Oxidation Resistance Of Alloys Research Articles

Selective atomic sieving across metal/oxide interface for super-oxidation resistance

Surface passivation, a desirable natural consequence during initial oxidation of alloys, is the foundation for functioning of corrosion and oxidation resistant alloys ranging from industrial stainless steel to kitchen utensils. This initial oxidation has been long perceived to vary with crystal facet, however, the underlying mechanism remains elusive. Here, using in situ environmental transmission electron microscopy, we gain atomic details on crystal facet dependent initial oxidation behavior in a model Ni-5Cr alloy. We find the (001) surface shows higher initial oxidation resistance as compared to the (111) surface. We reveal the crystal facet dependent oxidation is related to an interfacial atomic sieving effect, wherein the oxide/metal interface selectively promotes diffusion of certain atomic species. Density functional theory calculations rationalize the oxygen diffusion across Ni(111)/NiO(111) interface, as contrasted with Ni(001)/NiO(111), is enhanced. We unveil that crystal facet with initial fast oxidation rate could conversely switch to a slow steady state oxidation.

Simultaneous improving high temperature oxidation resistance and room temperature toughness of Nb[sbnd]Si based alloy via appropriate Ta content addition strategy

NbSi based alloys are expected to become the application materials for high pressure turbine blades of aircraft engines. This paper investigates the impact of Ta addition on room temperature fracture toughness and isothermal oxidation behavior at 1250 °C of four NbSi based alloys with compositions of Nb-16Si-20Ti-8Zr-4Hf-1.5Al-xTa (x = 0, 1, 2, and 4 at.%) fabricated through vacuum non-consumable arc-melting. The results show that the room temperature fracture toughness and 1250 °C oxidation resistance of the alloys increase first and then decrease with the addition of Ta element. The room temperature fracture toughness of 1Ta alloy is the best, reaching 17.1 MPa·m1/2. Adding a moderate amount of Ta (1 at.%) significantly enhances the alloy's oxidation resistance, but an excessive Ta content diminishes this enhancement. This research has obtained a Nb-16Si-20Ti-8Zr-4Hf-1.5Al-1Ta alloy with high room temperature fracture toughness and excellent high temperature oxidation resistance simultaneously, which provide an ideal path for designing NbSi alloys with superior comprehensive properties.

Superior oxidation resistance of a Y-Hf co-doped Al18Co30Cr10Fe10Ni32 eutectic high-entropy alloy at 1100–1300 °C

We report a study on the oxidation behavior of Al18Co30Cr10Fe10Ni32 eutectic high-entropy alloy co-doped with reactive elements (RE) Y and Hf at 1100–1300 °C. The highly stable eutectic microstructure of γ’/β phases within this alloy contributes to a low coefficient of thermal expansion, thus a low residual stress in the Al2O3 scale. The spinel with a low thickness is formed at the top of Al2O3 scale at 1100 °C due to the low Al diffusion coefficient of γ’-phase and low aspect ratio of β-phase in maze-like eutectic region. As the oxidation temperature increases, the oxidation products transition to exclusive Al2O3 at 1200 °C and 1300 °C, facilitated by the increased Al diffusion coefficient. The Al2O3 scale exhibits a dominated columnar grain microstructure at 1100–1300 °C, suggesting that the inward O diffusion plays more critical role than Al diffusion and thus leads to the low oxidation rate. Besides, the segregation of S to scale/metal interface is inhibited by the uniform RE distribution in the alloy resulting from the fine eutectic microstructure in the alloy. Overall, this alloy exhibits low residual stress in the oxide scale, slow oxidation rate, and the lack of interfacial sulfur segregation, thus contributing to its superior oxidation resistance. The strong oxidation resistance of Y-Hf co-doped Al18Co30Cr10Fe10Ni32 eutectic high-entropy alloy makes it a potential candidate for advanced oxidation-resistant alloy or coating applications.

Effect of Ti and C addition on oxidation resistance of FeCoCrNiMn high entropy alloys prepared by powder metallurgy

Purpose The purpose of this paper is to study the high temperature oxidation behavior of Ti and C-added FeCoCrNiMn high entropy alloys (HEAs). Design/methodology/approach Cyclic oxidation method was used to obtain the oxidation kinetic profile and oxidation rate. The microstructures of the surface and cross section of the samples after oxidation were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Findings The results show that the microstructure of the alloy mainly consisted of FCC (Face-centered Cubic Structure) main phase and carbides (M7C3, M23C6 and TiC). With the increase of Ti and C content, the microhardness, strength and oxidation resistance of the alloy were effectively improved. After oxidation at a constant temperature of 800 °C for 100 h, the preferential oxidation of chromium in the chromium carbide determined the early formation of dense chromium oxide layers compared to the HEAs substrate, resulting in the optimal oxidation resistance of the TC30 alloy. Originality/value More precipitated CrC can preferentially oxidize and rapidly form a dense Cr2O3 layer early in the oxidation, which will slow down the further oxidation of the alloy.

