Protective Oxide Research Articles

A facile high-efficiency preparation strategy for Al-containing multi-component boride microcrystals with superior comprehensive performance

Multi-component transition group metal borides (MMB2) have become a research hotspot due to their new composition design concepts and superior properties compared with conventional ceramics. Most of the current methods, however, are complicated and time-consuming, the mass production remains a challenge. Herein, we proposed a new high-efficiency strategy for synthesis of MMB2 using molten aluminum as the medium for the first time. The prepared Al-containing multi-component borides (TiZrHfNbTa)B2 microcrystals had a homogeneous composition with a hexagonal AlB2 structure and ultra-high hardness value of ∼35.3 GPa, which was much higher than data reported in the literature and the rule of mixture estimations. Furthermore, combined with the First-principles calculation results, we found that the Poisson's ratio (v) values exhibit a clearly ascending trend from 0.17 at VEC = 3.5 to 0.18 at VEC = 3.4, then to 0.201 at VEC = 3.2 with the increasing of Al content. This indicates that the intrinsic toughness of multi-component boride microcrystals is obviously enhanced by the trace-doped Al elements. Besides, the fabricated Al-containing multi-component boride microcrystals have superior oxidation activation energy and structural stability. The enhanced oxidation resistance is mainly attributed to the formation of a protective Al2O3 oxide layer and the lattice distortion, both of which lead to sluggish diffusion of O2. These findings propose a new unexplored avenue for the fabrication of MMB2 materials with superior comprehensive performance including ultra-hardness and intrinsically improved thermo-mechanical properties.

High temperature oxidation behaviors of TaCrTiW and TaCrTiZrW alloy coatings

The high-temperature oxidation behaviors of a series of refractory high entropy alloys TaCrTiW and TaCrTiZrW alloy coatings at 1073 K in air were studied. A complex protective oxide layer consisting of Cr2O3, TiO2, and CrTaO4 oxides was generated on the alloys surface. Among the TaCrTiW alloy coatings, the presence of TiO2 inhibited the generation of unfavorable oxides and promoted the generation of CrTaO4. The Ta41.7Cr50.3Ti4.5Zr1.6W1.9 exhibits excellent oxidation resistance. The addition of Zr not only accelerated the initial oxide formation but also promoted the rapid formation of Cr2O3.

Exploring the Influence of Nanocrystalline Structure and Aluminum Content on High-Temperature Oxidation Behavior of Fe-Cr-Al Alloys.

The present study examines the high-temperature (500-800 °C) oxidation behavior of Fe-10Cr-(3,5) Al alloys and studies the effect of nanocrystalline structure and Al content on their resistance to oxidation. The nanocrystalline (NC) alloy powder was synthesized via planetary ball milling. The prepared NC alloy powder was consolidated using spark plasma sintering to form NC alloys. Subsequently, an annealing of the NC alloys was performed to transform them into microcrystalline (MC) alloys. It was observed that the NC alloys exhibit superior resistance to oxidation compared to their MC counterparts at high temperatures. The superior resistance to oxidation of the NC alloys is attributed to their considerably finer grain size, which enhances the diffusion of those elements to the metal-oxide interface that forms the protective oxide layer. Conversely, the coarser grain size in MC alloys limits the diffusion of the oxide-forming components. Furthermore, the Fe-10Cr-5Al alloy showed greater resistance to oxidation than the Fe-10Cr-3Al alloy.

Effect of Copper Surface Roughness on the High-Temperature Structural Stability of Single-Layer-Graphene.

Graphene (Gr) has shown great potential in the field of oxidation protection for metals. However, numerous studies have shown that Gr will suffer structural degradation on metal surface during high-temperature oxidation, which significantly limited the effectiveness of their oxidation protection. Therefore, understanding the degradation mechanism of Gr is of great interest to enhance their structural stability. Here, the effect of copper (Cu) surface roughness on the high-temperature structural stability of single-layer graphene (SLG) was examined using Cu covered with SLG as a model material. SLG/Cu with different roughness values was obtained via high-temperature annealing of the model material. After high-temperature oxidation at 500 °C, Raman spectra analysis showed that the defect density of the oxidized SLG increased from 41% to 81% when the surface roughness varied from 37 nm to 81 nm. Combined with density functional theory calculations, it was found that the lower formation energy of the C-O bond on rough Cu surfaces (0.19 eV) promoted the formation of defects in SLG. This study may provide guidance for improving the effectiveness of SLG for the oxidation protection of metallic materials.

