Isothermal Oxidation Behavior Research Articles

Preparation and interdiffusion behaviour of a NiCrAlY coating with high entropy ceramic diffusion barrier

In order to solve the problem of elemental interdiffusion between the superalloy and coating, the diffusion barrier of (AlCoCrNiRe) and (AlCoCrNiRe)O between the N5 superalloy and NiCrAlY coating was prepared by magnetron sputtering. Isothermal oxidation behaviour of the NiCrAlY coatings with diffusion barrier was evaluated at 1050 °C. The results show that the application of (AlCoCrNiRe) and (AlCoCrNiRe)O diffusion barriers significantly reduced the precipitation of TCP phase in the substrate. (AlCoCrNiRe)O high entropy ceramic diffusion barrier has a better effect of inhibiting interdiffusion because of its own properties and the oxides formed in situ. Furthermore, the NiCrAlY coating with (AlCoCrNiRe)O high entropy ceramic diffusion barrier provides higher resistance to high-temperature oxidation for the substrate.

High‐temperature oxidation of Cu–Al–Ni–Mn shape‐memory alloy

AbstractThe isothermal oxidation behavior of the Cu‐11.35Al‐3.2Ni‐3.5Mn (wt.%) shape‐memory alloy (SMA) in the temperature range of 500–900°C in oxygen was studied using the thermogravimetric (TG) method. TG curve showed that the alloy has parabolic isothermal oxidation characteristics. The effect of oxidation on the surface morphology and chemical composition of the Cu–Al–Ni–Mn alloy was determined by scanning electron microscopy, energy‐dispersive spectroscopy, and X‐ray photoelectron spectroscopy (XPS) analyses. The oxidation rate of SMA increases up to 700°C, remains stable at 800°C, and increases again up to 900°C. The XPS analysis identified that the corrosion products mainly contained MnO2, MnO/Mn2O3, and Al2O3.

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.

Non-isothermal and isothermal oxidation behavior and kinetics of shale oil during air injection

Non-isothermal and isothermal oxidation behavior and kinetics of shale oil during air injection

Numerical modeling and experiment for isothermal selective external oxidation behavior of Fe-Mn binary alloys

This paper described work undertaken to the selective external oxidation of Fe-Mn binary alloys during isothermal recrystallization annealing. The effect of different peak temperature, soaking time, dew point conditions on external oxidation of Fe-Mn alloys were investigated. Based on an image segmentation technology, external oxidation behavior was evaluated by the equivalent diameters and coverage fraction of external oxides. A numerical kinetics model of the coupled selective internal-external oxidation during isothermal annealing of Fe-Mn binary alloys was proposed. The model allowed the case of internal and external oxidation simultaneously occurred. Based on the assumptions of oxidation reaction at the steel/atmosphere interface reached an instantaneously local thermodynamic equilibrium, the coupled relationship was described by two interactions. The surface dissolved oxygen content could be controlled by both the annealing atmosphere and the coverage fraction of external oxides on the surface, while the diffusion of oxidant and oxygen inside the steel were blocked by the precipitation behavior of internal oxides. Therefore, the model achieved predict quantitatively the coverage of oxides on the external surface of the steel and the mass fraction profiles of Mn after annealing. The correctness of the calculation results was verified experimentally.

High-temperature oxidation behavior of Mar-M247 and Mar-M247LC for aero-engines at 800–950 °C in air

The isothermal oxidation behavior of Mar-M247 and Mar-M247LC was investigated in air at 800–950 °C for 500 h. The oxidation activation energies of 327.7 kJ/mol and 281.4 kJ/mol were obtained, respectively. The oxidation kinetics and oxide layer evolution indicated that the Cr3+ outward diffusion dominated the oxide film growth. Firstly, NiO replaced Cr2O3 as the outer layer above 900 °C. Next, the formation of the internal Al2O3 was closely related to the γ' phase dissolution. The size of the γ' and the γ/γ' interfacial area may be one of the possible reasons for the minor differences in the Mar-M247 and Mar-M247LC oxidation properties. And finally, it is speculated that the oxide pegs in the oxide layer enhance the adherence of the oxide film to the substrate.

