Oxidation Behavior of Fe-Ni-Co Based Superalloys and Influence of Yttrium Addition

1. IntroductionThe Fe-Ni-Co based 907 alloy is a controlled thermal expansion superalloy for use in casting rings andseals for aircraft gas turbine engines where the servicetemperature is up to 649oC. The coefficiellt of thermal expansion of this alloy is low, about half of that ofconventional superalloys. The absence of Cr in the alloy ensures the low thermal expansion, however leadsto an inherent lack of environmental resistance compared with other superalloys containing Cr[1]. Theoaldati…     

Improvement on the Oxidation Resistance of a Ti3Al Based Alloy by Cr1-xAlxN （0≤x≤0.47） Coatings

Cr1-xAlxN coatings have been deposited on a Ti3Al based alloy by reactive sputtering method. The results of the isothermal oxidation test at 800-900℃ showed that Cr1-xAlxN coatings could remarkably reduce the oxidation rate of the alloy owing to the formation of Al2O3＋Cr2O3 mixture oxide scale on the surface of the coatings. No spallation of the coatings or oxide scales took place during the cyclic oxidation at 800℃. Ti was observed to diffuse into the coatings, the diffusion distance of which was very short, and the diffusion ability of it was proportional to the AI content in the coatings. Compared to Ti, Nb can diffuse much more easily through the whole coatings and oxide scales.     

Improvement on the Oxidation Resistance of a Ti3Al Based Alloy by Cr1-xAlxN (0≤x≤0.47) Coatings

Cr1-xAlxN coatings have been deposited on a Ti3Al based alloy by reactive sputtering method. The results of the isothermal oxidation test at 800-900 ℃ showed that Cr1-xAlxN coatings could remarkably reduce the oxidation rate of the alloy owing to the formation of Al2O3 Cr2O3 mixture oxide scale on the surface of the coatings. No spallation of the coatings or oxide scales took place during the cyclic oxidation at 800℃. Ti was observed to diffuse into the coatings, the diffusion distance of which was very short, and the diffusion ability of it was proportional to the Al content in the coatings. Compared to Ti, Nb can diffuse much more easily through the whole coatings and oxide scales.     

Oxidation of Hastelloy-XR Alloy for Corrosion-Resistant Glass-Coating

The oxidation behavior of Hastelloy-XR alloy was investigated to obtain the optimum surface condition for corrosion-resistant glass-coatings. The surface morphology of oxide scales changed significantly with variation of temperatureand oxygen partial pressure (po2 ). The oxidation kinetics was mainly parabolic independent of oxidation conditions.The oxide scales were consisted of inner Cr2O3 and outer spinel layers. The phase component of spinel layers wereMn1.5Cr1.5O4 and (Mn,Ni)(Cr,Fe)2O4 for the oxygen partial pressures po2<10 kPa and po2>10 kPa, respectively.The optimum oxidation condition to obtain an oxide scale for well-adhered glass-coating to the substrate was 1248 Kand po2 =0.01 kPa for the oxidation time of 43 ks.     

Oxidation of Ni-based single crystal after grit-blasting during exposure at high temperature

The effect of grit-blasting on the oxidation of Ni-based single crystal at 1150 and 1250 °C was studied. The oxide scales formed on the samples with or without grit-blasting were characterized by SEM, XRD, EDS, and EPMA. The results indicate that grit-blasting introduces a plenty of oxide nodules with lamellar structure into the oxide scale of samples after oxidation. The oxide nodule is composed of external and internal part. The external part is multi-layered with outer Cr₂O₃ layer, inner Al₂O₃ layer and transitional layer. The internal part includes several alternative alloy layers lack of Al and Al₂O₃ layer. Hf and Ta segregate at the oxide/alloy and oxide/oxide interface in two parts. Two recrystallized grains are formed under the blasted alloy surface after grit-blasting and heat exposure. The formation of oxide nodules accelerates the development of equiaxed recrystallization. Grit-blasting introduces abundant paths of oxygen diffusion and residual stress into the alloy, promoting the formation of oxide nodules and recrystallization.     