Phase composition, surface chemistry and electrochemical studies of electrodeposited AlMnFeCuNi high entropy alloy composite coatings incorporated with carbon nanotubes

AlMnFeCuNi high entropy alloy (HEA) coatings were electrodeposited onto mild steel substrate with and without incorporation of carbon nano tubes (CNT). This paper focused on the morphology, hardness, wear and corrosion behaviour for as deposited HEA and HEA-CNT coatings. Both the coatings constituted simple solid solution with face-centered cubic (FCC) structure. The addition of carbon nano tubes in the HEA coatings as revealed by scanning electron microscopy showed more smaller granules and compact morphology with least coating thickness value (5 ± 0.35 μm). Enhanced Anti-wear performance results in higher hardness and lower coefficient of friction. The presence of CNTs resulted improvised corrosion resistant properties in 3.5% NaCl corrosive media. The formation of more protective oxides such as Alox +3, Mnox +2 and Feox +3 on passive oxide layer in HEA-CNT coatings acted as a barrier, protected it from corrosion.

Four-dimensional electrochemical impedance spectroscopy: Role of microstructure on corrosion behaviour of Al-Si alloys additive-manufactured by laser powder bed fusion

Four-dimensional (4D) electrochemical impedance spectroscopy was applied to clarify the role of microstructures on the corrosion behaviour of Al-Si alloys additively manufactured by laser powder bed fusion in the immersion of NaCl solution. 3D complex impedance plots, comprising real, imaginary, and time axes, indicate that the impedance increases gradually at initial stage and then does not show apparent time variation. These behaviours, following surface morphology analysis, are strongly related to the remaining fine silicon particles on the surface due to the preferential Al dissolution, which suppress the further dissolution from underlying along with the protective oxide film formation.

Oxidation Behavior of Pre-Strained Polycrystalline Ni3Al-Based Superalloy.

The harsh service environment of aeroengine hot-end components requires superalloys possessing excellent antioxidant properties. This study investigated the effect of pre-strain on the oxidation behavior of polycrystalline Ni3Al-based superalloys. The growth behaviors of oxidation products were analyzed by scanning electron microscope, transmission electron microscope, X-ray Photoelectron Spectroscopy and Raman spectroscopy. The results indicated that the 5% pre-strained alloys exhibited lower mass gain, shallower oxidation depth and more compact oxide film structures compared to the original alloy. This is mainly attributed to the formation of rapid diffusion paths for Al atoms diffusing to the surface under 5% pre-strain, which promotes the faster formation of protective Al2O3 film while continuing to increase the pre-strain to 25% results in less protective transient oxidation behavior being aggravated due to the increase in dislocation density within the alloy, which prevents the timely formation of the protective Al2O3 film, resulting in uneven oxidation behavior on the alloy.

Investigation on microstructures, mechanical properties, and corrosion behavior of novel biodegradable Zn-xCu-xTi alloys after hot rolling fabricated by self-developed newly gradient continuous casting

