Stainless Steel Thin Films Research Articles

Electron beam evaporated vs. magnetron sputtered nanocolumnar porous stainless steel: Corrosion resistance, wetting behavior and anti-bacterial activity

Stainless steel (SS), widely used because of its outstanding corrosion protection properties, does not possess any particular anti-stain or anti-bacterial activity as required for household and sanitary applications. This work reports the fabrication of SS thin films that, keeping a similar corrosion resistance than the bulk material, presents hydrophobicity and anti-bacterial activity. These thin films are prepared at ambient temperature by physical vapor deposition (PVD), either electron beam evaporation (EBE) or magnetron sputtering (MS), at oblique angles (OAD). According to their scanning electron microcopy and atomic force microscopy analysis, the microstructure of the OAD-SS thin films consisted of tilted and separated nanocolumns defining a surface topology that, characterized by a high percentage of void space, varied with the deposition conditions and procedure, either EBE or MS. It has been shown that particularly the nanocolumnar MS-OAD thin films preserved and even improved the high corrosion resistance of compact SS, as determined by electrochemical analysis. Besides, all OAD-SS thin films depict hydrophobicity and a high antibacterial activity. These features, particularly remarkable for the MS-OAD thin films, have been related with their tip-like termination at the surface and the existence of large void spaces separating the nanocolumns. This topology appears to affect negatively the bacteria’s deployment onto the surface and therefore the survival rate. Differences in the corrosion and antibacterial performance between EBE and MS-OAD thin films have been related with the specificities of these two PVD methods of thin film preparation. A relatively high abrasion resistance, as determined by abrasion tests, supports the use of MS-OAD thin films for the protection of commodity materials.

Preparation of functional thin films with elemental gradient by sputtering with mixed powder targets

Functional thin films with a compositional gradient were deposited by a sputtering method with mixed powder targets. The composition ratio of nickel (Ni) and stainless steel (SUS304) was varied over the film thickness using several types of nickel oxide and stainless steel mixed powder targets. Our results indicate that mixed nickel-doped stainless-steel thin films were successfully prepared on both stainless-steel and Si substrates and the mixing ratio was controlled by the composition of the nickel oxide and stainless steel mixed powder.

Effect of resin lamination on tensile strength characteristics of SUS304 stainless steel thin film

Effect of resin lamination on tensile strength characteristics of SUS304 stainless steel thin film

An electrochemical dopamine sensor based on RF magnetron sputtered TiO2/SS thin film electrode

Titanium Dioxide (TiO2) coated Stainless Steel (SS) thin film (TiO2/SS) as electrochemical Dopamine (DA) sensing electrode materials are synthesized via a Radio Frequency Magnetron Sputtering (RFMS) method. TiO2 nanomaterial is uniformly dispersed on the surface of SS, thus enhancing the electronic conductivity and preventing the aggregation of TiO2/SS thin film. The TiO2/SS thin film exhibit good efficiency which is 0.0219 ± 0.01 µA/µM for the linear range of 50 µM – 450 µM with a detection limit of 23 nM.

Tunable hydrophilicity in a surface nano-textured stainless steel thin film deposited by DC magnetron sputtering

In this article a series of Stainless steel thin films are fabricated by DC power magnetron sputtering of a SUS316 stainless steel target at various argon working pressure. The sample film compositions retain that of an austenitic stainless steel, while XRD spectra reveal that all films possess a single phase, body-centered cubic ferrite crystal structure. At working pressure 6 mTorr and above, the film exhibits a textured surface morphology made up of nano-sized pyramids. Cross-sectional images show that increasing argon pressure cause a microstructural evolution from dense, fibrous grain to coarse tapered grains. This observation agrees with the prediction by Thornton's structural zone model and causes a drastic reduction in static water contact angle (WCA) from ~65° to ~17°. With further increase of argon pressure, a minimum WCA of 11° at 8 mTorr can be achieved. In addition, our textured film deposited at 12 mTorr exhibits both excellent hydrophilicity and low contact angle hysteresis (CAH) at the same time. In summary, this work reports a convenient way of depositing a stainless steel-like hydrophilic coating, in which the wetting properties are tunable via working pressure control.

