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The FTIR spectra of chromium oxide coatings deposited on silicon wafer at various deposition powers and a constant oxygen flow rate of 10 sccm.
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Chromium oxide coatings prepared by radiofrequency reactive magnetron sputtering on stainless steel substrates were exposed to Ringer’s physiological solution and tested for their electrochemical corrosion stability using an open circuit potential measurement, potentiodynamic polarization, electrochemical impedance spectroscopy and Mott–Schottky an...
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Nanostructured metals (Ti and Ti alloys, stainless steels, Mg alloys) with enhanced static and fatigue strengths are promising materials for medical implants [1]. The use of severe plastic deformation (SPD) methods leads to significant strengthening of the metallic materials due to their nanostructuring when the formation of ultrafine grains is com...
Citations
... Chromium oxide thin films are widely used for many purposes, such as protective coatings in tribological applications [1], gas sensors [2], solar energy absorbers [3], corrosionresistant applications in semiconductors [4], magneto-electric random access memories and THz spin-orbitronic devices [5], and for transparent conducting oxide applications [6] because of its high hardness (from 18 to 29.7 GPa) and wear resistance [7], high melting point (~2435 • C) [8], good corrosion and chemical resistance [9], and magneto-electric [10] and catalytic properties [11]. These coatings are deposited using different methods such as sol-gel [12], electrodeposition [13], plasma spray pyrolysis [14], thermal evaporation [15], molecular beam epitaxy [16], magnetron sputtering [17], pulsed laser deposition [18], chemical vapor deposition [19], and atomic layer deposition (ALD) [20]. ...
... These changes in deposition density can be explained by differences in the adsorption properties of Cr 2 O 3 and TiO 2 surfaces. A higher growth rate of TiO 2 on RuO 2 in comparison with its growth rate on a Si substrate using TiCl 4 reported previously due to the excessive oxygen present on the RuO 2 surface compared to the TiO 2 surface [49]. Unlike chlorine-free pure Cr 2 O 3 films, the doped films contained a small amount of chlorine (0.06 to 0.03 atomic%) which was lower than the amount of Cl in the pure TiO 2 film (0.08 atomic%) or in the TiO 2 films deposited previously on the Si substrate using TiCl 4 and O 3 at 300 • C [49]. ...
Cr2O3 thin films were grown on a Si (1 0 0) substrate using Cr(thd)3 and O3 by atomic layer deposition (ALD) at substrate temperatures (TG) from 200 to 300 °C. X-ray amorphous films were deposited at a TG ≤ 225 °C, whereas at higher temperatures (TG ≥ 250 °C), the eskolaite phase was observed in the films. The growth rate of the films increased from 0.003 to 0.01 nm/cycle by increasing TG from 200 to 275 °C. The relatively low growth rate of Cr(thd)3—O3 makes it appropriate for the ALD of precisely controllable solid solution-type ternary-component thin films. The Ti-doped Cr2O3 film showed higher hardness (16.7 GPa) compared with that of the undoped film (12.8 GPa) with similar thickness. The band gap values of the pure Cr2O3 corresponding to the indirect transition model showed no dependence on TG; however, doping the Cr2O3 with Ti decreased its band gap energy value from 3.1 to 2.2 eV.
... At higher and lower frequencies, the circuit acted as capacitive and resistive, respectively. The atomic arrangement of synthesized HEA was amorphous, and high temperature leads to thermally active movement of atoms resulting in the formation of a small-ordered crystal structure, as depicted in Figure 3. Due to this movement, the compactibility of the coating is compromised, resulting in high current densities at elevated temperatures [47], as shown in Table 2. In the synthesized thin film, Mo-O and Cr-O generate a passivation mechanism by providing a healing effect to the coating. ...