The poor mechanical properties exhibited by pure Zn effectively prohibit its utilization as a viable material for biodegradable implants. Hence, the primary area of interest has been directed towards alloy design and process strategies of biodegradable Zn alloys. To this end, novel biodegradable Zn-xCu-xTi (Cu: x = 0.001–2.72 and Ti: x = 0.03–1.21) alloys were designed and fabricated using a gradient continuous casting method followed by homogenization and rolling. The fabricated samples were then investigated in terms of their microstructures, mechanical properties, and corrosion behavior. The results showed that the as-cast Zn-0.001Cu-0.037Ti and Zn-1.50Cu-1.06Ti alloys possess better mechanical properties and corrosion resistance. The yield strength, elongation, and highest charge transfer resistance (Rct) of Zn-0.001Cu-0.037Ti were 137 MPa, 60 %, and 2227.9 Ω, respectively. On the other hand, the Zn-1.50Cu-1.06Ti alloy exhibited 250 MPa yield strength, 12.7.% elongation, and 11113.0 Ω Rct, respectively. Higher Cu and Ti content also led to larger second phases. However, as-hot rolled Zn-1.50Cu-1.06Ti alloy displayed better mechanical properties as compared to the Zn-0.001Cu-0.037Ti alloy due to a very fine nanocrystalline structure. Furthermore, the hot-rolled Zn-xCu-xTi alloys demonstrated superior corrosion resistance compared to their as-cast counterparts, as evidenced by the analysis of the potentiodynamic polarization and electrochemical impedance spectroscopy data. This improved corrosion resistance is attributed to the refined grain size, fractured second phases which reduce both the anode and cathode areas, and the formation of protective oxide layers. Lastly, the corrosion products primarily consisted of carbon, phosphorus, calcium, and oxygen, suggesting the presence of Zn(OH)2, carbonates, and phosphates.

Titanium a novel catalyst and high energy dense material: an opportunity for composite propellants with enhanced performance

ABSTRACT Whereas aluminum with combustion enthalpy of 32 KJ/g is the universal reactive metal particles, its passive protective oxide layer could encounter its efficient combustion. While titanium can offer low combustion enthalpy (20 KJ/g), it does not expose passive oxide layer. The impact of both reactive particles on ammonium perchlorate (AP) decomposition enthalpy was investigated via DSC. Aluminum and titanium particles secured an increase in AP decomposition enthalpy by 46.9%, and 80.7% respectively. This significant impact of titanium particles was ascribed to full exploitation of metal energy content. The impact of titanium particles on AP decomposition kinetics was assessed via Kissinger, KAS, and FWO models using TGA. Whereas virgin AP demonstrated average apparent activation energy of 155 KJ/mol, Ti/AP demonstrated average apparent activation energy of 141.2 KJ/mol. Solid rocket propellant formulations based on 17 wt % metal (Al or Ti) were developed via mixing and vacuum casting. Ballistic performance was investigated using small-scale ballistic evaluation rocket motor. Ti-based formulation offered an increase in propellant burning rate, average operating pressure, average thrust by 18.2%, 26.5%, and 19.7% respectively. It was concluded that titanium particles have a dual effect as efficient high energy dense material and as a catalyst.

Plasma-sprayed GNP/CNT reinforced lanthanum-cerate coatings: Hot corrosion assessment in Na2SO4-V2O5 environment

This study investigates the hot-corrosion behavior of Carbon nanotube/Graphene-nanoplatelets (CNT/GNP)-reinforced lanthanum cerate (LC) coatings in a Na2SO4–V2O5 molten salt environment at 1350 °C for varying durations. Coatings were prepared using APS and characterized using XRD, FESEM, Raman, XPS, etc., techniques. The CNT/GNP-reinforced LCGC hybrid composite coating exhibited superior hot-corrosion resistance compared to LC and LCG coatings. The uniform dispersion of GNPs/CNTs within the coating matrix and the creation of protective LC oxides enhanced corrosion resistance. These findings highlight the potential of GNP/CNT-reinforced coatings in protecting high-temperature components like combustion chambers and gas turbine engines from hot corrosion.

Ceramic metal oxide coatings formation by hybrid plasma electrolytic treatment: Interaction scenarios of ceramic NPs with oxide layers