Microstructure evolution and failure mechanism of Cr-coated Zry-4 in air and steam at 1200 °C

The dense and uniform Cr coating is successfully applied to the Zry-4 (zircaloy-4) substrate using multi-arc ion plating as an accident-tolerant fuel cladding. The isothermal oxidation behavior of the Cr-coated Zry-4 is investigated in air and steam at 1200 °C. The mass gain, microstructure evolution and phase composition of the Cr-coated Zry-4 after different oxidation times are compared. The mass gain of Cr-coated Zry-4 in air is higher than in steam. In air, the dense Cr2O3 layer consisted of bulk Cr2O3, while protruding flake Cr2O3 is found on the surface of the Cr coating in steam. The degradation process and oxidation failure mechanism of the Cr-coated Zry-4 in air and steam at 1200 °C are analyzed.

Study on eutectic-oxidation coupling reaction of Cr-Zr system in high temperature steam environment

The isothermal steam oxidation behavior of Cr-coated Zr-1Nb alloy at 1350 ℃ and 1400 ℃ was investigated. The temperatures are above the Cr-Zr eutectic temperature. The reliability of the experimental setup and methodology was confirmed by conducting isothermal steam oxidation experiments on bare Zr-1Nb specimens at 1100∼1400 ℃, and the corresponding oxidation kinetics correlation was obtained. After the eutectic-oxidation reaction, the surface of the coated specimens exhibited a “crocodile skin” morphology composed of “ridges” and “hollows”, which was attributed to the non-uniform eutectic reaction. Due to the much higher O affinity of Zr compared to Cr, and the higher solubility of Cr in β-Zr compared to α-Zr(O) and ZrO2, the ZrO2 and α-Zr(O) layers initially grew on the Cr-Zr eutectic during oxidation. Cr continuously diffused inward and eventually precipitated as Cr-rich phases within the metallic matrix. Three types of Cr-rich phases were observed, with varying oxygen content and reflecting the oxidation process of the Cr-rich phases. The Cr-rich phases were ultimately oxidized into a mixture of Cr2O3 and ZrO2. The parabolic weight gain rates for the oxidation of Cr-Zr eutectic are compared with the oxidation kinetics correlation derived from the bare Zr-1Nb specimens, and the model applicability of the oxidation kinetics correlations of Zr alloys in the simulations of Cr-Zr eutectic-oxidation reaction is discussed.

Preparation of Cr2AlC powder and its isothermal oxidation behavior in dry air and pure steam

As a promising candidate ceramic for using in harsh environments, Cr2AlC ternary carbide possesses numerous unique properties at elevated temperatures. Herein, high-purity Cr2AlC powders had been synthesized by using a facile method with a mixture of Cr7C3, Cr3C2 and Al powders at 1200 °C for 3 h. Subsequently, the oxidation behaviors of Cr2AlC powders were investigated in dry air and pure steam at temperatures ranging from 900 to 1100 °C, respectively. In addition, the oxidation products were characterized and the mass gain curves were analyzed via the real physical picture (RPP) kinetic model. As a result, thicker Al2O3-rich oxide scale and porous Cr7C3 subscale were generated during dry air oxidation compared to pure steam oxidation. Notably, the oxidative active energy of Cr2AlC was 446.5 kJ/mol in pure steam, while in dry air it was decreased by 14.4%. Theoretical calculations further verified that Cr2AlC oxidizes more sluggishly in steam than in dry air.

Isothermal low-temperature oxidation behavior and kinetics of heavy oil

In this study, the isothermal low-temperature oxidation (LTO) behavior of heavy oil was investigated by thermogravimetry combined with Fourier transform infrared spectroscopy. Furthermore, the kinetics analysis was conducted using general reaction rate models. The findings revealed that the LTO process of heavy oil could be divided into three distinct phases. The first phase, occurring between 50 and 100 °C, exhibited minimal mass loss and low absorbance of gas-phase products. In the second phase (100–250 °C) the produced gas predominantly consisted of saturated hydrocarbons and substances containing C=O groups. Lastly, in the third phase (250–300 °C), the signals of CO2 and CO in the produced gas were significantly higher compared to the 50–250 °C range, indicating a shift in the oxidation mode of heavy oil from oxygenation to bond cleavage for temperatures higher than 250 °C. Kinetics analysis demonstrated an initial increase in reaction order and reaction rate from 50 to 100 °C, followed by a decrease from 100 to 250 °C, and a final increase from 250 to 300 °C. The negative activation energy observed in the second temperature interval was attributed to the negative temperature coefficient effect. This study provided valuable insights into the isothermal LTO reactions of heavy oil.

