High Temperature Oxidation Behavior Research Articles

Effects of Mo and Nb on the microstructure and high temperature oxidation behaviors of CoCrFeNi-based high entropy alloys

A series of CoCrFeNi(Mo, Nb) high entropy alloys (HEAs) were prepared using vacuum arc-melting. The effect of Nb and Mo on the microstructure and high temperature anti-oxidation properties of HEAs was investigated. The addition of only Mo was found to not cause formation of new phase, but did increase the lattice distortion. After the addition of Nb, as-prepared CoCrFeNiMo0.2Nb0.1 and CoCrFeNiMo0.2Nb0.2 alloys are characteristic of duplex-phase structures of FCC and Laves, in which the Laves phase is semi-coherent with FCC matrix. Our studies also revealed that the oxidation kinetics of the alloys followed parabolic rate law and the corresponding oxidation rate constants were calculated. Due to the synergistic effects of Mo and Nb, the anti-oxidation properties of HEAs improved significantly. It was also discovered that the new Laves phase containing Mo and Nb at the inner oxidation layer hindered the outward diffusion of active metal cations, ergo improving the oxidation resistance of HEAs. With increase of Nb content, it was further recognized that the layered structure of Laves phase was thinner and denser. Therefore, the oxygen ion diffusion process in the CoCrFeNiMo0.2Nb0.2 alloy can be inhibited effectively by the new formation of duplex-phase structures with undulated Laves phase and FCC matrix.

The Impact of Various Superalloys on the Oxidation Performance of Nanocrystalline Coatings at High Temperatures

Nanocrystalline coatings with the same chemical composition as an N5 superalloy were prepared on K38 and N5 superalloys by magnetron sputtering. The effect of different superalloys on the high temperature oxidation behavior of nanocrystalline coatings was investigated through oxidation kinetics, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and wavelength dispersive spectrometry (WDS). The results indicated that K38-N5 had better oxidation resistance than N5-N5 due to the diffusion of Zr from the K38 superalloy into the oxide scale. In addition, no interdiffusion occurred in the K38 superalloy. The formation of Ta-rich phases in the Al2O3 scale leads to decrease the oxidation resistance of nanocrystalline coatings. However, the presence of Zr inhibits the formation of Ta-rich phases.

Insights into the role of W/B alloying on high-temperature oxidation behavior of Ti42Al5Mn alloy

In this study, the oxidation behavior of Ti42Al5Mn, Ti42Al5Mn0.5 W, Ti42Al5Mn0.5W0.1B, and Ti42Al5Mn0.8 W was investigated at 800 °C. Due to the inability to form a dense protective Al2O3 layer, Ti42Al5Mn suffered severe spallation during oxidation at 800 °C and the mass gain was significant. The intermediate layer between the scale and the substrate was first composed of Laves/Z phase but changed to α2/Z phase with prolonged oxidation. The intermediate layer with high Ti/Al ratio favors the formation of a thick Al2O3 + TiO2 mixed layer in the oxide scale which is prone to initiate cracks and cause the spalling of oxides. The doping of W in TiO2 effectively inhibited its generation and promoted the formation of a dense Al2O3 layer, resulting in a significant improvement in the oxidation resistance of the alloy. Compared to Ti42Al5Mn alloy, Ti42Al5Mn0.8 W showed no spallation after 300 h cyclic oxidation and the kinetic curve changed from liner law to parabolic law. The intermediate layer of Ti42Al5Mn0.8 W alloy was composed of a single Laves phase and remained unchanged even after 1000 h oxidation at 800 ℃, offering a favorable basis for the generation of a stable protective oxide layer in the alloy. The addition of 0.1 at.% B to Ti42Al5Mn0.5 W alloy refined its microstructure and further improved its spallation resistance to a level close to that of Ti42Al5Mn0.8 W alloy.