Insight into the role of Sc on microstructure, mechanical properties and high temperature oxidation resistance of NiCoCrAlSiSc alloys

The microstructure and mechanical properties of Ni–20Co–20Cr–2Al–1Si-xSc (x = 0, 0.1, 0.3, 0.5, 1 wt %) alloys were investigated, and the oxidation behavior of the alloys with different Sc contents at 1000°C was studied. The results indicate that NiCoCrAlSi alloy without Sc solidified into coarse columnar grains, with the addition of Sc, the grain size significantly decreased. Sc enriched at the grain boundaries of the alloy and promotes the segregation of Si and Ni towards the grain boundaries, forming the compound NiScSi. Within the range of 0∼1% (wt.%) Sc content, as the Sc content increased, there is an increase in the yield strength (σ0.2) of the alloy, a decrease in elongation, a little variation in tensile strength, and an enhancement in Vickers hardness. After cyclic oxidation at 1000°C and 120 h for alloys with different Sc contents, composite oxide films were formed on the surfaces of the alloys, but the properties and microstructure of the oxide films were significantly different. As the Sc content rised, the integrity of the oxide films was significantly improved, and the oxidation resistance of the alloys gradually enhanced at a high temperature of 1000°C.

Revealing the superior oxidation resistance of alloy 690 in deaerated supercritical water at 600 °C through advanced characterization

The corrosion behavior of a well-polished Alloy 690 in deaerated supercritical water at 600 °C was examined. The study found that the weight gain follows a near-cubic rate law. A key observation was that the direct external oxidation and the rapid transition from internal to external oxidation within the initial 24-h exposure are responsible for its superior oxidation resistance. As exposure time increases, the transformation of Cr-rich spinel oxides and Ni-rich networks in the internal oxidation zone into Cr2O3 leads to the expansion of the protective chromia layer, effectively slowing down the oxidation process. Conversely, the Cr2O3 layer at the grain boundaries (GBs) was less effective at preventing oxidation, resulting in a significantly faster oxidation rate in these areas compared to the bulk grains. The extensive GB oxidation exhibits little consequential correlation with carbides.

Investigating the Replacement of Nickel-based Superalloys with Niobium-Based Superalloys in the New Generation of Turbine Blades in the Aero-space Industry

To improve the thermal properties of superalloys or replacing them with new materials is necessary to increase engine efficiency. When considerable progress in superalloys is unlikely, researchers started to turn their attention to alternative materials. Metallic silicide alloys are cheaper choices for increasing engine efficiency. The melting point for molybdenum and niobium silicide is much higher than the melting point of the current alloys. This shows these alloys have the potential to increase temperature in gas turbine engines. These alloys have poor oxidation resistance. Improving oxidation resistance of each alloy system is a significant step toward a new material for turbine blades. To improve oxidation resistance in these alloys, many experiments have been done in which alloy elements such as Ti, Cr, Al, Zr, Ta, and Sn have been used. According to these experiments, it can be concluded that Zr is practically ineffective and it cannot improve oxidation resistance in alloys. In some temperatures, Ta is even harmful for oxidation resistance. Sn has the best function to increase oxidation resistance by forming a rich layer of Sn, oxygen penetration into depth is prevented. Despite these alloy elements, they are not enough resistant to oxidation to function in higher temperatures. To be replaced by nickel-based superalloys in gas turbine blades in the aerospace industry they need to have higher oxidation resistance.

Enhancement of mechanical properties and oxidation resistance of TiAl alloy with addition of Nb and Mo alloying elements

In this study, small button-shaped ingots were prepared by a non-self-consuming vacuum arc melting method. The effect of the content of Nb and Mo elements on the microstructure, mechanical properties and oxidation resistance of TiAl alloys were investigated. The as-cast TiAl alloy presented laminar microstructure. When only adding Nb element, a small amount of β phase was distributed in the form of dots at the grain boundaries of α2/γ lamellar structure. When adding both Mo and Nb, the precipitated β phase started to precipitate in lines inside the α2/γ lamellar structure. The microhardness of the alloy increased with the increasing Nb and Mo content. The compressive strength of the alloys increased firstly with the increasing Nb content and decreased when the content of Nb exceeded 7 wt%. However, with the addition of Mo, the compressive strength of the alloys decreased drastically. The optimal compressive strength of the alloy, i.e. 2250 MPa, was obtained with 5 wt% Nb and 5 wt% Mo addition. The oxidation resistance of the alloys were enhanced with the addition of Nb and Mo elements and the TiAl–5Nb–5Mo alloy also showed the best oxidation resistance at 800 °C.