Effect of coatings on oxidation behavior of a fourth generation Ni-based single crystal superalloys at ultra high temperature

PtAl and MCrAlY coating were prepared on the fourth generation single crystal superalloy. The isothermal oxidation tests of superalloys with different coatings were performed at 1150 °C and 1200 °C in a muffle furnace with static air for 500 h. The isothermal oxidation behavior and mechanism of two coatings at 1150 °C and 1200 °C was investigated. MCrAlY coating improved oxidation resistance by forming adhesive oxide scales with pegs, and PtAl coating formed dense and coherent oxide scales on surface to hinder the diffusion of oxygen. Compared with two coatings, a smaller oxidize increasing weight of PtAl coating (0.54 mg/cm2) than MCrAlY coating (2.48 mg/cm2) indicated that PtAl coating presented a better oxidation resistance during oxidation test at ultra high temperature, although a significant interdiffusion behavior occurred between PtAl coating and substrate. Besides, the interactive behavior between Ru and coatings was also investigated. Ru in fourth generation single crystal superalloy could diffuse into β-NiAl phase of coatings, maintaining the integrity of coatings. The major difference between MCrAlY coating and PtAl coating came in the amounts of β-NiAl phase, which leading to the difference on the oxidation resistance between MCrAlY and PtAl. The mechanism about influence of temperature on the oxidation property on bare alloy, MCrAlY-DD91 and PtAl-DD91 was also discussed. Ultra high temperature would promote more elements to participate in the reaction with oxygen, change the compositions of oxide scale and phases, resulting to the spallation of oxide scale and decrease of oxidation resistance.

Degradation of the Cr2O3 layer protectiveness caused by grain refinement during high-temperature oxidation of Cr coatings

To enhance the understanding of the failure mechanism of Cr coatings under simulated loss of coolant accident (LOCA) conditions in pressurized water reactors, an investigation into the isothermal oxidation behavior of Cr coatings in 1200 °C steam was conducted. The structure evolution of Cr coatings was characterized by scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) methods. The obtained results reveal the formation of a three-layer structure during the 1200 °C steam oxidation process. This structure comprises a Cr2O3 layer, a residual Cr layer, and a ZrCr2 layer. Over time, the grains in the Cr2O3 layer undergo refinement, leading to an increase in grain boundaries. This phenomenon promotes the inward diffusion of oxidizing medium, contributing to understanding of the degradation of Cr2O3 layer protectiveness after prolonged oxidation. These findings offer valuable insights into the failure mechanism of Cr coatings in high-temperature steam environments.

Effect of molybdenum on isothermal oxidation behavior of 4th generation nickel-based single crystal superalloys

The isothermal oxidation behavior of fourth-generation nickel-based single crystal superalloys with 2-4 wt% Mo content were studied at 900 °C and 1100 °C.At 1100 °C, the oxide layer can be divided into three layers, the outermost layer is Ni–Co oxide, the intermediate layer is spinel and heavy metal element oxide, and the innermost layer is Al2O3 layer. With the increase of Mo content, the oxide layer accumulates more growth stress, resulting in more severe spallation. At 900 °C, the oxide layer can be divided into three layers, the outermost layer is Ni–Co oxide, the intermediate layer is Cr–Al oxide, and the innermost layer has obvious selective oxidation of Al element. The volatilization of oxide promotes the diffusion of O into the matrix, thus promoting the oxidation of heavy metal elements in the matrix. With the increase of Mo content, this phenomenon is more obvious. The results show that the increase of Mo content of alloy promotes the oxidation of Mo, W and Re elements, which let the volatilization of the oxide and the spalling of the oxide layer more severe, thus decreasing the oxidation resistance of the alloy.