High-temperature oxidation behavior of a single-crystal high-entropy superalloy strengthened by dense intermetallic nanoparticles

High-temperature oxidation behavior of a single-crystal high-entropy superalloy strengthened by dense intermetallic nanoparticles

Heat Treatment Induced Structural Transformations and High-Temperature Oxidation Behavior of Al21Co22Cr22Fe13Ni22 High-Entropy Coatings Produced by Non-Vacuum Electron Beam Cladding

In this study, Al21Co22Cr22Fe13Ni22 high-entropy coatings were produced on steel substrates by non-vacuum electron beam cladding of Co, Cr, and NiAl powders. The high-temperature oxidation behavior of the coatings was studied by holding the specimens at 900 °C in air. The microstructure and phase constitution of the samples were studied both in the as-cladded state and after the heat treatment. The microstructure was characterized using light microscopy (LM) and scanning electron microscopy (SEM). Synchrotron X-ray diffraction (SXRD) and energy-dispersive X-ray spectroscopy (EDX) were used to study the phase constitution of the coatings and the “coating-substrate” interface. The coating consisted of disordered bcc (A2), ordered bcc (B2), and disordered fcc (A1) phases. Annealing the coatings for 50 h at 900 °C led to the formation of fcc precipitates in the bcc dendritic grains and a mixture of fcc and σ-phase particles in the interdendritic regions. Needle-like nanosized B2-precipitates were formed due to annealing in the fcc grains at the coating/substrate interface. The microhardness at the top of the as-cladded coating was 585 HV and gradually decreased towards the substrate. A more uniform distribution of the microhardness was obtained after the annealing. Its average value was 441 HV. Rhomboid Cr2O3, needle-like Al2O3, and spinels of a different morphology were found on the surface of the samples after oxidation at 900 °C.

High temperature oxidation behaviour of polycrystalline and single crystal Ta stabilized γ'-strengthened Co-Ni-Al-Ta-Cr alloys

Isothermal oxidation was carried out on the polycrystalline and single crystal γ'-strengthened Co-Ni-Al-Ta-Cr alloys at 800–1000 ℃. The oxidation kinetic of both alloys follows logarithmic, cubic and parabolic law at 800 ℃, 900 ℃ and 1000 ℃, respectively. The polycrystalline alloy exhibits superior oxidation resistance at 800–1000 ℃, which can be explained by the effects of grain boundary. Grain boundary diffusion enhances the formation of the protective spinel oxides layer at 800–900 ℃. The beneficial effect of the grain boundary on the spallation resistance of oxides results that the polycrystalline alloy maintains better oxidation properties at 1000 ℃.

A Comparative Study on High-Temperature Oxidation Behavior, Microstructure Characterization, and Texture of UNS R30155 Superalloy Weldment Joint Using Pulsed Current and Constant Current Gas Tungsten Arc Welding

A Comparative Study on High-Temperature Oxidation Behavior, Microstructure Characterization, and Texture of UNS R30155 Superalloy Weldment Joint Using Pulsed Current and Constant Current Gas Tungsten Arc Welding

Oxidation behavior of CoCr2−xFeNi2.1Nbx high entropy alloys

High entropy alloys (HEAs) are one of the prominent alloy systems being studied for high-temperature applications. One of the key aspects to consider for high-temperature applications is to understand their oxidation behavior. When Nb is added as the alloying element to base FCC alloy like CoCrFeNi it promotes the formation of dual phase HEA. In the present study, the high-temperature oxidation behavior of annealed CoCr2−xFeNi2.1Nbx (x = 0.25, 0.5 and 1) isothermally at 800 °C in the air is studied. As-homogenized microstructure of these alloys shows a dual phase containing FCC and Laves phase. The amount of Laves phase increases with increasing Nb content. The oxidation kinetics of the three compositions follows parabolic kinetics at 800 °C. The characterization (XRD, Raman, SEM) of the oxide layer reveals the formation of Cr2O3 as the main oxide layer. The cross-sectional SEM images of the oxide samples after 96 h of oxidation confirms absence of internal oxidation and a thin Laves-rich region below the Cr2O3 layer. The preferential formation of Cr2O3 over Nb oxides is explained using the assessment of their thermodynamic activity in the FCC phase.