Preparation of Ni-doped stainless steel thin films on metal to prevent hydrogen entry via sputter deposition with a powder target

Nickel-doped stainless steel thin films with high hydrogen-entry resistance were prepared on a metal and Si surface via sputter deposition. For this, mixed nickel oxide (NiO) and stainless steel (SUS304) powders were used as the sputtering target. The experimental results indicated that nickel-doped stainless steel thin films could successfully be prepared both on the stainless steel and Si substrate surface. XPS measurements demonstrated that the deposition rate was dependent on the processing conditions such as input RF power, and the thin-film Ni/SUS304 concentration ratio strongly depended on the powder target composition.

X-ray Diffraction Investigation of Stainless Steel—Nitrogen Thin Films Deposited Using Reactive Sputter Deposition

An X-ray diffraction investigation was carried out on nitrogen-containing 304 stainless steel thin films deposited by reactive rf magnetron sputtering over a range of substrate temperature and bias levels. The resulting films contained between ~28 and 32 at.% nitrogen. X-ray analysis was carried out using both the standard Bragg-Brentano method as well as area-detector diffractometry analysis. The extent of the diffraction anomaly ((002) peak shift) was determined using a calculated parameter, denoted RB, which is based on the (111) and (002) peak positions. The normal value for RB for FCC-based structures is 0.75 but increases as the (002) peak is anomalously displaced closer to the (111) peak. In this study, the RB values for the deposited films were found to increase with substrate bias but decrease with substrate temperature (but still always >0.75). Using area detector diffractometry, we were able to measure d111/d002 values for similarly oriented grains within the films, and using these values calculate c/a ratios based on a tetragonal-structure model. These results allowed prediction of the (002)/(200) peak split for tetragonal structures. Despite predicting a reasonably accessible split (~0.6°–2.9°–2θ), no peak splitting observed, negating the tetragonal-structure hypothesis. Based on the effects of film bias/temperature on RB values, a defect-based hypothesis is more viable as an explanation for the diffraction anomaly.

Pitting Corrosion in Steel Controlled By the Electrochemical Potential Combined with Synchrotron X-Rays

Corrosion of metal alloys such as steel is a crucial field of study [1-4] due to its direct implication in various aqueous environments (seawater, rain, surface or ground water, etc.). The pitting corrosion of stainless steel (SS), occurring at the atomic level, critically weakens structures [5] locally, eventually leading to their failure. A variety of pit shapes have been reported to be related to the surface chemistry of the alloy/electrolyte interface and the presence of structural defects [6]. However, the very first stage of the pit formation, shown to occur suddenly, is not clear yet [7]. Stainless steel (SS) is a complex alloy which can incorporate several metallic (Fe, Cr, Ni, Mo, Mn, etc.) and non-metallic (C, Si, N, P, S, etc.) elements. Those elements can potentially favour both the corrosion propagation (e.g. Fe oxidation leading to rust formation) and prevention (e.g. Cr oxidation giving rise to passivating Cr2O3) [8-9]. Hence, a combination of experimental methods involving synchrotron radiation was utilised in electrochemical conditions to study the early stage of the SS disintegration. Thin films of SS304L (low carbon, Mo free alloy) of different thicknesses have been grown in India, using DC Magnetron Sputtering [10], on two different substrates, i.e. (Si (100) and Ru/B4C multilayer; 39.1Å bilayer on Si). Thin films are used to enhance the sensitivity of the different experimental techniques to the very surface of the samples and reduce the bulk signal. We first report on this process, using X-Ray Powder Diffraction (XRPD) and X-Ray Reflectivity (XRR) to characterise the structural composition and thickness of the film respectively. The chemical composition of the films was then characterised using X-ray Fluorescence Spectroscopy (XFS). The evolution of the films deposited on Si (100) and Ru/B4C multilayer was investigated using X-ray Absorption Near Edge Structure (XANES) and X-ray Fluorescence Spectroscopy in X-ray Standing Wave conditions (XFS-XSW) respectively. The evolution was obtained by comparing the XANES and XFS-XSW spectrums of the pristine films to the same films after electrochemical treatments in an alkaline electrolyte (0.1M KCl). XANES comparison between the pristine SS 304L thin film (500Å on Si (100)) and references (SS 304 and Fe foils) revealed that the spectrum is well fitted by a linear combination of 56% SS 304 in a fcc structure, 29% Fe in a bcc structure and 15% of Fe3O4 oxide layer. The Ru/B4C multilayer substrate is used to generate a XSW with its planes parallel to the surface, probing the very few atomic layers of the surface, the SS thin film in this case. The relative position of the XSW normal to the surface can be shifted, thus allowing to probe the depth distribution of metal components like Fe, Ni and Cr with respect to SS thin film surface with sub-submonolayer resolution. From the XFS-XSW on SS 304L (30Å on multilayer) before and after electrochemical treatments, we observe some significant change in composition in terms of positions and coherent fraction [11] obtained from XSW analysis. We will present first results of in-situ experiments were the thin film / electrolyte interface is probed continuously whilst the electrochemical treatment is applied. The aim is to further comprehend the chemical and structural processes initiating the pitting corrosion of stainless steel.

