Oxide-substrate Interface Research Articles

Comparative study on the effect of Nb/Mo alloying on the oxidation behavior of Ti42Al5Mn alloy

The oxidation behavior of Ti42Al5Mn0.5Nb, Ti42Al5Mn0.8Nb, Ti42Al5Mn0.5Mo, and Ti42Al5Mn0.8Mo alloys (in at%) was investigated at 800 °C. In the Nb-containing alloys, the oxide scale exhibits a multi-layered structure with TiO2 layer/Al2O3 layer/TiO2-rich layer from the outside to the inside, and the intermediate layer at the oxide-substrate interface remained composed of Laves/Z phase until 1000 h of oxidation. The oxide scale of the Mo-containing alloys was incorporated with a thick mixed layer and is highly susceptible to cracking, the intermediate layer changed from Laves/Z phase to Laves/Z/βo phase with prolonged oxidation. While Nb increases the oxidation resistance of the alloy, a higher Mo content led to an increased oxidation mass gain and exfoliation of the oxide scale.

Tailoring oxidation resistance of Cantor alloy by addition of Ta and Al

High-entropy alloys are widely investigated for applications in the nuclear engineering field, the aerospace sector, and various other high-temperature applications. High-temperature oxidation behaviour is a typical issue in such applications. In the current work, an effort is made to tailor the oxidation behaviour of Cantor alloy (CoCrFeMnNi) in the air at 1000 °C with the addition of Ta and Al. Both CoCrFeMnNiTa as well as CoCrFeMnNiAl alloys exhibit considerable resistance to oxide scale spallation as well as develop multi-layered complex oxide scales. CoCrFeMnNiTa primarily forms rutile-type CrTaO4 oxide, which drastically reduces the inward diffusion of oxygen and nitrogen and suppresses the escape of other alloying elements. Nonetheless, the better result is obtained through the Al addition, as evidenced by the comparatively lower oxidation rate constant of CoCrFeMnNiAl in comparison to CoCrFeMnNiTa alloy. This is attributed to the superior oxidation resistance for CoCrFeMnNiAl could be related to the emergence of distinctive Cr2O3 and Al2O3 scales. Additionally, the oxide scale of CoCrFeMnNiTa was not completely smooth and showed some spallation whereas the oxide scales of CoCrFeMnNiAl remained smooth, continuous, and had stronger oxide-substrate interface adhesion.

Surface roughness effects on electrochemical anodization behavior of binderless tungsten carbide and oxide boundary generation

Electrochemical anodization has been utilized to reduce the surface hardness of Tungsten Carbide (WC) so that to increase its machinability. In this study, experiments have been conducted to illustrate the impact of surface roughness on electrochemical anodization of binderless WC. Anodization was performed on binderless WC that had different surface roughness by applying a constant voltage and utilizing Sodium Hydroxide (NaOH) as the electrolyte. Oxide generation mechanism during the anodization process has been analyzed in detail, through the investigation of current behavior, surface characterization, surface hardness reduction, surface profile change. It has been observed that during the anodization process, multiple peaks in current curves were produced as a result of discharge channels, induced by the cavities at oxide-substrate interface. When the electric barrier is broken, there was an increase in the formation of oxide layers. Hardness decreased significantly across all substrate conditions. Pristine WC substrate had a robust hardness of 33.34 GPa, while non-polished, semi-polished, and polished substrates had 8.26, 9.545, and 9.411 GPa, respectively. These findings demonstrate the significant impact of anodization on WC's mechanical characteristics, resulting in a 71.6 % decrease in hardness across substrate states. A hypothesis has been presented to describe the overall anodization behavior and boundary oxide generation mechanism of binderless WC. Polished WC substrates have lower surface roughness, indicating more controlled and homogeneous anodization as compared to non-polished and semi-polished WC substrates. The present study enhances the understanding of the impact of surface roughness on the electrochemical anodization of binderless WC, which will further facilitate its incorporation with machining techniques.

