Surface Of 304L Stainless Steel Research Articles

Enhancement of corrosion resistance of 304L stainless steel treated by massive laser shock peening

The effects of laser shock peening (LSP) on the pitting corrosion behaviour of austenite stainless steel in an acid chloride environment are investigated in this work. The results reveal that LSP treatment improves the pitting corrosion resistance of 304L stainless steel, resulting in a higher pitting potential and a lower metastable pitting nucleation rate of larger pits. However, the augmented effect is only significant in the case of massive LSP impacts. The effects of LSP on microstructure, surface morphology, residual stress, and chemical composition of the surface are studied and analyzed. The significant compressive residual stress and grain refinement on the surface of 304L stainless steel treated by massive LSP impacts are attributed to the enhancement of pitting corrosion resistance, as the former helps minimize microcracks between the intermetallic and matrix metals, and the latter allows for forming a thicker inner layer supplied by Cr2O3 in the passive film.

Surface Modification of 304L Stainless Steel and Interface Engineering by HiPIMS Pre-Treatment

A clean and defect-free substrate/coating interface is required to guarantee good adhesion of coatings under service conditions. For this purpose, an etching pre-treatment using High-Power Impulse Magnetron Sputtering (HiPIMS) was performed to modify the surface of 304L stainless steel. The effect of three etching procedures on the substrate properties, such as corrosion resistance and adhesion, was investigated with unprecedented spatial resolution and spectroscopic details. Glancing angle X-ray diffraction showed modification in phase content but no neoformation after steel etching. X-ray photoelectron spectroscopy confirmed the presence of etchant species (6–7 at.%) on the extreme surface of the substrate. Transmission Electron Microscopy and Atomic Probe Tomography showed that the interface was less than a few nanometers wide. Polarization curves in a nitric acid solution at boiling temperature showed, for the first time, that the Ti+ and Zr+ etchings decreased the corrosion current density compared to the untreated original surface. Scratch-test measurements indicated better substrate/coating adhesion using HiPIMS metal ion etching. Electrochemical characterization revealed that Zr etching and thin coating improve the anti-corrosion properties of stainless steel in strong nitric acid conditions.

Effect of laser surface cleaning of corroded 304L stainless steel on microstructure and mechanical properties

In this study, a high-power Nd:YAG laser is used to remove a corrosion layer on the surface of 304L stainless steel (SS304L). A laser power of 1140 W with different hatch distances and the number of repetitions is employed for corrosion removal. As shown by an electron probe X-ray microanalyzer, corrosion removal is successfully achieved via laser surface cleaning (LSC) with the small hatch distance or the large number of repetitions. However, corrosion residues remain at the surface of SS304L after the LSC process with the large hatch distance and the small number of repetitions. The effect of LSC process on the microstructure and mechanical properties of SS304L is investigated. The electron backscatter diffraction and transmission electron microscopy analyses reveal that the microstructure of SS304L depends significantly on the LSC conditions. In the LSC process with the large hatch distance and the small number of repetitions, only an increase in dislocation density is discovered. However, the LSC process with the small hatch distance or the large number of repetitions introduces dense dislocation structures, deformation twins, grain refinement, and precipitation. This microstructural alteration owing to the LSC process modifies the mechanical properties of SS304L in terms of hardness and tensile strength.

Coupling hybrid of HBN nanosheets and TiO2 to enhance the mechanical and tribological properties of composite coatings

Epoxy resin (EP) composite coatings enhanced with hexagonal boron nitride (HBN) nano-sheets, TiO2 particles and HBN-TiO2 hybrid material were fabricated successfully on the surface of 304L stainless steel. The structural and morphological features of HBN, TiO2 and HBN-TiO2 hybrid obtained from mechanical peeling and sol-gel method were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), Raman spectroscopy, XRD patterns, FT-IR spectra and XPS spectra. Moreover, tribological characteristic of composite coatings was investigated by UMT-3 tribometer. Mechanical behavior, worn surface, steel ball surface and debris size distribution of composite coatings were detected to investigate the tribological mechanism. The results demonstrated that HBN/EP, TiO2/EP and HBN-TiO2/EP composite coatings showed remarked promotion of mechanical behavior compared with the neat EP, especially for the improvement of hardness. The HBN-TiO2/EP composite coating, whose wear rate decreased by 65.8 % in comparison with the neat EP, manifested prominent tribological performance ascribed to the load carrying capacity of TiO2 and the reduction of self-lubricating effect on the size of debris.