Effect of aging and α’ segregation on oxidation and electrochemical behavior of FeCrAl alloys

FeCrAl alloys are promising candidates for next generation nuclear fuel cladding applications due to their high resistance to hydrothermal corrosion, high temperature steam oxidation, fretting, and creep properties. However, a potential area of concern for FeCrAl alloys is the precipitation of Cr-enriched α’ phase which could have an implication on the mechanical, oxidative degradation as well as electrochemical behavior. Studies in this area are limited since most of the past applications of FeCrAl alloys have been in high temperatures above the miscibility gap. In this work, we investigate the high temperature oxidation and electrochemical behavior of a modified APMT (Fe21Cr5Al3Mo) alloy in unaged condition in comparison with a thermally aged condition having α’ phase segregation. The α’ is shown to have no major role in steam oxidation resistance of FeCrAl alloys. The electrochemical behavior in chloride environments shows that the presence of α’ slightly reduces the pitting potential but shows an overall increase in polarization resistance indicating that α’ may enhance corrosion resistance in chloride environments by increasing passivation.

High-temperature oxidation behaviors of dense TMC (TM= Ta, Nb, Ti and Zr) ceramics in air

This study investigated the high-temperature oxidation behaviors of TMC ceramics. The results indicate that the high-temperature oxidation curves of the four TMC ceramics follow a parabolic law, suggesting a diffusion-controlled process. The activation energies for the oxidation of TaC, NbC, TiC, and ZrC ceramics are 105.4, 124.3, 169.3, and 78.7 kJ/mol, respectively, with oxidation rate constants at 1000 °C of 16.84, 40.45, 0.18, and 14.43 mg2/cm4·h for each ceramic, respectively. The temperatures at which the ceramics disintegrate into fragments in high-temperature air are 800, 800, >1000, and 600 °C, respectively. The anti-oxidation performance of the four TMC ceramics ranks as follows: TiC > TaC > NbC > ZrC. In comparison to the reported high-entropy carbide ceramics, the TiC ceramic in this study demonstrates superior anti-oxidation performance due to dense TiO2 layer formation, characterized by significantly low oxidation rates and excellent structural stability.

MICROSTRUCTURE AND OXIDATION BEHAVIOR OF THE OXIDE DISPERSION STRENGTHENED STAINLESS STEEL 316L WITH ZIRCONIA DISPERSION

Synthesis of the oxide dispersion sODS steels was performed by dispersing 0.5 wt % zirconia to the stainless steel SS 316L by the powder metallurgy method. The ball milling process was carried out for pre-alloying the elements continued with the consolidation performed by the compaction and sintering process using the APS (Arc Plasma Sintering). Analysis of microstructure was performed by observing the morphology, identify the phase and evaluate the oxide distribution. An oxidation test was carried out at 700oC for 8 hours using the MSB (Magnetic Suspension Balanced) apparatus to evaluate the primary oxidation curve. The same grain fineness consists of 2 dominant phases, so the presence of an austenitic phase and a ferritic phase has been analyzed from the X-Ray Diffraction pattern. The homogeneous distribution of zirconia was observed, followed by improvements in mechanical properties, which could be identified by hardness testing. The parabolic phenomenon oxidation curve was explained by the excellent high-temperature oxidation behaviour of the ODS steel, followed by the formation of ZrO2 oxide protective thin layer.

Advancements in Nickel-Phosphate/Boron Based Electroless Composite Coatings: A Comprehensive Review of Mechanical Properties and Recent Developments.

Nickel-Phosphate/Boron (Ni-P/B) electroless coatings have been widely used to improve physical and mechanical properties in various industrial applications, including the automotive, aerospace, chemical processing, food, oil and gas, electronic, textile, and printing industries. Electroless nickel coatings are one of the most popular surface-coating methods due to their low cost and short processing time. The purpose of this review is to look at several coating materials and the existing processes for making electroless coatings on different materials. The improvement of Ni-P/B composite coatings by the incorporation of secondary particles into an alloy matrix at the macro, micro, and nano levels is explained in detail. Process parameters like type of surfactant, annealing temperature, size of the reinforcement material, and reducing-agent percentage on mechanical characteristics like hardness, high-temperature oxidation behaviour, friction, coefficient, wear, and corrosion have been broadly researched and illustrated clearly.

