焙烧气氛对Ti-6Al-4V合金微弧氧化陶瓷膜相组成影响

在铝酸钠体系中,利用微弧氧化脉冲电源在Ti-6Al-4V合金表面制备了以Al2TiO5为主晶相的陶瓷膜层.试样分别在1000℃下空气和氩气2种气氛中进行焙烧,通过XRD,SEM,XRF等技术分析了陶瓷膜层焙烧前后不同层面的相组成、表面形貌和元素含量变化情况.结果表明:在1000℃空气气氛下,Al2TiO5分解较快,完全分解时,陶瓷膜外层α-Al2O3和金红石相二氧化钛相比例为44:55.而在氩气气氛下,Al2TiO5分解较慢,随反应的不断进行,Al2TiO5含量逐渐减少,完全分解时,陶瓷膜外层为α-Al2O3.膜层由表及里Al2O3含量降低并有Ti2O3生成.焙烧前后陶瓷膜层的形貌变化也不相同,氩气中颗粒较空气中的均匀、细化、孔隙小.膜内元素Ti,Al,P,O的含量在反应前后略有变化.     

Ti14合金半固态下的氧化行为研究

半固态氧化温度升高，氧化增重急剧增加。Ti14合金经半固态氧化后，氧化皮仅为TiO2，不存在任何形式的Cu的氧化物，这是Cu的氧化物挥发的结果。1050℃后，因为CuO的挥发，导致增重有降低的现象。Ti14合金半固态氧化后，氧化层分为3个层次，最外层为疏松的TiO2(在1100℃以上时已经基本脱落)；次外层为比较致密的TiO2和Al2O3，该层以Al2O3为主；再次层由较疏松的TiO2及Cu的氧化物组成，该层中以TiO2为主。Ti14合金半固态氧化后，因为低熔点相Ti2Cu的存在，熔化晶界成为氧向基体扩散的优先通道。半固态下钛合金不具有任何抵抗氧化的能力。     

焙烧气氛对Ti-6Al-4V合金微弧氧化陶瓷膜相组成影响

在铝酸钠体系中，利用微弧氧化脉冲电源在Ti-6Al-4V合金表面制备了以Al2TiO5为主晶相的陶瓷膜层。试样分别在1000℃下空气和氩气2种气氛中进行焙烧，通过XRD，SEM，XRF等技术分析了陶瓷膜层焙烧前后不同层面的相组成、表面形貌和元素含量变化情况。结果表明：在1000℃空气气氛下，Al2TiO5分解较快，完全分解时，陶瓷膜外层α-Al2O3和金红石相二氧化钛相比例为44：55。而在氩气气氛下，Al2TiO5分解较慢，随反应的不断进行，Al2TiO5含量逐渐减少，完全分解时，陶瓷膜外层为α-Al2O3。膜层由表及里Al2O3含量降低并有Ti2O3生成。焙烧前后陶瓷膜层的形貌变化也不相同，氩气中颗粒较空气中的均匀、细化、孔隙小。膜内元素Ti，Al，P，O的含量在反应前后略有变化。     

Ti50Al和Ti45Al8Nb合金高温初期氧化行为

利用SEM、XPS和AES研究了Ti50Al和Ti45Al8Nb(原子分数,%)合金在900 ℃空气中的初期氧化行为.结果表明:Nb的加入显著提高了合金的抗氧化性.氧化90 min后,Ti50Al合金表面为粗大的富TiO2颗粒,冷却过程中部分表层氧化膜脱落,脱落后内层为多孔、疏松的Ti和Al的混合氧化物(可能有氮化物);Ti45Al8Nb合金表面生成很薄的氧化膜,其外层为细小富Al2O3颗粒,Nb只存在于内层(富TiO2层)和混合层,在外层Al2O3内没有发现,Nb5 取代TiO2中的Ti4 ,降低氧空位浓度从而减慢氧的向内扩散,抑制TiO2的生成,同时促进了外层纯Al2O3层的形成,该层阻碍氧以及合金元素的进一步扩散.     

Ti60高温钛合金氧化行为研究

研究Ti60高温钛合金在600～750 ℃范围内的氧化行为.氧化增重试验及XRD、SEM分析结果表明,Ti60合金在600～750 ℃范围内氧化0～100 h条件下,由Wagner的氧化经验公式计算得氧化指数n在1～2之间,氧化激活能为256 kJ/mol,氧化符合线性-抛物线混合规律.在600 ℃氧化100 h及750 ℃氧化10 h,氧化产物为TiO2,经750 ℃、100 h长时间氧化后,表面有少量Al2O3生成,氧化物优先沿原始β晶界形核.氧除了会在试样表面形成氧化层外,还会向基体中扩散形成脆性富氧层,从而影响合金力学性能.随着氧化温度的升高和时间的延长,富氧层厚度增厚.     

