The Effect of Al Implantation on the Thermal Oxidation of Stainless Steel in Aggressive Environments

AISI-321 steel samples were implanted with Al ions (implantation-energy:40 keV; dose: 2×10¹⁷ ions/cm²). Thermal oxidationof the samples was performed at 450, 550, 600, and 650°C for periodsvarying from 1 to 6 days in air and in a corrosive CO₂-containingenvironment. Nuclear Reaction Analysis (NRA) and Rutherford BackscatteringSpectrometry (RBS) were used to investigate the oxidized samples. Asignificant improvement of the oxidation resistance of the implantedmaterial in comparison to the nonimplanted material was observed. Thisespecially applies for samples oxidized at high temperatures. The aluminumdepth distribution determined by NRA [using the resonance at 992 keV of the²⁷Al(p, )²⁸Si nuclear reaction] and RBS,indicated no variation of the Al profile in the temperature region450–600°C, whereas at 650°C a slight Al diffusion wasobserved. Scanning electron microscopy (SEM–EDS) was applied to studythe surface morphology and the constitution of the oxide scale formed, aswell as to explain the influence of Al implantation on the oxidation behaviorof AISI-321 austenitic stainless steel.     

The beneficial role of Y-implantation on the aqueous corrosion of stainless steel

The corrosion behaviour of Y-implanted austenitic stainless steel AISI 321 samples was investigated in 0.5 M H₂SO₄ at ambient temperature using potentiodynamic polarization and cyclic voltammetry. The implantation of 1 × 10¹⁶ Y-ions/cm² of 40 keV energy did not lead to an improvement of the corrosion resistance of the material because of sputtering effects. On the other hand, a significant improvement of the corrosion resistance was observed by increasing of the dose (2 × 10¹⁷ Y-ions/cm² implanted in the presence of oxygen) and the implantation energy (55 and 80 keV). The elemental composition of the near-surface layers of the implanted steel samples prior and after the corrosion attack was determined by Rutherford backscattering spectrometry (RBS) and Nuclear Reaction Analysis (NRA) using alpha particles, protons and deuterons as projectiles. The surface morphology and microstructure of the non-corroded and corroded samples were examined by Scanning Electron Microscopy (SEM). The corrosion resistance of the implanted materials was found to be related with the thickness and the composition of the implanted layer.     

The preparation, characterization and corrosion behaviour of ion-implanted and ceramic-coated AISI 321 steel samples

Ion Beam Techniques were used to modify near-surface layers of austenitic stainless steel AISI 321 samples in order to improve their corrosion resistance. Mg-, Y- (implantation energy: 40 keV) and Al-implantation (implantation energy: 40, 60, 80 and 200 keV), as well as Dynamic Ion Mixing (DIM) (SiC deposition and mixing with 160 keV Xe ⁺ ions) and Sputtering (Si₃N₄ deposition with 15 keV Ar⁺ ions) were applied for this purpose. The characterization of the samples was performed using Nuclear Reaction Analysis (NRA) and ⁴He-Rutherford Backscattering Spectroscopy (RBS). The corrosion behaviour was investigated in 1N H₂SO₄ using cyclovoltammetry and potentiodynamic polarization. The values of the critical and passivation current density as well as of the corrosion, passivation and repassivation potentials, showed an increase of the corrosion resistance of the treated steel samples. This improvement is connected with the properties of the modified region (thickness, adhesion, formation of oxide films). The surface morphology and microstructure of the specimens before and after the corrosion experiments were investigated by Scanning Electron Microscopy (SEM).     