Deposition of Stainless Steel Thin Films: An Electron Beam Physical Vapour Deposition Approach.

This study demonstrates an electron beam physical vapour deposition approach as an alternative stainless steel thin films fabrication method with controlled layer thickness and uniform particles distribution capability. The films were fabricated at a range of starting electron beam power percentages of 3–10%, and thickness of 50–150 nm. Surface topography and wettability analysis of the samples were investigated to observe the changes in surface microstructure and the contact angle behaviour of 20 °C to 60 °C deionised waters, of pH 4, pH 7, and pH 9, with the as-prepared surfaces. The results indicated that films fabricated at low controlled deposition rates provided uniform particles distribution and had the closest elemental percentages to stainless steel 316L and that increasing the deposition thickness caused the surface roughness to reduce by 38%. Surface wettability behaviour, in general, showed that the surface hydrophobic nature tends to weaken with the increase in temperature of the three examined fluids.

Research on the Corrosion Behavior of the Stainless-Steel Thin Films Coated by PVD Method, Magnetron Assisted

Research on the Corrosion Behavior of the Stainless-Steel Thin Films Coated by PVD Method, Magnetron Assisted

Investigation of phase transformation for ferrite–austenite structure in stainless steel thin films

In this work we report on phase transformation of 304 stainless steel thin films due to heat treatment. Ex-situ annealing was applied for evaporated 304 stainless steel thin films inside an ultra-high vacuum chamber with a pressure of 3×10−7Pa at temperatures of 500°C and 600°C. The structure of thin films was studied by X-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS) techniques. The results revealed a transformation from α-phase that exhibits a body-centered cubic structure (BCC) to γ-phase that exhibits a face-centered cubic (FCC) due to annealing. In addition, the percentage of γ-phase structure increased with the increase of annealing temperature. Annealing thin films increased the crystal size of both phases (α and γ), however, the increase was nonlinear. The results also showed that phase transformation was produced by recrystallization of α and γ crystals with a temporal evolution at each annealing temperature. The texture degree of thin films was investigated by XRD rocking curve method, while residual stress was evaluated using curvature method.

Stainless-Steel Thin Film as Passive Radiative Cooling Materials

Spectrally selective glazing system attracts great attention for energy efficient radiator applications. The present work reports the possibility of a specific shield (Stainless steel/Borosilicate glass) to provide passive cooling for the purpose of reducing the use of classical active method. Radiative cooling devices require a convective shield that blocks all incoming solar radiation, but should selectively reemit radiation in the “atmospheric-window” region. In this study, borosilicate glass substrate coated with a stainless steel thin film was prepared by thermal evaporation and low pressure (6.3 × 10-3 bar) DC plasma sputtering, in order to achieve the radiative cooling effect. The optical properties of the optimal thickness thin film were measured in the wavelength range of 0.3-20 μm by an OL-750 double-beam spectroradiometer. The thin film has high visible band reflectance with high infrared band emissivity across the full 8-13 μm; which indicates that stainless steel thin film can be used as good radiative cooling material.