焙烧对钛合金微弧氧化陶瓷层相组成和表面形貌的影响

在铝酸钠体系中,利用微弧氧化双脉冲电源在Ti-6Al-4V合金表面制备了以Al2TiO5为主晶相的陶瓷层.试样分别在1 000 ℃下空气和氩气气氛中进行焙烧,通过XRD和SEM技术分析了相组成与表面形貌.结果表明,在空气中,焙烧使微弧氧化陶瓷层中的Al2TiO5相分解较快.在氩气中,陶瓷膜外层生成α-Al2O3,膜层从外至内Al2O3含量降低并有Ti2O3生成.氩气焙烧后陶瓷层表面颗粒较焙烧前均匀和细化.     

微等离子体氧化陶瓷膜对钛合金耐蚀性的影响

在偏铝酸钠溶液中，利用双向脉冲微等离子体氧化技术，在TC4钛合金表面原位生长复合氧化物陶瓷膜．分析表明，陶瓷膜由Al2TiO5、α-Al2O3和金红石型TiO2构成，其中Al2TiO5为主晶相，金红石型TiO2含量由膜外层向内层逐渐增多，而α-Al2O3含量由外向内逐渐减少；整个膜层分为致密层和疏松层两部分．陶瓷膜提高了钛合金的耐盐酸和硫酸腐蚀性能．微等离子体氧化陶瓷膜使得钛合金的耐点蚀性能明显提高，同时使TCA钛合金与LY12铝合金之间的电偶腐蚀得到改善．     

TC4钛合金沉积NiCrAlY涂层的氧化行为

采用电弧离子镀（AIP）技术在TC4（Ti-6Al-4V）钛合金基体表面沉积制备NiCrAIY涂层,测定TC4钛合金和NiCrAIY涂层在700-900℃的氧化动力学曲线。通过扫描电镜（SEM）、能谱（EDS）分析与X射线衍射分析（XRD）研究TC4钛合金和NiCrAIY涂层氧化前后物相组成和组织形貌,讨论氧化过程中元素的扩散行为。结果表明：在700-900℃静态空气中氧化100h,NiCrAIY涂层能明显提高TC4钛合金的抗氧化性能,TC4钛合金氧化后形成A12O3层和TiO2层交替出现的氧化膜层;经700和800℃氧化后,NiCrAIY涂层保持其原始的相组成,但在表面形成Al2O3和Cr2O3混合氧化膜;经900℃氧化后,氧化膜由Al2O3和TiO2组成;经700℃氧化时,主要发生Ti和Ni两种元素的扩散;经800和900℃氧化时,由于Ti及Ni元素的剧烈扩散,界面附近出现Kirkendall疏孔带和约100μm的β相稳定区;经900℃氧化时,Ti扩散到涂层表面形成氧化物导致氧化速率提高,Cr元素开始向基体扩散并在近界面处富集。     

Ti3AlC2陶瓷在空气中的高温氧化行为

采用热压烧结法,在1450 ℃保温2 h制备Ti3 AlC2陶瓷,研究其在1000 ℃空气中的断续氧化行为.结果表明,Ti3AlC2在1000 ℃的空气中氧化30 h后,动力学曲线服从抛物线规律.氧化层厚度约为350 μm,由多层组成,从外到内依次为TiO2的富集层,TiO2和Al2O3的富集层,TiO2、Al2O3以及还有少量孔洞层,Al2O3富集层.整个氧化过程主要由Al3+和Ti4+的向外扩散和O2-的向内扩散组成.     

掺杂HfO2对钛合金微弧氧化膜层特性的影响

在电解液中添加HfO2对Ti-6Al-4V钛合金进行微弧氧化处理,通过表征微弧氧化膜表、截面形貌,膜层成分及电化学行为,并测量膜层厚度、硬度、粗糙度等参数来研究添加HfO2对钛合金微弧氧化膜层特性的影响。结果表明：添加HfO2后,微弧氧化膜层主要成分是Al2TiO5、TiO2和γ-Al2O3。较合适浓度的HfO2能促进成膜反应,改善微弧氧化膜的微观结构,提高膜层的厚度、硬度并降低表面粗糙度,且膜层试样具有双层膜结构,膜层试样的耐腐蚀性能好于原基体。HfO2浓度为3.0g/L时所获得的微弧氧化膜层综合性能最佳。     

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.