Oxidation Behavior Of Alloys Research Articles

Investigating the oxidation behavior of Mg-Zn alloy: Effects of heating rates, gas flow, protective atmosphere, and alloy composition

Magnesium-zinc alloys offer promising lightweight properties but are prone to oxidation during high-temperature processing and usage. In this study, the oxidation behavior of Mg-Zn alloy was examined according to the inert gas type flow rate, heating rate and alloy amount. Initially, alloys were produced by adding zinc at weight percentages of 0.5%, 1.5%, and 2% using the casting method. The alloys were characterized using X-ray fluorescence (XRF), X-ray Diffraction (XRD), and scanning electron microscope (SEM) analyses, revealing the formation of dendritic Mg-Zn intermetallic within the alloy. The oxidation behavior of these alloys was examined via differential thermal analysis (DTA) and thermogravimetric analysis (TGA), considering factors such as heating rate, gas flow rate, type of protective atmosphere, and amount of alloying element. The results indicated that the onset temperature of oxidation decreased with increasing heating rate. The effect of gas flow rate varied depending on the heating rate and the type of gas. Under a nitrogen atmosphere, conditions with a heating rate of 20°C∙min‒1 and a gas flow rate of 5 cm3∙min‒1 resulted in the least oxidation. In an argon atmosphere, a gas flow rate of 5 cm3∙min‒1 was found to be sufficient to prevent oxidation. However, at a gas flow rate of 1 cm3∙min‒1, a heating rate of 20°C∙min‒1 was more effective in preventing oxidation. The alloying element (zinc) likely reduced oxidation, particularly at the 1.5% addition level, possibly due to the formation of intermetallic compounds.

Influence of dissolved hydrogen and IG Cr carbide on the oxidation behavior of Alloy 600 in hydrogenated primary water

The internal oxidation (IO) and preferential intergranular oxidation (PIO) behavior of Alloy 600 depending on the dissolved hydrogen (DH) content and the IG Cr carbide in hydrogenated primary water were characterized in detail using analytical electron microscopy techniques. The oxidation layer was unstable when the DH concentration was such that Ni was in the vicinity of Ni/NiO equilibrium and it could easily be peeled off. Hence, the grain boundaries of the bare metal were attacked. PIO occurred and Cr-rich oxide identified as Cr2O3 was formed at the oxidized grain boundary. NiO emerged when the DH concentration was such that Ni was in an oxidizing state, whereas Ni enrichment occurred inside the oxidized grain boundary when the DH concentration was such that Ni was in a reducing state with respective to Ni/NiO equilibrium. The IG Cr carbide strongly affected the PIO behavior by means of the consumption of oxygen penetrating into the grain boundary. The depth of the IO layer decreased as the DH concentration increased. The different oxidation behaviors depending on the DH content and IG Cr carbide are believed to affect the PWSCC resistance of Alloy 600 significantly.

Investigating the Impact of Surface Finishing and Residual Stress on the Oxidation Behavior of Alloy 800

Investigating the Impact of Surface Finishing and Residual Stress on the Oxidation Behavior of Alloy 800

New Insights into Internal Oxidation of Alloy 690 and Model Alloys in Hydrogenated Steam

The oxidation behavior of Alloy 690 and Ni-xCr-10Fe model alloys exposed to 480°C hydrogenated steam, in the nickel metal stability region, was studied using a variety of techniques, including time-resolved scanning electron microscopy, transmission electron microscopy, time-of-flight secondary ion mass spectrometry, and electron energy loss spectroscopy. The alloy underwent internal oxidation intragranularly, resulting in the expulsion of metallic Ni nodules to the surface. A compact Cr-rich “healing” layer developed over time at the intragranular internal oxidation front near grain boundaries and significantly retards further internal oxidation. Protective external Cr-rich oxide formed at and very near the grain boundaries, hindering intergranular oxidation. In view of the fact that the protective oxide forms micrometers away from the grain boundaries, one cannot simply say that Cr diffuses up the boundary and forms an oxide that spreads laterally—internal stress relief must play a role, just as it does within the grains, only with different mechanisms at play.

Effect of Water Jet Cavitation Peening on Short-Period Oxidation Behavior of Alloy 600 in PWR Primary Water

Water jet cavitation peening (WJCP) was used to strengthen the surface of nickel-based alloy 600. Residual stress, hardness, surface roughness, microstructure, and short-period oxidation behavior in untreated (UT) and WJCP-treated alloy 600 were characterized. A continuous oxide film was formed on the WJCP-treated surface after a short period of exposure, while it was discontinuous in the UT specimen. The change in oxidation behavior was attributed to the ultrafine grain and dislocation structure resulting from the WJCP treatment.

