DZ445镍基高温合金高温长时间氧化形成的多层膜结构

研究了高Cr/Al比和中Ta含量的DZ445镍基高温合金在900℃下300～2600 h的氧化行为。结果表明,900℃氧化≥500 h,氧化膜呈现多层结构,最外层氧化物相为NiCr₂O₄、Cr₂O₃和TiO₂,次外层为CrTaO₄和TiO₂,次内层为Al₂O₃、NiCr₂O₄和NiO,最内层主要是Al₂O₃。次外层和次内层的出现使得合金氧化速率降低,表现为动力学方程的指数大幅度增加和氧化速率常数急剧下降。这2层的出现也使得合金氧化机理发生转变,次外层形成后氧化过程由合金元素Cr、Ti、Ni向外扩散转变为由Al的向外扩散和O的向内扩散所控制;次内层形成后,氧化过程转变为Ni、Cr的向外扩散和O的向内扩散所控制。这种多层氧化膜结构使得DZ445合金表现出优异的抗氧化能力。     

一种镍基单晶高温合金的恒温氧化行为

通过静态增重法对一种镍基单晶高温合金在900℃和1000℃的恒温氧化行为进行了测定,并利用X射线衍射和扫描电镜对氧化产物进行了分析。结果表明,该合金在900℃和1000℃均为完全抗氧化级,900℃的氧化速率明显低于1000℃的氧化速率。合金的氧化产物以(Ni,Co)O为主,并形成了较多的α-Al₂O₃ 和较少量的Cr₂O₃,同时形成了CrTaO₄及（Ni,Co）Al₂O₄和 Co(Al,Cr)₂O₄等尖晶石氧化物。氧化物呈层状分布,(Ni,Co)O在最外层,而Al₂O₃在内层。另外,在靠近α-Al₂O₃层的合金基体中出现了内氮化物。     

309SMOD奥氏体耐热不锈钢的高温氧化行为

采用增重法分析了309SMOD奥氏体不锈钢板材在不同温度下的氧化行为,获得了该钢高温氧化的抛物线动力学曲线,利用SEM、EDS及XRD对氧化物的形貌和物相进行了分析。结果表明,800 ℃氧化物形貌为板状和块状,900 ℃、1000 ℃的氧化物主要为尖晶石颗粒。309SMOD奥氏体不锈钢表面由于高温氧化生成具有3层结构的混合氧化物膜,最外层结构为MnCr₂O₄和FeCr₂O₄,次外层结构的氧化物为Cr₂O₃,最内层结构的氧化物为SiO₂,这种结构的氧化膜使得309SMOD奥氏体不锈钢具有良好的抗高温氧化性能。     

Mar-M247高温合金900℃下的氧化行为研究

为探究燃气轮机用高温合金在服役环境中组织结构变化及其对合金氧化性能的影响,利用扫描电镜和能谱表征了MarM247镍基高温合金在900℃长时效后的显微组织,研究其在1000、3000、5000、8000h时效后的氧化性能。结果表明,时效1000h的氧化初期合金表面氧化物相变化较快,Al₂O₃氧化膜不完整,氧化膜增厚较快;随着氧化时间增加,富W氧化膜内生成大量孔洞和岛状不连续WO2,导致内层Al₂O₃膜界面发生剥落,外层氧化膜结构得到简化,内层Al₂O₃膜增厚且变得均匀;时效8000h后氧化层总厚度和内层Al₂O₃膜变化幅度明显减小,整个氧化膜结构趋于稳定。由于内层保护性Al₂O₃膜的增厚和结构均匀连续,使得合金的氧化性能提高。     

Ti2AlNb合金不同温度下的高温氧化行为

研究了Ti₂AlNb合金在不同温度下的高温氧化行为。采用连续氧化增重的方法计算了合金氧化动力学规律;用XRD、SEM、EDS等手段研究氧化后的表面相结构和表面、截面形貌以及元素分布。结果表明,Ti₂AlNb合金在650 ℃和750 ℃下的连续氧化动力学曲线近似符合抛物线规律,而在850 ℃时符合直线规律。氧化层分层现象明显,且都未形成连续致密的Al₂O₃保护层。氧化产物主要为TiO₂,少量的Al₂O₃、Nb₂O₅,以及微量的AlNbO₄、Nb₂TiO₇、AlNb₂。氧化温度越高,分层越明显,富氧层越厚,危害性氧化物越多。     