A curvature-dependent chemo-mechanical coupling model for two-dimensional oxidation on the curved surface

Understanding the chemo-mechanical coupling effect during oxidation at elevated temperatures is of critical importance for revealing complicated oxidation mechanism and oxidation behavior, as well as proposing countermeasures for oxidation protection. There has been an intensive investigation of the chemo-mechanics in planar oxidation, while much less attention is paid to the issue of non-planar oxidation. In this work, we proposed a curvature-dependent chemo-mechanical coupling model to investigate the two-dimensional oxidation process on curved surfaces. The oxidation kinetics including the oxide thickness and oxide growth rate on the curved surfaces, as well as the stress distribution and evolution at the substrate-oxide interface, were demonstrated. Comparisons between the experimental observations and theoretical predictions validated the accuracy of the proposed model, and the phenomenon of inhibition of oxidation on both convex and concave surfaces was explained by the stress-curvature effect on the oxidation process. Furthermore, based on the proposed model, we proposed a parameter and established a phase diagram to characterize the interactions between the curvature effect and the oxide growth effect.

Improving the Adhesion of a Hard Oxide Layer on Ti6Al4V by a Three‐Step Thermal Oxidation Process

Thermal oxidation is a promising technique to improve the tribological properties of Ti6Al4V. Herein, a single‐step process consisting of oxidation in air, a two‐step process with an additional solid‐state oxide layer reduction step under vacuum, and a three‐step process with an appended final oxidation step in air are applied to Ti6Al4V. The oxide layer adhesion after the three‐step process is improved compared with the single‐step process. This improved adhesion is not due to a different nature of the oxide layers because oxide layers obtained during the single‐step and three‐step process show a similar morphology and composition. Instead, it is ascribed to the presence of an optimized oxygen diffusion zone with two distinct regions: a gradual decrease in oxygen concentration from the maximum possible oxygen concentration at the oxide–substrate interface until a depth of 20 μm followed by a near‐linear decrease until a depth of about 85 μm. Both regions are also visible in the correlated microhardness‐depth profile.

On the growth of copper oxide nanowires by thermal oxidation near the threshold temperature at atmospheric pressure

This study focuses on the growth of copper oxide nanowires networks (CuO NWs) close to the onset temperature, found to be 310 ℃. The NWs were obtained by thermal oxidation in air of polycrystalline copper foils on hot plate. The investigated oxide layers with the NWs network on their surface grown between 200 ℃ and 440 ℃, were characterized by: SEM-EDX, STEM-EDX, XRD, and micro-Raman techniques. The accurate determination of copper content in self-exfoliated oxide sheets is above the stoichiometric concentration. XRD reveals nano-crystallites of 20–40 nm, in Cu2O phase of thick oxide sheets located close to the oxide-substrate interface. Statistical data on the average length of the NWs versus annealing time indicates unexpected early saturation in between 10 and 40 min at 320–340 ℃. A semi-empirical model proofs quantitatively that the emerging delays of the NWs relative to the start of copper oxidation determine the plateau of the average length versus time. The excess concentration of copper found in the cuprous oxide layer is cautioned to accompany the early saturation effect having critical restrictions regarding the oxidation time and temperature. This study sustains the development of control and monitoring methods, applied to the growth of CuO NWs.

Wear Performance of incoloy 800HT and inconel 617 in various surface conditions for high-temperature gas-cooled reactor components

Incoloy™ 800HT and Inconel™ 617 are primary candidate structural materials for high-temperature gas-cooled reactors (HTGRs). Impurities (e.g., H2O, CH4) in the coolant induce corrosion reactions that affect tribological behavior. We investigate the high-temperature tribological performance of the alloys under surface conditions including: conditioned in H2O-containing helium at elevated temperatures, hardened via the carbon-diffusion Kolsterising® treatment, and conditioned after hardening. Initial friction coefficients and volume removed serve as metrics for wear performance. We find that wear mechanisms including scuffing, glaze-oxide formation, and oxide-layer wear and break-through are governed by surface hardness, chemistry, and applied load. The formation of a glaze-oxide layer is achieved with an oxide of sufficient mechanical integrity if the oxide-substrate interface is strong and the load is low.

