内氧化对渗铝钢循环氧化性能的影响

通过循环氧化试验和SEM观察，研究了内氧化对扩散型热浸渗铝钢循环氧化性能的影响.结果表明，经高温扩散处理后，热浸镀铝钢扩散层的次外层和过渡层之间均有空洞产生.随扩散温度升高和时间延长，次外层和过渡层之间空洞逐步聚集连接成平行于表面的波浪线状空洞带，使高温氧化过程中扩散层产生了内氧化，氧化动力学曲线偏离平方抛物线规律而呈现抛物线—直线规律.因此，渗铝钢的长期氧化速度同时受扩散层内氧化和外氧化的控制.探讨了扩散层空洞带和内氧化的形成机理.      

热浸镀铝钢的扩散工艺研究

通过对热浸镀铝的20号碳钢进行不同扩散工艺试验，研究了渗铝层在800℃氧化过程中的组织形貌变化和抗氧化性能。结果表明，当扩散温度为750℃时，在2～6h扩散时间内，随时间延长，氧化速率增加；当扩散温度为850。C时，在2～4h扩散时间内，随时间延长，氧化速度减慢，4h时达到极小值，而后随时间延长，氧化速度又逐渐增大；当扩散工艺为900℃×2h时，抗氧化性能最好。研究表明，在高温氧化期间，经扩散处理后渗铝层／基体界面空洞逐步连接成平行于表面的线状裂纹，其内产生了内氧化，对扩散型热浸镀铝钢的抗氧化性能有直接影响。     

稀土对渗铝层/基体界面空洞生长和抗高温剥落性能的影响

通过高温氧化实验以及测量空洞平均直径和形核数量随氧化时间的变化,研究稀土对渗铝层抗高温剥落性能和渗铝层/基体界面空洞生长的影响,并与渗纯铝试样进行了比较.结果表明:渗铝层/基体界面空洞的生长可划分为快速生长和稳定生长两个阶段;但当渗稀土铝后,空洞生长速度比渗纯铝试样降低约1/3;稀土可抑制界面空洞的形核和生长,阻止空洞聚集成波浪线状空洞带和线状裂纹,提高渗铝钢的抗高温剥落性能;热浸镀稀土铝后,试样表面自由铝层减薄,从而降低了高温下渗铝层/基体界面铝的浓度梯度,这是稀土抑制空洞形核和生长的主要原因.     

碳钢浸镀扩散渗铝复合渗硼及其表面性能研究

对Q235、45、GCr15钢在720℃±5℃的条件下进行了热浸渗铝,分别扩散1h、2.5h和5h后再进行950℃×6h高温渗硼。利用光学显微镜、扫描电镜、X射线等手段研究了Q235、45钢的热浸渗铝和热浸渗铝复合渗硼层的组织结构。探讨了热浸扩散渗铝复合渗硼中的硼化物的形成机理及硼的迁移机制。采用高温氧化试验和耐热腐蚀试验考察了这两种渗层在高温下的氧化机制,并比较了它们的耐高温氧化性能和耐热腐蚀性能,以及它们在干摩擦条件下的耐磨性。试验结果表明,热浸渗铝经扩散处理后,渗层明显,渗层组织由表及里出现了η相(Fe2Al5)、β1相(Fe3Al)和α相固溶体等组织。热浸渗铝复合渗硼所形成渗层具有与单一渗硼相类似的齿状形态。X射线衍射分析表明,渗层主要由Fe2B、Fe2AlB2及Fe2Al5组成。Q235钢热浸镀铝复合渗硼处理在950℃高温下不具有明显的抗氧化的作用。而热浸渗铝的Q235钢950℃氧化后仍然为扩散处理后的灰色外观。而650℃循环氧化中,这两种渗层的抗氧化能力相当。800℃熔盐腐蚀试验中热浸渗铝与热浸渗铝复合渗硼处理均具有较高的耐蚀胜,比未经处理的试样高10倍左右。在干摩擦条件下,热浸渗铝复合渗硼试样比渗铝扩散处理具有更高的耐磨性。     

