Isothermal Oxidation Behavior Research Articles

Characterization of the High Temperature Isothermal Oxidation Behaviour of an ATI425® Titanium Alloy

Characterization of the High Temperature Isothermal Oxidation Behaviour of an ATI425® Titanium Alloy

Long-term isothermal oxidation behavior of two industrial polycrystalline nickel base alloys in air at 700 °C – Evaluation of intergranular oxidation distribution and kinetic

Chromia forming Alloy 718 and AD730™ have been submitted to isothermal long-term air exposure up to 10 000 h at 700 °C. The resulting very low specific mass gain led to consider two alternatives to determine the oxidation kinetics. Measurements of the external layer thickness and of the intergranular oxide amount were carried out on SEM micrographs evidencing the intergranular oxidation contribute around 30% to the total specific mass change. AD730™ with a thicker external scale and a higher amount of intergranular oxide showed a twofold faster oxidation rate than Alloy718. The results demonstrated the need of even longer tests.

Oxidation behaviour of NiCoCrAlYHfZr coating on a fourth generation single crystal superalloy

The NiCoCrAlY coating and NiCoCrAlYHfZr coating were prepared on a fourth generation single crystal superalloy by arc ion plating. The cyclic and isothermal oxidation behaviours of the two coatings were both investigated in static laboratory air. Numerous large voids were formed in the oxide scale of NiCoCrAlY coating and they were responsible for the scale spallation. While the NiCoCrAlYHfZr coating showed better oxidation performance due to the enhanced scale adhesion. The advantage of Hf and Zr addition in the coating were discussed as well as the mutual diffusion behaviour between the coating and the substrate.

The Influence of Surface Shot Peening on the Isothermal Oxidation Behavior of NiCrAlYSi Coating

The Influence of Surface Shot Peening on the Isothermal Oxidation Behavior of NiCrAlYSi Coating

Laser re-melting influence on isothermal oxidation behavior of electric current assisted sintered CoCrFeNi, CoCrFeNiAl0.5 and CoCrFeNiTi0.5Al0.5 high entropy alloys

In this study, it was aimed to determine the effect of laser re-melting on the oxidation behavior of high entropy alloys produced with electric current assisted sintering (ECAS). CoCrFeNi, CoCrFeNiAl0.5 and CoCrFeNiAl0.5Ti0.5 high entropy alloys (HEAs) were produced using ECAS. After the production of HEAs, the laser re-melting (LR) process was applied to the surface of sintered samples. Then, isothermal oxidation tests were carried out to HEAs at 1000 °C for 5, 25 and 75 h. Before and after the oxidation tests, the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) mapping analysis. The obtained results show that the LR process significantly improved the microstructural properties of ECAS-HEAs. More homogeneous microstructure, lower porosity and single-phase formations were observed in HEAs after LR. This has enabled a more stable microstructure compared to ECAS samples. After the oxidation tests, lower oxide layer thickness, lower oxide growth rates and lower inner oxide formation were obtained in laser re-melted HEAs. The presence of Al-rich phases enables the formation of alumina layer on the surface of HEAs. The best oxidation performance was obtained with laser re-melted CoCrFeNiAl0.5.

High-Temperature Oxidation Behavior of a Cu-Bearing 17Cr Ferritic Stainless Steel.

The isothermal oxidation behavior of 17Cr-0.85Si-0.5Nb-1.2Cu ferritic stainless steel in air was studied from 850°C to 1050°C by analyzing its weight gain after oxidation. The kinetic curves were plotted using the oxidation weight-gain data, and the structure, surface morphology, and element distribution of the oxide films were analyzed by XRD, SEM, and EDS. The results showed that the oxidation kinetics curves at 850°C and 950°C followed a parabolic law, and a continuous and dense oxide film composed of Cr2O3 and MnCr2O4, FeCr2O4, and Cu-Cr rich spinel was formed, which reveals that the steel displayed good oxidation resistance. When the temperature was increased to 1050°C, the oxidation kinetics curves gradually changed from parabolic to linear after 40 h exposure, which indicated that the oxidation resistance significantly worsened. A lower oxidation resistance was observed at 1050°C due to the formation of a large amount of Fe2O3 on the surface and the volatilization of the inner Cr2O3 layer.

