李鑫
LI Xin
中图分类号: TG142
文章编号: 1005-3093(2016)04-0263-06
通讯作者:
收稿日期: 2015-12-3
网络出版日期: 2016-04-25
版权声明: 2016 《材料研究学报》编辑部 《材料研究学报》编辑部
基金资助:
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摘要
对中铬铁素体不锈钢18CrNb在700-1000℃间不同温度下开展了连续氧化实验, 绘制了该钢种的氧化动力学曲线, 并利用XRD、SEM和EDS等方法对氧化皮结构进行了分析和表征。结果表明, 18CrNb铁素体不锈钢在900℃以下可形成连续致密的富Cr氧化皮, 使其具备优良的抗氧化性能。当温度提高至950℃以上时, 氧化膜表面的组成由富Cr的氧化物向富Cr的铬锰氧化物、富Mn的锰铬氧化物、铁的氧化物和纯铁的氧化物转变; 内层氧化物由富Cr氧化物向富Fe的Fe/Cr氧化层转变, 这种转变使氧化皮疏松, 从而导致异常氧化, 表明该钢不适合在950℃以上使用。
关键词：
Abstract
18CrNb is a kind of ferritic stainless steel and widely used as parts at the hot end of automobile exhaust system due to its good formability, high temperature strength and oxidation resistance. In this paper, the oxidation of 18CrNb steel in a temperature ranging from 700℃ to 1000℃ was studied through continuous oxidation behavior test. The oxide scale was then characterized by XRD, SEM and EDS, while the oxidation dynamic curve of this steel was plotted based on the weight-gain data after oxidation. The results indicate that 18CrNb steel has excellent oxidation resistance at temperatures lower than 900℃ due to the formation of continuous and dense Cr-rich oxide scale. When the temperature rises up to 950℃, the oxide scale turn to be complex, of which the outer portion composed of Cr-rich Cr-Mn oxide, Mn-rich Mn-Cr oxide, Fe oxide and pure iron oxide; the inner portion composed of Fe-rich Fe/Cr oxide; thereby the scale became loose leading to breakaway oxidation. According to the results of this work, 18CrNb is not suitable for application at temperatures above 950℃.
Keywords：
传统奥氏体不锈钢, 如AISI 304和AISI 316L等, 曾被广泛应用于汽车排气系统高温端排气管的制造中。铁素体不锈钢不含镍, 从而降低了合金成本, 同时还具有较低的热膨胀系数、良好的耐高温氧化性能和抗高温热疲劳性能等优点[1-3], 可大量替代奥氏体不锈钢, 已广泛应用于能源、汽车等工业领域。
作为一种中铬铁素体不锈钢, 18CrNb铁素体不锈钢具有良好的抗氧化性能和较佳的高温强度。其中, Nb不仅作为稳定化元素提高材料的耐晶间腐蚀性能, 更重要的是通过析出强化和固溶强化共同提高材料的高温强度和抗高温蠕变性能[4, 5]。有研究[6, 7]表明, Nb的添加对抗氧化性能也有一定的促进作用, 这样设计的合金体系具备非常好的高温强度以及抗氧化性能, 目前已成为耐热不锈钢的首选材料。因而, 对其在各种使用环境下抗氧化性能的研究成为国内外学者关注的焦点[8, 9]。