High-entropy alloys (HEAs) contain more than five alloying elements in a composition range of 5–35% and with slight atomic size variation. Recent narrative studies on HEA thin films and their synthesis through deposition techniques such as sputtering have highlighted the need for determining the corrosion behaviors of such alloys used as biomaterials, for example, in implants. Coatings composed of biocompatible elements such as titanium, cobalt, chrome, nickel, and molybdenum at the nominal composition of Co30Cr20Ni20Mo20Ti10 were synthesized by means of high-vacuum radiofrequency magnetron (HVRF) sputtering. In scanning electron microscopy (SEM) analysis, the coating samples deposited with higher ion densities were thicker than those deposited with lower ion densities (thin films). The X-ray diffraction (XRD) results of the thin films heat treated at higher temperatures, i.e., 600 and 800 °C, revealed a low degree of crystallinity. In thicker coatings and samples without heat treatment, the XRD peaks were amorphous. The samples coated at lower ion densities, i.e., 20 µAcm−2, and not subjected to heat treatment yielded superior results in terms of corrosion and biocompatibility among all the samples. Heat treatment at higher temperatures led to alloy oxidation, thus compromising the corrosion property of the deposited coatings.
... XRD (X-ray Diffraction) [43,44] was conducted using a Rigaku MiniFlex 600 and an Empyrean 100 instrument with a Cu-Kα (λ = 1.54 Å) source at 40 kV and 15 mA (Rigaku)/10 mA (Empyrean) current. The angle (2Ɵ) was ranged between 10 • to 80 • . ...
The mechanisms leading to corrosion in stainless steel containments for thermal energy storage through phase change materials, such as carbonates and chlorides, are crucial for understanding the degradation of these steel alloys. A comprehensive study of this area will allow for down-selection of materials suitable for solar thermal energy storage (TES) operation at an elevated temperature range. Samples of stainless steel (SS) 316L were subjected to a cyclic heat environment of 550-750 • C in air and argon headspace environments, in the presence of a carbonate salt phase change material (PCM). A series of complementary microscopy, spectroscopy and diffractometry analytical techniques were applied to the corroded SS316L. Corrosion rate, interface formation and chemical products with respect to thermal cycling are presented with associated degradation mechanism explained and comparisons are made among different gas environments and varied immersion conditions. In the PCM under ambient air conditions, steel surfaces were mainly corroded by the penetration of oxidants from air, such as H 2 O or O 2 , along grain boundaries. SS316L samples demonstrated more severe degradation when exposed to air with a small fraction of PCM vapour present compared to when they were exposed to liquid or solid PCM. Cycling in Ar resulted in less corrosion in samples as opposed to when they were exposed to an air environment. In an Ar environment corrosion is driven via the formation of chromite, while the SS316L showed a less degradation when exposed to Ar with a small fraction of PCM vapour compared to when it was immersed in PCM. The mechanisms for degradation in air and in Ar are common in that the corrosion products of Cr and Ni dissolve in the PCM thus removing any layer that could protect against corrosion. The present study provides insight into corrosion of stainless-steel when exposed to carbonate salts, in air and inert gas environments, and contributes to down-selection of materials for solar thermal energy storage.
... environmental degradations [1][2][3][4][5]. Chromium oxide thin films generally exhibit high wear-resistant, hardness, chemical inertness, and low friction coefficient [6][7][8] and can be prepared using various deposition techniques such as electron-beam evaporation, chemical vapour deposition, sputtering, pulse laser deposition, chemical spray pyrolysis and arc ion plating [6,[9][10][11][12][13][14]. ...
The deposition parameters used during the sputtering process are instrumental in determining the properties of the deposited films and can be optimised to produce thin film coatings that are suitable for specific engineering applications. Deposition parameters such as radio frequency (RF) power, oxygen flow rate, and substrate temperature can be varied during deposition to alter or tune the film structure, stoichiometry, and invariably the functional properties of the prepared thin films. In this paper, chromium oxide thin films prepared by reactive magnetron sputtering under various RF powers were characterised for their work function property and stability in Ringer’s solution. The structural, oxide phase and growth modes of the films were probed with X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). The electrochemical stability and corrosion behaviour of the films were evaluated using an open circuit potential (OCP) measurements, cyclic polarisation, and Mott–Schottky analysis, while the work function (WF) was determined with a Kelvin probe. The XRD and Raman investigations showed that the films are predominantly amorphous with Cr2O3 being the main oxide phase. A mixture of columnar and layer-by-layer growth modes was observed in the deposited films with 500 W, 10 sccm sample showing rougher morphology due to the higher sputtering power. The OCP and cyclic polarisation results showed that the film prepared at a deposition power of 300 W and at an oxygen flow rate of 10 sccm possesses higher film passivation and breakdown potentials, hence, better corrosion resistance when compared to films prepared at higher deposition powers. The finding is further supported by the Mott–Schottky and work function investigations where the same film also showed lower defect density and higher work function values compared to the films deposited at higher powers. A correlation was found between the corrosion, work function and defect density which suggests that both parameters can possibly be used to predict and rank corrosion in thin films. We expect our findings to be significant for future corrosion and wear applications for metals/alloys requiring protection against environmental degradation.