Understanding the formation of protective ceramic metal oxide (CMO) coatings (layers) on the surface of light alloys remains a pressing task in light of products operating in extreme conditions. Plasma electrolytic oxidation (PEO) of light alloy surfaces has recently been modified by introducing various ceramic nanoparticles (NPs) into the electrolyte to perform hybrid plasma electrolytic treatment (HPET). In this work, the general and distinctive features of the interaction mechanisms of TiC, SiO2 and ZrO2 nanoparticles (NPs) with the CMO coating formed by HPET of Al–Si and Mg-based alloys were summarized and theoretically substantiated. The interaction of charged ceramic NPs accelerated by an electric field with the oxide layer is determined by transformation of the NPs kinetic energy into heating and plastic deformation, into phase transformations, as well as into the creation of new surface defects. One of the controlling factors is the ratio of the particle and the oxide layer hardnesses. In the case of SiO2 in Al–Si alloys, the formed coating is harder than the ceramic NPs while in other cases, the NPs are harder than the CMO coating, which determines the different scenarios for the interaction of NPs with the coating under HPET. In summary 7 different scenarios for the interaction of ceramic NPs added to the electrolyte with the СМO layer during its formation put forward, which depending on the ratio of the hardness of the CMO layer and the added particles, temperature/pressure conditions of the phase transformations in the NP (including its melting), the particles size distribution and the base PEO process parameters.

The potency of hydrophobic modification of alginate for a self-assembly matrix in fish oil encapsulation

To act as an emulsifier and a matrix for fish oil encapsulation, alginate is required to be modified due to its hydrophilicity. The purpose of this study was to modify alginate using dodecenyl succinic anhydride (DSA) under pH-controlled conditions and to apply it for stabilizing emulsion and encapsulating fish oil. The modification that followed the first-order reaction improved the hydrophobic properties of alginate as shown by the reduction of surface tension but improving the water contact angle, with CMC of 0.18 mg/l. A higher concentration of modified alginate was better in stabilizing fish-oil emulsion than the native one, as supported by the results of zeta potential, viscosity, and droplet size of the emulsion. Freeze-dried particle of this modified alginate emulsion showed better encapsulation efficiency and oxidation protection ability. Thermal properties of alginate were changed after hydrophobic modification and oil encapsulation. The freeze-dried particles of this modified alginate emulsion showed better encapsulation efficiency and protection ability. This study confirmed the protective ability of the modified alginate using DSA as an oil-based active ingredient encapsulant.

Corrosion Behaviour of Ni-based Alloys 230, 617 and 601 in CO2 Gas at 750 and 850 °C

This paper investigated the corrosion behavior of three nickel-based alloys (230, 617 and 601) at 750 °C and 850 °C in a carbon dioxide environment for up to 500 h. All three alloys showed good oxidation resistance by forming mainly a protective chromia layer with low weight gains. Internal Al2O3 was precipitated beneath a thin chromia layer in all cases. For 230 and 617 alloys, NiO and Cr-rich spinel outer layers were formed, but for 601 less iron and nickel outward diffusion was observed at both temperatures. Furthermore, some minor alloy elements (Mn, Ti, and Co) were also observed in the chromia layers. Very limited carburization due to the CO2 reaction was revealed in the matrix underneath the oxide scale. Wagner’s theory was applied to examine the critical chromium concentration for forming a protective chromia scale. This prediction indicated that alloy concentrations were marginal for chromia formation at both temperatures and the critical chromium concentration decreased with increasing the oxidation temperature. The presence of other alloying elements, e.g. Al, Mn, Ti, Si etc could increase corrosion resistance of these alloys by forming either additional protective oxide barriers or integrating with chromium oxide to enhance its protection.

Electrochemical and hot corrosion behaviour of annealed AlCoCrFeNi HEA coating over steel

The ability to endure extreme corrosion in challenging environments is reduced in stainless steel. This can be addressed by appropriate surface modification techniques to redefine the surface with the required properties. The characteristics of the atmospheric plasma sprayed AlCoCrFeNi High Entropy Alloy (HEA) on SS316l are presented in this study. The coating characterisation revealed uniform coating with homogeneous deposition of gas-atomized AlCoCrFeNi HEA spanning for 150 µm. The coated substrates were further annealed for 2 h at 400 °C, 550 °C, 700 °C and 850 °C and the annealing at 550 °C offered enhanced microstructure. Annealing the coated sample at 550 °C offered a 46% improvement in microhardness against the uncoated sample post-annealing. The electrochemical corrosion tests showcased improved corrosion resistance after annealing through the formation of a protective oxide layer and the influence of HEA. Hot corrosion tests at 900 °C resulted in 10.1%, 8.49%, and 10.36% improved corrosion resistance for the coated sample annealed at 550 °C than the coated sample pre annealing and 44.09%, 44.25%, and 42.09% than the uncoated sample pre annealing under three salt mixtures respectively. The microstructural analysis examines various corrosion modes and verifies the presence and formation of protective oxide layers.