水蒸气温度对700℃先进超超临界锅炉候选合金GH2984氧化行为的影响

采用X射线衍射仪、扫描电子显微镜对比研究GH2984合金在750℃和850℃纯水蒸气中的氧化行为。结果表明:GH2984合金的氧化动力学遵循抛物线规律;温度升高,Cr挥发加速,外氧化和内氧化的速率急剧增加,氧化膜的组成结构发生明显的变化。750℃时,合金表面形成单层致密的(Cr,Mn)_2O_3膜;温度升至850℃,氧化膜中空洞的数量大幅增加,氧化膜转变为由薄的外层Fe_2TiO_5和厚的次外层(Cr,Mn)_2O_3及薄的内层(Nb,Mo)_2O_5组成的三层结构。Ti,Al优先于晶界处发生内氧化,分别形成TiO_2和Al_2O_3;两种内氧化产物的尺寸和数量均随温度升高而增加。     

Ceramic-ceramic. composites II

The growth mechanisms of the oxide scales of Ti-50Al and Ti-45Al-8Nb (at%) alloys at 900°C in air were investigated. The results revealed that the oxidation of γ-TiAl alloys during experiments was divided into four stages. The Ti-50Al alloy showed severe spallation after 3 h of oxidation. Nb addition to γ-TiAl alloys could improve the oxidation resistance effectively. The oxide scale growth was much slower and every oxide layer was more chemically uniform and homogeneous with Nb addition. The Ti-45Al-8Nb alloy showed no spallation even after 100 h of oxidation.     

Oxidation of Ion Plated Ni—Cr Alloy Film at 300℃

Investigation by using LAS 3000 surfaceanalysis system showed that the oxide of Fe,Cr,Al formed during oxidation were Cr_2O_3,Fe_2O_3and Al_2O_3,but only small amount of nickel oxidewas found.The composition of oxide layers for differentoxidation durations varied in a similar way.In all cases,there exists an oxygen concentrationpeak in the composition profile of oxide layer.There is a transitional zone between oxide layerand alloy film.The thickness of oxide layerincreases logarithmically with the time of oxida-tion.The ion plated Ni-Cr alloy film has verydense oxide layer and good oxidation resistance.     

Oxidation of FeCrAl foils at 500–900°C in dry O2 and O2 with 40% H2O

Abstract

High temperature resistant FeCrAl alloys are frequently used in high temperature applications such as heating elements and metal based catalytic converter bodies. When exposed to high temperatures an adherent, slowly growing, dense aluminium oxide layer forms on the surface, which protects the underlying alloy from severe degradation. The composition, structure and properties of the formed oxide layer are strongly dependent on the alloy composition, temperature and oxidation environment. In this study, the Sandvik 0C404 FeCrAl alloy, in the form of 50 μm thick foils, was exposed isothermally in the temperature range 500–900°C for 168 hours in dry O₂ and in O₂ with 40 vol.% H₂O. The surface morphology, composition and microstructure of the grown oxide scales were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), grazing incidence X-ray diffraction (GIXRD), Auger electron spectroscopy (AES), and time of flight secondary ion mass spectrometry (TOF-SIMS). The oxidation process was faster at 900°C than at 500 and 700°C. At 500°C a thin (10–20 nm) mixed oxide of Fe, Cr and Al was formed. Exposure at 700°C resulted in a similar (40–50 nm) duplex oxide, in both dry O₂ and in O₂ with 40 vol.% H₂O. These oxide scales consisted of an inner and an outer relatively pure alumina separated by a Cr-rich band. This type of duplex oxide scale also formed at 900°C with a thin inward growing α–Al₂O₃ at the oxide/metal interface and an outward growing layer outside a Cr-rich band. However, at 900°C the outward growing layer showed two types of oxide morphologies; a thin smooth base oxide and a much thicker nodular oxide grown on top of substrate ridges. In dry O₂ atmosphere, the main part of this outward growing layer had transformed to α–Al₂O₃. Only in the outer part of the thick oxide nodules, metastable alumina was found. When exposed in the presence of water vapour the main part of the metastable alumina remained untransformed.     

