Short-term Oxidation Behavior Research Articles

Short-term oxidation behavior of powder metallurgy Al0.8Co0.5Cr1.5CuFeNi HEA in high-temperature solid and semi-solid intervals

In this work, possible short-term thermal exposure oxidation in hot processing including semi-solid processing is focused. We aim to investigate the short-term oxidation behavior of a novel powder metallurgy Al0.8Co0.5Cr1.5CuFeNi high entropy alloy (HEA) in high-temperature solid (1000–1100 °C) and semi-solid (1125–1225 °C) intervals. From 1000 to 1225 °C, mass gain increases from 0.31 to 0.45 mg cm–2 after 60 min oxidation, presenting superior oxidation resistance in the semi-solid state compared with other semi-solid alloys. Equiaxed α-Al2O3 grains are the predominant component of oxide scales and no obvious internal oxidation layer occurs in both solid and semi-solid intervals. Al2O3 scale growth is predominantly determined by outward Al3+ diffusion. For solid oxidation, different scale formation kinetics occur on various phases and the BCC(B2) phase has faster scale formation kinetics. This is attributed to outward Al3+ diffusion rate differences in various component systems. During semi-solid oxidation, the increased degree of chaos and number of vacancies in the liquid phase provide a diffusion channel, leading to rapid Al2O3 formation. Oxidation resistance in the semi-solid state is attributed to dense Al2O3 scales formed through selective oxidation of Al.

High temperature and short-term oxidation behavior of a TiBw/TA15 network composite in an air environment at 950 °C

The oxidation behavior of materials used in aerospace is crucial for their service life, and short-term oxidation behavior is an essential means to reveal the oxidation mechanism. The high temperature and short-term oxidation behavior of the TiBw/TA15 network composite in an air environment at 950 °C for 5 min, 15 min, 30 min, and 60 min was investigated. The experimental result indicates that the composite shows a slight mass change over the whole test times. The all-oxide scale mainly contains two-layer. From the top to the bottom of the oxide scale, an Al2O3 layer and a TiO2 layer existed, which increased with the oxidation time. The oxidation mechanism of the initial oxidation behavior of the network composite has been established, which is crucial for promoting its application in high-temperature service environments.

Short-term oxidation behavior of 304 stainless steel in N2-21 vol％O2 environment between 900 and 1200 °C

Oxidation behavior and microstructure evolution of 304 stainless steel at 900–1200 °C in N2-21 vol％O2 were investigated. At 900 °C, Cr2O3 protective oxide is formed on the surface of the steel. With the increase in temperature (1100 °C), an inner oxide layer is formed consisting of two phases (Fe, Cr)3O4 oxide and remaining Ni-Fe metallic. The oxide scale formed at 1200 °C has a unique morphology consisting of the inner Cr-rich oxidation region, middle gap region, outer porous Fe3O4 oxide region, and outermost dense Fe2O3 oxide scale. A discontinuous SiO2 layer appears in the oxide scale.

Improving the high-temperature oxidation resistance of Fe-18Cr-8Ni austenitic stainless steel by cold-rolling treatments

The effect of different degrees of cold rolling on the short-term oxidation behavior of Fe-18Cr-8Ni stainless steel oxidized at 1000 °C in N2-21 vol%O2 for 3 h was investigated. The results show that cold rolling deformation reduces the grain size and coincident site lattice (CSL) grain boundary fraction of the alloy. When the deformation exceeds 20%, the oxidation mechanism changes from internal to external oxidation. And the critical concentration of Cr and Si required for forming the protective oxide scale decreases. The formation of continuous Cr2O3 and SiO2 layers on the alloy prevents the diffusion of oxygen from the surface to the matrix. The cold-rolling treatments improve the oxidation resistance of the Fe-18Cr-8Ni austenitic stainless steel at 1000 °C.

