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.     

Preferential oxidation of carbon during the initial stage of oxidation of an Fe-0.8%C alloy at 400°C

The preferential oxidation of carbon in an Fe-0.8%C alloy during the first 60 min of oxidation in air at 400°C was studied by a thermogravimetric method and by measuring the quantity of evolved carbon oxides. The morphology of the external oxide surface depended on the type of exposed phase—a rosettelike oxide grows over ferrite, whereas the oxide surface over cementite is relatively smooth. A possible mechanism for the preferential oxidation of carbon and its subsequent cessation is proposed.Formerly of Institute of Materials Engineering, Academy of Mining and Metallurgy, Cracow, Poland.     

INTERNAL OXIDATION OF Fe_3Al DURING HIGH TEMPERATURE OXIDATION

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High-temperature oxidation under time-dependent gas pressure: An application to steel oxidation

A study on the high-temperature growth of thick wustite films on low-carbon steel under a time-dependent oxygen partial pressure law is reported. The experimental data were interpreted using a general formulation of oxidation under non-time-constant gas activity. Good agreement between the theory and the experimental data was obtained. The physical reasons that justify the change of the oxygen activity at the steel-atmosphere interface as observed during the oxidation process are discussed also.     

高温合金Inconel625切削用刀具材料抗氧化性能研究

通过化学热力学从理论上推导高温合金Inconel625切削用刀具材料在高温下可能发生的氧化反应,选用硬质合金(YG8)、涂层硬质合金和陶瓷三种刀具材料,利用高温加热炉对不同刀具材料进行抗氧化实验,并对高温氧化产物进行扫描电镜(SEM)和X射线衍射(XRD)分析。结果表明: 在高温氧化试验中,YG8和涂层硬质合金的刀具材料中的WC和Co部分被氧化成WO₃、Co₃O₄,且随着温度的升高,氧化反应更加剧烈;而陶瓷刀具中只有TiC被氧化成了TiO₂,表现出较好的抗氧化性能;三种刀具材料的抗氧化性的顺序为：陶瓷刀具＞涂层硬质合金＞YG8。     

Fe-Ni合金在600 ℃空气中的氧化行为

采用称量法研究了两种Fe-Ni合金（Ni含量分别为5%和9%,质量分数）在600 ℃静态空气中的高温氧化行为,对比分析了两种合金的氧化动力学特征,采用扫描电镜（SEM）、X射线衍射（XRD）和能谱分析（EDS）等手段分析了表面氧化膜的物相组成及显微结构。结果表明：Fe-5%Ni和Fe-9%Ni合金在 600 ℃空气中的氧化行为基本类似,氧化前期Ni-5合金质量增加量较高,16 h后发生逆转,其氧化动力学遵循近似抛物线规律,表明氧化膜内的离子扩散过程受氧化过程控制。两种合金的表面氧化膜均由Fe3O4 和 Fe2O3 组成,同时含有尖晶石相(Ni, Fe)3O4。Ni-9合金氧化膜中尖晶石相含量相对较高,是导致氧化质量增加发生逆转的主要原因。     

High-temperature oxidation of Ti3Al−Nb alloys

Titanium aluminide (Ti₃Al–Nb) has potential for high-temperature applications because of its low density and high-temperature strength. This research is aimed at improving the high-temperature oxidation resistance of a Ti₃Al–Nb alloy by modification of its composition. The oxidation rates of Ti₃Al–Nb alloys were measured from 600 to 900°C in air. The oxide layer was examined by X-ray diffraction, scanning electron microscopy, and electron probe microanalysis. The experimental results reveal that alloys with added Nb tend to form denser oxide layers and that oxidation rate can be reduced by increasing Nb content (up to 11 at.% in this study), which is in good agreement with other investigators. The only exception is a Ti₆₅Al₂₅Nb₁₀ alloy, which shows better oxidation resistance than the commercial Ti₆₅Al₂₄Nb₁₁ alloy. The oxidation resistance of Ti₆₅Al₂₅Nb₁₀ alloy can also be improved slightly by the addition of small amounts of Si or Cr. An increase in the oxidation resistance of Ti₆₅Al₂₅Nb₁₀ alloy containing Y was observed at 900°C but not at 800°C or below. The parabolic oxidation rate equation is adequate to describe the high-temperature oxidation reaction of the Ti₃Al–Nb alloys in the atmosphere.     