Influence of Implantation Dose on the High-Temperature Oxidation of Al-Implanted AISI-321 Steel

The influence of implantation dose on the oxidation behavior of AISI-321 stainless steel was investigated. The steel samples were implanted with Al⁺ ions of energy 40 keV (doses, 0.5 to 3×10¹⁷ ions/cm²) and oxidized in air at 650°C for 48 hr. For comparison purposes, samples were also implanted with a dose of 2×10¹⁷ ions/cm² of energy 200 keV and treated in a similar way. Nuclear-reaction analysis (NRA) and Rutherford backscattering spectrometry (RBS) were used in order to investigate the oxidized samples and to determine the oxygen-depth distribution on the implanted samples. The depth distribution of the steel constituents was determined by secondary-ion mass spectroscopy (SIMS), whereas X-ray diffraction (XRD) was applied to the investigation of the formed oxide scales. The composition and the morphology of the modified region were examined by scanning electron microscopy (SEM-EDS). Al-implantation improves the oxidation resistance of the steel and affects the thermal behavior of the material depending on the implantation dose and energy. The influence of the implantation dose and energy are discussed and mechanisms to explain the experimental results are proposed.     

A complex structure in the (β+γ0) region of the Cu–Al alloys

The identification, characterization and stability range of the phases present in a series of Cu–Al alloys, with Al content from 11.0 to 15.0 wt.%, were studied by Differential Thermal Analysis (DTA), Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED), Auger Electron Spectroscopy (AES), Energy Dispersive X-Ray Spectroscopy (EDX) and X-Ray Diffraction (XRD). In some alloys and in a temperature range from 790°C to 850°C the presence of black spots exhibiting regular shapes and an homogeneous distribution was noticed through metallographic microscopy. Data from TEM and AES indicate that these spots are made of two monocrystalline phases having different Al contents and a crystallographic orientation relationship.     

Effect of bacterial biofilm on 316 SS corrosion in natural seawater by eis

The electrochemical behavior of AISI 316 stainless steel in natural seawater collected from Canary Archipelago was investigated. A comparative study on a large number of samples immersed during three weeks in this environment with and without sulfate-reducing bacteria (SRB) was made. Open circuit potential measurements, cyclic polarization, Scanning Electron Microscopy (SEM) and Electrochemical Impedance Spectroscopy (EIS) were used. The obtained results permitted an interpretation of the contribution of biofilms to corrosion of stainless steel and a mechanism of the process is checked.     

Improvement of corrosion and wear resistances of AISI 420 martensitic stainless steel using plasma nitriding at low temperature

The influence of low temperature plasma nitriding on the wear and corrosion resistance of AISI 420 martensitic stainless steel was investigated. Plasma nitriding experiments were carried out with DC-pulsed plasma in 25% N₂ + 75% H₂ atmosphere at 350 °C, 450 °C and 550 °C for 15 h. The composition, microstructure and hardness of the nitrided samples were examined. The wear resistances of plasma nitrided samples were determined with a ball-on-disc wear tester. The corrosion behaviors of plasma nitrided AISI420 stainless steel were evaluated using anodic polarization tests and salt fog spray tests in the simulated industrial environment.The results show that plasma nitriding produces a relatively thick nitrided layer consisting of a compound layer and an adjacent nitrogen diffusion layer on the AISI 420 stainless steel surface. Plasma nitriding not only increases the surface hardness but also improves the wear resistance of the martensitic stainless steel. Furthermore, the anti-wear property of the steel nitrided at 350 °C is much more excellent than that at 550 °C. In addition, the corrosion resistance of AISI420 martensitic stainless steel is considerably improved by 350 °C low temperature plasma nitriding. The improved corrosion resistance is considered to be related to the combined effect of the solid solution of Cr and the high chemical stable phases of ?-Fe₃N and α_N formed on the martensitic stainless steel surface during 350 °C low temperature plasma nitriding. However, plasma nitriding carried out at 450 °C or 550 °C reduces the corrosion resistance of samples, because of the formation of CrN and leading to the depletion of Cr in the solid solution phase of the nitrided layer.     