Oxidation behavior of ultrafine WC-based cemented carbides with AlxCoCrCuFeNi high-entropy alloy binders

The isothermal oxidation behavior of WC-based cemented carbides with AlxCoCrCuFeNi (x = 0, 0.5, 1.0, 1.5) high-entropy alloy (HEA) binders at 600–800 °C in air was studied by a thermogravimetric method, as well as WC-Co for comparison. The oxidation of the WC-HEA cemented carbides accompanies swelling and follows a linear law that is controlled by reaction at the oxide layer/matrix interface. The WC-HEA cemented carbides show better oxidation resistance than WC-Co, even though WC-Co has a denser microstructure and coarser WC grain size. With increase of Al content in the HEA binder, the oxidation rate of WC-HEA decreases, and the specific mass gains of the samples with HEA binder containing Al are at least 20% smaller than that of WC-Co after isothermal oxidation at 800 °C for 2 h. Moreover, as the HEA content increases from 5 to 20 wt%, the specific mass gain reduces from 61.89 to 24.55 mg/cm2. Selective oxidation of the HEA binder occurs, and the excellent anti-oxidation property of the HEA binder impedes inward diffusion of oxygen to the oxide layer/matrix interface, which suppresses oxidation of the matrix and enhances oxidation resistance of the WC-HEA. The results also indicate that the improved oxidation resistance of the WC-HEA system should not be attributed mainly to the formation of a dense oxide layer with high tungstate content during oxidation.

Isothermal and Cyclic Oxidation Behavior of HVOF-Sprayed NiCoCrAlY Coatings: Comparative Investigations on the Conventional and Nanostructured Coatings

Conventional and nanostructured NiCoCrAlY coatings were deposited using the high-velocity oxy-fuel thermal spraying technique. The nanostructured NiCoCrAlY powder feedstock for the coatings was produced by the ball-milling method. The microstructures of the as-received and nanostructured powders as well as their developed coatings were investigated by x-ray diffraction, a field-emission scanning electron microscope equipped with energy-dispersive x-ray spectroscopy, and a transmission electron microscope. Williamson–Hall measurements were also carried out to estimate the crystalline size of the powders and coatings. For the evaluation of the oxidation kinetics, the free-standing coating specimens were subjected to short- and long-term isothermal and cyclic oxidation at 1000 and 1100 °C, respectively, under a laboratory air atmosphere. The results indicated that the as-received NiCoCrAlY coating had parabolic oxidation behavior in short- and long-term exposure tests. For the nanostructured NiCoCrAlY coating, in contrast, the long-term oxidation kinetics deviated from parabolic behavior and showed instead sub-parabolic rate behavior. The obtained results also revealed that the nanostructured NiCoCrAlY coating had greater oxidation resistance to both isothermal and cyclic conditions on account of the formation of a dense and slow-growing Al2O3 layer on the coating surface.

Isothermal oxidation behavior of micro-regions in multiphase Ni3Al-based superalloys

The isothermal oxidation behavior of micro-regions in multiphase Ni3Al-based superalloys (high Fe and Cr contents) was investigated at 600 °C in air. The oxide scale is mainly composed of the outer mixed oxide layer (NiO, NiFe2O4 and Al2O3) and the inner single Al2O3 layer. In particular, Cr2O3 is formed in the outer oxide scale of γ' + γ dendrite with enrichment in Cr element. The relative dense continuous Al2O3 layer is formed in the interdendritic region (β phase with high Al content). In addition, γ' envelope (connecting the γ' + γ dendrite and interdendritic β phase) shows preferential oxidation featuring significant cellular bulge (NiO and NiFe2O4 mixed oxides).