Tuning Mo/W ratio to improve high temperature oxidation resistance of single crystal nickel base superalloys

The effect of different Mo/W ratios of three single crystal nickel base superalloys on the oxidation behavior was investigated at 1100 °C. Both isothermal and cyclic oxidation tests showed that increasing Mo/W ratio corresponds to lower weight change and improved resistance. The microscopic observation uncovers that the harmful effect of Mo is limited by the dense Al2O3 scale. In contrast, excessive W leads to fast growth of interlayer and its premature spallation. This research proposes and verifies a new way to improve oxidation resistance of alloy, namely, balancing the harmful effect of refractory elements.

Ultra-high temperature oxidation resistant refractory high entropy alloys fabricated by laser melting deposition: Al concentration regulation and oxidation mechanism

Poor oxidation resistance is a critical factor limiting the application of metalllic materials at ultra-high temperature environments. In this contribution, Alx(CrMoTaTi)1−x (x = 0.05, 0.1, 0.15) refractory high entropy alloy (RHEA) system was fabricated by laser melting deposition. The as-deposited RHEA was composed of two body-centered-cubic phases (BCC1 and BCC2). It was found that the volume fraction of BCC2 was increased with increasing the Al concentration from 0.05 to 0.15 and, surprisingly Al0.15(CrMoTaTi)0.85 could thermally grow an external Al2O3 scale during oxidation in air at 1300 °C. The insights into the microstructure-based oxidation mechanism of the RHEA were illustrated.

Preparation of VZrHfNbTa High-Entropy Alloy-Based High-Temperature Oxidation-Resistant Coating and Its Bonding Mechanism.

Ultra-high Temperature Oxidation-Resistant Alloys (UTORAs) have received a lot of attention due to the increased research demand for deep space exploration around the world. However, UTORAs have the disadvantages of easy oxidation and chalking. So, in this study, a UTORAs is prepared by hot-press sintering on VZrHfNbTa (HEA: High Entropy Alloys can generally be defined as more than five elements by the equal atomic ratio or close to the equal atomic ratio alloying, the mixing entropy is higher than the melting entropy of the alloy, generally forming a high entropy solid solution phase of a class of alloys.) a substrate coated with hafnium. The bonding mechanism, resistance to high-temperature oxidation, and hardness of the sample tests are carried out. The results show that zirconium in the matrix will diffuse into the hafnium coating during the high-temperature sintering process and form the HfZr alloy transition layer, the coating thickness of the composite is about 120 μm, and the diffusion distance of zirconium in the hafnium coating is about 60 μm, this transition layer chemically combines the hafnium coating and the HEA substrate into a monolithic alloy composite. The results of high-temperature oxidation experiments show that the oxidation degree of the hafnium-coated VZrHfNbTa composite material is significantly lower than that of the VZrHfNbTa HEA after oxidation in air at 1600 °C for 5 h. The weight gain of the coated sample after oxidation is 56.56 mg/cm2, which is only 57.7% compared to the weight gain of the uncoated sample (98.09 mg/cm2 for uncoated), and the surface of the uncoated HEA shows obvious dents, oxidation, and pulverization occurred on the surface and interior of the sample. In contrast, the coated composite alloy sample mainly undergoes surface oxidation sintering to form a dense HfO2 protective layer, and the internal oxidation of the hafnium-coated VZrHfNbTa composite alloy is significantly lower than that of the uncoated VZrHfNbTa HEA.