有关18CrNb铁素体不锈钢高温抗氧化性能的评价和研究目前主要集中在850℃以下的使用环境, 很少涉及900℃以上的温度范围。Badin等[10]就18CrNb和316L不锈钢在1100℃下的短期抗氧化性能开展了对比研究, 结果表明: 在20 min以内连续氧化测试过程中, 18CrNb不锈钢的氧化层很薄且致密, 而316L不锈钢则明显表现出异常氧化特征。然而, 在实际使用过程中, 尤其是在汽车排气系统领域, 其高温端零部件长时间暴露于高温环境中, 其氧化行为及机理有别于短时氧化行为, 目前鲜有这方面的研究报道, 尤其缺乏针对该钢种在900℃以上的抗氧化性能的研究。本文采用恒温氧化试验, 研究18CrNb铁素体不锈钢在700-1000℃长时间下的氧化行为, 并对氧化皮结构及形成机理进行分析。
实验材料为1.5 mm厚18CrNb铁素体不锈钢商业成品板, 其化学成分见表1, 高温氧化实验试样系采用线切割法截取的25 mm×20 mm矩形样。首先, 用水磨砂纸将试样表面研磨至1200#, 用乙醇超声波清洗后烘干; 再利用千分尺测量试样尺寸并计算其表面积; 为了避免实验过程中由于氧化皮剥落对氧化增重的影响, 本实验测量氧化前和氧化后的质量数据均为坩埚和试样的总质量。在高温氧化实验前, 需将坩埚在1100℃下焙烧20 h去除水分以保证高温氧化过程中其自重无变化。
表1 18CrNb钢的化学成分
Table 1 Chemical Composition of 18CrNb ferritic stainless steel (%, mass fraction)
| C | Si | Mn | P | S | Cr | Nb | Ti | N | Fe |
|---|---|---|---|---|---|---|---|---|---|
| 0.009 | 0.47 | 0.27 | 0.025 | 0.002 | 17.81 | 0.463 | 0.17 | 0.0085 | Bal. |
将试样置于恒重的氧化铝坩埚内, 再连同坩埚一起放入高温电阻加热炉中。为研究不同连续氧化温度对测试钢种的高温氧化行为的影响, 温度分别定为700℃、800℃、900℃、950℃和1000℃。在700℃、800℃、900℃时的最长氧化时间为300 h, 在实验的前20 h内取样间隔为3-5 h, 氧化进行20 h以后取样间隔为20 h。而在950℃和1000℃时的最长氧化时间均为100 h。当加热炉加热到目标温度后, 取样间隔为5 h, 置于干燥皿中冷却至室温, 将试样连同坩埚一起测量重量变化, 称重在精度为10 μg的METTLER TOLEDO XS205型电子天平上测量, 并绘制其氧化动力学曲线。
在PANalytical X'pert PRO MPD型X射线衍射仪(XRD)上分析氧化膜的组成, CoKα, λ = 0.179 nm, 2θ=20°-110°, 步长为0.02°。采用Quanta 400扫描电镜(SEM)观察氧化膜表面形貌, 电压为20 kV, 氧化膜化学成分采用扫描电镜自带的能谱仪分析。
图1是18CrNb铁素体不锈钢在温度为700℃-1000℃的空气中连续氧化动力学曲线。由图可见, 18CrNb铁素体不锈钢的氧化增重随着温度的升高而增加, 氧化动力学曲线基本符合抛物线规律。在温度为700-950℃范围内, 该钢没有发生快速氧化的现象; 但是在1000℃时, 18CrNb铁素体不锈钢快速氧化, 在前15 h的氧化过程中氧化呈直线规律, 后85 h呈近抛物线规律; 连续氧化100 h后, 其氧化增重达到了23.08 mgcm-2, 是950℃下氧化增重1.358 mgcm-2的近17倍。由此可见, 18CrNb铁素体不锈钢在950℃及其以下温度具有良好的抗氧化性能, 在1000℃时会发生快速氧化, 氧化增重明显。
图1 18CrNb铁素体不锈钢在不同温度下氧化动力学曲线
Fig.1 Oxidation kinetic curves of ferritic stainless steel 18CrNb oxidized at different temperatures, (a) 700-900℃, (b) 950-1000℃