The effect of amorphous coating on high temperature oxidation resistance of Ni-based single crystal superalloy

Amorphous Al2O3 coating was prepared on Ni-based single crystal superalloy via atomic layer deposition (ALD) for high temperature oxidation protection. The oxygen inward transport and outward-cation diffusion were hindered by amorphous Al2O3 coating, and the coated alloy showed high oxidation resistance. The low oxygen partial pressure at the alloy/coating interface altered the alloy oxidation behavior, allowing the priority oxidation of protective Al and Cr elements. The oxidation process was controlled by the growth of Cr2O3 and Al2O3. The coating exhibited high spallation resistance. Degradation of the coating, the formation of NiAl2O4 phase in amorphous Al2O3 layer, was observed.

High-Temperature Steam Oxidation of Accident-Tolerant Cr/Mo-Coated Zr Alloy at 1200–1400 °C

The oxidation resistance under LOCA conditions of bilayer Cr/Mo coating deposited on Zr-1Nb zirconium alloy was investigated in this paper. The bilayer Cr (8 μm)/Mo (3 μm) coatings were deposited by magnetron sputtering. Then, oxidation resistance under high-temperature oxidation at 1200–1400 °C in a water steam was studied. The use of a Mo sublayer resulted in limiting Cr-Zr interdiffusion under high-temperature oxidation. It was shown that the Mo barrier sublayer (~3 μm) can provide the protective behavior of the Cr/Mo-coated Zr at 1330 °C in a water steam for at least 720 s. The weight gain of the bilayer Cr/Mo samples was comparable with the monolayer Cr samples after oxidation at 1400 °C. In addition, the analysis of the Cr/Mo-coated Zr alloy oxidation behavior at 1400 °C was carried out.

The oxidation behavior of stir-cast and heat-treated EV31A at high temperatures in an air atmosphere

This study examines the influence of heat treatment techniques on the oxidation behavior of stir-cast EV31A magnesium alloy. The oxidation behavior of the alloy was examined under isothermal conditions at three different temperatures: 390 °C, 455 °C, and 520 °C, by evaluating its weight change. Before and after oxidation, FE-SEM with EDS and XRD were used to detect the alloy's shape, composition, and phases. In contrast to heat-treated alloy, the as-cast material oxidizes quickly. The oxidation behavior of EV31A follows linear kinetics. It creates a dense oxide layer with a thickness of 17.97 µm, which may be resistant to further oxidation. At 520 ⁰C, the oxidation behavior of EV31A changed. The oxidation rate of the as-cast alloy is greater than that of the heat-treated alloy. The formation of dual phase of MgO – Nd2O3 on the surface is noticeable. It confirms that the intermetallic phases significantly modify the oxidation behavior.

High-temperature oxidation behaviors of an equiatomic CrMnFeCoNi high entropy alloy

Due to the limited information in the literature on the oxidation mechanism of high-entropy alloys, we have investigated the high temperature oxidation behavior of an equiatomic Cr20Mn20Fe20Co20Ni20 high-entropy alloy (CrMnFeCoNi HEA) to demonstrate the oxidation mechanism. The evolution of the surface morphology and the specific oxide growth processes and elemental distributions were analyzed by scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), and X-ray diffractometer (XRD). The findings reveal that the alloy undergoes three oxidation stages, which are i) surface reaction between O2- ions and metal ions at low temperatures (750–850 °C), ii) thickening of the sample surface due to chemosorption of O2 atoms at moderate temperatures (950–1050 °C), and iii) thinning of the sample due to oxide spalling at high temperatures (1050–1150 °C). Three oxide layers were detected, extending from the outside to the inside of the cross sections of the sample and were composed of MnFe2O4 +Mn3O4, (Mn,Cr)xO4, and Cr2O3, respectively. Subsequently, the high-temperature oxidation behavior of the alloy was determined by thermodynamic and kinetic calculations. As a result, an oxidation mechanism model was established. The results of this study have paved the way for new applications of HEAs.

Influence of Al content and low oxygen pressure preoxidation on high‐temperature oxidation resistance of Ni–25Cr–xAl–1Si–0.5Y alloys

AbstractThe influence of Al content and low oxygen pressure preoxidation on the high‐temperature oxidation resistance of the Ni–25Cr–xAl–1Si–0.5Y (x = 0, 1, 3, 5 wt%) alloys were studied. The formation of oxides in low oxygen pressure preoxidation was investigated. The oxidation behavior of alloys with different Al content at 1000°C with and without preoxidation under low oxygen pressure was discussed. A protective oxide film was formed on the surface of alloys with different Al content in low oxygen pressure pre‐oxidation at 950°C for 5 h, but there were great differences in microstructures and properties. With the increase of Al content, the outermost oxide film of the alloy gradually changed from continuous Cr2O3 to Al2O3, and the oxidation resistance of the alloy increased gradually at 1000°C. By comparison, the oxidation resistance of Ni–25Cr–xAl–1Si–0.5Y (x = 0, 1, 3, 5 wt%) alloys can be significantly improved at 1000°C by low oxygen pressure preoxidation treatment.

