γ-TiAl表面NiCrAlY/Al复合涂层的高温氧化行为

采用磁控溅射和电弧离子镀技术在γ-TiAl合金表面制备NiCrAlY/Al复合涂层,研究了复合涂层对提高γ-TiAl合金抗高温氧化性能的作用机理。经950℃恒温氧化100 h后,涂层表面未发现裂纹和脱落,涂层试样氧化增重值较基体大幅减小。对氧化层进行了SEM、EDS和XRD分析,结果表明无保护涂层的基体γ-TiAl合金表层疏松多孔,无法抵抗高温环境下氧气对基体合金的侵蚀。复合涂层表面的NiCrAlY镀层在氧化过程中形成了Cr2O3,α-Al2O3和β-NiAl相组成的致密防护涂层,阻隔了氧气与基体的接触,中间的Al层为表层持续生成Al2O3提供了Al源。NiCrAlY/Al复合涂层显著提高了基体在950℃下的抗高温氧化性能。     

等离子喷涂 NiCoCrAlY / Al2 O3 高温固体润滑耐磨涂层的抗氧化性能研究

目的研究等离子喷涂NiCoCrAlY/Al2O3高温固体润滑耐磨涂层在850℃时的高温抗氧化性能和抗氧化机理。方法采用喷雾造粒、化工冶金包覆技术制备NiCoCrAlY/Al2O3复合粉体,并采用等离子喷涂技术在45#钢表面制备NiCoCrAlY/Al2O3复合涂层。采用SEM和XRD研究粉体和涂层的显微结构和物相组成,并采用马弗炉研究复合涂层在850℃的恒温氧化动力学曲线,通过研究氧化96 h以后涂层表面的组织形貌,探讨NiCoCrAlY/Al2O3复合涂层的抗氧化机理。结果 NiCoCrAlY合金层均匀致密地包覆在Al2O3颗粒的表面,包覆层厚度约为3~5μm。复合粉体的主要组成为Al2O3相和NiCoCrAlY合金相,没有其他杂质相的存在。等离子喷涂NiCoCrAlY/Al2O3复合涂层氧化动力学曲线分为大斜率直线、抛物线和系数几乎为0的抛物线等3个阶段。氧化96 h以后,涂层的氧化质量增量为4.9 mg/cm2左右,表面形成了一层连续的氧化物保护膜,经EDX分析,氧化膜层主要由Al,O,Cr和Ni组成。结论等离子喷涂NiCoCrAlY/Al2O3复合涂层具有良好的高温抗氧化性能,涂层中Ni,Cr,Al的氧化以及硬质相Al2O3的加入是涂层抗氧化的主要原因。     

爆炸喷涂制备NiCrAlY/NiAl/ZrO2-Y2O3体系热障涂层

为了提高热障涂层的高温抗氧化性，采用爆炸喷涂技术在M22合金上制备了Ni-25Cr-5Al—0．5Y／Ni-50Al/ZrO2—8Y2O3(质量分数，％)体系的热障涂层．喷涂态Ni-50Al(NiAl)扩散阻挡层由δ-Ni2Al3，3-NiAl和NiAl3组成．对该涂层进行1050，1100和1150℃下的等温氧化，研究了NiAl层对氧化膜生长机制的影响．结果表明，NiCrAlY／NiAl／YSZ体系的氧化增重明显小于双层结构热障涂层的，其氧化动力学在1050和1100℃下符合四次方规律，在1150℃下符合抛物线规律，NiAl层有阻碍粘结层元素向外扩散、促进以Al2O3为主的氧化膜形成的作用．     

退火处理对离子镀NiCrAlY涂层热腐蚀性能的影响

为了进一步改善离子镀NiCrAlY涂层的抗热腐蚀性能,对NiCrAlY涂层在1050℃进行真空退火2h,研究了涂层退火前后的热腐蚀行为.结果表明,退火处理消除了离子镀NiCrAlY涂层的一些孑L洞,涂层形成了γ/γ' β多相平衡组织,使涂层组织更致密;在25%NaCl 75%Na2SO4(质量分数)盐膜下850℃热腐蚀20h时,未退火的NiCrAlY涂层生成的是外层Cr2O3、内层Al2O3的双层氧化膜,退火后的NiCrAlY涂层仅生成一层Al2O3膜,孕育期增长,在一定程度上提高了抗热腐蚀寿命.     

水蒸气对NiCrAlY涂层抗高温氧化性能的影响

采用热重分析及现代表面分析方法研究了低压等离子喷涂Ni CrAlY涂层在纯氧以及含5%水蒸气的O2中的高温氧化行为,结果表明：在纯氧的氧化环境中 ,NiCrAlY涂层氧化动力学遵循抛物线规律,在含有5％的水蒸气的O2中,NiCrAlY涂层在氧 化至110 h后氧化动力学几乎呈直线规律.XRD及SEM分析显示,NiCrAlY涂层在O2中氧化180 h后,表面形成一层致密的Al2O3;而在含5%水蒸气的O2中氧化180 h后表面氧化层中 除了有Al2O3外,还有NiO和Cr2O3.其原因在于水蒸气中的氢在氧化物中的溶解,致 使Ni2+扩散 速度增加,使氧化层变得疏松,降低其抗氧化性.     