A comprehensive study on the oxidation behavior and failure mechanism of (γ’+β) two-phase Ni-34Al-0.1Dy coating treated by laser shock processing

Laser shock processing (LSP), as a novel surface modification technology, exhibits tremendous potential to improve the oxidation resistance of alloys. In this paper, (γ’+β) two-phase Ni-34Al-0.1Dy coatings were prepared by electron beam physical vapor deposition (EB-PVD) and then treated by LSP with different pulse energy (4 and 5 J). Their oxidation behavior (including isothermal oxidation and cyclic oxidation) at 1150 °C was compared. In the isothermal oxidation case, the LSP-treated samples exhibited good oxidation resistance due to high dislocation density and refined grains caused by the LSP. For the cyclic oxidation, however, the LSP-treated samples were subjected to undesirable thermally grown oxide (TGO) spallation. In the early oxidation stage (within 30 min), the residual compressive stress introduced by the LSP rapidly released, resulting in a severe plastic deformation at the coating/TGO interface. As a result, the mismatch between coating and TGO gave rise to the TGO spallation. With the increase in the oxidation time, work hardening, which continuously limited the synchronous deformation of the TGO/coating interface, became the dominant mechanism controlling the TGO spallation of 5 J-treated coatings. The continuous TGO spallation affected the Al supply and thus deteriorated the cyclic oxidation behavior.

The effect of Al and Ti on the microstructure, mechanical properties and oxidation resistance of γ′-Ni3(Al, Ti) strengthened austenitic stainless steels

Both Al and Ti are the key elements for the formation of γ′-Ni3(Al, Ti) phase and protective oxide scale in the γ′-Ni3(Al, Ti) precipitation strengthened austenitic stainless (AS) steels. To obtain good mechanical properties, especially at elevated temperatures, high volume fraction of γ′ phase is required, which is strongly dependent on the total amounts of Al and Ti. For a given concentration of (Al + Ti), changing Al or Ti addition also has significant effects on the microstructure, mechanical properties and oxidation resistance of alloys. In this study, three alloys are designed by moderately adjusting Al and Ti addition while keeping (Al + Ti) concentration constant (8.7 at.%). It is found that increasing Ti and decreasing Al addition lead to fine Laves precipitates and close spacing between them, which in turn refine grain size and enhance strength at temperature lower than 750 °C. But at about 800 °C, the strength of there alloys is almost the same. Increasing Al and decreasing Ti addition have no apparent influence on the γ′ phase but promote the formation of B2–NiAl phase, resulting in reduced ductility at elevated temperature. Besides, high Al addition facilitates the formation of continuous protective oxide layer (mainly alumina) and is beneficial for oxidation resistance at 750 °C for 500 h. As Ti replaces Al, the integrity of protective alumina layer is destroyed and the discontinuous Al-rich oxides are interlaced with Cr-rich and Ti-rich oxides.

Optimizing chemistry for designing oxidation resistant FeCrAl alloys

Traditionally, FeCrAl alloys played an important role in high-temperature applications due to their ability to form a passive Al oxide film at temperatures above ~ 800 °C. Recently, FeCrAl alloys became of interest for the application of accident tolerant nuclear fuel cladding. This study covers work done at GE Research for better understanding the role of Al, Cr, and Mo in oxidation kinetics and thermodynamics. Several models and commercial prototype alloys have been tested in hydrothermal corrosion autoclave loops, at low temperature steam exposure (~ 400 °C), high temperature steam exposure (~ 1000 °C or higher), and high temperature air exposures. The results provide insights on how chromium and aluminum play a significant role in both high temperature and low temperature oxidation of FeCrAl. Additionally, machine learning tools are used to gain further insights on both predicting future optimized chemistries for balancing the properties of hydrothermal corrosion, low and high temperature steam oxidation, and thermal aging (which is exacerbated due to radiation in a nuclear reactor environment). GE plans to use this framework to further optimize the FeCrAl alloy system for use in nuclear reactor environments.Graphical abstract

Microstructure and oxidation behavior of Co–Cr–Ta ternary alloys

The improvement of oxidation resistance of alloys is one of the key points to develop components for ultra-high temperature applications. The formation of a CrTaO4 oxide layer has attracted attention because of its thermal stability and good protection against oxidation above 1000 °C where more commonly used protective oxide layers such as Cr2O3 show their limits. This study investigates the microstructure evolution and oxidation resistance of the Co-Cr-Ta ternary alloys in comparison to the Calphad predictions. The Co-Cr-Ta samples tested here are composed of an FCC Co-rich phase and a C15 laves phase, and an increase of Cr content was linked to the formation and growth of an additional σ phase. Thermogravimetric analysis, together with the isothermal oxidation tests in air at 1200 °C proved that alloys exhibited good oxidation resistance formed a continuous CrTaO4 layer. Also, optimization of Co-Cr-Ta composition with improved oxidation resistance was attempted using data-driven strategy and the results demonstrated the potential of such approach for the future of alloy design.