Preparation and antioxidant mechanism of TiSi2–Si–SiC/SiC bilayer coating on matrix graphite

A two-step pack cementation technique was applied to synthesize the TiSi2–Si–SiC/SiC bilayer coating on the surface of graphite spheres for improving its antioxidant performance. Then, an investigation was conducted into the microstructure, phase composition, formation mechanism, and the isothermal oxidation behavior in static air of the coating. According to the research results, the coating consists of an internal SiC layer and an external TiSi2–Si–SiC layer. In the external layer, the gap between SiC particles filled with Si phase ensures the sufficient compactness of the as-prepared coating, while the small TiSi2 particles are embedded in SiC particles. In the oxidizing environment, TiSi2 is preferentially oxidized to reduce the consumption of SiC, thus ensuring the stability of the coating. The structure of the external layer is capable to ensure the excellent antioxidant performance of the coating. After being oxidized in static air at 1500 °C for 200 h, the weight gain of the coated graphite sphere reached merely 0.96 w.t.% and the thickness of the oxide layer was approximately 20 μm.

Oxidation behaviour and related microstructural changes of two β0–phase containing TiAl alloys between 600 °C and 900 °C

A comparative study on the isothermal oxidation behaviour of the two β0–containing titanium aluminide alloys GE 4822 and TNM-B1 in the HIPed condition has been conducted at temperatures between 600 °C and 900 °C for up to 1000 h in air. The two alloys exhibit clear differences in their oxidation behaviour, however, both suffer from undesirable embrittlement due to oxidation after exposure for 100 h even at 600 °C. Phase transformations in the subsurface zone were shown to have a strong impact on the mechanical properties at room temperature.

Microstructural evolution during exposure in air and oxidation behavior of a nickel-based superalloy

Microstructural evolution and isothermal oxidation behavior of a cast Ni-based superalloy have been investigated at 800 °C, 900 °C and 1000 °C in air. Results show that the oxidation kinetics of the Ni-based superalloy follows parabolic law at elevated temperatures. Oxide scales after oxidation can be divided into external layer, continuous Cr2O3 layer linked with internal TiO2, discontinuous Al2O3 layer and γ′-depletion zone. Due to the segregation of alloying elements, densely granular zone and porous zone are formed at 800 °C. External oxide layer is a mixed oxides zone, which mainly consists of TiO2 and Cr2O3 at 800 °C and 900 °C, NiO and NiCr2O4 at 1000 °C. The formation condition of NiO and NiCr2O4 is mainly after 50 h oxidized at 1000 °C. Thickness growth rate of Cr2O3 and Al2O3 layers decrease gradually during oxidation process, indicating that external oxides can effectively prevent the inward diffusion of oxygen. The oxidation activation energy of the experimental Ni-based superalloy is confirmed to be 205.3 kJ mol−1 and the oxidation process is controlled by diffusion of oxygen, Ti and Cr ions.

Isothermal Oxidation Behavior of Fe-33Ni-18Cr Alloy in Different Heat Treatment Temperature

This research study describes the influence of different heat treatment temperature on isothermal oxidation of Fe-33Ni-18Cr alloy. The Fe-33Ni-18Cr alloy was undergone heat treatment at three different temperatures, namely 1000 °C, 1100 °C and 1200 °C for 3h soaking time followed by water quench to vary the grain size of the alloy. This alloy was ground by using several grit of silicon carbide papers as well as weighed by using analytical balance and measured by using Vernier caliper before oxidation test. The heat-treated Fe-33Ni-18Cr alloy was isothermally oxidized at 800 °C for 150h. The characterization of oxidized samples was carried out using optical microscope, scanning electron microscope equipped with energy dispersive x-ray (SEM-EDX) and x-ray diffraction (XRD). The results showed that, increasing the heat treatment temperature was increased the average grain size. The kinetics of oxidation followed the parabolic rate law which represents diffusion-controlled oxide growth rate. Fine grain structure of 1000 °C sample shows minimum weight gain and lower oxidation rate compared to samples of 1100 °C and 1200 °C that indicated oxide spallation and porous structure. Besides, phase analysis showed that the oxidized sample formed several oxide phases.