Graphical abstract
... The oxide layer's composition also matters significantly due to the defect density in the said oxide layer. For example, chromium oxide layers typically exhibit a very low defect density, preventing oxygen diffusion [30][31][32] . Material constants are typically determined experimentally by fitting a curve to the data. ...
Bimetallic structures and coatings through additive manufacturing (AM) have demonstrated a high degree of freedom for tailoring properties depending on the application. In this study, Inconel 718 and CoCrMo were used as both are common alloys and exhibit unique properties, such as high-temperature oxidation, wear, and fatigue resistance. Using directed energy deposition-based metal AM, bimetallic structures containing these two alloys were manufactured, and the resulting structures exhibited no intermetallic phase formation, cracking, or porosity. Scanning electron microscopy and energy dispersive spectroscopy revealed a smooth elemental transition between the two compositions. Hardness testing showed a linear transition in the interfacial zone, validating no brittle intermetallic phase formation. Compression testing and fracture surface analysis revealed that the failures were not dependent on the interface properties. High-temperature oxidation showed no distinct effect on the interface, a firmly attached chromium oxide layer on the Inconel 718 side and a loosely attached chromium oxide layer on the CoCrMo side. There was also evidence of pit formation on the Inconel 718 surface, but not on the CoCrMo. These findings confirm a stable bimetallic system in which one of the two alloys can be used on the other material to improve the structure’s high-temperature oxidation or wear/corrosion resistance.
... Presence of the CrO x layer is thought of as a passivation front against further migration of Ni and Fe in the bulk, and reactions with oxidants [ [28][29][30][31]. However, with continuous cycling in PCM, Cr on the token surface depleted and eventually dissolved into the liquid PCM from the decreasing contribution of Cr at the outermost layer. ...
The formation and mechanism that drive corrosion in stainless steel as a containment material in the presence of phase change materials is of importance in solar thermal energy storage systems. In our work, half-immersed stainless steel 316 tokens in a carbonate-based phase change material (PCM 638) have been investigated. The samples were thermally cycled in air and Nitrogen environment up to 500 times within a high-temperature range, allowing the PCM to transform between solid and liquid states repeatedly. As a consequence of thermal cycling, severe thickness loss on steel token was observed, indicating a degree of oxidation occurring, which depleted the uncorroded steel. Cross-sectional microstructural analysis was carried out to determine the elemental distribution and structural morphology along the corrosion layers. This study shows that thermal cycling of SS 316 in PCM results in active Ni and Cr migration to the surface, leading to a significant depletion of Cr from steel moving into the PCM. Cr and Fe on the surface are found to oxidise with varying degrees, with respect to the exposure time. The depletion of Cr was found to be higher in SS 316 immersed in PCM, while also increasing with exposure time.
... This is due to the fact that tribological and corrosion processes substantially influence the biocompatibility of materials. For instance, pains, pseudotumor formation, and inflammation in patients are the direct effects of wear debris and toxic ions released by Fe, Cr, and Ni chemical element presented in 316L SS which, however, can be prevented by applying a wear, corrosion, and biocompatible protective coating material on the implant surface (Oje and Ogwu 2017). In this context, various ceramic coatings have been employed by different researchers for biomedical applications. ...