Alloy Design for Additive Manufacturing: Early-Stage Oxidation of Nickel-Based Superalloys

This body of work aims to inform alloy design for additive manufacturing by investigating the early-stage oxidation behavior of Ni-based superalloys processed by laser-powder bed fusion. The oxidation of 14 Ni-based superalloys—some novel and some heritage—at 1000 °C for 24 hours is studied through thermo-gravimetric analysis. The mass gain, oxide layer thickness, oxide scale composition, and gamma ^prime depletion zone size are measured. The influence of the alloy composition on these variables is assessed in order to elucidate how increasingly processable and oxidation resistant alloys can be developed. The alloy compositions with Al content greater than 9 at. pct form continuous Al2O3 scales at 1000 °C and display markedly lower parabolic rate constants, mass gain, oxide layer thickness, and gamma ^prime depletion zone size. The alloys of lesser Al content have reduced oxidation resistance and formed oxide scales of predominantly Cr2O3. Alloys with Ti content of 2.7 at. pct and greater formed Ti-rich oxide phases in their oxide scales as well as TiN subscale. A trade-off between alloy processability and oxidation resistance is identified, dictated by the deleterious effect of Al content on the ductility dip and the benefit of Al for oxidation resistance. A property space along the pareto front is highlighted which is ideal for having oxidation resistance and processability.

Effect of aluminum on the FeCr(Al) alloy oxidation resistance in steam environment at low temperature (400 °C) and high temperature (1200 °C)

The effect of aluminum in the FeCr(Al) alloys on the corrosion behavior was studied at two temperatures (400 °C and 1200 °C). For the Fe-21Cr alloy, Cr2O3 layer was formed upon exposure to both temperatures. The addition of Al altered the corrosion mechanism of the alloy. At 1200 °C, a thin α-Al2O3 is formed on the Fe-21Cr-5.5Al alloy. Whereas, at low temperature, a continuous Cr2O3 is formed at the top with an internal Al2O3 layer. These results show that FeCrAl alloys hold promise as Fuel Cladding Materials with Al playing a crucial role under operational as well as accident-like conditions.

In-situ Raman spectroscopic studies on electrochemical oxidation behavior of chromium in alkaline solution

The electrochemical oxidation mechanism of Cr in alkaline solution was deduced by combining electrochemistry with in-situ Raman spectroscopy. • Combined electrochemistry and in-situ Raman spectroscopy to study the electrochemical oxidation behavior of chromium in the alkaline condition. • A method for the determination of chromate by chromium electrode was presented. • The method can be applied to the determination of chromate in the electroplating solution. Chromium is a metal with high hardness, and strong oxidation resistance, doping chromium in the alloy will improve the alloy's oxidation resistance and corrosion resistance. However, the mechanisms of chromium electrodeposition, electrochemical oxidation, and corrosion are still controversial and only stay in the field of electrochemical research and lack in-situ data support. Therefore, we combine electrochemistry and in-situ Raman spectroscopy to study the electrochemical oxidation behavior of Cr in 0.5 M NaOH solution. The results show that the electrochemical oxidation behavior of Cr in the alkaline solution includes two steps. The first step is that the Cr layer loses six electrons and combines with OH − oxidized to CrO 4 2− , the second step is CrO 4 2− enriched on the Cr layer, and the Cr layer loses six electrons again oxidized to Cr 2 O 7 2− . We develop an electrochemical method for CrO 4 2− concentration detection in the chromium plating solution based on this mechanism. We obtain the linear correlation curve between CrO 4 2− concentration (0.1∼2.0 mol·L −1 ) and peak current density, which has simple, fast, and broad linear range characteristics.

Oxidation resistance of magnesium alloyed by different elements: a brief review

The application of magnesium (Mg) and its alloys in automotive and aerospace industry is promoted gradually because of its outstanding properties, such as light weight, high specific strength and excellent castability. However, as a chemically active metal, Mg and its alloys generally possess low oxidation resistance in air at high temperatures because of the high affinity of Mg for O. This has caused a lot of industrial waste and a short service life. In the present work, according to the relevant mechanism of Mg alloy oxidation in air at high temperature, the effect of alloying elements on the oxidation of pure Mg and Mg alloys as well as the research progress of oxidation resistant Mg alloys are briefly reviewed.

The Effect of Niobium and Carbon on the Oxidation Resistance of Alloys Based on Fe3Al at 900°C

The Effect of Niobium and Carbon on the Oxidation Resistance of Alloys Based on Fe3Al at 900°C