Minimizing the Nyquist-plot semi-circle of pseudocapacitive manganese oxides through modification of the oxide-substrate interface resistance

Manganese oxides are promising pseudocapacitive materials for electrochemical capacitors, and their capacitance, resistance and frequency response can be characterised using electrochemical impedance spectroscopy. Often, though not universally, the Nyquist plots of these materials evidence a semi-circular feature, which is typically attributed to the pseudocapacitive reaction's charge-transfer resistance. However, we show, for the first time, that the origin of the semi-circle is in fact the oxide-substrate interface resistance. The interface is varied through heat treatment of the manganese oxide and by electrodepositing the manganese oxide on different metals (stainless steel and platinum). Additionally, our novel manganese oxide double-deposition – in which a thin layer of manganese oxide on the interface is heat treated but the bulk of the film is hydrous – separates the interface and pseudocapacitive responses. Films with a low interface resistance (e.g., with a heat-treated interface or deposited on Pt) evidence a 98% smaller semi-circle than those with a poor interface (films deposited on stainless steel with no heat treatment). Conversely, there is no correlation between the amount of psuedocapacitance and semi-circle size. Thus, the Nyquist semi-circle is associated with the interface resistance, and proper modification of this interface can reduce the performance limitations associated with this resistance.

Fundamental aspects to localize self-catalyzed III-V nanowires on silicon

III-V semiconductor nanowires deterministically placed on top of silicon electronic platform would open many avenues in silicon-based photonics, quantum technologies and energy harvesting. For this to become a reality, gold-free site-selected growth is necessary. Here, we propose a mechanism which gives a clear route for maximizing the nanowire yield in the self-catalyzed growth fashion. It is widely accepted that growth of nanowires occurs on a layer-by-layer basis, starting at the triple-phase line. Contrary to common understanding, we find that vertical growth of nanowires starts at the oxide-substrate line interface, forming a ring-like structure several layers thick. This is granted by optimizing the diameter/height aspect ratio and cylindrical symmetry of holes, which impacts the diffusion flux of the group V element through the well-positioned group III droplet. This work provides clear grounds for realistic integration of III-Vs on silicon and for the organized growth of nanowires in other material systems.

Non-Isothermal Oxidation Behavior and Mechanism of a High Temperature Near-α Titanium Alloy.

Non-isothermal oxidation is one of the important issues related to the safe application of high-temperature titanium alloys, so this study focuses on the non-isothermal oxidation behavior and mechanism of near-α titanium alloys. The thermogravimetry-differential scanning calorimetry (TGA/DSC) method was used to study the non-isothermal oxidation behavior of TA29 titanium alloy heated from room temperature to 1450 °C at a heating rate of 40 °C/min under pure oxygen atmosphere. The results show that non-isothermal oxidation behavior can be divided into five stages, including no oxidation, slow oxidation, accelerated oxidation, severe oxidation and deceleration oxidation; for the three-layer TiO2 scale, Zr, Nb, Ta are enriched in the intermediate layer, while Al is rich in the inner layer and Sn is segregated at the oxide-substrate interface, which is related to their diffusion rates in the subsurface α case. The oxidation mechanism for each stage is: oxygen barrier effect of a thin compact oxide film; oxygen dissolution; lattice transformation accelerating the dissolution and diffusion of oxygen; oxide formation; oxygen barrier effect of recrystallization and sintering microstructure in outer oxide scale. The alloying elements with high valence state and high diffusion rate in α-Ti are favorable to slow down the oxidation rate at the stage governed by oxide formation.

Microstructural homogenization and high-temperature cyclic oxidation behavior of a Ni-based superalloy with high-Cr content

A new Ni-based superalloy with high-Cr content was designed for industrial gas turbines application. The microstructural homogenization and high-temperature cyclic oxidation behavior was investigated systematically. The results showed that the optimum heat treatment condition was 1563 K (1290 °C)/4 h + 1573 K (1300 °C)/6 h, A.C. (air cooling) + 1393 K (1120 °C)/2 h, A.C. + 1143 K (870 °C)/24 h, A.C., which can completely dissolve the γ/γ′ eutectic and the Ni3(TiTa) phase in the interdendritic region. The cyclic oxidation results showed that a multilayer of continuous and dense oxide-rich regions formed and the kinetic curves followed a parabolic law. The mass gain at 1323 K (1050 °C) and 1343 K (1070 °C) was 4.02 mg/cm2 and 4.23 mg/cm2, respectively. No severe spallation of the oxide-rich region was observed. The outer layer of the oxide-rich region mainly consisted of Cr2O3, TiO2, and (Ni, Co)Cr2O4 spinels, while the layer at the substrate-oxide interface was found to be Al2O3. The results show that this new superalloy has a better cyclic oxidation resistance at 1343 K (1070 °C) than the commonly used IN738 and GTD-111 superalloys.