Oxidation and sulfidation of implanted and unimplanted AISI 446 steel

AISI 446 steel exhibited parabolic rate kinetics from the beginning during isothermal oxidation in oxygen at 850°C. On the other hand, a pronounced transient oxidation with faster kinetics was observed in Ce- and Xe-implanted AISI 446 steels. The implantation, however, did not affect the steady-state parabolic rate constant, 3.77±0.18×10^–5 mg²/cm⁴ min. The initial response of implanted steels to oxidation with pronounced transient oxidation was attributed to the physical defects of implantation. The oxide grains formed on AISI 446 early in the process of oxidation were rich in Fe and Cr, and after long exposure the spinel MnCr₂O₄ became the major constituent of the scale. Ce-implantation did not have any effect on the corrosion behavior of AISI 446 in H₂/H₂O/H₂S/Ar at 850°C. The scale had three zones: an outer layer with FeS, (FeCr)S, and spinel oxide; an intermediate layer of (FeCr)S; and an inner layer of Cr-rich oxide and (FeCr)S below the original metal surface.     

Codeposited chromium and silicon diffusion coatings for Fe-Base alloys via pack cementation

The simultaneous deposition of Cr and Si into plain carbon, low-alloy, and austenitic steels using a halide-activated pack-cementation process is described. Equilibrium partial pressures of gaseous species have been calculated using the STEPSOL computer program to aid in designing specific processes for codepositing the desired ratios of Cr and Si into a given alloy. The calculations indicate that NaCl-activated packs are chromizing, while NaF-activated packs deposit more Si with less Cr. The use of a dual activator (e.g., NaF+NaCl) allows for the deposition of both Cr and Si in the desired amounts. Single-phase ferritic coatings (150–250 microns thick) with a surface concentration of 20–35 wt.% Cr and 2–4% Si have been grown on AISI 1018, Fe-2.25 Cr-1.0Mo-0.15C, and Fe-0.5 Cr-0.5 Mo-0.2C steels using packs containing a 90 wt.% Cr-10Si binary source alloy, a NaF+NaCl activator, and a silica filler. Two-phase coatings (approximately 75 microns thick) containing 20–25 wt.% Cr and 2.0–2.4% Si have been obtained on 304 stainless steel using packs containing a 90 wt.% Cr-10Si binary source alloy, a NaF activator, and an alumina filler. The same pack chemistry allowed the diffusion of Cr and Si into the austenitic Incoloy 800 alloy without a phase change. A coated Fe-2.25 Cr-1.0 Mo-0.15 C coupon with a surface concentration of Fe-34 wt.% Cr-3Si was cyclically oxidized in air at 700°C for over four months and 47 cycles. The weight gain was very low (<0.2 mg/cm²) with no scale spalling detected. Coated coupons of AISI 1018 steel, and Fe-0.5 Cr-0.5 Mo-0.2C steel have shown excellent oxidation-sulfidation resistance in reducing, sulfur-containing atmospheres at temperatures from 400 to 700°C and in erosion and erosion-oxidation testing in air at 650 and 850°C.     

Effect of interfacial oxidation occurring during the duplex process combining surface nanocrystallisation and co-rolling

This paper presents an investigation of the interface quality of nanocristallised 316 L stainless steel multilayer structures. They were produced by a duplex process, combining the Surface Mechanical Attrition Treatment (SMAT) and the co-rolling process at two different annealing temperatures (550 °C and 650 °C). Oxide layers were observed at the interfaces between the sheets and their morphology was characterised by optical microscopy. Their chemical composition was determined by Energy Dispersive X-ray spectrometry. The microstructure near the interfaces was analysed by Transmission Electron Microscopy (TEM). In the laminate co-rolled at 550 °C, the presence of ultrafine grains was demonstrated. Additional tensile tests have shown an influence of the annealing temperature on the yield strength, as well as on the resistance of the interfaces of the co-rolled multilayer structures.     