高温含水气氛对Pt改性NiCoCrAlY合金氧化行为的影响

为了研究Pt改性NiCoCrAlY合金在高温含水气氛中的高温抗氧化行为,进一步理解高温含水气氛对Pt改性涂层表面形貌以及产物的影响,采用电镀方式在NiCoCrAlY合金表层制备了一层1.5μm厚的Pt层,然后对涂层进行热处理。对Pt改性NiCoCrAlY涂层在1 050℃的空气和含水气氛下的高温氧化行为进行对比研究。采用扫描电镜(SEM)观察表面形貌,采用X射线衍射仪(XRD)、能谱(EDS)分析了涂层的相结构及成分。结果表明:在含水气氛下,Pt改性合金表面生成针状Al_2O_3,基体不同相β-NiAl与γ'-Ni_3Al在含水气氛中表现出不同的Al_2O_3生长速率,从而导致氧化层中生长应力的堆积,导致氧化层的剥落。     

Influence of the oxidation environment on scale morphology and oxidation rate of Fe–22Cr

Abstract

The oxidation behaviour of a commercial Fe–Cr alloy with 22 wt% Cr was investigated at 1173K in Ar–9 H₂ with 1% H₂O (pO₂ = 9.8 × 10^?19), in air with 1% H₂O (pO₂ = 0.208), and in a combination of the two atmospheres. The oxide morphology was investigated with X-ray diffraction and scanning electron microscopy. The oxide layer consisted of MnCr₂O₄ on top of Cr₂O₃.

Small oxide whiskers were present at the surface after oxidation in Ar–9 H₂ with 1% H₂O but not after oxidation in air with 1% H₂O. For samples initially oxidised in air with 1% H₂O, the oxide/alloy interface was wrinkled and covered with a SiO₂ layer. SiO₂ particles had developed at a rather flat oxide/alloy interface for samples initially oxidised in Ar–9% H₂ with 1% H₂O. The results obtained can be explained assuming that oxide growth occurs by cation diffusion only in Ar–9 H₂ with 1% H₂O, whereas both cation and anion diffusion contribute to the growth in air/H₂O.     

Scale formation mechanisms of martensitic steels in high CO2/H2O-containing gases simulating oxyfuel environments

Abstract

In oxyfuel power plants, metallic components will be exposed to service environments containing high amounts of CO₂ and water vapour. Therefore, the oxidation behaviour of a number of martensitic 9–12%Cr steels in a model gas mixture containing 70% CO₂–30% H₂O was studied in the temperature range 550–700°C. The results were compared with the behaviour in air, Ar–CO₂ and Ar–H₂O. It was found that in the CO₂- and/or H₂O-rich gases, the mentioned steels tended to form iron-rich oxide scales with significantly higher growth rates than the Cr-rich surface scales formed during air exposure. The iron-rich scales were formed as a result of a decreased flux of chromium in the bulk alloy toward the surface because of enhanced internal oxidation of chromium in the H₂O-containing gases and carbide formation in the CO₂-rich gases. Additionally, the presence of water vapour in the exposure atmosphere led to buckling of the outer haematite layer, apparently as a result of compressive oxide growth stresses. The Fe-base oxide scales formed in CO₂(–H₂O)-rich gases appeared to be permeable to CO₂ molecules resulting in substantial carburization of the steel.     

Improvement of high-temperature oxidation resistance of titanium-based alloy by sol–gel method

Sol–gel dip coating of SiO₂ was applied on a TiAl-based alloy, and subsequent heat treatment was performed. XRD and SEM/EDS analysis revealed that an amorphous silica coating was formed on the alloy. Isothermal oxidation and cyclic oxidation at 600 and 700 °C in static air of the specimens with or without coating were performed to investigate the effect of the SiO₂ coating on the oxidation behavior of the alloy by thermogravimetry. The average parabolic rate constants of the coated specimens were greatly reduced due to the presence of the coating. Severe cracks and spallation of the scales were observed on the blank specimens, but not on the coated ones. The oxide scales formed on the uncoated specimens were stratified. For the coated samples, a mixture layer of rutile TiO₂ and Al₂O₃ occurred beneath the applied film.     