... In this context, various ceramic coatings have been employed by different researchers for biomedical applications. Among them, diamond-like carbon (DLC), chromium nitride (CrN), hydroxyapatite (HA), titanium nitride (TiN), and titanium niobium nitride (TiNbN) have been extensively investigated (Fisher et al. 2002(Fisher et al. , 2004Roy and Lee 2007;Serro et al. 2009;Love et al. 2013;Gotman and Gutmanas 2014;van Hove et al. 2015;Oje and Ogwu 2017). TiN and TiNbN coatings have been commercially used in hip and knee prostheses, while other coating systems are still under the different stages of investigation (Serro et al. 2009;Gotman and Gutmanas 2014;Oje and Ogwu 2017). ...
... Among them, diamond-like carbon (DLC), chromium nitride (CrN), hydroxyapatite (HA), titanium nitride (TiN), and titanium niobium nitride (TiNbN) have been extensively investigated (Fisher et al. 2002(Fisher et al. , 2004Roy and Lee 2007;Serro et al. 2009;Love et al. 2013;Gotman and Gutmanas 2014;van Hove et al. 2015;Oje and Ogwu 2017). TiN and TiNbN coatings have been commercially used in hip and knee prostheses, while other coating systems are still under the different stages of investigation (Serro et al. 2009;Gotman and Gutmanas 2014;Oje and Ogwu 2017). DLC coatings show poor adhesion on the substrates due to a high level of internal stress generated during the coating process, and a severe delamination of DLC coatings usually occurs during in vivo tests which is still the main drawback for practical application (Anttila et al. 1999;Taeger et al. 2003). ...
316L stainless steel (SS) implants suffer from tribological and biocompatibility problems which limit their service lifetime. In order to improve the surface properties of 316L SS for orthopedic implant applications, hard chromium oxide coatings were applied on 316L SS substrates using a reactive magnetron sputtering technique. The morphological, structural, and phase compositional analyses were conducted on the deposited coatings by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. The Rockwell-C indentation tests were performed on the coated substrates to qualitatively evaluate the adhesion of coatings on the steel substrates. The surface characteristics of coatings were measured by using an optical profilometer. The mechanical properties of coatings were reported by measuring the Hardness and Young’s modulus. The corrosion resistance of coated and uncoated SS substrates was compared using potentiodynamic polarization tests. An inductively coupled plasma optical emission spectrometry (ICP-OES) was employed to analyze the biocompatibility of the samples by measuring the amount of toxic Cr ions released after the immersion test. The results show that the coatings are adherent and composed of a single Cr2O3 phase with a hardness of 25 to 29 GPa. The corrosion resistance of the SS has been improved by applying a chromium oxide coating. The coated SS samples have also demonstrated better wear resistance and lower friction coefficient compared to bare SS samples under a reciprocating sliding condition in saline solution. The biocompatibility of the SS has been enhanced by the Cr2O3 coating as much less Cr ions were released after immersion tests. These results indicate that the hard Cr2O3 coatings can be considered as a candidate for extending the lifetime of SS implants.
... eV, indicating Cr 2 O 3 and Cr(OH) 3 as the primary corrosion products for both coating systems. For the Cr2p 1/2 , BE peaks obtained at 584.4 and 586.2 eV are related to organic compounds and non-stoichiometric oxides [44,45]. N1s peaks are associated with BE's of 396.4 and 398.5 eV, corresponding to CrN and NH 3 , respectively. ...
The effect of bias voltages (40 V, 80 V, and 40/60/80 V) on microstructure and electrochemical properties of arc-PVD CrN coatings were evaluated. Increasing the bias voltage produced microstructural changes, from well-defined columns to columnar grains, and increased defect size. The electrochemical response proved susceptible to the defect type. Nano-droplets promoted the formation of oxides, while large pores allowed the migration of the electrolyte to the substrate/CrN interface. An impedance equivalent circuit based on the Bisquert transmission line was proposed to fit the experimentally obtained impedance spectra. The equivalent circuit allowed correlating the coating electrochemical response to the defect densities and sizes. Samples deposited with 40 V showed the lowest corrosion current (0.05 μA/cm² ± 0.01), which was supported by the highest resistances to the transport of ions through the pores (Rp = 1047 ± 88 kΩꞏcm²). Films obtained with 80 V reduced Rp values by two magnitude orders compared to CrN 40 V. The increase of pore resistance in CrN 40 V was associated with the oxidation of nano-droplets (proposed auto-protection phenomenon), which blocks open pinholes due to the smallest average size of defects. Tailoring a gradual increase of the bias voltage (40/60/80 V) preserves the auto-protection mechanism of droplets and improves the surface finish of the coating.