当金属材料的高温氧化动力学符合抛物线型规律时, 其动力学可用Δmn= kpt及kp = k0exp(-Q/RT) 表示[11, 12]。该式中, Δm为单位面积氧化增重(mgcm-2), n为氧化指数, t为氧化时间(h), kp为氧化速率常数, k0为常数, Q为氧化激活能(kJmol-1), T为氧化温度(K), R为气体常数, 即8.314 Jmol-1K-1。利用该式对氧化动力学符合抛物线规律的700-1000℃温度区间的实验结果进行回归分析, 可求出不同温度下的n, kp及Q, 结果见表2。可以看出, 18CrNb不锈钢在950℃及以下温度kp值都很小, 而在1000℃ kp为5.310-10 g2cm-4s-1; 对于氧化激活能Q而言, 18CrNb不锈钢在950℃以下温度Q值均保持在均值238 kJmol-1, 而在1000℃时Q值下降到200 kJmol-1, 同时也加速了氧化。
表2 试验用钢在700-1000℃的kp值、n值和氧化激活能Q值
Table 2 Values of kp, n, and Q of stainless steel 18CrNb at different temperatures
| T/℃ | kp/ g2cm-4s-1 | n | Q / (kJ/mol) |
|---|---|---|---|
| 700 | 1.4 × 10-14 | 2.25 | 237 |
| 800 | 1.1 × 10-13 | 2.18 | 242 |
| 900 | 2.4 × 10-12 | 2.24 | 235 |
| 950 | 5.1 × 10-12 | 2.19 | 237 |
| 1000 | 5.3 × 10-10 | 2.27 | 200 |
图2是18CrNb不锈钢在700℃-950℃不同温度下连续氧化100和300 h后表面氧化产物组成的XRD谱。18CrNb不锈钢在700℃下连续氧化300 h后表面几乎无氧化膜产生; 在800℃和900℃下连续氧化300 h后表面氧化膜主要为锰铬的氧化物和富铬的氧化物, 其主要成分为Mn1.5Cr1.5O4和Cr1.3Fe0.7O3; 而18CrNb不锈钢在950℃下连续氧化100 h后, 表面氧化膜除含锰铬的氧化物Mn1.5Cr1.5O4和富铬的氧化物Cr1.3Fe0.7O3外, 还有Fe2O3氧化物生成。也就是说, 18CrNb不锈钢在700℃-900℃下连续氧化后表面氧化膜都有一定的保护作用, 氧化速率较低; 而在950℃及以上温度连续氧化时, 氧化膜表面会有大量Fe的氧化物生成, 氧化开始加重, 1000℃下连续氧化100 h后试样已经出现严重的异常氧化(分离氧化), 表面形成瘤状氧化物, 并伴随氧化皮脱落(未进行XRD分析)。从已有分析结果[1]可以看出, 只有形成富Cr的氧化膜, 才具有比较好的保护性, 从而阻止氧化的进一步进行; 随着连续氧化温度的升高, 18CrNb不锈钢的氧化加剧。
图2 18CrNb不锈钢在不同温度下表面氧化皮结构的XRD谱
Fig.2 XRD spectra of oxidation products on the stainless steel 18CrNb oxidized at different temperatures
图3为18CrNb在连续氧化温度为700℃、800℃和900℃时的氧化皮截面及表面形貌。可以看出, 在900℃以下, 18CrNb不锈钢的氧化皮生长极其缓慢, 在700℃氧化300 h后几乎观察不到氧化皮; 而随着氧化温度的升高, 氧化皮厚度有所增加。从图中还可以看出, 在800℃连续氧化300 h后氧化膜的厚度很薄, 约为2 μm, 在900℃连续氧化300 h后氧化膜的厚度增至8 μm。能谱分析表明, 18CrNb不锈钢在800℃和900℃连续氧化300 h后氧化膜的组成是类似的, 即外层为富铬锰的氧化物, 而内层为富铬的氧化物, 这与Grolig[13]的研究中所观察的现象一致。从试样表面形貌也可看出, 3组试样均未出现剥落情况, 且氧化温度越低, 氧化膜就越细小致密。当氧化温度达900℃时, 在试样表面能够观察到一些尺寸相对较大的突起或瘤状氧化物, 能谱分析显示其组成为富Cr的铬锰氧化物。有研究结果表明[9], 18CrNb不锈钢在氧化的最初期就会形成Mn-Cr尖晶石, 且会随着氧化温度的提升而聚集长大, 这种聚集会降低氧化皮对基体的保护效应, 从而使抗氧化性能恶化。