Short-Term Oxidation Behavior, Microstructure Evolution and Compression Behavior of Nickel-Based Superalloy GH4037 in Solid and Semi-Solid States

Semi-solid processing combines the advantages of traditional forging and casting methods, so it has received much attention recently. However, the research on semi-solid behaviors of Nickel-based superalloys has been rarely reported. In order to investigate the behaviors of Nickel-based superalloy at solid and semi-solid states, oxidation experiments, isothermal treatment experiments and deformation experiments of GH4037 alloy were studied. Short-term oxidation experiments of GH4037 alloy were carried out at a solid temperature (1200 °C) and a semi-solid temperature (1360 °C). The results indicated that the oxides formed at 1200 °C were mainly composed of TiO2, Cr2O3 and a small amount of spinels NiCr2O4, while the oxides formed at 1360 °C consisted of the spinels of NiCr2O4, NiWO4 and NiMoO4 besides TiO2 and Cr2O3. Microstructure evolution of GH4037 alloy after semi-solid isothermal treatment at 1370 °C and 1380 °C was studied. The results indicated that semi-solid microstructures consisted of equiaxed solid grains and liquid phases. The average grains size and shape factor of solid grains were affected by melting mechanism and grain growth mechanism. Compression behaviors of GH4037 alloy after compressed at 1200 °C and 1360 °C were investigated. The results indicated that the flow stress of 1360 °C decreased significantly compared to that of 1200 °C. The deformation zones in the specimens were divided into three parts: the difficult deformation zone, the large deformation zone, and the free deformation zone. At 1200 °C, the deformation mechanism was plastic deformation mechanism. At 1360 °C, sliding between solid particles (SS), liquid flow (LF), flow of liquid incorporating solid particles (FLS), plastic deformation of solid particles (PDS) coexisted in the compression specimen.

The interaction between Dy, Pt and Mo during the short-time oxidation of (γ’ + β) two-phase Ni Al coating on single crystal superalloy with high Mo content

Mo, as a typical refractory element in Ni-base superalloys , will diffuse outward to the protective coating on the alloy surface during high-temperature oxidation, which will do harm to mechanical properties of the alloy and oxidation resistance of the coating. In this paper, (γ’ + β) two-phase Ni-34Al-0.3Dy coatings with or without Pt were prepared on a single crystal superalloy with high Mo content by electron beam physical vapor deposition (EB-PVD) and Pt electroplating. The short-term oxidation behavior of the coatings was investigated at 1100 °C aiming to explore the role of Dy and Pt on the harmful effect of Mo diffusion and its oxides. The results show that for Pt-free coating, Mo had already diffused to the coating surface after only 1 h. The pre-existing Dy 2 O 3 would react with MoO 3 to form Dy 2 MoO 6 thus suppressed the volatilization of MoO 3 at the early stage of oxidation. However, as the oxidation proceeded, Dy 2 MoO 6 would decompose due to its poor thermal stability. While for Pt-doped coating, no Mo-rich oxides were detected throughout the entire oxidation process due to the suppression of outward Mo diffusion by the Pt layer at coating/substrate interface. The possible mechanisms were discussed in detail. • Pt-free/doped (γ’ + β) NiAlDy coatings are prepared on IC21 with high Mo content. • The role of Dy and Pt on suppressing the formation of harmful MoO 3 is focused on. • Dy delays volatilization of MoO 3 by forming Dy 2 MoO 6 which is not completely stable. • Pt inhibits diffusion of Mo by enhancing Al content in Pt-rich layer at interface. • Weak inter-attraction between Pt and Mo contributes to the Mo diffusion inhibition.

High temperature and short-term oxidation behavior of CoCrCu1.2FeNi high entropy alloy in solid and semi-solid state

The short-term oxidation behavior of CoCrCu1.2FeNi high entropy alloy in solid and semi-solid state was investigated. Except for the two-stage parabola characteristic at 1340 ℃, the oxidation kinetics of other temperatures showed single-stage parabola characteristic. The oxidation products and oxide scales were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersion spectrum (EDS). During solid oxidation, the oxide scales were composed of outer oxide layer (CuO and Cu2O) and inner oxide layer (Co, Cr, Fe, Ni3O4) spinel oxides. During semi-solid oxidation, internal and external diffusion was significantly enhanced, liquid flow and holes became diffusion channels.