Improved oxidation resistance of Cr/FeCrAl coating on Zr alloy in high-temperature steam environment

A new bi-layer Cr/FeCrAl coating was successfully fabricated on the Zr-4 plates through multi-arc ion plating in order to take advantage of the two materials of FeCrAl and Cr. The high-temperature steam oxidation behavior of the Cr/FeCrAl-coated Zr-4 at 1000–1200 °C was investigated and compared with that of bare and single-layer FeCrAl-coated Zr-4. Various analytical techniques including scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for the microstructural and compositional analysis of the as-deposited and oxidized samples. Results indicated that the FeCrAl-coated Zr-4 could only withstand up to 1000 °C because of the severe FeZr interdiffusion. Whereas the introduction of the Cr interlayer effectively prevented fast FeZr interdiffusion and consequently improves the overall oxidation resistance of the Zr substrate below 1200 °C steam environment. After 1100 °C steam oxidation, the weight gain of the Cr/FeCrAl-coated Zr-4 was about 8 times and 2 times lower than that of the uncoated and FeCrAl-coated Zr-4 alloys, respectively. These facts make possible the use of FeCrAl coating on Zr cladding which has excellent high-temperature mechanical properties and oxidation resistance.

Hot salt corrosion behavior of Ti–6Al–4V alloy treated with different surface deformation strengthening processes

In this study, the effects of shot peening (SP) and ultrasonic surface rolling process (USRP) on the high-temperature oxidation and hot salt corrosion (HSC) behavior of the Ti–6Al–4V alloy were systematically investigated. The results showed that the high-temperature oxidation resistance of this titanium alloy can be significantly improved by the above two treatments. However, the hot salt corrosion resistance of Ti–6Al–4V alloy cannot be improved by SP due to surface roughness increasement, the surface defects and the complete relaxation of compressive residual stress (CRS) at high temperature. On the contrary, the hot salt corrosion resistance of USRP treated specimen was remarkably improved because USRP treatment significantly reduced the surface roughness and introduced deep CRS field with good thermal stability. In addition, the refined surface microstructure promoted the formation of a protective oxide film, which was also beneficial for inhibiting hot salt corrosion.

Influence of the W and Ta content on the High-Temperature Oxidation Resistance of Multinary Co/Ni-Based Superalloys at 1050 °C and 1150 °C

Outstanding inherent environmental resistance is a precondition for the use of superalloys in high-temperature applications. Besides high Al and Cr levels, also refractory metal concentrations (W and Ta) are reported to affect protective scale formation, as these elements are expected to affect the chemical activity and also the transport of protective scale formers within the alloy. In this study, we elucidate the high-temperature oxidation behavior of 3 Co-based (Co/Ni ratio: 1.4) and 3 Ni-based (Co/Ni ratio: 0.7) superalloys differing in W and Ta levels. Time-resolved thermogravimetric analysis (TGA) in synthetic air at 1050 °C and 1150 °C for 100 h, scanning electron microscopy analysis (SEM), thermodynamic calculations using the CALPHAD software Thermo-Calc, and diffusion couple experiments were conducted to assess the impact of the Co/Ni ratio and the refractory metal content on the oxidation performance. The results indicate that a low W content (3 vs. 5 at.%) and a high Ta content (2.1 vs. 1.5 at.%) beneficially affect the oxidation resistance, as alumina scale formation is facilitated.

High temperature oxidation behavior of TiAl alloy with electrodeposited SiOC coating

SiOC coating was electrodeposited on TiAl alloy to improve the high temperature oxidation resistance. The mass gain of the compact SiOC coating is 0.06 ± 0.026 mg cm-2, which is one order of magnitude lower than that of TiAl alloy. The SiOC coating exhibits good thermal stability and partial amorphous SiOC transforms into crystal SiO2 or SiC. After oxidation, no obvious pore can be found in the coating. Moreover, an Al2O3 layer is generated due to the enrichment of Al and the low oxygen partial pressure at the coating/substrate interface, therefore improving the barrier property of the oxide scale.

Effect of Mo on the high-temperature oxidation behavior of Cr-Ni-Mo hot-work die steels

To investigate the effect of molybdenum (Mo) on the high-temperature oxidation behavior of low-carbon hot-work die steels in a Cr-Ni-Mo system, five 3Cr3MoxNiW steels were prepared. The addition of Mo resulted in a decrease in the grain size of the 3Cr3MoxNiW steel, as well as an improvement in its oxidation resistance. The addition of Mo to 3Cr3MoxNiW steel reduces the inward diffusion of oxygen and the outward diffusion of iron, which accelerates the formation of chromium oxide. The oxide of Mo can then also participate in the process of protective oxide film formation, thus improving its oxidation resistance.