图3 18CrNb不锈钢在不同温度下连续氧化的截面与表面(插图)形貌及其EDS分析
Fig.3 SEM images of the cross section and surface (inset) of oxide layers in 18CrNb stainless steel oxidized at 700℃ (a), 800℃ (b), 900℃ (c) and EDS analysis of nodular oxide in
图4a和b分别为18CrNb不锈钢在950℃连续氧化100 h后的氧化膜截面形貌。显然, 不锈钢表面已不能形成具有一定保护性的富铬氧化膜, 而是形成一定厚度的铁的氧化物, 氧化物外层是纯Fe的氧化物, 其下是一层富铁的铁铬混合氧化层, 沿不锈钢基体是以铬为主的内氧化区。图4c和d为18CrNb不锈钢在1000℃连续氧化100 h后的氧化膜截面形貌, 很显然, 不锈钢表面已形成很厚的铁的氧化物, 氧化物的外层是纯Fe的氧化物, 其下是富铁的铁铬混合氧化层。与950℃下连续氧化的试样不同之处是, 沿不锈钢基体处以铬为主的内氧化区完全消失, 只能观察到富Fe的Fe/Cr氧化物。对于不锈钢, 由于选择性氧化效应, Cr的优先氧化可形成连续致密的富Cr氧化层, 从而阻止O离子的扩散, 阻止氧化进一步进行。然而, 本实验结果表明, 当氧化温度很高时, 18CrNb表面已无法形成致密的具有保护性的富Cr氧化皮, 而富Fe的氧化层相对比较疏松, Fe、O、Cr和Mn元素的离子扩散通道畅通, 从而使氧化皮在1000℃的氧化条件下不具备保护能力。氧化增重曲线也体现出了这一趋势, 在该温度下连续氧化100 h后氧化增重达到了23.08 mg/cm2, 是950℃下氧化增重的近17倍。图5为在该试样表面上观察到的瘤状氧化物, 能谱分析表明其为Fe的氧化物, Cr的含量极低, 这种瘤状氧化物的产生表明在1000℃下已经开始发生异常氧化。
图4 18CrNb不锈钢在950℃和1000℃下连续氧化100 h的氧化皮截面形貌
Fig.4 Cross-sectional morphologies of the oxide layers in 18CrNb oxidized at different temperatures (a, b) 950℃, cross-section and oxide nearby the substrate; (c, d) 1000℃, cross-section and oxide nearby the substrate
图5 18CrNb铁素体不锈钢在1000℃氧化100 h后表面瘤状氧化物及其能谱分析
Fig.5 SEM image (a) and EDS analysis (b) of the tuberculate oxide in 18CrNb stainless steel oxidized at 1000℃ for 100 h
综上所述, 随着连续氧化温度的升高, 氧化膜的厚度增加, 且在氧化初期的氧化速率显著提高。在长时间连续氧化后, 随着温度的升高, 氧化膜表面的组成由富Cr的氧化物向富铬的铬锰氧化物、富锰的锰铬氧化物、铁的氧化物和纯铁的氧化物转变; 内层氧化物由富Cr的氧化物向富铁的Fe/Cr氧化层转变, 这种转变会破坏氧化皮的致密性, 导致氧化进一步进行。结合氧化动力学分析可以得知, 18CrNb不锈钢在900℃以下具备非常优异的抗氧化性能, 在950℃时具备一定的抗氧化性能, 但是已经出现了瘤状氧化物, 见图4(a), 这说明在该条件下如果氧化时间足够长, 依旧具备发生异常氧化的风险。当氧化温度提高至1000℃时, 18CrNb抗氧化性能显著恶化。
1. 18CrNb铁素体不锈钢在900℃以下具备优良的抗氧化性能, 当环境温度达到950℃时氧化增重明显, 且有瘤状氧化物产生; 在1000℃下抗氧化性能显著恶化。
2. 在700-1000℃范围内, 随着温度的升高, 氧化膜表面组成由富Cr的氧化物向富Cr的铬锰氧化物、富Mn的锰铬氧化物、铁的氧化物和纯铁的氧化物转变; 内层氧化物由富Cr的氧化物向富Fe的Fe/Cr氧化层转变, 这种转变使氧化皮疏松, 导致抗氧化性能降低。
3. 18CrNb铁素体不锈钢不适合应用于950℃以上的高温氧化环境。
The authors have declared that no competing interests exist.