In-situ synthesis of MoSi2 coating on Mo substrate under carbon protection and its short-term oxidation behavior

MoSi2 coating was in-situ synthesized on pure Mo substrate by a simple and improved packing method, in which carbon powder was used for providing a protective atmosphere. The microstructure and phase composition of the coated samples were characterized by SEM, EDS and XRD techniques. The mechanism of coating preparation was discussed. Results showed that the addition of carbon could effectively protect Mo from oxidizing during the coating preparation. A compact MoSi2 coating with a loose surface layer was obtained. It was suggested that the trace oxygen availed the formation of the compact internal structure and the loose surface layer. And this particular coating structure was expected to contribute to a better oxidation resistance in high temperature. Additionally, the short-term oxidation behavior of the as-prepared MoSi2 coating was investigated. The as-prepared MoSi2 coating provided an unexceptionable protection for the Mo substrate from oxidation at 1600 °C for 1 h. The presence of a glassy silica layer that formed on the MoSi2 coating during the oxidation exposure was proposed to explain the behavior. It shows the simple and improved packing method with carbon powder as protective medium is promising potential for the preparation of various anti-oxidation coatings.

On the Pre-oxidation Treatments of Four Commercial Ni-Based Superalloys in Air and in Ar–H2O at 950 °C

The short-term oxidation behaviour of RA 602CA, Inconel 693, Manaurite 40XO and Sumitomo 696, which are four alloys recommended for hydrocarbon processing, was studied both in air and in Ar–H2O to determine the conditions of pre-oxidation treatments. Regardless of the considered material, the oxidation rate at 950 °C was systematically higher in Ar–H2O than in dry air. Surface examination of the Al-containing alloys indicated that they were not uniformly oxidized all over the surface. All Al-containing alloys (from 1.6 to 3.2% wt) formed an external protective alumina scale and behaved as alumina-forming alloys in dry air at 950 °C. In contrast, these alloys developed a rate-controlling chromia scale and severe internal oxidation in a H2O-containing atmosphere. Compared with their oxidation behaviour in air + H2O, the phenomenon was significantly enhanced in the atmosphere that coupled water vapour with a low oxygen pressure. Consequently, the Al-containing alloys should not be pre-oxidized in a water vapour atmosphere prior to long exposure to a corrosive atmosphere. In contrast, the chromia-forming Al-free 696 alloy exhibited identical oxidation behaviour in both atmospheres, demonstrating that the degradation of this alloy was not significantly affected by water vapour.

Short Term Oxidation Behavior of Si-Free Low-Cr Alloy Sputtered Coating

A sputtered coating of a low-Cr alloy without Si was deposited on the cast alloy with the same composition. The short term (100 h) oxidation behavior of the sputtered coating and the cast alloy was evaluated in air at 800 °C. The results indicated that the sputtered coating exhibited a higher oxidation resistance than the cast alloy. It was found that the mass gain of the cast alloy increased continuously with oxidation time and was higher than that of the sputtered coating, which demonstrated only a slight increase in mass gain with oxidation time after 5 h thermal exposure. During the initial thermal exposure of 0.5 h, the oxide scale formed on the cast alloy consisted of Fe2O3 and (Fe,Co,Cr)3O4 spinel with a small amount of Cr. However, (Fe,Co,Cr)3O4 spinel and Fe2O3 were thermally grown on the sputtered coating. After oxidation for 100 h, the oxide scale formed on the cast alloy consisted of Co3O4 and (Fe,Co)3O4 with internal oxide of Cr, while a double-layer oxide consisting of an outer (Fe,Co,Cr)3O4 spinel layer and an inner Cr2O3 layer was developed on the sputtered coating.