Emergence of Ag particles and their effects on the mechanical properties of TaN-Ag nanocomposite thin films

TaN-Ag nanocomposite films were deposited by reactive co-sputtering on tool steel substrates. The films were then annealed using RTA (Rapid Thermal Annealing) at 350 °C for 2, 4, 8 min respectively to induce the nucleation and growth of Ag particles in TaN matrix and on film surface. C-AFM (Conductive Atomic force Microscopy) and FESEM (Field-Emission Scanning Electron Microscopy) were applied to examine the Ag nano-particles emerged on the surface of these thin films. A nano-indenter and a pin-on-disk tribometer were used to study the effect of annealing on the films' mechanical properties. The results reveal that annealing by RTA can cause Ag nano-particles to emerge on the TaN surface. Consequently, the mechanical properties of the films will vary depending on annealing conditions, Ag content, and Ag particle emergence.     

The direct observation and investigation of the oxidation of aluminum in the transmission electron microscope

The authors studied the oxidation of thin aluminum films free of oxide layers in situ prepared by evaporation directly in the electron microscope under ultra-high-vacuum conditions. The oxidation was realized at various temperatures (350–500°C) and at various oxygen pressures (1–10^–3 Pa). The formation and growth of the amorphous and crystalline products have been studied.     

Air Oxidation of Ni–Ti Alloys at 650–850°C

The oxidation of pure Ni and three Ni–Ti alloys containing 5, 10, and 15 wt.% Ti over the temperature range 650–850°C in air was studied to examine the effect of titanium on the oxidation resistance of pure nickel. Ni–5Ti is a single-phase solid solution, while the other two alloys consisted of nickel solid solution (-Ni) and TiNi₃. The oxidation of Ni–Ti alloys at 650°C follows an approximately parabolic rate law and produces a decrease in the oxidation rate of pure Ni by forming an almost pure TiO₂ scale. At higher temperatures, Ni–Ti alloys also follow an approximately parabolic oxidation, and their oxidation rates are close to or faster than those of pure Ni. Duplex scales containing NiO, NiTiO₃ and TiO₂ formed. Some internal oxides of titanium formed, especially at 850°C. In addition, the two-phase structure of Ni–10Ti and Ni–15Ti was transformed into a single-phase structure beneath the scales.     

Study of the initial oxidation of a Ni-20Cr alloy in the temperature range 550–830°C: Influence of mechanical deformation

The influence of a uniaxial deformation on the initial oxidation rate of a Ni-20Cr polycrystalline alloy was studied between 550 and 830°C at 10^–4 Pa of oxygen. At 550, 650, and 750°C, it was shown that the defects induced by a mechanical predeformation accelerate chromium-oxide formation on the alloy surface. This homogeneous oxide film is characteristic of the low-pressure-oxidation conditions. The film appeared on the sample after various incubation periods for the experimental conditions used. Microanalyses (scanning Auger microanalyses, composition profiles) reveal that growth of this oxide is heterogeneous and that it needs preferential orientations with the substrate. Furthermore, near chromium-oxide areas, an incorporation of oxygen at concentrations higher than the solubility was noted. At 830°C, this chromium oxide does not grow, because the superficial defects disappear by thermal annealing and the oxygen incorporation does not apparently depend on mechanical deformation.     

Effects of the composition and low-temperature thermomechanical treatment on the mechanical properties of structural steels

Conclusions The investigation of the effect of thermomechanical treatment on the mechanical properties of steels with different compositions makes it possible to put in evidence the effect of alloyed elements. The addition of up to 1.2–1.5% Si (particularly with vanadium) makes it possible to increase the tempering temperature to 350°C without significantly decreasing the strengthening effect of low-temperature thermomechanical treatment. An increase of the concentration of chromium from 1.5 to 3–5% also increases the resistance of the steel. In steel containing 3–5% Cr and also molybdenum, vanadium, and tungsten, the effect of low-temperature thermomechanical treatment is retained after tempering at temperatures up to 500°C, the plasticity remaining rather high. Low-temperature thermomechnical treatment of batches 8 and 10 followed by tempering at 500°C resulted in the following mechanical characteristics: _b=240–255 kg/mm² when =10–13% and =30–35%; after tempering at 350°C _b=255–265 kg/mm², ₅=8–12%, and =28–36%.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 36–40, April, 1963     