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Effect of cerium on high-temperature oxidation resistance of 00Cr17NbTi ferritic stainless steel ,
The influence of cerium addition on the isothermal oxidation behavior of 00Cr17 NbTi ferritic stainless steel was studied at temperature up to 1,000 掳C for 100 h in air. The results show that cerium additions can reduce the grain size of this ferritic stainless steel, improve the diffusion of chromium and decrease the critical concentration of chromium to form protective Cr2O3 layer. With the increasing of cerium addition, the oxide particles become smaller and this can increase the rupture strength and spalling resistance of oxide layers. The transport mechanism through the oxide layer is varied from metal transport outward from steel to principally oxygen transport inward with the increase of cerium content,which leads to the lower oxidation rate and the better scale adherence of 00Cr17 NbTi ferritic stainless steel.
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In order to understand the effect of Mo element on the high-temperature fatigue behavior of 15 CrNbTi ferritic stainless steel, the stress-controlled fatigue tests have been performed for both 15 CrNbTi and 15Cr0.5MoNbTi ferritic stainless steels at 800 掳C in laboratory air. The fatigue test results indicate that the fatigue resistance of 15Cr0.5MoNbTi steel is manifestly higher than that of 15 CrNbTi steel at the maximum stress below 57 MPa; the 15Cr0.5MoNbTi steel possesses a fatigue limit of 35 MPa, which is higher than that of 15 CrNbTi steel. The TEM observations reveal that the Mo element can suppress the formation of coarsened Fe3Nb3 C precipitates and result in the fatigue resistance enhancement.The dislocation networks formed during the cyclic load favor to improve the fatigue resistance of 15Cr0.5MoNbTi steel at800 掳C.
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ABSTRACT Stainless steel started to be used as material for decoration trims in automobile. However, in recent years, it is mostly used as material for the exhaust system. It is because that stainless steels with good performance of high temperature character- istics and high corrosion resistance meet the social needs for clean exhaust gases and reduced weight for better fuel economy. In this paper, the structure of automo- tive exhaust system and the materials used for the exhaust system are described. Then, the past change and future prospect of materials for the exhaust system of automobile are described and also those for exhaust system of motor bicycle in which stainless steel starts to be used recently are described.
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To improve the fuel economy and clean the exhaust gas of automobiles, the temperature of exhaust gas is getting higher and higher. Niobium added ferritic stainless steels are often being used in automotive exhaust systems, because of their excellent heat resistant properties, especially thermal fatigue resistance, which is very important for materials of exhaust manifold. However, coarse precipitates containing niobium, which cause degradation in high temperature strength and thermal fatigue resistance, are unavoidable during high temperature service. In this study, changes of microstructures and high temperature properties in high temperature aging were investigated using several Nb added ferritic stainless steels. It has been found that the microstructure stability of Nb–Ti–Mo alloyed steels in high temperature aging is superior to that of Nb added steels. The microstructure stability leads to less degradation in high temperature strength during high temperature aging and to longer thermal fatigue lives of Nb–Ti–Mo alloyed steels than in Nb added steels.
