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ABSTRACT: This article presents the preparation, characterization, and hot-salt oxidation behavior of nitrogen-containing type 316L
stainless steel (SS), surface modified with intermetallic coatings. Three different types of intermetallic coating systems,
containing aluminum, titanium, and titanium/aluminum multilayers, were formed by diffusion annealing of type 316L austenitic
SS containing 0.015, 0.1, 0.2, and 0.56 pct nitrogen. Analysis by using X-ray diffraction (XRD), scanning electron microscopy
(SEM), and secondary ion mass spectroscopy (SIMS) confirmed the formation of various intermetallic phases such as AIN, Al13Fe4, FeAl2, FeTi, Ti2N, and Ti3Al in the coatings. Hot salt oxidation behavior of the uncoated and surface-modified stainless steels was assessed by periodic
monitoring of the weight changes of NaCl salt-applied alloys kept in an air furnace at 1023 K up to 250 hours. The oxide scales
formed were examined by XRD and stereomicroscopy. Among the various surface modifications investigated in the present study,
the results indicate that the titanium-modified alloys show the best hot-salt oxidation resistance with the formation of an
adherent, protective, thin, and continuous oxide layer. Among the four N-containing alloys investigated, the titanium and
Ti/Al multilayer modified 0.56 pct N alloy showed the best hot-salt oxidation resistance as compared to uncoated alloys. The
slower corrosion kinetics and adherent scale morphology indicate that the surface-modified titanium intermetallic coatings
could provide high-temperature service applications up to 1073 K, particularly in chloride containing atmospheres, for austenitic
stainless steels.
Metallurgical and Materials Transactions A 04/2012; 35(6):1799-1806. · 1.54 Impact Factor
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Journal of Nuclear Materials 01/2008; · 2.05 Impact Factor
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07/2007; , ISBN: 9783527610426
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Surface Engineering 01/2007; · 0.94 Impact Factor
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ABSTRACT: The influence of laser surface alloying (LSA) with Cr and Cr + Ni on the corrosion behaviour of type 304L stainless steel (SS) was investigated using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) in chloride (0·5M NaCl) and acidic (1 N H2SO4) media. Surface alloying was carried out by laser cladding type 304L SS substrate with premixed powders of AISI type 316L SS and the desired alloying elements. The results indicated that Cr surface alloyed specimen exhibited a duplex (? + ?) microstructure with Cr content of ?24 wt-%, whereas Cr + Ni surface alloyed specimen was associated with austenitic microstructure with Cr and Ni contents of ?22 wt-% each. The potentiodynamic polarisation results in chloride solution indicated that LSA with Cr + Ni considerably enhanced the pitting corrosion resistance compared with LSA with Cr alone. In acidic media, such beneficial effects were not observed. Electrochemical impedance spectroscopy results showed an increase in semicircle arc for both chloride and acidic media for both Cr and Cr + Ni clad samples indicating improvement in the oxide film stability compared with untreated specimen. The polarisation resistance was higher and capacitance values of the laser clad specimen were lower than those in the untreated specimen. The microstructural changes and compositional variations produced by LSA are correlated to the corrosion behaviour.
Materials Science and Technology 09/2006; 22(10):1185-1192. · 0.77 Impact Factor
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ABSTRACT: The present work investigates the aqueous corrosion behaviour of type 316L stainless steel (SS) containing various matrix nitrogen contents (0·015, 0·1, 0·2 and 0·56%N), surface modified by diffusion annealing of a precoated film of titanium/aluminium. Type 316L SS specimens were precoated with a Ti/Al multilayer by the electron beam deposition method and surface diffusion annealed at 1173 K for 1 h in vacuum. X-ray diffraction analysis indicated the formation of Ti3Al, Al5Ti2, Al2Ti and Al13Fe4 intermetallic phases. Nitrides such as Ti2N were also observed, particularly in high nitrogen steels. The interaction between the titanium/aluminium coating and the matrix constituents, particularly with nitrogen, was characterised by secondary ion mass spectrometry (SIMS). The nitrogen content at the modified surface increased with increase in the nitrogen content of the substrate matrix. SEM observation of cross-sectionally mounted surface modified alloys indicated the formation of thick adherent layers. The role of such intermetallic phases in corrosion resistance in both 0·5 M H2SO4 and 0·5 M NaCl is discussed in detail based on open circuit potential-time measurements, potentiodynamic polarisation studies and electrochemical impedance spectroscopy (EIS) investigations. The role of matrix nitrogen in the formation of intermetallic coatings and its role in corrosion resistance in acidic and chloride media are investigated.