Structural, mechanical, and magnetic properties of ferrite–austenite mixture in evaporated 304 stainless steel thin films

In this paper, we investigate the structure, composition, magnetic, and mechanical properties of stainless steel thin films formed by thermal evaporation technique. These thin films reveal novel structural and physical properties where they were found to consist of nanocrystals that are ~90 % body-centred cubic crystal structure which holds ferromagnetic properties (α-phase), and ~10 % face-centred cubic crystal structure which is paramagnetic at room temperature (γ-phase). The presence of the above phases was quantified by X-ray diffraction, transmission electron microscopy, and conversion electron Mossbauer spectroscopy. The magnetic properties were evaluated by a superconducting quantum interference device magnetometer, and they confirmed the dual-phase crystal structure of the stainless thin films, where the presence of γ-phase reduced the magnetization of the produced thin films. In addition, the fabricated stainless steel thin films did not contain micro-cracks, and they exhibit a tensile stress of about 1.7 GPa, hardness of 7.5 GPa, and elastic modulus of 104 GPa.

Electrochemical Corrosion Behavior of Nanocrystalline Metal Thin Film Prepared By Magnetron Sputtering -- a Recent Work Report

The small grain size and the high volume fraction of grain boundaries result in significantly different corrosion behavior between nanocrystalline materials and corresponding coarse crystalline materials. The results by several electrochemical techniques indicate that in active dissolution, nanocrystallization accelerates the corrosion reactions; in passivation, nanocrystallization increases the passive ability. Further researches indicate that for passive materials such as stainless steel, Al alloys and Ni alloys, nanocrystallization changes the composition of the passive film, which improves the enrichment of passive elements such as Cr. In local corrosion, nanocrystallization increases the unstable points on the surface of the materials, which increases the possibility of local corrosion. However, the excellent ability of element diffusion helps heal the local corrosion point, which inhibits the growth of the local corrosion. In recently, we use the first principles calculation to study the energy change in the passive film and on the interface. We found that NC thin film promotes the formation of more Cr2O3 to increase the growth rate of passive film: more Cr2O3 increases the formation energy Ef of the passive film. Cr2O3 is apt to form at the interface to make the system most stable, which possesses lowest ER. The diffusion rate of defects and others across the passive film is promoted on NC thin film, which results in the formation of a Cr atom enriched layer at the oxides scale/metal interface. All of those reflect the super passive ability of nanocrystallization structure. And our group also found a thin membrane passive film over the growing pit on sputtering nanocrystalline stainless steel thin film for the first time, which has two layer structures and possesses higher elastic modulus and hardness. This thin membrane passive film will influence the corrosion behavior of material, especially pitting corrosion.

Crevice Corrosion Behavior of Nanocrystalline Stainless Steel Fabricated by Magnetron Sputtering in Chloride Containing Solution

The crevice corrosion behavior of a nanocrystalline stainless steel (NCss) thin film fabricated by magnetron sputtering has been studied in chloride containing solution as compared to the coarse-grained stainless steel (CGss). The results show that the crevice corrosion resistance of the NCss thin film is much higher than that of the CGss. The pitting corrosion is the pre-step of the crevice corrosion for both samples, and crevice corrosion initiates from the metastable pitting. For the NCss, the nanostructure and uniform composition distribution decreases the pitting corrosion and promotes the formation of the continuous and uniform passive film, therefore increases the crevice corrosion resistance of the NCss.