Investigation on failure mechanism and interfacial diffusion behavior of NiCoCrAlYTa coating at high temperature

The isothermal oxidation behavior of NiCoCrAlYTa coating deposited by arc ion plating (AIP) technology on DZ22B substrate was systematically investigated at 1050 ℃ and 1100 ℃ for 200 h. The results revealed a transition in oxide scale composition, which of undulation degree was also increased. The growth process of oxide scale involved additional control mechanisms except internal diffusion of oxygen. Interdiffusion at coating/substrate interface transformed γ into γ' phase in substrate, precipitating MC carbides. MC carbide underwent progressive disintegration, transforming into M6C carbide. The results could provide experimental data and theoretical support for the design of long-life protective coatings at ultra-high temperatures.

Multi-component-doped NiCoCrAlYNbHfTa coating with enhanced oxidation resistance produced by HVAF spraying technology

To enhance the oxidation resistance of the coatings, a multi-component-doped NiCoCrAlYNbHfTa coating was prepared on an IN718 substrate by HVAF spraying technology. The impact of multi-component doping on the phases, microstructure characteristics, and isothermal oxidation behavior of the coatings was investigated. The experimental results showed that a dense and uniform coating was obtained under optimized spray coating parameters. The microstructure of the NiCoCrAlYNbHfTa coating differed from that of the commercial NiCoCrAlY coating in terms of the amount of γ’ and partial β phases. The NiCoCrAlYNbHfTa coating consisted of a significant amount of β solid solution and a certain quantity of γ’ intermetallic compounds, which improved the oxidation resistance and mechanical performance. The NiCoCrAlYNbHfTa coating demonstrated an excellent oxidation resistance with an oxidation rate of 3.8 × 10−14 cm2/s at 1000 °C, which was attributed to more β-phase solid solution, increased refractory metal oxides, and large-sized equiaxed grains in the oxide layer.

Cyclic and Isothermal Oxidation Behavior of a Directionally Solidified Ni-Al-Ti-Co-Cr Superalloy

Nickel based superalloys are widely used in such applications as gas turbine blades due to their excellent mechanical properties at elevated temperatures. Oxidation is one of the life limiting factors at such temperatures since it accelerates failure mechanisms, e.g. fatigue and creep. In this project, oxidation behavior of Ni-3Al-4.8Ti-9.5Co-14Cr (wt.%) superalloy was investigated under various testing conditions. The alloy was investment-cast with preferential crystal growth direction [100]. Isothermal oxidation tests were carried out at 800°C for 150h. Cyclic oxidation tests were then conducted between 100-800°C for 150 one-hour cycles. An additional one-hour cycle was tested to replicate real-life working condition of the alloy, which consisted of heating the samples up to 800°C followed by slow cooling to 400°C. During the testing, samples were periodically taken from the furnace and weighted with an accuracy of 10-4 g to calculate the weight gain and to analyze the microstructure of formed oxide. Scanning electron microscopy (SEM) combined with energy-dispersive spectroscopy (EDS) and X-ray diffraction were used to study the microstructure of oxidation products. The results reveal that the highest amount of weight gain is obtained in isothermal testing, while the lowest in cyclic. Diffusion of Ti and Ni to the free surface results in the early-stage formation of needle-shaped oxide phases followed by severe oxidation of Cr and Al. The layer of chromium oxide is continuous while aluminum oxide is blocky at the deepest position from the free surface. Cracks form at the interface of carbide particles and gamma phase near the free surface of cyclic oxidation samples due to concentration gradient of Ni and Al. Precipitate-free zone are observed near the free surface of all the samples at the end of the tests, but internal oxidation does not occur significantly in all the samples. It is found that temperature fluctuation increases oxide spallation, which causes crack formation. At the same time, in isothermal testing, dense, crack-free layer of oxide form on the surface of superalloy.