Comparison of Short-Term Oxidation Behavior of Model and Commercial Chromia-Forming Ferritic Stainless Steels in Dry and Wet Air

A high-purity Fe–20Cr and commercial type 430 ferritic stainless steel were exposed at 700 and 800 °C in dry air and air with 10% water vapor (wet air) and characterized by SEM, XRD, STEM, SIMS, and EPMA. The Fe–20Cr alloy formed a fast growing Fe-rich oxide scale at 700 °C in wet air after 24 h exposure, but formed a thin chromia scale at 700 °C in dry air and at 800 °C in both dry air and wet air. In contrast, thin spinel + chromia base scales with a discontinuous silica subscale were formed on 430 stainless steel under all conditions studied. Extensive void formation was observed at the alloy–oxide interface for the Fe–20Cr in both dry and wet conditions, but not for the 430 stainless steel. The Fe–20Cr alloy was found to exhibit a greater relative extent of subsurface Cr depletion than the 430 stainless steel, despite the former’s higher Cr content. Depletion of Cr in the Fe–20Cr after 24 h exposure was also greater at 700 °C than 800 °C. The relative differences in oxidation behavior are discussed in terms of the coarse alloy grain size of the high-purity Fe–20Cr material, and the effects of Mn, Si, and C on the oxide scale formed on the 430 stainless steel.

In situ x-ray diffraction investigation on early stages of oxidation at 900 °C of γ-TiAl dipped in a phosphoric acid solution

The short term oxidation behavior of γ-TiAl treated in low-concentration phosphoric acid solution has been investigated at 900 °C in air. A pyrophosphate film isomorphous to TiP2O7 is formed during the initial thermal treatment step and is responsible for a subsequent large reduction in the oxidation rate. During the initial course of oxidation at 900 °C, the pyrophosphate film transforms into a TiO2 solid solution containing phosphorus. This transformation impedes the usual oxides external growing mechanisms and leads to an internal development of the oxide scale with an associated reduced oxidation rate.

Effects of Pt on the short-term oxidation behavior of γ-Ni+γ′-Ni<SUB>3</SUB>Al alloys

Effects of Pt on the short-term oxidation behavior of γ-Ni+γ′-Ni<SUB>3</SUB>Al alloys

Effects of Pt on the short-term oxidation behavior of γ-Ni+γ′-Ni3Al alloys

The aim of this study was to elucidate the beneficial role played by platinum addition in promoting the formation of a protective Al2O3 scale on γ′-Ni3Al+γ-Ni alloys during oxidation at high temperatures. To do this, the early-stage oxidation behavior of γ′-Ni3Al-based alloys of composition (in at.%) Ni–22Al and Ni–22Al with 10, 20, and 30 Pt was investigated in terms of oxidation kinetics, scale evolution and resulting composition profiles during heating to 1150°C in air. Platinum addition did not appear to affect the nature of the native oxide layer present on the γ′-based alloys at room-temperature; however, it was found that the presence of increasing Pt content aided in promoting the establishment of a continuous Al2O3 scale during heating above about 600°C. This beneficial effect can be primarily ascribed to the fact that Pt is non-reactive and its addition decreases the chemical activity of aluminum in γ′. Related to the latter, Pt partitions almost solely to the Ni sites in the ordered L12 crystal structure of γ′, which has the effect of amplifying the increase in the Al:Ni atom fraction on a given crystallographic plane containing both Al and Ni. Such an effective Al enrichment at the γ′ surface kinetically favors the formation of Al2O3 relative to NiO. A further contributing factor is that the Pt-containing γ′-based alloys showed subsurface Pt enrichment during the very early stages of oxidation. This enrichment reduces Ni availability and can increase the Al supply to the evolving scale, thus kinetically favoring Al2O3 formation.