不锈钢表面等离子喷涂梯度涂层耐蚀性能的研究

利用等离子喷涂技术在不锈钢表面喷涂由底层（NiCrAlY）和面层（ZrO2＋Y2O3）组成的梯度涂层。用SEM和XRD方法表征了梯度涂层的显微组织和相结构；用显微硬度仪测量涂层的显微硬度；采用CS300P型电化学腐蚀工作站检测了梯度涂层的耐蚀性能。结果表明，在不锈钢表面等离子喷涂NiCrAlY＋（ZrO2＋Y2O3）梯度涂层的厚度约为300μm，相成分主要是ZrO2和Ni3Al,显微硬度值达到1000HV；在1．0mol／L的稀硫酸腐蚀液中，喷涂后的试样表面腐蚀速率显著减慢，耐蚀性能得到明显提高。     

大气等离子喷涂NiCoCrAlY/Al2O3-30%B4C复合涂层的氧化性能

采用化工冶金包覆、喷雾造粒和固相合金化技术制备了NiCoCrAlY/Al2O3-30%B4C粉体,利用大气等离子喷涂技术制备了NiCoCrAlY/Al2O3-30%B4C复合涂层,对粉体和涂层的显微结构进行了分析,并对涂层的氧化性能进行了研究。结果表明,Al2O3和B4C表面均包覆一层致密的NiCoCrAlY合金,包覆层厚度为3~5 μm。涂层呈典型的层状结构,涂层由NiCoCrAlY、Al2O3和B4C相组成。在850 ℃时,涂层的恒温氧化动力学曲线分为氧化初期的大斜率直线、氧化中期的小斜率直线和氧化后期的抛物线3个阶段。850 ℃下氧化96 h后,涂层表面生成一层连续的氧化物保护层,其外层主要由Al2O3组成,而内层则由Cr2O3和Al2O3组成。     

两种NiCrAIY涂层1050℃恒温抗氧化性能

用低压等离子喷涂(LPPS)和爆炸喷涂(DS)方法,在镍基单晶高温合金上制备NiCrAlY涂层.涂层在1050℃恒温氧化300 h,借助XRD、SEM和EDS,对涂层表面氧化膜进行分析,检测其恒温抗氧化能力.结果表明两种涂层表面均能形成Al2O3保护膜,二者的氧化动力学曲线均符合抛物线规律.DS涂层的微孔内含残留气体,涂层内氧化严重,氧化增重大,氧化速率常数近似LPPS涂层的二倍.氧化300 h后,DS涂层表面边角处氧化膜有少量剥落,而LPPS涂层保持完好,只在个别突起处有微小开裂.     

两种IC-6高温合金防护涂层的氧化行为

研究了IC-6高温合金及其防护性涂层NiCrAlY和NiCoCrAlY涂层在900～1100℃时的氧化.结果表明沉积NiCrAlY和NiCoCrAlY涂层后大大改善了IC-6合金的抗氧化性.在1000和1100℃时,NiCrAlY涂层的抗氧化性优于NiCoCrAlY涂层.900℃时,NiCrAlY涂层氧化膜主要是α-Al2O3,同时还含有少量的Cr2O3;而NiCOCrAlY涂层氧化膜为单一的α-Al2O3,但由于NiCoCrAlY涂层表面氧化膜不致密,降低了涂层的抗氧化性.1000℃氧化时,NiCrAlY涂层和NiCoCrAlY涂层的氧化膜主要由α-Al2O3和Cr2O3构成.     

渗铝改性离子镀NiCrAlY涂层的高温热腐蚀行为

为了进一步改善离子镀NiCrAlY涂层的抗热腐蚀性能,采用粉末包埋法在离子镀NiCrAlY涂层表面上进行渗铝,研究了涂层渗铝前后在850℃含氯硫酸盐膜下的热腐蚀行为.结果表明:在25%NaCl 75%Na2SO4熔盐中850℃热腐蚀40h时,未渗铝的NiCrAlY涂层生成的是外层以Cr2O3为主的氧化膜,渗铝后的NiCrAlY涂层仅生成一层Al2O3膜;未渗铝的NiCrAlY涂层在腐蚀50h后失去保护作用,而渗铝涂层在腐蚀100h后表面仍形成以Al2O3为主的保护膜.因此,渗铝处理可以明显提高原涂层的抗热腐蚀性能.     

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。     

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。     

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.     

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.     

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.