Development of targeted chloride-responsive Ag/Ca-MoO4-LDH for synergistic corrosion resistance

Layered double hydroxides (LDHs), as novel corrosion inhibitor in reinforced concrete, face instability in chloride consolidation due to sensitivity to environmental anions. This study explored the use of nano-Ag loaded on MoO4-intercalated CaAl-LDH (Ag/Ca-MoO4-LDH), based on isomorphic substitutes for cement hydration products (AFm), to target and stabilize chloride ion fixation in alkaline environments, thereby enhancing steel corrosion resistance. The mechanism of targeting and the enhancement of corrosion resistance were explored through comprehensive experimental and theoretical analyses. Results showed that Ag/Ca-MoO4-LDH enhanced chloride ion consolidation stability, increased the threshold of chlorides needed to trigger corrosion in simulated chloride-contaminated concrete pore (SCCP) solutions, and boosted steel’s anti-corrosion effectiveness. Unlike direct application methods, Ag/Ca-MoO4-LDH released MoO42− in response to chloride presence, providing superior corrosion prevention. The study elaborated on the stability of Ag+ and Cl− interactions in SCCP solutions, the spontaneous exchange reactions between LDH-MoO4 and both LDH-OH and LDH-Cl, and various anti-corrosion mechanisms, including the formation of protective oxide films on steel surfaces and the precipitation of CaMoO4.

HEAT RESISTANCE OF CORROSION-RESISTANT STAINLESS STEEL CRNI65MWU AFTER VARIOUS TYPES OF FULL ANNEALING

The article discusses the influence of additional heat treatment of corrosion-resistant steel CrNi65MWU on increasing its heat resistance, as well as on changing the chemical composition of the protective oxide layer formed on the surface. The relationships between heat treatment modes and changes in the corrosion rate of selected steel under operating conditions in glass-forming production are shown. Research has also been carried out on the direct interaction of the melt of various types of glass with a heat-treated steel surface.

The cyclic oxidation behavior and kinetics of W-Cr-Nb-Y2O3 alloys processed by powder metallurgy route

In the present investigation, yttria (Y2O3) has been added to the W-Cr-Nb alloys to study the cyclic oxidation behavior of on W-Cr-Nb- Y2O3 alloys processed by the powder metallurgy route. The cyclic oxidation tests are performed at 800 °C, 1000 °C, and 1200 °C for 15 h in the air. The oxidation kinetic analysis and implementation of a double Voigt function to calculate the domain size (crystallite size) and microstrain are also investigated. The results show that the cyclic oxidation tests on the sintered W-Cr-Nb-Y2O3 samples have exhibited that [(W0.5Cr0.5)90Nb10]98 - (Y2O3)2 alloy is marginally more oxidation resistant than [(W0.7Cr0.3)90Nb10]98 - (Y2O3)2 alloy at temperatures 800 °C and 1000 °C. In contrast, the [(W0.7Cr0.3)90Nb10]98 - (Y2O3)2 composite shows more oxidation resistance than [(W0.5Cr0.5)90Nb10]98 - (Y2O3)2 composite at temperature 1200 °C, apparently due to the formation of a large number of protective oxides like Cr2WO6, 2NbO5.7WO3 and Y2WO6, and absence of WO3 oxide on the former composite at 1200 °C in air. The values of oxidation exponent n ≈ 2 obtained for the oxidation tests on the [(W0.5Cr0.5)90Nb10]98 - (Y2O3)2 indicate that approximately parabolic rate law is being followed in the range of 800–1200 °C. In the case of [(W0.7Cr0.3)90Nb10]98 -(Y2O3)2 alloy (1 < n < 2) indicates that the rate of oxidation is faster than that predicted by the parabolic rate law but slower than that expected from the linear relationship between mass change per unit area (Δm/S) and time (t).