Examining the thermodynamic stability of mixed principal element oxides in AlCoCrFeNi high-entropy alloy by first-principles

Understanding the complex oxidation behavior of alloys consisting of multiple principal elements is critical to realize their potential for high temperature structural applications. We examine the thermodynamic stability of primary and mixed oxides for one such extensively examined high-entropy alloy (HEA), AlCoCrFeNi, using first-principles calculations. Our predictions indicate that Cr2O3 and Al2O3 are the most stable oxides both at the ground state and elevated temperatures, with the relative ordering for oxide stability at higher temperatures being similar to that at 0 K. The presence of both Al with Cr are most likely to form protective oxide layers, while that produced by Ni and Cr are the least stable. Nevertheless, the gradient of formation energies for the stable mixed Cr2O3-type oxides with increasing concentration of other principal elements becomes steeper with increasing temperature.

High-temperature oxidation behavior of additively manufactured IN625: Effect of microstructure and grain size

High-temperature oxidation of additively manufactured (AM) Ni-base alloy IN625 has been studied in air and Ar-5%H2-3%H2O at 900–1000 °C. AM material is found to oxidize faster than the conventionally manufactured (CM) IN625 due to severe intergranular oxidation observed in the former. The AM IN625 was heat treated at 1100–1250 °C and hot rolled at 980 °C in order to modify the AM microstructure, primarily grain size, and analyze its role in alloy oxidation behavior. Grain size is shown to affect overall oxidation kinetics but not the intergranular oxidation morphology.

Effect of Water Vapor on Lifetime of 625 and 120 Foils During Oxidation Between 650 and 800 °C

The oxidation behavior of alloy 625 and 120 foils was studied at 650, 700 and 800 \(^\circ\)C in dry air and flowing air + 10% H\(_2\)O up to 10,000 h (alloy 625) or 30,000 h (alloy 120). The effect of water vapor on Cr loss was investigated. Manganese and iron in the 120 foil induced faster Cr depletion in the foil and breakdown of the Cr\(_2\)O\(_3\) scale into Fe and Cr-rich oxide compared to the alloy 625 foil. In the latter case, the presence of Nb led to the formation of Nb and Cr-rich oxide after breakdown of the Cr\(_2\)O\(_3\) scale. Simultaneous Cr loss due to oxidation and volatilization of the Cr\(_2\)O\(_3\) oxide scale was predicted and compared to experimental Cr loss measurements for exposures up to 30,000 h.

Oxidation behavior of AlCoCrFeNiSix high-entropy alloys at 1100 ℃

AlCoCrFeNiSix high-entropy alloys containing different Si contents (x = 0, 0.2, 0.5, 0.8, 1.0 in molar ratio) were prepared by vacuum arc-melting. The microstructure and oxidation behavior of these alloys at 1100℃ for 200 h were investigated. After adding Si, the alloys mainly consist of BCC and Si-rich precipitates, and both the size and quantity of the Si-rich precipitates increase with increase in the Si content. A suitable content of Si in the alloys improves the oxidation resistance for promoting the formation of a dense single Al2O3 scale, while excessive Si imposes an adverse effect by forming easy-peeling scales composed of Al2O3 outer layer and mixed oxides inner layer. Formation and failure mechanisms of the oxide scales on these alloys during oxidation have been discussed.

Decomposition behavior in the early-stage oxidation of Sm2Co17-type magnets

Irredeemable magnetic loss caused by oxidation remains a critical concern for the application of Sm2Co17-type permanent magnets. Herein, oxygen induced decomposition in the early-stage oxidation of a Sm(CobalFe23.5Cu4.9Zr1.7)7.5 magnet is studied using aberration-corrected TEM. Upon oxygen penetration along the 1:3R Z-plates, the 1:5H cell boundaries are decomposed into separate Sm and Co(Fe) lamellae with thicknesses of ~5 nm. Subsequently, the Fe-rich 2:17R cells are decomposed into similar metal lamellae. Besides the normal hexagonal stacking, the Sm lamellae also exhibit a twinned face-centered cubic (FCC) structure. The decomposed Co(Fe) lamellae and Cu particles are FCC-structured. The nano-twinned Cu particles are sparsely distributed. Interestingly, the closely-packed planes of these metal lamellae tend to align with the {0001}2:17R plane. The metal lamellae enriched with oxygen interstitials finally turn into nano-oxides by oxidation. This work offers in-depth insights into the initial oxidation behavior of alloys.