Optimization of Oxidation Temperature for Commercially Pure Titanium to Achieve Improved Corrosion Resistance

Thermal oxidation of commercially pure titanium (cp-Ti) was carried out at different temperatures, ranging from 200 to 900 °C to achieve optimum corrosion resistance of the thermally treated surface in simulated body fluid. Scanning electron microscopy, x-ray diffraction, Raman spectroscopy and electrochemical impedance spectroscopy techniques were used to characterize the oxides and assess their protective properties exposed in the test electrolyte. Maximum resistance toward corrosion was observed for samples oxidized at 500 °C. This was attributed to the formation of a composite layer of oxides at this temperature comprising Ti2O3 (titanium sesquioxide), anatase and rutile phases of TiO2 on the surface of cp-Ti. Formation of an intact and pore-free oxide-substrate interface also improved its corrosion resistance.

Evaluation of corrosion performance of Superni 600 hung in secondary chamber of medical waste incinerator operating at 1050 °C

Incineration technique is widely used to dispose of contaminated waste, municipal waste or medical waste. Burning medical waste causes formation of highly corrosive environment inside the chambers. Present study deals with the performance of Ni based Superalloy Superni 600 hanged inside the secondary chamber of medical waste incinerator for 1000 h under cyclic condition. Superni 600 showed good corrosion resistance under this environment. Formation of dense and compact layer of Cr2O3 was observed at substrate oxide interface which acts as a diffusion barrier for corrosive species.

Effect of Chromium and Water Vapor of Low Carbon Steel on Oxidation Behavior at 1050 °C

The high-temperature oxidation behavior of Cr-containing steels are investigated by using continuous thermogravimetric analysis (TGA), in which the coupon samples are exposed at 1050 °C in dry and wet air for up to 60 min. The results showed that the oxidation kinetics of Cr-containing steels followed the parabolic law. The phase of oxide scale is examined by X-ray diffraction (XRD), and the surface and cross-sectional morphologies of the specimens after oxidation are studied in detail with scanning electron microscope (SEM) and the electron probe microanalysis (EPMA). Addition of chromium in steel can promote the formation of Fe–Cr spinel layer and Cr2O3 layer to reduce the oxidation rate at high temperatures, especially in dry air. In wet air, the rate of high-temperature oxidation is increased due to the reaction between H2O and FeO, Cr2O3 and Fe, which can generate volatile hydroxide of CrO2(OH)2 to transform the Fe–Cr spinel from dense layered structure to porous structure. In addition, the amount Cr lost in different steam content is calculated by the classical method of chromium vaporization rates. The oxidation mechanism is proposed based on ions diffusion, chemical reaction, and microstructure of oxide–substrate interface.

Effect of Carbide Particles on the Behaviour of the Oxide Layer

In this study, an FE simulation was used to simulate the contact established between a High-Speed Steel (HSS) work roll and a hot strip material in hot rolling, in which the top layer and the substrate represented the HSS roll and the tip of the indenter represented a particle from oxide scale formed on the strip steel. As the oxidation behaviour of carbides affects the homogeneity of the oxidised surface of work rolls, this has an important influence on wear and therefore it is instructive to investigate the effect that carbide particles have on the behaviour of the oxide layer. This study focused on the interaction between the carbide and the asperity by an abrasive. The evolution of strain fields during the simulation tests was recorded at room and high temperature. The 3D FE model was able to show the interaction between the indenter and the carbide particle reinforcements of these following scenarios: particles above, along and below the scratch path. The results indicated that the strain at high temperature is higher than at room temperature which leads to a higher sensitivity to failure. Increasing the strain means high probability of particle movement that produces delamination of the layer. The strains for particles on the oxide-substrate interface at both temperatures are higher than the particle in the substrate. The interaction between the tip and the particle significantly influences the strains.