ISOTHERMAL OXIDATION BEHAVIOR AND THERMAL SHOCK RESISTANCE OF THREE-KIND Cr COATINGS ON PCrNi3MoVA STEEL

Isothermal oxidation behavior at 900 °C for 5 h and thermal shock resistance at 900 °C of three-kind Cr coatings prepared by electroplating, magnetron sputtering and multi arc ion plating technologies on PCrNi3MoVA steel were investigated. Micromorphologies of three-kind Cr coatings before and after tests were observed by the scanning electron microscopy and crystallization phase identification was studied by the X-ray diffraction. Oxidation of three-kind Cr coatings showed characteristic morphologies of electroplating Cr coating with microcrack, magnetron sputtering Cr coating with columnar crystal and multi arc ion plating Cr coating with microdroplet during coating preparation were main reasons for different properties. Correspondingly, the failure mechanisms of delamination, through spalling caused by through cracks and through spalling caused by surface spalling of droplet were obtained by thermal shock test. The results indicate that multi arc ion plating, for its property of high temperature resistance, could be a more effective approach to prolong gun barrel life.

An investigation of oxidation, hot corrosion, and thermal shock behavior of atmospheric plasma-sprayed YSZ–Al2O3 composite thermal barrier coatings

Abstract In the current study, different types of thermal barrier coatings with various mass fractions were investigated in terms of oxidation, hot corrosion, and thermal shock resistance. The thermal barrier coatings consisted of six different samples, which included the usual YSZ, Al2O3, hybrid composites with 65 wt.% YSZ and 35 wt.% Al2O3, 50 wt.% YSZ and 50 wt.% Al2O3, 35 wt.% YSZ and 65 wt.% Al2O3 and the final one, which was a double layer composite (Al2O3 and YSZ). High temperature isothermal oxidation behavior of the coatings was tested at 1050 °C, using an air furnace for 48 h, 80 h, and 120 h respectively. Hot corrosion tests were applied at 1050 °C using a 45 wt.% Na2SO4 and 55 wt.% V2O5 mixture of salts. The microstructure and phase stability of coatings were evaluated by means of scanning electron microscopy and X-ray diffraction techniques. The usual YSZ showed better hot corrosion and thermal shock resistance, while Al2O3 showed the lowest hot corrosion and oxidation resistance. Thermally grown oxide formation, thermal expansion coefficient mismatch and phase transformation in the thermal barrier coatings could be the main causes of degradation after thermal shock testing.

Effect of substrate temperature on the oxidation behaviour of NiCrAlY coating

ABSTRACT NiCrAlY coating was deposited on the IN-738LC Ni-based superalloy by cathodic arc deposition at the substrate temperatures of 400°C and 700°C. The effects of the substrate temperature on the microstructure and the isothermal oxidation behaviour of the coatings were then investigated. SEM image and XRD analysis were used to characterize the deposited coatings. It was found that when the substrate temperature was raised from 400°C to 700°C, the degree of coating crystallinity was increased from 23% to 58%. After the 20-hr oxidation at 1000°C in air, the γ′-depletion layer was formed in the substrate. The growth rate constants of the γ′-depletion layer after the 100-hr oxidation were 1.310−4 μm (sb)−1 and 6.410−5 μm (sb)−1 for the deposited coatings at 400°C and 700°C, respectively. The results, therefore, indicated that with increasing the substrate temperature from 400°C to 700°C, the oxidation resistance was improved.

The role of Re in effecting isothermal oxidation behavior of β-(Ni,Pt)Al coating on a Ni-based single crystal superalloy

Two β-(Ni,Pt)Al coatings with or without Re doping and a PtAl diffusion coating were prepared on a single crystal Ni-based superalloy. Isothermal oxidation behavior of all the coatings was investigated at 1100 ℃ for 300 h. The Re doped β-(Ni,Pt)Al coating possessed the best isothermal oxidation resistance because Re reduced the oxidation rate and extent of β to γ′ phase degeneration. The oxidation mechanism of the PtAl diffusion coating and advantageous roles of Re on the effect of the morphologies, anti-spallation and rumpling behavior of thermally grown oxide (TGO) were discussed as well.