Effect of Mn content on the high-temperature oxidation behaviors of Mn-substituted-for-Ni alumina-forming austenitic stainless steel

We studied high Mn-substituted-for-Ni AFA steel (Fe-14Cr-(6–12) Mn-10Ni-2.5Al-3Cu-Nb-C AFA steel) oxidation behaviors at 800 °C in air. (6–12) Mn AFA steel formed a three-layered scale: the outer layer is (Mn, Fe)-rich oxide, such as (Mn0·983Fe0.017)2O3, the intermediate is Cr-rich oxide, and the inner layer is Al2O3. (6–8) Mn-AFA steels formed a protective Al2O3 layer with stronger oxidation resistance than (10–12) Mn-AFA steels. The oxidation rate constants of 6Mn- and 8Mn-AFA steels are 1.7 × 10−3 and 2.4 × 10−3 mg2/(cm4·h), respectively, approximately 10 times higher oxidation resistance than that of 10Mn- and 12Mn-AFA steels. (10–12) Mn-AFA steels cannot form a continuous Al2O3 layer. The discontinuous Al2O3 layer allows the elements to diffuse outward, eventually forming Mn-Fe-Nb-rich oxide nodules on the surface of the steel. Mn concentrations with the potential to form protective alumina at 800 °C were identified.

Enhancing the wear and high-temperature oxidation behavior of NiCrBSi coatings by collaboratively adding WC and Cr3C2

A composite coating was deposited by collaborative modification with tungsten carbide (WC) and Cr3C2 ceramic particles to improve the wear resistance of NiCrBSi coating over a wide temperature range. The original NiCrBSi coating and the composite coatings with WC and Cr3C2 collaboratively (NiCrBSi +20 wt% WC–Cr3C2–Ni) and exclusively (NiCrBSi +20 wt% WC and NiCrBSi +20 wt% Cr3C2–NiCr) added were designed and deposited by plasma spraying. The microhardness of the composite coatings added with the ceramic phase was higher than that of the NiCrBSi coating. The composite coating with the addition of WC showed the maximum microhardness (896.8 HV). The wear mechanism of the four coatings at room temperature was dominated by fatigue spalling, whereas oxidative and abrasive wear prevailed at 700 °C. The composite coating (NiCrBSi +20 wt% WC–Cr3C2–Ni) showed excellent abrasion resistance at room temperature and 700 °C. The wear volume of the composite coating (NiCrBSi +20 wt% WC–Cr3C2–Ni) decreased by 83.5 % and 46.9 % at room temperature and 700 °C, respectively, compared with the wear volume of the NiCrBSi coating. In general, high WC hardness was favorable for improving the microhardness of the coating. The preferential oxidation of Cr3C2 instead of WC promoted the formation of a dense oxide film on the surface of the coating and reduced oxidation within the coating. This study revealed the mechanism of the collaborative enhancement of NiCrBSi coatings by WC and Cr3C2 and the improved wear resistance of the NiCrBSi coatings at room and high temperatures.

Microstructure and high-temperature oxidation behaviour of MoSi2 protective coatings on Mo-based combustion chamber in rocket engines

This paper presents a detailed characterization of the microstructure and high-temperature oxidation behaviour of MoSi2 coatings obtained by pack cementation methods on a Mo-based substrate. The author focused on the challenges of applying Mo-based combustion chambers in rocket engines. Due to these assumptions, the high-temperature oxidation resistance of MoSi2 coatings was analyzed in the temperature range of 1200–1700 °C. A particular area of interest was the surface condition of MoSi2 coatings after oxidation tests, characterized by their roughness. The presented studies showed very beneficial behaviour of oxidized MoSi2 coatings from the point of view of both protective coating's morphology and durability under these conditions and the surface roughness responsible for the gas flow stability in actual working conditions. The identified microstructural phenomena related to MoSi2-based coating formation, its thermal stability and oxidation interaction were described from the thermodynamic point of view. Those analyses revealed that thermodynamically the most stable silicide compound during the first stage of coating formation is Mo5Si3, not MoSi2. It suggests that the interaction between the Si-rich gas atmosphere and the Mo5Si3 layer determines the growth progress of silicide coating. The necessary condition for further growth is an excess of active silicon sources in the reactive atmosphere in the pack cementation process.