一种铸造镍基高温合金的氧化行为

利用静态增重法研究了铸造镍基高温合金Ni48Cr28在950~1 150℃温度范围内的氧化动力学,其氧化动力学曲线符合抛物线规律。环境扫描电镜和能谱分析表明,Ni48Cr28合金的氧化膜最外层是比较致密的Mn与Cr氧化物混合层,中间层是性质致密的Cr2O3氧化层,内层是疏松的SiO2。通过研究添加稀土元素的Ni48Cr28在950~1 150℃高温抗氧化性能,结果表明适当的稀土元素能提高合金在950~1 150℃的抗氧化性能。     

Al含量对Fe-22Cr-25Ni含铝奥氏体耐热钢高温抗氧化性能的影响

以HR3C合金成分为基础,通过调控Cr、Ni含量和添加1.5%,2.5%和3.5% (质量分数) 的Al制备了Fe-22Cr-25Ni型含铝奥氏体耐热钢,并研究了合金的高温抗氧化性能。利用SEM、EDS和XRD对含铝奥氏体钢700、800和900 ℃氧化后的氧化膜组成、结构进行了表征。结果表明：22Cr-25Ni-2.5Al和22Cr-25Ni-3.5Al含铝奥氏体耐热钢在700和800 ℃下具有优异的抗高温氧化性能。氧化后表层形成了连续致密的Al₂O₃保护膜,提高了其高温抗氧化性能。3种耐热钢经900 ℃氧化时形成外层为Cr₂O₃和MnCr₂O₄的复合氧化层,且氧化层下存在Al₂O₃内氧化物和AlN析出相,不能对基体起到有效保护作用。     

选区激光熔化AlCoCrCuFeNi高熵合金的高温氧化行为研究

基于选区激光熔化技术制备了AlCoCrCuFeNi高熵合金，研究其显微组织及800、1000和1200℃下的高温氧化行为，采用X射线衍射仪和扫描电镜等方法表征分析了氧化膜的物相组成和形貌特征。结果表明：所制备的AlCoCrCuFeNi高熵合金主要包含bcc相、bcc/B2相和少量的fcc相，显微组织为长直柱状枝晶和等轴胞晶结构组成的非平衡异质结构。AlCoCrCuFeNi高熵合金在3种不同温度下的高温氧化性能优异，氧化动力学曲线基本符合抛物线定律，氧化速率对温度有明显的依赖性，其随着温度的提高而增加，并且氧化反应导致氧化膜中产生了明显的空洞和裂纹，为金属元素的持续扩散提供了通道，加剧了氧化反应，所引起的剥落现象愈加严重，氧化膜主要成分为Cr₂O₃、Al₂O₃和MCr₂O₄尖晶石混合氧化物，较为致密的氧化膜可以有效地抑制基体受到进一步氧化，提高抗氧化性能。     

Al对Fe-20Cr-35Ni-0.6Nb合金显微组织和抗氧化性的影响

采用增量法研究了不同Al含量(0.5%、1.5%、2.5%,质量分数)的Fe-20Cr-35Ni-0.6Nb含Nb合金在1000 ℃空气条件下的抗氧化。采用SEM、EDS、TEM、拉曼光谱等手段研究了合金的显微组织和氧化膜特性。结果表明,3种含Nb合金组织为单相奥氏体,基体中存在少量弥散分布的NbC沉淀相,氧化前后沉淀相含量和晶粒大小保持不变。添加0.5%和1.5%的Al后,含Nb合金的表面形成多层结构的氧化膜,最外层和第三层为Cr₂O₃,次表层主要为NiCr₂O₄、NiFe₂O₄和Fe₂O₃,最内层为Al₂O₃内氧化层。基体中的NbC析出相和氧化膜中少量Nb的氧化物(Nb₂O₅)加剧了氧化膜的疏松。当Al含量增加到2.5%时,含Nb合金表面形成连续致密的Al₂O₃氧化膜,降低了Fe-20Cr-35Ni-0.6Nb合金的氧化速率,提高了抗氧化性。     

DZ125合金表面Cr-Al-Y涂层抗高温氧化性能及摩擦性能

目的 提高DZ125合金的抗高温氧化性能和耐磨性。方法 采用包埋渗技术在DZ125合金表面制备Cr-Al-Y涂层,分析Cr-Al-Y涂层经高温氧化后的组织结构和相组成,对比研究涂层与基体的摩擦行为。结果Cr-Al-Y涂层具有多层组织结构,经高温氧化100 h后,涂层的平均质量损失量仅为0.85 mg/cm²。由于在高温氧化过程中Cr-Al-Y涂层形成了连续致密的Al₂O₃和Cr₂O₃氧化膜,随着氧化温度的升高,涂层表面的氧化速率增大,导致氧化产物剥落,并出现表面缺陷。Cr-Al-Y涂层的摩擦因数明显低于DZ125基体的摩擦因数,DZ125合金的摩擦因数约为0.45,Cr-Al-Y涂层的摩擦因数约为0.2。在摩擦过程中,DZ125合金发生了犁削磨损和磨粒磨损,涂层表面发生了磨粒磨损。结论 该涂层具有优异的抗高温氧化性能,连续致密的Al₂O₃氧化膜和Cr₂O₃氧化膜能够有效阻挡氧化性气氛与基体直...     

