MoSi2及其复合材料的高温和低温抗氧化性能研究

采用热质量分析法(TGA)和X射线衍射(XRD)对MoSi2及其复合材料的高温氧化性能、低温氧化机理和影响因素进行了研究.结果表明,40vol%SiC/MoSi2复合材料在1300℃高温等温氧化条件下具有优异的高温抗氧化性;通过提高MoSi2的纯度、添加与氧有亲和力的元素及高温预氧化形成致密的SiO2保护膜都有利于改善和提高MoSi2材料的抗低温氧化性能.     

TiC-MoSi_2复合材料的原位合成及其低温氧化特性

为了改善MoSi2力学性能和低温抗氧化性能,选用TiC颗粒来增强补韧MoSi2,通过XRD和SEM表征合成MoSi2基复合材料的微观结构并研究了预氧化对MoSi2基复合材料低温抗氧化性能的影响.结果表明,采用Mo、Si、Ti、C粉末可以自蔓延原位合成20 v01%TiC-MoSi2复合材料.复合材料在500℃氧化240 h增重1.261 mg·cm-2,氧化动力学呈线性关系,生成疏松多孔的氧化层导致"粉化"现象发生.经1200℃预氧化处理,20 v01%TiC-MoSi2复合材料在500℃氧化240 h增重4.83×10-mg·cm-2.预氧化处理后的材料表面形成致密的TiO2和SiO2复合膜抑制了TiC-MoSi2材料出现低温"粉化"现象.     

MoSi2含量对原位生成MoSi2/Si3N4复合材料高温氧化性能的影响

摘要：研究了不同MoSi2含量的MoSi2/Si3N4复合材料的高温氧化行为，用XRD和SEM分析材料氧化以后的相组成及显微结构，探讨了该材料的氧化机理和氧化膜的破坏方式。结果表明，不同MoSi2含量的MoSi2/Si3N4复合材料在1400℃空气中氧化100h的氧化增量符合抛物线规律，随着MoSi2的含量的增加，材料的氧化活化能升高，氧化后的强度损失率减小。     

SiC/MoSi2复合材料500℃氧化行为研究

研究了不同SiC体积分数（30%-50%）的SiC/MoSi2复合材料低温500℃的氧化性能。结果表明：SiC/MoSi2复合材料在低温（500℃）时具有优异的抗氧化性能,氧化500h没有发生氧化粉化现象。复合材料的氧化增重随SiC体积分数的增加而减少。复合材料表面的抗氧化保护层均匀致密,材料内部缺陷少,材料内部晶界没有发生Mo与Si的氧化,材料的抗低温氧化性能得到显著提高。     

预氧化对TiC-TiB2/MoSi2复合材料低温氧化行为的影响

研究了20vol％TiC-TiB2/MoSi2复合材料和高温预氧化处理后材料在500℃的低温氧化行为.结果表明,该复合材料在500℃的氧化动力学基本呈线性关系,氧化240h后增重1.67 mg· cm-2,表面生成的氧化层呈疏松多孔并出现“粉化”现象;1200℃预氧化处理的材料在500℃氧化240h后仅增重0.062 mg· cm-2,没有出现“粉化”现象;预氧化处理后的材料表面形成致密的TiO2和SiO2复合保护膜提高了复合材料的低温抗氧化能力.     

TiC-TiB2增强MoSi2复合材料的力学性能及抗氧化行为

以MoSi2、Ti和B4C粉为原料,采用高温热压技术合成不同体积分数TiC-TiB2增强MoSi2复合材料,研究TiC-TiB2颗粒对MoSi2基体材料显微组织、力学性能和高温氧化性能的影响.结果表明:30%TiC-TiB2/MoSi2(体积分数)复合材料的抗弯强度和维氏硬度分别达到468.3 MPa和17.07 GPa,比纯MoSi2的分别增加了63.2%和83.5%.随着TiC-TiB2体积分数的增加,复合材料的断裂方式由以沿晶断裂为主向以穿晶断裂为主转变,强化机制是细晶强化和弥散强化.在800～1 200 ℃氧化192 h时,30%TiC-TiB2复合材料的增质是10%TiC-TiB2复合材料的2.38～3.23倍.氧化层中没有发现低熔点的B2O3,而TiO2和SiO2的存在使材料具有较好的抗氧化性.     

MoSi2 材料的强韧化

综述了MoSi2及其复合材料的国内外研究现状和发展趋势.MoSi2具有良好的综合性能而被作为重要的高温发热元件材料和高温结构材料,但其室温脆性、低温氧化和高温蠕变制约了其工业应用.研究结果表明,合金化和复合化是MoSi2室温增韧和高温补强的主要途径.     

MoSi2涂层高温抗氧化性能研究进展

综述了MoSi2作为C/C复合材料和难熔金属的高温抗氧化涂层的氧化性能的研究进展,比较研究了MoSi2高温抗氧化涂层的制备工艺,提出了MoSi2涂层技术的未来发展方向,即研发高温长寿命高可靠性抗氧化涂层、超高温抗氧化涂层,以满足航空发动机及航天飞机在恶劣工况条件下的使用要求.     

La2O3-Mo5Si3/MoSi2复合材料的力学性能和高温氧化行为

通过自蔓延高温合成了稀土协同Mo5Si3复合强韧化MoSi2的复合粉末,研究了La2O3-Mo5Si3/MoSi2复合材料的室温力学性能和高温氧化特性。结果表明:与纯MoSi2相比,稀土和Mo5Si3细化了材料的晶粒,提高材料的室温弯曲强度和断裂韧性,其强化机制为细晶强化,韧化机制为细晶韧化、裂纹偏转、裂纹分支和微桥接;当Mo5Si3含量不超过30%(摩尔分数)时,随着Mo5Si3含量的增加,材料的抗氧化性能降低,而RE-40%Mo5Si3/MoSi2(摩尔分数)复合材料出现粉化现象;RE-Mo5Si3/MoSi2复合材料抗氧化性的降低,主要是由于Mo5Si3较差的抗氧化性、材料致密度的降低以及晶粒细化的结果;0.8%稀土(质量分数)协同5%Mo5Si3(摩尔分数)的RE-Mo5Si3/MoSi2复合材料具有较好的综合力学性能和高温抗氧化特性。     

MoSi2-AlCr2准二元系合金的低温抗氧化性能

通过热重量分析(TGA)、X射线衍射(XRD)和扫描电镜(SEM)等研究了MoSi2及MoSi2-AlCr2准二元系合金在500℃下的低温抗氧化性能.结果表明:采用热压烧结方法制备的纯MoSi2及MoSi2-AlCr2准二元系合金在500℃低温循环氧化条件下具有良好的低温抗氧化性,氧化100 h均未发生“Pesting”现象.同时发现,纯MoSi2的氧化动力学曲线符合抛物线形规律,而MoSi2-AlCr2准二元系合金在20 ～100 h阶段,氧化动力学曲线基本上呈直线型.由此可见,添加AlCr2可显著提高MoSi2的低温抗氧化能力.     

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.     

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.     

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     

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.     

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。     

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.     

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.     

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。     

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 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.