溅射Ni11Co26Cr6Al0.5Y涂层对镍基合金在1000 ℃氧化行为的影响

通过对有/无Ni11Co26Cr6Al0.5Y涂层镍基合金在1000℃进行氧化动力学曲线测定,及组织结构观察,研究了Ni11Co26Cr6Al0.5Y涂层对镍基合金高温氧化行为的影响。结果表明:高温氧化期间,合金发生外氧化和内氧化,外氧化层由NiO、NiCrO_4、CoWO_4构成,中间氧化物由TiO_2、Al_2O_3、NiWO_4构成,中间层氧化物层抑制了基体中Al元素向外扩散,形成平直连续的Al_2O_3内氧化物层;合金氧化动力学曲线呈现起伏波动的特征。镍基合金经溅射Ni11Co26Cr6Al0.5Y涂层,可有效改善合金的抗氧化性能;涂层的氧化动力学曲线仅在氧化初期有轻微增重而后趋于平稳,遵循抛物线规律,其形成的Al_2O_3氧化膜未发生明显剥落,仅在涂层内及近涂层/基体界面区域存在少量Al_2O_3内氧化物。     

The influence of reactive element additions to β-NiAlCr alloys on the morphology of thermally grown oxides

Abstract

The effect of the reactive elements (REs), Y and Zr, on oxidation of β-NiCrAl alloy at 1373 K in a gas mixture of argon with 20 vol.% oxygen at atmospheric pressure was evaluated using X-ray diffractometry, scanning electron microscopy, electron probe X-ray microanalysis and secondary ion mass spectroscopy. The oxide surfaces and interface morphologies, compositions and growth kinetics were studied for alloys with 0.32 at.% Zr and 0.24 at.% Y additions and for an undoped alloy. The oxide layer produced on the three different alloys contains mainly α-alumina and some intermediate alumina modification, Cr₂O₃ and RE-oxides. A needle-like morphology was seen on top of the oxide layer for the undoped and Zr alloy. Needle formation on the Y alloy was suppressed by the formation of a thin Y₂O₃ layer during the initial stage of oxidation. Needles were maintained to long oxidation times for the undoped alloy, but disappeared on the doped alloys indicating that some cation diffusion is possible when REs are present. Fewer intermediate alumina modifications are seen for the oxide layers on the RE alloys showing that the REs promote the formation of the α-alumina phase. Oxide layer growth occurs in two stages for all alloys. Initially, oxide growth is rapid with outward diffusion of aluminium. The second stage of oxidation is slow and is initiated by the formation of a closed α-alumina layer limiting further oxidation to inward oxygen diffusion. This stage is characterised by parabolic growth kinetics associated with a constant aluminium interface concentration. The oxide layer is thinnest for the Y alloy due the fine Y₂O₃ layer acting as a diffusion barrier. The oxide/alloy interface for the undoped alloy is flat and shows many voids, whereas voids are not seen for the RE alloys. This is due to the promotion of a closed α-alumina layer giving predominantly inward growth early in the oxidation process. Oxide pegs of the RE are also seen growing into the alloys. The lack of voids and the oxide pegs are advantageous for oxide layer adhesion to the doped alloys.     

The effect of carbon on the high temperature oxidation of Fe-31 Mn-9Al-0.87C alloy

The alloy with the composition Fe-31Mn-9Al-0.87C was employed to investigate the effects of carbon on the oxidation behaviour at 800, 900 and 1000° C in dry air. Electron and optical microscopy were applied to examine the morphology and elemental redistribution in the oxide scale. Oxidation kinetics of the alloy oxidized at 800 and 900° C exhibited three-stage and two-stage parabolic rate laws, respectively. For the alloy oxidized at 1000° C, a carbon-induced breakaway three-stage oxidation mechanism developed. The carbon addition had a detrimental effect on the oxidation resistance and resulted in a porous initial oxide layer, which was favourable to the oxidation of manganese as well as the formation of a uniform and bulky oxide. As the oxidation temperature was increased, the diffusion rates of the metallic elements and the healing ability of oxide scales were enhanced. However, when the carbon content in alloy was above the saturation value, a breakaway scaling may have occurred due to the carbon-induced oxidation.     