铸造镍基合金K444在900℃空气中的长期氧化行为

用热重法研究镍基高温合金K444在900℃下氧化1000 h的动力学。结果表明,K444合金氧化动力学遵从抛物线规律,以x射线衍射、扫描电镜和能谱分析及电子探针成分分析测定氧化膜的组成,结果表明氧化膜由多层组成,外层为TiO₂,内层以Cr₂O₃为主还包括内氧化层和贫Υ′层。观察到沿晶界偏聚的碳化物氧化,提出了氧化饥制。     

Oxidation characteristics of Ti-25Al-10Nb-3V-1Mo

Static oxidation kinetics of Ti-25Al-10Nb-3V-1Mo (atomic percent) were investigated in air over the temperature range of 650–1000°C using thermogravimetric analysis. The oxidation kinetics were complex at all exposure temperatures and displayed up to two distinct stages of parabolic oxidation. Breakaway oxidation occurred after long exposure times at high temperatures. Oxidation products were determined using x-ray diffraction techniques, electron microprobe analysis, and energy dispersive x-ray analysis. Oxide scale morphology was examined using scanning electron microscopy of the surfaces and cross-sections of oxidation specimens. The oxides during the parabolic stages were compact and multilayered, consisting primarily of TiO₂ doped with Nb, a top layer of Al₂O₃ and a thin bottom layer of TiN. The transition between the first and second parabolic stage is linked to the formation of a TiAl layer at the oxide-metal interface. Porosity also formed in the TiO₂ layer during the second stage, causing degradation of the oxide and breakaway oxidation.     

Effects of aluminum on the oxidation of 25Cr-35Ni cast steels

The oxidation kinetics and morphological development during reaction of two cast austenitic steels at 1000°C in pure dry oxygen at 20 kPa are reported. Both steels contained approximately 25 wt.% Cr and 35 wt.% Ni and, in addition, one steel contained 3.3 wt. %. Both steels oxidized to form external scales consisting mainly of Cr₂O₃ with a thin outer layer of manganese rich spinel. Scale growth kinetics were parabolic, and somewhat faster rates were observed for the aluminum bearing steel. In both steels, deep internal oxidation occurred at the site of primary (interdendritic) carbides. The kinetics of this process were parabolic, and rate control was attributed to oxygen diffusion along the interface between internal oxide and matrix metal. In the aluminum-free steel, interdendritic carbides were converted to chromium rich oxide, but when aluminum was present, a sheath of aluminum rich oxide formed around the carbides. In this latter case, the rate of interdendritic penetration was somewhat slower. The aluminum bearing steel also formed large numbers of rod-shaped Al₂O₃ precipitates within the austenitic dendrites. Deepening of the Al₂O₃ precipitate zone also proceeded according to parabolic kinetics at a rate consistent with rate control by diffusion of oxygen along the oxide-alloy interfaces.     

等离子喷涂NiCrCoAlY涂层氧化控制研究

利用等离子喷涂技术制备了NiCrCoAlY粒子和涂层,研究了等离子喷涂过程中NiCrCoAlY粒子的氧化行为以及屏蔽气体对NiCrCoAlY涂层抗高温氧化性能的影响。结果表明,粒子在飞行过程中存在对流氧化和扩散氧化两种氧化机制,对NiCrCoAlY粒子来说,在距喷嘴55 mm以内的射流中心处以对流氧化为主,在距离喷嘴55 mm以外将以扩散氧化为主;除飞行中的氧化外,粒子在喷涂过程中还发生形成涂层后的氧化,NiCrCoAlY粒子以飞行中的氧化为主;添加屏蔽气体能减少喷涂过程中涂层的氧化,提高涂层的抗高温氧化性能     

纯钛TIG焊接接头的高温氧化行为

对纯钛氩弧焊焊接接头在550 ℃下氧化不同时间（2,4,6,8 h）以及在不同温度（650,750,850,950 ℃）下氧化4 h的氧化动力学、氧化形态和氧化产物进行了研究。结果表明,在550 ℃下,氧化时间对焊接接头氧化行为的影响有限,而氧化温度对纯钛焊接接头的氧化行为有显著影响,且温度越高,氧化越严重。在低温下,纯钛焊接接头的氧化动力学接近准线性定律,随着温度升高,氧化速率呈指数增长。此外,焊接接头表面产生的氧化产物是具有锐钛矿和金红石结构的TiO₂,温度对TiO₂的类型没有明显影响。纯钛焊接接头的氧化过程可描述为：氧气在表面被吸收;氧化物优先在缺陷区形核;氧化物横向生长、增厚。在较高温度下,氧化膜中出现裂纹或空隙,成为O原子传输通道,导致O和Ti原子的高扩散速率和氧化速率。     