Effect of boron on isothermal oxidation behavior of a nickel-base superalloy with high Al and Ti contents

The influence of boron on the oxidation resistance of conventionally cast U720Li alloy was investigated at 1130 °C and analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDX) and electron probe microanalysis (EPMA). It has been found that the boron-undoped and -doped alloys all obey a super-parabolic rate law, but the oxidation rate is obviously increased by the boron addition. These alloys all show non-uniform oxidation between dendritic and interdendritic areas due to the serious microsegregation, while the oxide scale morphology of the high-boron alloy is quite different from that of the boron-undoped alloy. For boron-doped alloys, in the initial stage of oxidation the outward diffusion of boron from borides formed in the interdendritic region results in the formation of discontinuous and non-uniform B-rich oxide layers beneath and inside the Cr2O3 layer, while as the oxidation proceeds further boron can also transfer from the B-rich oxide to outer layers which eventually leads to disappearance of the B-rich oxide layers. The formation of B-rich oxide layers destroys the continuity of Cr2O3 layer and decomposition of B-rich oxide layers makes Cr2O3 layer more porous, which significantly reduce the protective property of the Cr2O3 layer and in turn decrease the oxidation resistance. Moreover, the eutectic (γ + γ′) highly enriched in Ti, Al is prone to be oxidized and form a thicker scale than the other regions, and hence the significant increase of its precipitation with boron addition also contributes to increasing the oxidation rate.

Laser Metal Deposition of an AlCoCrFeNiTi0.5 High-Entropy Alloy Coating on a Ti6Al4V Substrate: Microstructure and Oxidation Behavior

Ti6Al4V has been recognized as an attractive material, due to its combination of low density and favorable mechanical properties. However, its insufficient oxidation resistance has limited the high-temperature application. In this work, an AlCoCrFeNiTi0.5 high-entropy alloy (HEA) coating was fabricated on a Ti6Al4V substrate using laser metal deposition (LMD). The microstructure and isothermal oxidation behaviors were investigated. The microstructure of as-deposited HEA exhibited a Fe, Cr-rich A2 phase and an Al, Ni, Ti-enriched B2 phase. Its hardness was approximately 2.1 times higher than that of the substrate. The oxidation testing at 700 °C and 800 °C suggested that the HEA coating has better oxidation resistance than the Ti6Al4V substrate. The oxide scales of the Ti6Al4V substrate were mainly composed of TiO2, while continuous Al2O3 and Cr2O3 were formed in the HEA coatings and could be attributed to oxidation resistance improvement. This work provides an approach to mitigate the oxidation resistance of Ti6Al4V and explore the applicability of the HEA in a high-temperature environment.

Preparation and oxidation behavior of Cf/C–TaC composites

Cf/C–TaC composites, which possesses excellent anti-ablation properties, are potential candidate materials for applications in the extreme environments associated with hypersonic flight and rocket propulsion. In this paper, Cf/C–TaC0.89 composites were prepared by chemical vapor infiltration to achieve a TaC matrix with a C/Ta atomic ratio of 0.89. The isothermal oxidation behavior of the composites at 1200–1600 °C was investigated, and the minimum time for the self-healing of microcracks on the composite surface was calculated based on the oxidation process obeying either a parabolic or a linear law. The results indicate that the oxidation process is controlled by surface kinetics in the initial 0–10 min at 1200–1400 °C and 0~5 min at 1500–1600 °C even if a dense oxide layer is formed. After that, the controlling mechanism becomes the diffusion of oxidative gases in a TaCxOy layer, a diffusion barrier layer existed in the oxidation of refractory carbides. The formation of the TaCxOy layer is attributed to the low C/TaC ratio of the TaC0.89 phase and the diffusion behavior of O atoms in Ta octahedral interstitial sites.