High temperature oxidation of non equi-atomic Al5Cr12Fe35Mn28Ni20 high entropy alloy

The Oxidation behavior of the Al5Cr12Fe35Mn28Ni20 high entropy alloy was investigated in air at temperatures 900 °C, 1000 °C and 1100 °C for 100 h isothermally. The oxidation kinetics at all temperatures obeys the parabolic rate law with an activation energy 100.6 kJ mol−1. The alloy was externally oxidized forming duplex layer consisted of manganese oxides that overlays Mn-Cr-Fe spinel oxides. While, it was observed that at 1000 °C and 1100 °C the samples were also oxidized internally forming Al2O3 deep in the alloy. The initial oxidation behavior of the alloy oxidized at 1000 °C for 1 and 24 h producing external scale of Mn3O4 overlaying Mn-Cr-Fe spinel oxide and Al2O3 precipitates.

In situ high temperature oxidation behavior of novel Co/Cr/W/Ni (KCN20WN) alloy at high temperature environment

The study of oxidation kinetics and material behavior at high temperature is inevitable to choose a suitable candidate material for strategic applications. Co-based alloys are predominantly used in aerospace industries because of their excellent thermo-mechanical properties. We propose in-situ high temperature oxidation study to understand the microstructural and oxidation behavior of KC20WN alloy (Co-based) under hasty heating to static high temperature conditions. The oxidation behavior of alloys was measured with the help of biologic potentiostat/galvanostat workstation (two cell electrode system) attached with the high temperature furnace. The alloy samples were heated at different time (200 s to 10000 s) and temperature (800 °C and 1000 °C) in inside the furnace and their simultaneous oxidation/microstructural response was recorded using frequency response analyzer (FRA). In situ oxidation behavior was analyzed by charge transfer resistance (Rct) using EC-LAB software. Further, the oxidized samples were characterized using X-ray diffraction (XRD), optical microscopy, field emission scanning electron microscope (FESEM) and micro hardness tester.

Production of NiAl–(Cr,Mo) Eutectic Alloys and Their Cyclic Oxidation Behavior at 800–1000°C

Ni–33Al–34Cr and Ni–33Al–28Cr–6Mo (at %) eutectic alloys were produced by the resistive sintering (RS) technique using elemental powders. The cycle oxidation behaviors of alloys at 800, 900, and 1000°C for 168 h in air atmosphere were investigated. The oxidation resistance of alloys was evaluated by the weight change measurements. The activation energy for NiAl–34Cr and NiAl–28Cr–6Mo alloys was 57 and 31 kJ mol–1, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) were performed to characterize the initial microstructure and the oxidation products. The obtained results showed that the oxidation products mainly consist of Cr2O3, α-Al2O3, NiO, and NiAl2O4 oxides.

Investigation on the effect of Si addition to the high temperature cyclic oxidation behaviour of β-NiAlDy alloy used in advanced jet engine applications

Abstract This work concentrates on the study of the effect of addition of Si to the β-NiAlDy alloy in improving its cyclic oxidation behaviour at high temperature namely 1000 0C. Silicon addition of 1%, 3% and 5% are carried out to prepare β-NiAlDy alloy groups by arc-melting and further by casting in inert atmosphere. The prepared alloy groups were further subjected to annealing in vacuum at temperature namely 1100 0C for a time period of 12 h. These alloy groups are subjected to cyclic oxidation tests up to 100 cycles with each cycle time duration of 5 h of atmospheric exposure at aforementioned temperature. The oxidation behaviour of the alloy groups were studied in detail by carrying out cyclic oxidation measurements, XRD, SEM and EDAX analysis. The results clearly show the variation of oxidation behaviour of the β- NiAlDy alloy when Si content is increasing from 1 to 5%. It is registered that the oxidation resistance of β-NiAlDy increase to a greater extent when 1 to 5% Si is added to the alloy.

Oxidation of Al-Co Alloys at High Temperatures.

In this work, the high temperature oxidation behavior of Al71Co29 and Al76Co24 alloys (concentration in at.%) is presented. The alloys were prepared by controlled arc-melting of Co and Al granules in high purity argon. The as-solidified alloys were found to consist of several different phases, including structurally complex m-Al13Co4 and Z-Al3Co phases. The high temperature oxidation behavior of the alloys was studied by simultaneous thermal analysis in flowing synthetic air at 773–1173 K. A protective Al2O3 scale was formed on the sample surface. A parabolic rate law was observed. The rate constants of the alloys have been found between 1.63 × 10−14 and 8.83 × 10−12 g cm−4 s−1. The experimental activation energies of oxidation are 90 and 123 kJ mol−1 for the Al71Co29 and Al76Co24 alloys, respectively. The oxidation mechanism of the Al-Co alloys is discussed and implications towards practical applications of these alloys at high temperatures are provided.