Ti600钛合金的氧化行为

研究了Ti600钛合金在700-1000℃范围内的氧化行为.结果表明,Ti600的100 h氧化动力学近似遵循抛物线-直线规律,氧化激活能为224 kJ·mol-1.Ti600试样在700℃氧化100h后其表面形成了致密的氧化皮,而在高于700℃氧化100 h后氧化皮出现多层结构并开始剥落,氧化皮主要由金红石型TiO2...     

Oxidation mechanism of Ni–20Cr thin strips and effect of a mechanical loading

Abstract

The oxidation behaviour of Ni-20Cr foils of 200 μm thickness was studied in air at 600°C and 900°C. The oxide morphology and nature were determined by SEM and TEM. The scales formed at all temperatures were complex, with an outer NiO layer and an intermediate layer of equiaxed NiO, NiCr₂O₄ and Cr₂O₃ grains. At 600°C, internal oxidation of chromium occurred in the substrate while a continuous Cr₂O₃ layer was observed at 900°C. The effect of a tensile load on the oxidation kinetics and mechanism of Ni–20Cr alloy was also examined. The results indicated that applying a tensile load did not modify the oxide nature and morphology but induced an increase of the oxidation rate, promoting the formation of internal oxidation at 600°C, and of a NiCr₂O₄ layer at 900°C.     

The effect of Ni additions on the oxidation behaviour of Co–Re–Cr high-temperature alloys

Abstract

The present study focused on the influence of Ni on the microstructure and oxidation behaviour of Co–Re–Cr-based alloys. Alloys with three different Ni contents were tested in laboratory air at 800–1100 °C. A refinement and a reduction of the σ phase volume fraction as well as a change in the matrix microstructure were observed. Thermogravimetric measurements showed that the alloys with higher Ni contents possess a better oxidation resistance when exposed to higher temperatures. All alloys suffered from continuous mass loss during oxidation at 800 °C due to the formation of porous oxides scales, consisting of Co₃O₄, Co(Ni)O and Ni-doped CoCr₂O₄, which allow the evaporation of Re-oxides. At 900–1100 °C, only the alloy with 25 at. % Ni showed parabolic oxidation kinetics after a short period of transient oxidation. This is a result of the fast formation of a protective Cr₂O₃ layer. It was also found that exposure to air at 1000 °C leads to a phase transformation of the bulk material; an oxidation-induced formation of fine hexagonal close-packed (hcp) grains was observed near the oxide scales. It is supposed that the improved oxidation resistance of Ni-containing Co–Re–Cr alloys is a result of enhanced Cr diffusion caused by the Ni addition. The extensive formation of the fcc phase in the alloy matrix had a detrimental effect on the oxidation behaviour of the Ni-containing Co–Re–Cr-based alloys.     

合金元素复合化对Ti_(2)AlNb合金高温抗氧化性能影响EI北大核心CSCD

Ti_(2)AlNb合金具有良好的工艺性能、综合力学性能和较低的密度等性能优势,是新型航空发动机的重要选材之一。为拓宽Ti_(2)AlNb合金的应用范围,需对传统Ti_(2)AlNb合金进行合金成分优化和工艺组织调控以进一步增强其高温抗氧化性能。本研究在传统Ti-Al-Nb三元合金体系基础上,综合设计Mo,Zr,W等合金复合化的方法提高Ti_(2)AlNb合金的抗氧化能力,通过对新型Ti_(2)AlNb合金在750℃和850℃的氧化增重行为分析、氧化层特征结构分析、表面氧化物种类和合金成分过渡分布分析等,发现Mo合金元素引起Ti_(2)AlNb合金在750℃上升至850℃时抗氧化性能的明显下降,Zr合金元素则始终保持着Ti_(2)AlNb合金良好的高温抗氧化能力;更为深入的截面试样SEM表征可将氧化层结构细分为氧化物层、富氧扩散层和组织演变层,Zr和W合金元素对850℃高温氧化过程中不同氧化层结构具有协同抑制作用,因此提出通过Zr和W合金元素复合的方法作为新型Ti_(2)AlNb合金抗氧化合金成分优化方向。