Thin films deposition on 304L stainless steel using e-gun technology for medical applications

The purpose of this article is to characterize surface of 304L stainless steel coating by e-gun technology with thin films of Ta2O5 and ZnO. ZnO films are used in pharmaceutical industries, in cosmetics and in medicine, grace of their better anticorrosive, antibacterial and photo catalytic properties. Ta2O5 films have rapidly evolved in medicine research with the promise of development of new types of biomaterials used in medicine. Ta2O5 coatings present an excellent biocompatibility, good dielectric properties, and high corrosion resistance. The biomaterials are realized by novel and special methods to resist of the biological reactions that occur in medical implants (protein adsorption, cell adhesion, cell growth, blood compatibility, etc.). The most important surface properties are physical properties, durability and biocompatibility. The physical properties of a biomaterial that must to be measure, are mechanical strength, permeability and elasticity. Biocompatibility is the response of the biomaterial or of the device to the proteins, cells and organisms action, when the implants are in contact with the biological tissue. The common method to characterize biomaterial surfaces are: contact angles, ESCA (XPS), Auger Electron Spectroscopy, SIMS, FTIR-ATR, STM, SEM and EDAX.

Stress corrosion cracking of laser alloyed 304L stainless steel with Ru in hot chloride solution

The exceptional ductility and good uniform corrosion resistance of austenitic stainless steels especially the commonly used 304L stainless steel is lost with its severe embrittling in aqueous conditions in the presence of chlorides at elevated temperatures. With the addition of ruthenium (Ru) the corrosion resistance of 304L stainless steel is enhanced, as well as the resistance to stress corrosion cracking. However, the cost of Ru is high and this limits the possibilities. Therefore, to lower the cost of Ru, a layer of approximately 950 ± 90 μm was laser cladded on the surface of 304L stainless steel. The purpose of this investigation is to evaluate the effectiveness of Ru additions to surface layer through laser cladding to mitigate cracking. Ru was applied to the surface of 304L stainless steel with a Nd:YAG laser as a metal powder with Ru concentrations of 1, 2, 5 and 10 wt%. With these methods, the cost of Ru is kept low while it can still cause inhibition of cracking. Three-point bend stressed samples were exposed to distilled water with 100 ppm sodium chloride at 200 °C with an initial dissolved oxygen concentration of 8 ppm at 25 °C. As expected the as-received 304L stainless steel was susceptible to stress corrosion cracking. With the addition of Ru to 304L stainless steel, the resistance to cracking improved markedly, the minimum and maximum crack propagation rate attained was 0.013 and 0.023 μm/s respectively. The crack propagation rate decreased as the Ru content was increased, and cracking was inhibited at 5 and 10 wt% Ru.

Tribocorrosion behaviors of multilayer PVD DLC coated 304L stainless steel in seawater

The multilayer DLC coating was successfully fabricated on the surface of 304L stainless steel and silicon wafers by unbalanced magnetron sputtering technology. The tribocorrosion tests were carried out in a triboelectrochemical cell using a ball-on-plate tribometer integrated with a potentiostat for electrochemical control. Results showed that the open circuit potential (OCP) and corrosion potential (Ecorr) of 304L substrate presented great fluctuation. However, the OCP and Ecorr values of the multilayer DLC coating remained relatively stable during these tests. Meanwhile, the friction coefficient decreased and the wear-loss increased with the polarization potential increased from −1 to 0.5V. In addition, with an increase in polarization potential, the mechanical wear decreased obviously and the corrosion-induced wear gradually occupied a dominant position for 304L substrate, nevertheless, the mainly volume loss of the multilayer DLC coating was mainly attributed to pure mechanical wear. Thus, the tribocorrosion resistance of the multilayer DLC coating was superior to 304L substrate in seawater, manifesting its good potential as a protective material for marine industry.