Influence of Peeling Rates in the Nominal Bonding Strength between the Fabricated Composite and Stainless Steel Thin Film / Sheet

Study here focuses on the efficient utilization of the advantages of organic polymeric materials such as their low mass density and high tensile strength, etc, and at the same time avoiding their disadvantages like low/soft stiffness and rapid deterioration of mechanical properties in the aggressive or corrosive environment. To realize this aim, one methodology is adopted in this work by introducing the stainless steel thin film or sheet in the design to improve the anti-corrosion behaviors of the fabricated composite. Mechanical tests are also carried out to measure the effects of peeling rates on the nominal bonding strength which is a key parameter to characterize and evaluate the reliability of the whole designed structure under various loading conditions. In this way, the applications of composites made of mainly organic polymeric materials may be extended to larger engineering areas. The influence of peeling rate over the bonding strength is also discussed.

The Electrochemical Corrosion Behavior of Nanocrystalline 304 Stainless Steel Prepared by Magnetron Sputtering

The electrochemical corrosion behavior of magnetron sputtered nanocrystalline (NC) 304 stainless steel (ss) thin film as well as that of the conventional rolled coarse crystalline (CC) 304ss has been studied in 0.05 M H2SO4 + 0.2 M NaCl solution using electrochemical and imaging techniques. The experimental results indicate that the NC thin film exhibits superior corrosion resistance compared to CC 304ss. The semi-conductor properties of the passive films on both materials as predicted by the Mott-Schottky equation show that the donor and acceptor concentrations of the passive film on NC thin film are higher than that of CC 304ss, while diffusion coefficients of carriers are lower than for CC 304ss. The composition of the passive film on NC thin film measured by X-ray photoelectron spectroscopy (XPS) has a higher the ratio of Cr oxides to Fe oxides. In-situ AFM observation found that the growth rate of the passive film on NC thin film was significantly faster than that of CC 304ss. The higher content of Cr oxides and better passivation ability of the passive film enhance the corrosion resistance of the nanocrystalline specimen together.

Development of CrN precipitates during the initial stages of PIII nitriding of stainless steel thin films

Stainless steel thin films produced by ion beam sputtering (IBS) were used as a model system to investigate the nitrogen diffusion and CrN formation after 10min of nitrogen plasma immersion ion implantation (PIII) at 350°C and 450°C. At 350°C, a thin nitrided layer of 70nm is formed, with additional diffusion of nitrogen along grain boundaries and the growth of CrN precipitates along these grain boundaries. For 450°C, a complete nitriding of the whole 400nm thick layer was observed, with the lower 75nm consisting of an expanded phase and the upper 330nm of a decomposed phase with CrN precipitates formed inside the original grains. Such a layered structure capturing the transformation process has not been observed before. A determination of time–temperature dependencies of this process and the transfer of these results for bulk material should be possible.

Influence of deposition rate on the formation of growth twins in sputter-deposited 330 austenitic stainless steel films

The authors have studied the influence of deposition rate on the formation of growth twins in sputter-deposited 330 austenitic stainless steel thin films. Transmission electron microscopy shows that the volume fraction of twinned grains increases with increasing deposition rate, whereas the average columnar grain size and twin spacing stay approximately unchanged. These experimental results agree qualitatively with their analytical model that predicts deposition rate dependent formation of growth twins. The film hardness increases monotonically with increasing volume fraction of twinned grains.

Fatigue strength of small-scale type 304 stainless steel thin films

This paper presents an experimental study of the fatigue strength of micrometer scale 304 stainless steel (SS) thin films using dynamic bending microbeams. The stress-life data was extended from the tests with R = 0.15 to the condition of fully reversed loading in order to compare with literature values of the bulk 304 SS. Fatigue damage process was characterized in detail. The results show that the fatigue endurance limit of the micrometer scale samples is higher than that of the bulk 304 SS. Fatigue damage was found to originate from cyclic strain localized regions within the grains. It is argued that fatigue damage behaviors in the micrometer scale 304 SS still follow that of the bulk material, but the fatigue strength has been enhanced due to the influences of both fine grain size and small geometrical dimensions.