The Effect of Crystallographic Orientation on the Oxidation Behavior of a Single-Crystal Nickel-Base Superalloy

The oxidation kinetics of DD100 nickel-base single-crystal alloy, with (221) and (100) surface orientations were tested in this study by thermogravimetry. A pronounced anisotropy in both the cyclic and isothermal oxidation resistance of DD100 alloy was observed. The (221) crystallographic surface of DD100 had a slower oxidation rate than the (100) surface when isothermally exposed to stationary air at 950°C, whereas the opposite results were obtained at 1050°C. When cyclically oxidized at 1100°C, the weight loss of samples with (221) surfaces was significantly greater than that of (100) surfaces, so that the cyclic-oxidation anisotropy was more remarkable at 1100°C than at 950°C. The different spatial alignment of the / interface is thought to be responsible for the anisotropic oxidation behavior of the nickel-base single crystal alloy.     

High temperature oxidation of metals under time-dependent gas pressure

A theoretical study on the high-temperature oxidation of thick oxide films grown under a time-dependent gas partial pressure is reported. The diffusion across the film is assumed to be the rate-limiting step of the overall reaction, and Wagner's hypotheses were used as the starting point for our reasoning. A general formulation for the oxidation under no time constant gas pressure, in terms of a time-dependent answer function is given. The effect of an external electric field on the reaction rate is also reported when a constant current density,J, is applied to the oxide scale. If the oxide is a good electronic conductor atJ=0 andt , we found that the reaction rate assumes formally the well-known Wagner's expression of the rate constant but with a gas partial pressure at oxide/gas interface which is a time function. If the oxide is a good ionic or electronic conductor, the effect due to an external electric field,J 0, on the reaction rate is the same as predicted by the Wagner's theory.     

Fe-Y合金在800℃空气中的氧化行为

研究了Fe-5Y和Fe-10Y合金在800℃空气中的氧化行为。结果表明：二元Fe-Y合金氧化动力学曲线不规则,此温度下Fe-10Y合金的氧化速率高于Fe-5Y合金的氧化速率。Fe-5Y合金及Fe-10Y合金形成了相似的氧化膜结构,且它们都发生了内氧化现象。同时合金未形成单一的Y₂O₃层,这归结于Y在Fe中非常低的溶解度及合金中两相共存而阻碍了Y通过合金向外扩散。     

V/Nb对Ti-45Al-9(V, Nb, Y)合金抗氧化性能的影响

βγ-TiAl合金具有良好的高温变形能力,为TiAl合金的发展开辟了新的途径。成功制备了不同x=V/Nb(x=1,1.5,2,3.5)的βγ-TiAlTi-45Al-9(V,Nb,Y)合金,研究了上述合金在800℃静止空气中的氧化行为。结果表明:当x=1时,Ti-45Al-9(V,Nb,Y)合金中形成条带状、连续致密的Al2O3氧化层,显著提高了合金的抗氧化能力。随着x=V/Nb的增加,Al2O3氧化层厚度变薄,合金的抗氧化能力下降。     

Oxidation resistance of eight heat-resistant alloys at 870°, 980°, 1095°, and 1150°C

Oxidation testing of heat-resistant alloys is described. The testing procedure utilized weight-gain measurements using one specimen, which was withdrawn and weighed at intervals of 1 week, for 10–18 weeks. The specimen was placed in a porcelain cup during exposure and covered upon cooling to retain spalled oxide. Weight gain was used to determine the kinetics of oxidation and was extrapolated to 3000 hr. The specimen was withdrawn at the end of the exposure, weighed, cathodically descaled, and reweighed. The ratio of oxygen ions to metal ions was determined for each alloy and test temperature. This ratio approaches the stoichemetric ratio for Fe₃O₄ or Cr₂O₃. The ratio for each test is used to convert weight gain to weight loss. The amount of adherent oxide was determined as well as the total amount of oxide, leading to an expression for oxide adherency. The oxidation resistance of Fe-Cr-Ni alloys increased with increasing Cr and Ni, with Cr being the most critical element. Additions of Si, Al, or Ce were shown to extend the usefulness of Fe-Cr-Ni alloys.