The effect of cysteine on the corrosion of 304L stainless steel in sulphuric acid

The effect of cysteine on the corrosion of 304L stainless steel in 1 mol l −1 H 2SO 4 was studied using open-circuit potential measurements, anodic polarization curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). All the electrochemical measurements obtained in the presence of low cysteine concentration (10 −6–10 −5 mol l −1) presented the same behaviour as those obtained in the absence of cysteine, a passivated steel surface. However, for higher cysteine concentrations (10 −4–10 −2 mol l −1), a different behaviour was observed: the corrosion potential stabilized at a more negative value; an active region was observed in the anodic polarization curves and the electrochemical impedance diagrams showed an inductive loop at lower frequencies and a much lower polarization resistance. These results show that the presence of cysteine at high concentration turns the surface of 304L stainless steel electrochemically active, probably dissolving the passivation layer and promoting the stainless steel anodic dissolution. SEM experiments performed after immersion experiments at corrosion potential were in good agreement with the electrochemical results.

Study on the surface topology of vacuum-fired stainless steel by scanning tunnelling microscopy

The surface of 304L stainless steel, after normal bakeout and vacuum firing, has been imaged in the scanning tunnelling microscope (STM). Probe tips with sharp apexes and well-known reproducible geometry which were previously characterized in the field ion microscope (FIM) were used. After bakeout the STM surface profiles show on chemical polished surfaces an average roughness of 3–5 nm and over 300–500 nm variations in height of 30–50 nm. After vacuum firing a significant change of the surface structure and topology is observed. Crystallites with almost (1 1 1) orientation show wide (1 1 1) terraces with monoatomic steps. On tilted crystallites again wide (1 1 1) terraces, intersected with bunched steps and facets forming nearly regularly pattern and corresponding in orientation almost to the (1 0 0) and (1 1 0) planes can be observed. From the general appearance of the surface after vacuum firing it can be concluded that the surface became less active with respect to gas surface interaction which supports the present understanding of outgassing of this material.

In Situ Micro Raman Spectroscopy for Characterization of Oxide Film Formed on the New Surface and for Measurements of the Stress of Oxide Film Formed on 304L Stainless Steel

Environmentally assisted cracking (EAC) consists of two distinct events viz., i) crack initiation and ii) crack propagation. On a smooth surface, the EAC initiates by the rupture or by the degradation of the surface film due to the combined action of stress and an electrochemical reaction of the materials with the environment. The mechanical properties of the surface oxide films are also important considerations when determining the susceptibility to EAC. In this research, Micro Raman Spectroscopy(MRS) was applied for in-situ oxides characterization and for in-situ measurements of the stress in oxide film formed on the surface of 304L stainless steel during the scratching electrode and the slow strain rate test (SSRT), respectively. The passive oxide film growth formed on the bare surface was continuously monitored by MRS as a function of time. For stress measurements, Cr2O3 was focused on and Raman shift at Cr2O3 peak of Raman spectrum was measured continuously. The strain rate was 8.2×10-7 /sec. . In the initial stage of SSRT, the Raman shift of surface film decreased gradually with strain. At 5% strain, the Raman shift of surface film increased rapidly to around the initial value of Raman shift. It is considered that the surface film was ruptured at this time. At 5% strain, the shift value of Raman peak of Cr2O3 reached to 5cm-1. This value (5cm-1) corresponds to 1.2GPa which value of tensile stress is calculated from reference data. These characteristics of oxide film will be implemented into the theoretical formulation of EAC and their implication to EAC growth rate will be discussed.

The In-situ Measurement of a Local Chemical Reaction by Raman Spectroscopy : Time dependent enrichment of chloride ions on the surface of 304L stainless steel(EAC1)

In this research, in situ microscopic Raman spectroscopy was used to measured and to analyze the local enrichment of chloride ions on the surface of 304L stainless steel in a sodium chloride solution where the potential of the sample was controlled by a potentiostat. The Raman Spectroscopy measurement was performed on the specimen under the potential control with an area of φ10μm. The local concentration of chloride ions was measured by the variation of the water Raman spectrum since the O-H stretching mode of water Raman scattering (at 3250 - 3400cm^<-1>) is very sensitive to changes in the electrolyte concentration. The parameter for a measurement of small bands fits by Raman difference spectroscopy (RDS) proposed in the recent literature, which can clearly indicates a small change in the Raman spectrum, was utilized in this investigation. Corrosion pits occurred on the specimen surface after 60 minutes under the condition of +200 mV(SCE) in 0.5 mol/l NaCl solution and, in this case, the parameter was monotonically increased with the exposure time. On the contrary, in the case where no corrosion pits occurred, no increase in the parameter was observed. These results demonstrate that the enrichment of chloride ion was observed only on the specimens where the corrosion pits were formed.