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Optimization of the electrical properties of Ti-Nb stabilized ferritic stainless steel SOFC interconnect alloy upon high-temperature oxidation: the role of excess Nb on the interfacial oxidation at the oxide-metal interface ,
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| [8] |
Oxidation behavior of stainless steel 430 and 441 at 800℃ in single (air/air) and dual atmosphere (air/hydrogen) exposures ,
<h2 class="secHeading" id="section_abstract">Abstract</h2><p id="">Intermediate temperature <span id="mmlsi9" onclick="submitCitation('/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0360319908000104&_mathId=si9.gif&_pii=S0360319908000104&_issn=03603199&_acct=C000228598&_version=1&_userid=10&md5=7059ca7992884c0a34d2129be1ca2bad')" style="cursor:pointer;" alt="Click to view the MathML source" title="Click to view the MathML source"><img height="13" border="0" style="vertical-align:bottom" width="57" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0360319908000104-si9.gif"></span> planar solid oxide fuel cells (SOFCs) allow the use of ferritic stainless steel (FSS) interconnects. SOFC FSS interconnects are used to stack individual cells into series, and are simultaneously exposed to air on the cathode side and fuel on the anode side, creating a “dual atmosphere” exposure. The thermally grown oxide (TGO) layers on the air side of FSSs 430 and 441 were analyzed as a function of simulated dual atmosphere exposures (moist air/moist hydrogen) for up to 300 h. FSS 430 showed some changes in oxidation behavior, with a slight Fe concentration increase and localized <span id="mmlsi10" onclick="submitCitation('/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0360319908000104&_mathId=si10.gif&_pii=S0360319908000104&_issn=03603199&_acct=C000228598&_version=1&_userid=10&md5=5d5cebda21204e3b06b38b3d024c6cfc')" style="cursor:pointer;" alt="Click to view the MathML source" title="Click to view the MathML source"><span class="formulatext" title="click to view the MathML source"><em>Fe</em><sub>2</sub>O<sub>3</sub></span></span> nodule formation observed in the dual atmosphere TGO layer relative to its single atmosphere (air/air) counterpart. Significantly accelerated and anomalous oxidation was observed with FSS 441 subjected to dual atmosphere exposures compared with air/air exposures. The TGO layer formed on the 441 exposed to air/air was comprised of Mn-rich, Cr and Fe-containing isomorphic spinel surface crystallites, with a <span id="mmlsi11" onclick="submitCitation('/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0360319908000104&_mathId=si11.gif&_pii=S0360319908000104&_issn=03603199&_acct=C000228598&_version=1&_userid=10&md5=bbd727efd84cefc69ab7a0e2a34aaa52')" style="cursor:pointer;" alt="Click to view the MathML source" title="Click to view the MathML source"><span class="formulatext" title="click to view the MathML source"><em>Cr</em><sub>2</sub>O<sub>3</sub></span></span> (eskolaite)-based bottom layer, having a total TGO layer thickness of <span id="mmlsi12" onclick="submitCitation('/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0360319908000104&_mathId=si12.gif&_pii=S0360319908000104&_issn=03603199&_acct=C000228598&_version=1&_userid=10&md5=f4ee42367d225ff7eb80337ba50afaad')" style="cursor:pointer;" alt="Click to view the MathML source" title="Click to view the MathML source"><img height="13" border="0" style="vertical-align:bottom" width="41" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0360319908000104-si12.gif"></span> after 300 h. In contrast, the TGO layer formed on 441 during dual atmosphere exposure was much faster-growing (<span id="mmlsi13" onclick="submitCitation('/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0360319908000104&_mathId=si13.gif&_pii=S0360319908000104&_issn=03603199&_acct=C000228598&_version=1&_userid=10&md5=4a9125fa87a099b845fa66e82040ba77')" style="cursor:pointer;" alt="Click to view the MathML source" title="Click to view the MathML source"><img height="13" border="0" style="vertical-align:bottom" width="41" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0360319908000104-si13.gif"></span> in 