Local strain analysis of the tertiary oxide scale formed on a hot-rolled steel strip via EBSD

This work presents a fine microstructure and local misorientation study of various oxide phases in the tertiary oxide scale formed on a hot-rolled steel strip via electron back-scattering diffraction (EBSD). Local strain in individual grains of four phases, ferrite (α-Fe), wustite (FeO), magnetite (Fe3O4) and hematite (α-Fe2O3), has been systematically analysed. The results reveal that Fe3O4 has a lower local strain than α-Fe2O3, in particular, on the surface and inner layers of the oxide scale. The multiphase oxides along the cracking or α-Fe2O3 penetration generally develop a high local misorientation. Localised stain along the cracks demonstrates that the misorientation tends to be strong near grain boundaries. The high fraction of small Fe3O4 grains accumulate at the oxide–substrate interface, which leads to a dramatic increase in the intensity of local stain. This variation is due mainly to the phase transformation among the oxide phases, i.e., the Fe3O4 particles during their nucleation and growth. The combined action of stress relief and re-oxidisation is proposed to explain the formation of Fe3O4 seam at the oxide–steel interface. The present study offers an intriguing insight into the deformation behaviour of the tertiary oxide scale formed on steels, and may help with understanding the stress-aided oxidation effect of metal alloys.

Analytical model of gate leakage current through bilayer oxide stack in advanced MOSFET

A compact model for gate tunneling current in advanced nano-scale MOSFET has been developed on the basis of both direct and Fowler–Nordheim tunneling through dual layer Silicon oxide–Hafnium oxide stack used as gate dielectric. Calculation includes the effect of different subbands of the semiconductor conduction band those arise due to quantum confinement of charge carriers in the oxide–substrate interface. Effect of charge trapping in the bulk of the oxides and at the localized energy levels at different interfaces of the oxides has also been taken into consideration. Tunneling probability as a function of gate bias has been determined considering Wentzel–Kramers–Brillouin (WKB) approximation to account for varying potential profile. Probability amplitude of an electron for tunneling has been calculated by solving Schrodinger equations at different regions in the effective mass approximation model of class I crystal interface. Tunneling current as a function of effective oxide thickness and gate bias estimated in this model shows substantial reduction in gate leakage current if HfO2 as high-k dielectric is used along with 1nm thick SiO2 with almost negligible change in threshold voltage.

Appearance of anodised aluminium: Effect of alloy composition and prior surface finish

Effect of alloy composition and prior surface finish on the optical appearance of the anodised layer on aluminium alloys was investigated. Four commercial alloys namely AA1050, Peraluman 706, AA5754, and AA6082 were used for the investigation. Microstructure and surface morphology of the substrate prior to anodising were analysed using scanning electron microscopy and atomic force microscopy. The optical appearance of the anodised surface with and without sealing was investigated using a photography setup, photospectrometry and bidirectional reflectance distribution function. It was found that the roughness of the as-etched surface increases with the degree of alloying due to second phase particles making the reflection more diffused, and that the as-etched surface morphology is similar to the oxide–substrate interface after anodising. Proper polishing is achieved on hard alloys and the glossy appearance was kept for alloys of high purity. Sealing made the specular reflection of the mechanically polished specimens more distinct.

Resistive switching effect on Al2O3/InGaAs stacks

Display Omitted HighlightsWe examine the post breakdown characteristics of metal gate/Al2O3/InGaAs.It is observed resistive switching (RS) effect.The oxide-substrate interface is studied by X-ray photoelectron spectroscopy spectra.The As-O bonds are responsible for large frequency deviations and the RS effect. The resistive switching (RS) phenomenon is currently attracting a lot of attention due to its potential applicability for nonvolatile memory devices. Among all the systems currently under consideration, the analysis of MG/Al2O3/InGaAs is very relevant since this stack is a strong candidate for the new generation of CMOS devices with high mobility channels.

Impact of the polysilicon doping level and thermal oxidation on the properties of P-MOS capacitor structures

In this paper, we present a study of different parameters characterising polysilicon/oxide/monosilicon structures, after extraction from the capacitance voltage C(V) and conductance voltage G(V) curves, at high frequency (1 MHz). The polysilicon films are elaborated by chemical vapour deposition at low pressure (LPCVD) from silane (SiH4) and boron trichloride (BCl3) gas mixture, at a temperature of 605°C. They have been subjected to thermal annealing in dry oxidising atmosphere at temperatures ranging between 850 and 1,100°C. The extraction of parameters such as the doping level at the oxide substrate interface, the flat band voltage, the oxide thickness and the interface states density has shown that they are strongly influenced by oxidation treatments and doping level. The results show that there are two competing phenomena in the case of boron doped polysilicon gate: the polydesertion and the diffusion. The study has demonstrated the polysilicon’s ability to play the gate’s material role, while preserving the dielectric’s quality on which it is deposited.