On the influence of cold work on the oxidation behavior of some austenitic stainless steels: High temperature oxidation

AISI 304, 314, 321, and Incoloy 800H have been subjected to several pretreatments: polishing, milling, grinding, and cold drawing. In the temperature range 800–1400 K, cold work improves the oxidation resistance of AISI 304 and 321 slightly, but has a relatively small negative effect on the oxidation resistance of AISI 314 and Incoloy 800H. Milling results in an enlargement of the surface area with a factor 2.5.     

High-temperature oxidation of Fe-2 1 4 Cr-1Mo in oxygen

The oxidation of a 2 ₁ ⁴ Cr-1Mo steel in dry flowing oxygen has been studied in the temperature range 550–700°C for periods of up to 100 hr. A detailed low-resolution microstructural investigation revealed a layered oxide consisting of a very fine-grained and finely pored innermost layer of doped spinel, a central columnar-grained relatively coarsely pored layer of magnetite, and an outer fine-grained hematite layer with fine pores and covered with whiskers of -Fe₂O₃. This structure is compared with previous results on Fe and model Fe-Cr alloys, as are the kinetics of the oxidation reaction.     

Effects of DBU, morpholine, and DMA on corrosion of low carbon steel exposed to steam

Effects of morpholine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and dimethylamine (DMA) on oxidation kinetics and oxide phase formation/transformation of AISI 1018 steel at 120 °C were evaluated. Low carbon steel samples were exposed to steam in an autoclave containing amine added aqueous solution at pH of 9.5 for 1, 2, 4, 6, 8, and 12 h. Control samples exposed to plain steam and amines showed the highest and lowest weight loss respectively. Fourier Transform Infrared Spectrophotometry (FTIR) showed that DBU containing steam favored formation of magnetite (Fe₃O₄) while steam with DMA formed more α and γ-FeOOH. Transformation of magnetite to hematite (α-Fe₂O₃) was fastest for morpholine. Analysis of oxides morphology was done utilizing Scanning Electron Microscopy (SEM). Oxides formed in plain or DMA containing steam exhibited acicular particles of goethite/hematite (α-FeOOH/α-Fe₂O₃) compared to DBU containing steam that showed equiaxed particles of magnetite/maghemite (Fe₃O₄/γ-Fe₂O₃). Morpholine containing steam promoted agglomeration of thin sharp platelets into coarse flakes of hematite.     

Polybenzoxazine/SiO2 nanocomposite coatings for corrosion protection of mild steel

A series of nanocomposite coatings (PBS) consisting of silane functional polybenzoxazine (PB-TMOS) and SiO₂ nanoparticles were developed for corrosion protection of mild steel. The influence of silica content on corrosion resistance of PBS coatings was investigated by electrochemical measurements. The surface chemistry of nanoparticles and its effect on morphology of the PBS coating was also studied utilizing Fourier Transforms Infrared Spectroscopy, ²⁹Si Nuclear Magnetic Resonance and Scanning Electron Microscopy analyses. The results indicate that the presence of the covalent bond between nanoparticles and PB-TMOS, greatly improves the interfacial interactions at the polymer/filler interfaces resulting in a better corrosion performance.     

Ni-YSZ films deposited by reactive magnetron sputtering for SOFC applications

Ni-YSZ films are deposited by reactive magnetron sputtering from a single Ni/Zr/Y metallic target at rates as high as 4 µm h^− 1. Tailoring both DC pulsed power and oxygen partial pressure, a stable deposition process was obtained. Columnar morphology was observed in the as-deposited films. Annealing in air at 900 °C was conducted, after which a fully crystallized structure was achieved. Chemical composition has been measured by Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA). To find optimal conditions for reactive deposition of the films, effect of oxygen flow rate on the discharge parameters was studied. Film deposition onto glass substrates was carried out to measure electrical conductivity.