20 h) and exhibited a continuous, porous <span id="mmlsi14" onclick="submitCitation('/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0360319908000104&_mathId=si14.gif&_pii=S0360319908000104&_issn=03603199&_acct=C000228598&_version=1&_userid=10&md5=11f4dbd5a0e03f9229b0b6e14b1aac07')" style="cursor:pointer;" alt="Click to view the MathML source" title="Click to view the MathML source"><span class="formulatext" title="click to view the MathML source"><em>Fe</em><sub>2</sub>O<sub>3</sub></span></span>-rich surface layer with a relatively thin <span id="mmlsi15" onclick="submitCitation('/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0360319908000104&_mathId=si15.gif&_pii=S0360319908000104&_issn=03603199&_acct=C000228598&_version=1&_userid=10&md5=d588bb87a33e0a7bd21839d23fe2c3ff')" style="cursor:pointer;" alt="Click to view the MathML source" title="Click to view the MathML source"><img height="13" border="0" style="vertical-align:bottom" width="51" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0360319908000104-si15.gif"></span> sublayer of similar composition to the TGO layer formed during the air/air exposure. Spontaneous TGO layer spallation was also observed for the air side of 441 exposed to dual atmosphere for <span id="mmlsi16" onclick="submitCitation('/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0360319908000104&_mathId=si16.gif&_pii=S0360319908000104&_issn=03603199&_acct=C000228598&_version=1&_userid=10&md5=ac2edea9970275ddb4d857fc941f6c64')" style="cursor:pointer;" alt="Click to view the MathML source" title="Click to view the MathML source"><img height="11" border="0" style="vertical-align:bottom" width="44" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0360319908000104-si16.gif"></span>. The observed oxidation behavior and TGO layer evolution of 441 in both air/air and dual atmosphere are presented, with possible mechanisms and implications discussed.</p>
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| [9] |
The effects of temperature and oxygen pressure on the initial oxidation of stainless 441 , |
| [10] |
Water vapor oxidation of ferritic 441 and austenitic 316L stainless steel at 1000℃ for short duration , |
| [11] |
Improved oxidation resistance of 15 wt.% Cr ferritic stainless steels containing 0.08-2.45 wt.% Al at 1000℃ in air , |
| [12] |
Oxidation behaviour of FeAl intermetallics.The effects of Y and/or Zr on isothermal oxidation kinetics ,
The isothermal oxidation behaviour of doped and undoped Fe–37 at% Al intermetallic compounds in an ambient atmosphere over the temperature range of 1000–1200°C was studied. The oxidation products were identified by X-ray diffraction (XRD). Characterisation of the specimens after oxidation was conducted using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The rate constants of the isothermal oxidation were determined using three methods. The effective diffusion coefficients for the oxidation of doped and undoped Fe–37Al are discussed based on oxide grain size and the effects of reactive elements in lattice and grain boundaries. The effects of reactive elements on the isothermal oxidation kinetics of Fe–37Al were analysed based on oxide morphologies and microstructures.
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| [13] |
Coated stainless steel 441 as interconnect material for solid oxide fuel cells: Oxidation performance and chromium evaporation ,
Reactive Element (RE) and RE/cobalt-coated stainless steel AISI 441 was exposed at Solid Oxide Fuel Cell (SOFC) cathode conditions (85002°C in air with 3% water content) for up to 50002h. The chromium evaporation was measured by applying the denuder technique. Uncoated material exhibited severe spallation which could be successfully prevented by using cerium or lanthanum coatings. By applying double layer coatings of cerium or lanthanum in combination with cobalt the oxidation rate was decreased and the chromium volatilisation was also about 90% lower than the uncoated material.
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