几种高温合金及其渗铝涂层的抗氧化性能研究

用Ｘ４０Ｔ３合金作对比，着重研究了低偏极合金Ｍ４１及其气相渗铝涂层的高温氧化性能。结果表明，９００℃下Ｍ４１Ｔ３合金的氧化增重近似，都比渗铝涂层的小，氧化膜均无明显剥落。１０５０℃下Ｍ４１合金的氧化增重小于Ｋ３合金，其氧化膜剥落较轻，但Ｋ３合金的氧化膜剥落严重，两合金的氧化增重大于渗铝涂层。渗铝涂层的氧化寿命在９００℃下较长，１０５０℃下则在大缩短。Ｋ４１合金形成Ａｌ２Ｏ３内氧化层，随温度的升高和     

退火处理对Ni-Al纳米复合镀层循环氧化性能的影响

研究在500℃真空扩散不同时间条件下的扩散合金化对Ni-Al纳米复合镀层的结构与抗循环氧化性能的影响。结果表明：扩散不仅导致Ni-Al纳米复合镀层的基体Ni晶粒粗化,还导致Al固溶在基体Ni中,Ni与Al之间形成金属化合物;随着扩散合金化时间的延长,Ni-Al合金涂层中的空洞减少,从而减少了合金涂层在循环氧化过程中出现的穿透性裂纹和内氧化,抑制了氧化膜剥落区瘤状NiO的形成,提高了Ni-Al合金涂层的抗循环氧化性能。     

钢的内氧化动力学理论分析及应用

本文简要评述了现有内氧化动力学方程;并根据扩散理论推导出了钢的内氧化动力学方程的具体表达式。由钢内氧化动力学的实验规律一抛物线规律,应用动力学方程,可计算氧在钢的内氧化层和钢中的扩散系数。     

钢的渗铝工艺技术及性能研究进展

钢材渗铝是通过化学和物理的方法将铝原子渗入钢材表面形成微合金层,改变钢材的表面化学成分和特性的热处理工艺。渗铝处理可以提高钢材耐氧化性能、耐腐蚀性能和硬度,作为一种简单有效的表面化学热处理工艺得到研究者的关注。简要介绍了当前常见的渗铝工艺,如热浸渗铝、热喷涂渗铝、粉末包埋渗铝、料浆渗铝,总结了常见渗铝工艺的特点与不足,随后介绍了研究人员开发出的新型渗铝工艺,如机械辅能助渗铝、电场辅助渗铝、流化床气相沉积渗铝和离子电镀渗铝。论述了渗铝钢的显微结构和渗层的生长机理,对渗铝后的渗铝钢具有耐氧化、耐腐蚀性能的机理进行了讨论说明。最后,对渗铝工艺的发展趋势进行了探讨和展望。     

T91钢高温空气氧化动力学及层脱落机理

通过扫描电镜对T91钢高温空气氧化层的形貌进行观察,利用X-Ray物相分析仪测试了氧化层的物相结构,利用热天平连续称重法对T91钢高温空气氧化速率进行测定,并分析了氧化层的脱落机理.结果表明:T91钢高温空气氧化的动力学曲线符合对数规律,氧化速率低于1级完全抗氧化性的标准;氧化层脱落的机理是界面裂纹和氧化层弓出弯曲破裂和剥落,也可以是氧化层内纵向裂纹的不穿透破裂剥落.     

钢表面粉末包埋渗铝的表面状态及元素扩散机理研究进展

钢铁作为基础性结构材料,应用在国民经济的各个领域。由于钢材在工程应用中会发生氧化、腐蚀,采用粉末包埋渗铝对钢材进行表面改性可提高其抗氧化性能和腐蚀性能。目前为止,关于渗铝工艺参数对渗层微观组织、表面状态和元素扩散机理的研究,比较零散,缺乏系统总结。综述渗铝工艺参数对粉末包埋渗铝钢的微观组织、表面状态及其性能的影响,分析渗铝工艺参数与渗层微观组织的关联;概括渗铝工艺参数对Fe-Al元素扩散系数和扩散激活能的影响规律,分析Fe-Al元素扩散机制;总结渗铝层预测模型,对粉末包埋渗铝钢的研究趋势进行展望。     

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.     

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。     

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.     

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.