SEM Electron-Beam-Induced Ultrathin Carbon Deposition Layer on Cu Substrate: Improved Dry Oxidation Protection Performance than CVD Single Layer Graphene.

An amorphous carbon deposition layer (CDL) with nanoscale thickness induced by scanning electron microscope (SEM) electron beam is studied as a carbon-based protective layer on copper (Cu). CDL is prepared by inducing the deposition of pollutants or hydrocarbons in the cavity of SEM through electron beam irradiation (EBI). Wrinkles and cracks will not form and the interfacial spacing of CDL/Cu is smaller than Graphene/Cu (Gr/Cu). The thickness and coverage of the interfacial oxide layer of CDL/Cu are all smaller than that of the Gr/Cu after the same oxidation conditions. Characterization of Raman mapping also demonstrates that CDL shows better oxidation inhibition effects than graphene. The structure of CDL is determined to be C = C and C = O, CH3- and C-O can be loaded vertically on CDL. Density functional theory (DFT) is employed for demonstrating the smaller interfacial gap of CDL/Cu, less wrinkles and cracks and larger adsorbing energy of water/oxygen compared with Gr/Cu. Molecular dynamic (MD) simulation also indicates that the diffusion of water or oxygen into CDL/Cu is more difficult and the oxidation of Cu covered by CDL is well suppressed. This work provides a new approach for the study of carbon-based antioxidant materials on Cu.

Oxide Layers in Ni-doped FeCrAl Alloy in 320°C Radioactive Hydrogenated Water

Iron-chromium-aluminum (FeCrAl) alloys have been the interest of the international nuclear energy industry as an accident tolerant fuel cladding replacement to the Zircaloy cladding alloys due to their enhanced corrosion resistance in both normal operation and accident conditions in light water reactors. It is important to understand the corrosion behaviors of FeCrAl before deploying it to nuclear power plants. This study aims to investigate if the addition of a small amount of nickel (Ni) could stabilize the oxide layer by forming the Ni-bearing spinel oxide, such as NiFe2O4, and increase the stability of the oxide layer under irradiation conditions. Current results show that the outer oxide crystals formed on the irradiated FeCrAl-Ni sample surface became larger than that on the FeCrAl sample, which indicates that the Ni addition facilitates the growth of oxide layers and that the FeCrAl-Ni sample exhibited a protective inner oxide layer in the harshest irradiation environment, indicating that Ni improves the corrosion resistance of FeCrAl in radioactive hydrogenated water.

Silver Nanowire-Based Transparent Electrodes for V2O5 Thin Films with Electrochromic Properties.

The development of electrochromic systems, known for the modulation of their optical properties under an applied voltage, depends on the replacement of the state-of-the-art ITO (In2O3:Sn) transparent electrode (TE) as well as the improvement of electrochromic films. This study presents an innovative ITO-free electrochromic film architecture utilizing oxide-coated silver nanowire (AgNW) networks as a TE and V2O5 as an electrochromic oxide layer. The TE was prepared by simple spray deposition of AgNWs that allowed for tuning different densities of the network and hence the resistance and transparency of the film. The conformal oxide coating (SnO2 or ZnO) on AgNWs was deposited by atmospheric-pressure spatial atomic layer deposition, an open-air fast and scalable process yielding a highly stable electrode. V2O5 thin films were then deposited by radio frequency magnetron sputtering on the AgNW-based TE. Independent of the oxide's nature, a 20 nm protective layer thickness was insufficient to prevent the deterioration of the AgNW network during V2O5 deposition. On the contrary, crystalline V2O5 films were grown on 30 nm thick ZnO or SnO2-coated AgNWs, exhibiting a typical orange color. Electrochromic characterization demonstrated that only V2O5 films deposited on 30 nm thick SnO2-coated AgNW showed characteristic oxidation-reduction peaks in the Li+-based liquid electrolyte associated with a reversible orange-to-blue color switch for at least 500 cycles. The electrochromic key properties of AgNW/SnO2 (30 nm)/V2O5 films are discussed in terms of structural and morphological changes due to the AgNW network and the nature and thickness of the two protective oxide coatings.