Oxidation behaviour of Zr added hypereutectic Nb-19Si-5Mo-20Ti alloy

The influence of Zr (3 at%) addition on non-isothermal and isothermal oxidation behaviour of the Nb-19Si-5Mo-20Ti (base alloy) has been investigated. During heating in a thermogravimetric analyser to 1300 °C in air, the mass-gain begins at ∼600 °C, and shows a more gradual rise as well as a lower peak value for the Zr-containing alloy compared to the base alloy. Furthermore, the Zr-containing alloy exhibits superior oxidation resistance in isothermal test for 24 h at 1100 °C, but not at 900 °C and 1200 °C, probably due to the differences in oxide scale growth kinetics and defect density. The oxidation products have been identified as Nb2O5, SiO2, TiO2, MoO2, TiNb2O7, Ti2Nb10O29 for both the alloys, with ZrO2 being additionally observed in the Zr-containing alloy. Analysis of the isothermal oxidation kinetics suggests an initial stage of interface-reaction controlled rapid mass increase followed by parabolic behaviour, where oxygen diffusion through the oxide scale is apparently rate-controlling. Slow down to parabolic kinetics is ascribed to the formation of a SiO2-rich compact oxide scale. The oxide scale becomes protective due to reduced oxygen anion diffusivity in Nb2O5 having Mo, Ti and Zr as substitutional solute, along with the formation of ZrO2 and TiO2 with Pilling-Bedworth ratio less than 2.

Optimizing isothermal oxidation behavior of the Y-containing Nb-Ti-Si based alloy: The role of precursor Y2O3

The effect of Y2O3 on the oxidation resistance of Nb-Ti-Si based alloys was investigated. Acicular Y2O3 is generated with Y content exceeding 0.3 at%. Oxidation tests reveal that the mass gain per unit area of the Y-containing alloys is lower than that of the Y-free alloy at 800 °C and 1200 °C. The oxide layer of the Y-free alloy will fracture and even pesting. After adding Y, the Y2O3 can react with Nb2O5 and TiO2 to generate YNbTiO6. The pinned YNbTiO6 at the interface enhances the adhesion between the oxide layer and substrate, slowing down the growth of the oxide layer.

Investigations of oxidation behavior and establishment of life-cycle model during the steam oxidation of Cr-coated Zry-4 at 1200 °C

The isothermal steam oxidation behaviors of Cr-coated and non-coated Zry-4 cladding at 1200 °C have been investigated systematically. The oxidation of Cr coating is divided into three stages based on the different oxidation kinetics. First is protective stage where a thick Cr2O3 layer is gradually formed on the outer surface. Second is transition stage where the coating failure occurs because ZrO2 short circuit paths accelerates the reduction of Cr2O3. The O2- of Cr2O3 is transferred inward and dissolves in the substrate as α-Zr(O). The last is the non-protective stage where the Cr coating is oxidized again and substrate is oxidized as well. The oxidation of substrate presents three periods based on the different oxidation rate, which are accelerated period, normal period and abnormal period. Intermetallic precipitates derived from inward-diffusion of Cr make the oxidation kinetics be logarithmic law in the abnormal period by restraining the oxygen diffusion and t-ZrO2 → m-ZrO2 transformation. In this study, we find that the Cr coatings has important effect in restraining Zry-4 oxidation even after Cr has been completely consumed.

Isothermal oxidation behavior of W-based alloy coatings doped with Ta, Cr, Ti, V

Tungsten-based multi-alloy coatings with the addition of Ta, Cr, Ti, and V were prepared by double glow plasma surface alloying (DGPSA) technology. The alloyed specimens showed bulges and pits on the surface with an island growth mechanism. The coating exhibits a single BCC phase. The hardness shows an increasing trend with the increase of alloyed elements. The maximum hardness value of WTaCrTiV is 1748 HV100g. The oxidation behavior of coatings at 800 °C was investigated, with emphasis on the effect of elemental doping on the antioxidant properties. With the addition of Ta, Cr, Ti, and V elements, the antioxidant properties of multi-alloy coatings were effectively improved compared the tungsten matrix. The WTaCrTi coating shows the optimum antioxidant properties with a dense Cr2O3 layer. As the number of elements in multi-alloy increases, the mixing entropy increases, leading to a decrease in the Gibbs free energy, which results in a more stable alloy.