Thermal aging effects on the microstructure and short-term oxidation behavior of a cast Ni 3Al alloy

Specimens of the castable nickel aluminide alloy IC221M were annealed in still air at 900 °C to examine the effects of oxidation and thermal aging on its microstructure. The alloy, which is comprised primarily of a γ–γ′ mixture but also contains a lower melting γ+Ni 5Zr eutectic, is used in applications that require casting. The as-cast microstructure is dendritic and exhibits microsegregation of the alloying elements. Microstructures of as-cast specimens annealed for periods up to 16,600 h were examined using scanning electron microscopy and energy dispersive X-ray spectroscopy with spectrum imaging. Although the material partially homogenizes with aging time, approximately 3 vol% of the γ+Ni 5Zr eutectic remains after 16,600 h, and there is a tendency for the eutectic colonies to spherodize. Oxidation products were identified using X-ray diffraction and energy dispersive X-ray spectroscopy. During the initial stages of oxidation, the oxide is predominantly NiO with small amounts of Cr 2O 3, ZrO 2, NiCr 2O 4, and θ-Al 2O 3. Initial oxidation occurs primarily in the interdendritic regions of the microstructure. With further aging, the predominant surface oxides become NiO and NiAl 2O 4, with a continuous film of α-Al 2O 3 forming immediately beneath them. Although these oxides are constrained to the near surface region, other oxides penetrate to depths greater than 10 times that of the continuous surface oxide, facilitated by oxidation of the γ+Ni 5Zr interdendritic eutectic. These oxides appear in the microstructure as long, thin spikes of ZrO 2 surrounded by a sheath of Al 2O 3.

The oxidation behaviour of an Fe,AI, Si alloy containing uranium as an impurity, oxidised for short times at high temperatures

The short term oxidation behaviour of an Fe,Al,Si alloy, oxidised at 1000°C in unpurified air, has been characterised using a range of techniques including transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). It was observed that this alloy formed a flat adherent alumina scale, even though analysis did not detect any conventional reactive elements. The research showed that the scale developed during the early stages of oxidation was similar to that formed at longer times (up to 24 hours) and that the tendency for the scale to remain flat and adherent was due to the presence of an impurity, uranium. Upon initial oxidation, uranium was found to segregate strongly to the metal/oxide interface, but was not detected at the oxide grain boundaries until oxidation times of approximately 20 minutes. Sulphur was observed within the scale during the initial stages of oxidation but was not associated with the uranium, the oxide grain boundaries or the metal/oxide interface. Therefore, uranium is not acting as a sulphur getter, reducing sulphur activity in the scale, but instead it appears to either block the sites at the oxide/metal interface where sulphur would normally segregate or change the chemistry of the interface in such a way as to make the segregation of sulphur thermodynamically unfavourable.

High-temperature oxidation of Ti-48Al-2Nb-2Cr and Ti-25Al-10Nb-3V-1Mo

The short-term oxidation behavior of aγ-TiAl alloy (Ti-48Al-2Nb-2Cr) was compared andcontrasted to that of anα2-Ti3Al base(Ti-25Al-19Nb-3V 1Mo) alloy. Oxidation ofTi-25Al-10Nb-3V-1Mo was found to occur at a moderate rate at 800°C, in aN2 + 20% O2 environment. A largeincrease in the oxidation rate occurred above thistemperature. This large weight increase was attributedto a breakdown in the protective oxide scale on the surface of theα2 intermetallic alloy, therebypermitting rapid diffusion of oxygen and nitrogen to thesurface of the intermetallic. The oxidation rate of thisalloy at 1200°C was not significantly higher thanthe oxidation rate at 1000°C. In contrast, theoxidation rate of Ti-48Al-2Nb-2Cr remained low up to1200°C. At this temperature, a significant increasein oxidation was observed and was attributed to acceleratedoxygen diffusion through the α2 phaseand increased solubility of oxygen in the gamma phase ofthe intermetallic microstructure. This weight increaseoccurred despite the fact that at 1200°C, theintegrity of the oxide layer formed on the surface ofthis alloy was maintained. The results of this studyillustrate the need for developing protectiveenvironmental coatings tailored to the individualintermetallic alloy.