressure arc discharge
Surface & Coatings Technology, 1999Co-Authors: Nathalie Renevier, H. Michel, Peter Collignon, Th CzerwiecAbstract:AISI 316L stainless steel (SS) and titanium Nitriding were studied in a low pressure arc-assisted Nitriding process where the substrate Temperature and the plasma parameters are uncoupled. Lower Nitriding Temperature limits were explored for constant plasma parameters in Ar–N2 gas mixtures and substrates at floating potential. Nitrogen superficial concentration, layer thicknesses and X-ray diffraction analyses were performed on SS specimens nitrided at two Temperatures (580 and 680 K) for different times and titanium Nitriding was studied in the Temperature range 750–1025 K. At low Temperature, the Nitriding performances are limited by a plasma–surface phenomenon that probably involves recombination of nitrogen atoms.
Luiz Carlos Casteletti - One of the best experts on this subject based on the ideXlab platform.
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ion Nitriding of a superaustenitic stainless steel wear and corrosion characterization
Surface & Coatings Technology, 2010Co-Authors: Frederico Augusto Pires Fernandes, Pedro A.p. Nascente, S C Heck, Ricardo Gomes Pereira, Carlos Alberto Picon, Luiz Carlos CastelettiAbstract:Abstract The superiority of superaustenitic stainless steel (SASS) lies in its good weldability and great resistance to stress corrosion and pitting, because of its higher chromium, molybdenum, and nitrogen contents, when compared to general stainless steels. However, some of its applications are limited by very poor wear behavior. Plasma-Nitriding is a very effective treatment for producing wear resistant and hard surface layers on stainless steels without compromising the corrosion resistance. In this work, UNS S31254 SASS samples were plasma-nitrided at three different Temperatures (400, 450, and 500 °C), under a pressure of 500 Pa, for 5 h, in order to verify the influence of the Temperature on the morphology, wear, and corrosion behavior of the modified surface layers. The plasma-nitrided samples were analyzed by means of optical microscopy, micro-hardness, X-ray diffraction, wear, and corrosion tests. Wear tests were conducted in a fixed ball micro-wear machine and corrosion behavior was carried out in natural sea water by means of potentiodynamic polarization curves. For the sample which was plasma-nitrided at 400 °C, only the expanded austenite phase was observed, and for the treatments performed at 450 and 500 °C, chromium nitrides (CrN and Cr 2 N) were formed in addition to the expanded austenite. Wear volume and Knoop surface hardness increased as the plasma-Nitriding Temperature increased. Higher wear rates were observed at high Temperatures, probably due to the increment on layer fragility. The sample modified at 400 °C exhibited the best corrosion behavior among all the plasma-Nitriding conditions.
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x ray diffraction characterisation of expanded austenite and ferrite in plasma nitrided stainless steels
Surface Engineering, 2010Co-Authors: L C Gontijo, R Machado, Luiz Carlos Casteletti, Sebastião Elias Kuri, Pedro A.p. NascenteAbstract:AbstractThe S phase, known as expanded austenite, is formed on the surfaces of austenitic stainless steels that are nitrided under low Temperature plasma. A similar phase was observed for nitrided ferritic stainless steels and was designed as expanded ferrite or ferritic S phase. The authors treated samples of austenitic AISI 304L and AISI 316L and ferritic AISI 409 stainless steels by plasma Nitriding at different Temperatures and then studied the structural, morphological, chemical and corrosion characteristics of the modified layers by X-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy and electrochemical tests. For both austenitic AISI 304L and AISI 316L stainless steels, the results showed that a hard S phase layer was formed on the surfaces, promoting an anodic polarisation curve displacement to higher current density values that depend on the plasma Nitriding Temperature. A layer having a high amount of nitrogen was formed on the ferritic AISI 409 stainless steel. X-ray ...
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corrosion resistance of the layers formed on the surface of plasma nitrided aisi 304l steel
Thin Solid Films, 2006Co-Authors: Leonardo Cabral Gontijo, R Machado, Luiz Carlos Casteletti, S E Kuri, Pedro A.p. NascenteAbstract:Austenitic stainless steels have good corrosion resistance, but their low hardness and low wear resistance limit their use whenever surface hardness is required. Nitriding treatments have been successfully applied to stainless steels to improve their mechanical and tribological properties; however, at Temperatures above 723 K, gas or salt bath Nitriding processes decrease the corrosion resistance due to the formation of CrN and other phases within the modified layer. Chromium compounds draw chromium and nitrogen from the adjacent regions, degrading the corrosion resistance. The plasma Nitriding technique permits the use of treatment Temperatures as low as 623 K without promoting degradation in the corrosion resistance of stainless steel. In this work, the pulsed glow discharge (PGD) technique was used for Nitriding steel (AISI304L) in order to investigate the effect of the Temperature of this treatment in the morphology and, as a consequence, in the anodic behavior of the formed layers, in solution with and without chloride ions. Four different Temperatures were employed (623, 673, 723, and 773 K). The samples were characterized by optical microscopy (OM), scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), microhardness measurements, and electrochemical tests with potentiodynamic anodic polarization curves. The Nitriding Temperature alters the anodic behavior due to a displacement of the polarization curve towards higher currents, in a solution free of chloride ions. In a chloride solution, the Nitriding Temperature increases the pitting potential up to the oxygen evolution region.
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study of the s phase formed on plasma nitrided aisi 316l stainless steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006Co-Authors: L C Gontijo, R Machado, Luiz Carlos Casteletti, E J Miola, Nelson Guedes De Alcântara, Pedro A.p. NascenteAbstract:Abstract Some tribological and corrosion resistance properties of austenitic stainless steels are enhanced by the formation of the S phase, also called expanded austenite. This phase is formed on the surfaces of austenitic stainless steels nitrided under certain conditions. In this work, AISI 316L steel was plasma-nitrided at 350, 400, 450, and 500 °C, and the samples were characterized by X-ray diffraction (XRD), conversion electron Mossbauer spectroscopy (CEMS), and wavelength dispersive spectroscopy (WDS) in order to investigate the S phase. XRD analysis identified the presence of a distorted cubic structure phase. The modified layer consists of an austenitic phase with different content of nitrogen, ranging from approximately 10 to 40 at%, and also γ′-Fe4N and ɛ-Fe2–3N phases. A diminution in the S phase occurs with the increase in Nitriding Temperature, and this decrease is related to the transformation of the S phase to the γ′-Fe4N phase.
R V Proskurnyak - One of the best experts on this subject based on the ideXlab platform.
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corrosion resistance of ti 6al 4v alloy with nitride coatings in ringer s solution
Corrosion Science, 2013Co-Authors: I M Pohrelyuk, V M Fedirko, O V Tkachuk, R V ProskurnyakAbstract:Abstract The corrosion behaviour of Ti–6Al–4V alloy with nitride coatings was investigated in Ringer’s solution at 36 and 40 °С. Nitride coatings of different composition, thickness and surface quality were formed because of changing nitrogen partial pressure from 1 to 10 5 Ра and Nitriding Temperature from 850 to 900 °С. Results shown that nitride coatings improve anticorrosion properties of alloy at both solution Temperatures. Corrosion resistance of alloy increases with the content increase of TiN phase in nitride coating. With increase of Temperature from 36 to 40 °С the corrosion resistance of alloy is determined significantly by quality of nitride coating.