The Isothermal and Cyclic Oxidation Behavior of a Titanium Aluminide Alloy at Elevated Temperature

The isothermal and cyclic oxidation behavior of Ti-47Al-2Mn-2Nb with 0.8 vol.% TiB₂ particle-reinforced alloy was investigated in air between 700 and 1000 °C. In the study, the kinetics of isothermal and cyclic oxidation were performed by using a continuous thermogravimetric method which permits mass change measurement under oxidation conditions. The oxide scales and substrates were characterized by scanning electron microscopy with energy-dispersive x-ray analysis and x-ray diffraction. At 700 and 800 °C, the alloy showed an excellent oxidation resistance under isothermal and cyclic conditions. After exposure to air above 800 °C, the outer scale of the alloy was dominated by a fast-growing TiO₂ layer. Under the coarse-grained TiO₂ layer was the Al₂O₃-rich scale, which was fine-grained. At 900 and 1000 °C, the extent of oxidation increased clearly. The oxidation rate follows a parabolic law at 700 and 800 °C. However, the alloy, upon isothermal oxidation at 900 °C, can be divided into several stages. During the cyclic oxidation at 900 and 1000 °C, partial scale spallation takes place, leading to a stepwise mass change.     

奥氏体不锈钢Cr18Ni3Mn11Cu3NbN高温抗氧化性能

采用称重法测得了奥氏体不锈钢Cr18Ni3Mn11Cu3NbN在不同温度下的高温氧化动力学曲线,结果表明,该钢在700℃和800℃的氧化曲线遵循抛物线氧化规律,根据平均氧化速度的评级标准,在此温度下钢＂完全抗氧化＂。利用扫描电镜、X射线衍射的方法对氧化膜表面的形貌及结构进行了研究,发现该钢700℃氧化膜致密完整,主要由Mn2O3、MnFe2O4（尖晶石结构）和Cr的氧化物组成;800℃氧化膜出现脱落,主要由Mn2 O3、MnFe2 O4（尖晶石结构）、Cr的氧化物和Fe的氧化物组成;900℃氧化膜脱落严重,主要由Mn2O3、Fe2O3、尖晶石结构的MnFe2O4组成。     

二元Ti—Al合金高温氧化机理

研究了Ｔｉ－３３．３％Ａｌ，Ｔｉ－４８％Ａｌ和Ｔｉ－５２％Ａｌ（原子分数）合金在１０７３和１１７３Ｋ空气中的恒温氧化行为，用Ｘ射衍射仪（ＸＲＤ）和配有能谱仪（ＥＤＳ）的扫描电子显微镜（ＳＥＭ）对氧化层表面的相组成，形貌以及氧化层剖面的显微结构和氧化机理进行了分析，结果表明：二元Ｔｉ－Ａｌ合金的氧化层由一系列薄层组成，其氧化过程可以为三个阶段，不同化层的生长方向及氧化反应的控制步骤略有差别，氧化动力     

氧化时间对钛表面微弧氧化膜层的影响

采用恒电流微弧氧化技术,在钛表面制得含HA的TiO2陶瓷膜,考察了氧化时间对氧化膜微观形貌、膜厚、相结构及耐体液腐蚀性能的影响。结果表明,随氧化时间增长,膜层表面多孔形貌变化明显,膜层厚度呈先增后降的趋势。氧化时间延长,膜层相组成由金红石、锐钛矿为主变为以羟基磷灰石为主。模拟体液极化曲线分析表明,微弧氧化膜的钝化行为随氧化时间延长而优异,但氧化时间超过20 min后,增大氧化时间对钝化效果的影响不再明显。