Surface Engineering 01/2004; 20(1):59-67. · 0.94 Impact Factor
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ABSTRACT: Pitting corrosion studies were carried out on cold worked (5%, 10%, 15%, 20%, 30% and 40%) nitrogen-bearing (0.05%, 0.1% and 0.22% N) type 316L austenitic stainless steels in neutral chloride medium. Potentiodynamic anodic polarisation study revealed that cold working up to 20% enhanced the pitting resistance, and thereafter a sudden decrease in pitting resistance was noticed at 30% and 40% cold working. Increase in nitrogen content was beneficial up to 20% cold work in improving the pitting corrosion resistance, beyond which it had a detrimental effect at 30% and 40% cold working. The role of nitrogen in influencing the deformation band width and dislocation configuration is explained based on the results of transmission electron microscopy investigations. Scanning electron microscopy observation of the pitted specimens indicated decreasing size and increasing density of pits, along the deformation bands with increasing nitrogen for 40% cold worked specimens. The macrohardness values increased as the cold working increased from 0% to 40%. X-ray diffraction studies revealed the increased peak broadening of austenite peak {0 2 2} with increase in cold working. The relationship between pitting corrosion and deformation structures with respect to nitrogen addition and cold working is discussed.
Corrosion Science.
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ABSTRACT: Zirconium and its alloys are considered as candidate materials for various applications in spent nuclear fuel reprocessing plants involving nitric acid of various concentrations at different temperatures. In the present work an attempt was made to study the corrosion behaviour of Zircaloy-4 (Zr-with Sn-1.5%, Fe-0.22%, Cr-0.1%) in wrought and welded forms in comparison with other candidate materials like commercially pure Titanium (CP-Ti), Ti–5%Ta and Ti–5%Ta–2%Nb. Manual TIG welding and electron beam welding was carried out with Zircaloy-4 pipes of 5 mm thick and 120 mm diameter, and radiography was made for choosing defect-free regions for making samples for corrosion investigations. Three phase corrosion testing in liquid, vapour and condensate regions was conducted in boiling 11.5 M nitric acid medium using a specially designed experimental set up. The results indicated that Zircaloy-4 exhibit superior corrosion resistance in both wrought and welded conditions in comparison with other materials. The electron beam welded samples did not show any deterioration and performed similar to wrought alloy. The detailed results of microstructure, microhardness, corrosion rate, morphology of attack and nature of surface film formed are presented in this paper. The results of the present investigation indicated that Zircaloy-4 could be a candidate material for nitric acid medium of high concentration and temperature in reprocessing plants and other industries.
Corrosion Science. 49(9):3527-3538.
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ABSTRACT: The semiconducting property of passive films of nitrogen-containing type 316LN stainless steels in different electrolytic media (0.5 M NaCl, borate buffer and borate buffer + 0.5 M NaCl) was investigated by electrochemical impedance spectroscopy (EIS). The nitrogen effect on the chemical composition of the passive films was investigated using X-ray photoelectron spectroscopy, (XPS). Based on capacitance results, the semiconducting parameters obtained from the Mott–Schottky plots indicated a decrease in the donor and acceptor density (ND and NA) with increase in nitrogen content, and variation in the flat band potential (EFB), depending on the electrolytic media. Thus indicating that the oxide layers of the passive film are modified by nitrogen addition. The presence of nitrogen and in the passive film was confirmed by the XPS analysis of the passive film. Cyclic polarization for pitting and repassivation corrosion studies indicated a decrease in hysteresis loop with increase in nitrogen content in 0.5 M NaCl solution. In the highest nitrogen-containing alloy (0.556 wt.% N), the hysteresis loop was small and negligible indicating that the pit initiation is minimum in this alloy. Based on the results obtained, an attempt was made to correlate the semiconducting nature of the passive films with pitting corrosion resistance.
Corrosion Science.
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ABSTRACT: The effects of hydrogen on the passivity and pitting susceptibility of type 316L stainless steels have been investigated with alloys containing different nitrogen contents (0.015, 0.198 and 0.556 wt.% N). The study revealed that electrochemically pre-charged hydrogen significantly reduced the pitting resistance of alloys conatining 0.015 and 0.198 wt.% nitrogen contents. In alloy with highest nitrogen content (0.556 wt.% N), an increase in the passive film current density with hydrogen was observed without affecting breakdown potential. Auger electron spectroscopy (AES) analysis of the passive film indicated the presence of nitrogen in the passive film. On other hand, for hydrogen charged samples, nitrogen was found to be significantly less in the passive film. In Electrochemical impedance spectroscopy (EIS) measurement, the decrease in semi-circle radius of Nyquist plot, and the polarization resistance, RP associated with the resistance of the passive film was observed with hydrogen, indicating that hydrogen decreased the stability of the passive film. The present investigation indicated that precharged hydrogen deteriorated the passive film stability and pitting corrosion resistance in these alloys, and the increase in nitrogen content of the alloy offsets the deleterious effect of precharged hydrogen.
Corrosion Science.