... This peak is centred at 547 cm À1 and is ascribed to the A 1 g modes.In addition, other less intense peaks at 305 and 347 cm À1 ascribe to vibrations in A 1 g and E g modes respectively are identified in the samples. These peaks are consistent with the peaks of Cr 2 O 3 which have been reported in literature [49,50]. It is also seen that at higher annealing temperature of 700 C, additional peak is observed at 857 cm À1 which could be assigned to the Cr VI eO vibrations of symmetric phonon modes. ...
A selective single phase black α-Cr2O3 nanoparticles was bio-synthesised via simple straight-forward green synthesis approach. The process involves extraction of phytochemicals contained in peels of sweet potatoes. Extraction was done in distilled water under constant magnetic stirring at a temperature of 70–80 °C resulting in a dusty yellow colour aqueous extracts. Afterwards, chromic nitrate salt was added to extracts resulting in reduction of metal salt to metal nanoparticles. Obtained precipitates were dried and annealed in the air for 2 h ready to be applied without further post synthesis modifications. SEM and EDS analysis of annealed precipitates reveal distinct shapes and high purity of nanoparticles. The effects of the annealing temperature are evident in the nanoparticle sizes. SAED and XRD patterns expose bright diffraction peaks which are harmonized to the rhombohedral structure of pure Eskolaiteα-Cr2O3. By quantitative analysis of XRD data, it was noted that lattice parameters and crystal sizes slightly decrease w.r.t increase annealing temperature. Raman spectra recorded peaks ascribe to vibrations in A1g and Eg mode whereas FTIR analysis show absorption bands at 641 and 632 cm⁻¹ which evidence the presence of α-Cr2O3 nanoparticles. UV–Vis absorbance peak generated Cr2O3 nanoparticles are observed at 402 nm yielding a band gap of 3.08eV. Magnetism results of α-Cr2O3 nanoparticles shows linear increase upon field increasing, which can be elucidated by the existing of uncompensated spins at the surface of the nanoparticles that may lead to nonmagnetic or antiferromagnetic state. Zero field cooling (ZFC) results of α-Cr2O3 nanoparticles were analysed based on Curie-Wien relation which yield values of magnetic moment (μeff) of the synthesised Cr2O3 nanoparticles close to the value that was assigned for Cr2+.The density functional theory (DFT) with the PW91, PBE, PBESOL and a Hubbard U Coulomb interactionwas utilized to study the optimum structure, electronic and magnetic properties of antiferromagnetically ordered Cr2O3. The computed results are consistent with the experimental measurements.
... On the other hand, other investigations have demonstrated that the CoCrMo alloy develops a chromium oxide passivation layer in air atmosphere with a thickness of a few nanometers that improves its corrosion resistance [32,33]. Positive E corr values above 200 mV have been observed for this oxide layer [34] which are alike to those found in our experiments (see E corr vales in Table 2). Then, because the BB process comprises a localized heat generation, the formation of an oxide passivation layer can be suspected in our samples. ...
The CoCrMo alloy is a biomaterial that has been employed for the production of permanent orthopedic implants, however, the release of metallic ions from debris due to tribocorrosion is the main drawback for its extended application. In this paper, we propose the use of the ball burnishing process to improve the surface properties of the CoCrMo alloy. A 32 factorial design of experiments (DoE) was conducted to achieve a basic understanding of the relationship between the surface hardness, roughness and corrosion current (response variables) and the force and number of passes of the burnishing tool (input factors). Statistical analysis showed that force is the most significant factor for changing the surface properties. At the best experimental conditions, hardness was improved by 41.4%, the roughness was decreased by 72.7% and the corrosion rate was noticeably reduced by 92.4%. Microscopy and X-ray diffraction analysis showed that ball burnishing introduces changes in the microstructure, generating a surface layer with improved properties. It is concluded that the ball burnishing process is suitable for improving the surface properties of the CoCrMo alloy under an appropriate combination of experimental conditions.
