High Temperature Oxidation Behavior of High Speed Steel for Roll in Water Vapor

The oxidation behavior of high speed steel (HSS) was researched by high temperature thermo balance at 500 to 800℃ in water vapor. The morphology was observed by scanning electron microscope, the microstructure of oxide scale was analyzed by energy dispersive spectrometer and X-ray diffraction spectrum. The results indicate that the mass gain of HSS increases with oxidation temperature rising, the effect of oxidation temperature on the morphology is obvious, water vapor temperature only affects mass gain and affects hardly morphology of oxide scale at the same oxidation temperature. The relevant oxidation mechanisms are also discussed.     

铝在高温水蒸气中表面氧化膜的性能

采用X射线衍射法(XRD)和扫描电镜(SEM)研究了纯铝在高温水蒸气中表面氧化膜的相组成及形貌特征.结果表明,本次实验条件下,在高温水蒸气中铝表面生成的是由一水软铝石AlO(OH)相组成的氧化膜,延长氧化时间氧化膜的相组成不发生改变,氧化膜表面的微观形态由微米数量级大小的颗粒构成,在一定临界值内,随着氧化时间延长,氧化膜厚度增加.     

Effect of Water Vapor on the Oxidation Mechanisms of a Commercial Stainless Steel for Interconnect Application in High Temperature Water Vapor Electrolysis

High temperature water vapor electrolysis is one of the most promising methods for hydrogen production. The interconnect is a key component in the electrolyse technology. In a previous paper, the high temperature corrosion resistance and the electrical conductivity of a commercial ferritic stainless steel, K41X (AISI 441), were assessed in both anode (95 %O₂–5 %H₂O) and cathode atmospheres (10 %H₂–90 %H₂O). In cathode atmosphere, ageing tests performed up to 1,000 h revealed the formation of a duplex oxide scale: an inner layer consisting of protective chromia and an outer layer comprised of a magnetite-type iron oxide. In this study, we further investigated the oxidation mechanisms of K41X alloy in cathode atmosphere by means of marker experiments using an inert marker (Au) and isotopes. SEM-EDX and SIMS characterizations were combined in order to determine the oxide scale growth processes. The roles played by hydrogen and water vapor are discussed and a diffusion mechanism is postulated.     

High Temperature Oxidation Behavior of TP304H Steel Coated with CeO2 in Water Vapor

The oxidation behavior of TP304H steel with electrodeposited CeO₂ in water vapor was investigated at 650 °C under isothermal conditions. The oxide scales were studied with glancing incident XRD, SEM and EDX. The results showed that the oxidation rate of the steel was effectively reduced, especially at the initial stage, and the adherence of the scale was improved by the CeO₂ coating. A Ce-rich oxide band was located between the inner and outer layers. Differing from reports in the literature, it was inferred from the current analysis that CeFeO₃ and CeO₂ were contained in the Ce-rich oxide band.     

M5和Zr-4合金高温水蒸气氧化性能

利用热分析天平,采用动态连续称重法分别对M5和Zr-4合金在380、400℃水蒸气条件下进行氧化试验,分析其氧化动力学规律,并利用扫描电镜观察氧化层形貌.结果表明:在380、400℃水蒸气下M5和Zr-4合金的氧化动力学均符合抛物线规律,随着氧化时间的延长,氧化速度减慢,氧化温度升高,氧化速度增快.M5和Zr-4合金在380、400℃水蒸气条件下形成的氧化膜厚度的规律和氧化单位面积总增重具有很强的一致性,氧化层致密,厚度均匀,氧化层最外层生长有柱状晶.M5合金在380、400℃水蒸气条件下的抗氧化性能优于Zr-4合金.     

T91钢高温高压水蒸汽氧化膜微观组织结构研究

利用扫描电镜和能谱仪对高温高压水蒸汽条件下的T91钢氧化层形貌和氧化膜成分进行观察和分析.结果表明:氧化层的外层主要是粗柱状晶组织,其根部为细等轴晶组织;内层是单相无晶界结构.在表面生成CrFe2O6氧化物的单相无晶界非晶体簿膜,它是在Cr、Fe与O的供应相对较充足的环境中,由直径约0.1～0.2 μm的纳米级CrFe2O6氧化物小粒子堆积而成;继续氧化时,在非晶体层表面生长出CrFe2O4氧化物晶体层,在该晶体层生长的初期,(Fe、Cr):O比与非晶体层一致,但Cr逐渐减少而Fe渐多,并且Fe、Cr离子在CrFe2O4氧化物晶体中严重缺位约37%.     

304L不锈钢在高温高压水蒸气中的应力腐蚀开裂行为

目的 研究304L不锈钢在高温高压水蒸气中的应力腐蚀开裂行为及机理。方法 采用慢应变速率试验分别研究了304L不锈钢在常温常压水、高温高压水、高温高压水蒸气环境中的应力腐蚀开裂行为。利用SEM、三维立体显微镜和XPS,分析试样氧化后断口区域的形貌及元素分布。结果 304L不锈钢在常温常压水中的抗拉强度为730 MPa,拉伸率为94.32%。在高温高压水、高温高压水蒸气环境中的抗拉强度分别为382、379 MPa,拉伸率分别为44.98%、47.38%。304L不锈钢在三种试验环境中慢拉伸后的断口表面布满大量韧窝,断口全貌呈韧性断裂特征,高温高压水、高温高压水蒸气中试样的抗拉强度较常温常压水中明显下降。304L不锈钢在高温高压水环境和水蒸气环境中得到的XPS谱图中各结合能峰位置几乎相同,峰的相对强度因载荷的不同而发生变化。施加载荷后,在高温高压水环境中304L不锈钢表面氧化物中的Cr含量增加,而在高温高压水蒸气环境中的Cr含量略有下降。结论304L不锈钢在高温高压水和高温高压水蒸气环境中具有相似的最大抗拉强度和最大应变值。施加载荷将影响304L不锈钢氧化过程中金属元素扩散的速度,进而影响氧化产物的成分。     

高温水蒸气环境中TP439不锈钢的应力腐蚀开裂敏感性

目的 研究TP439不锈钢在高温水蒸气环境中的应力腐蚀开裂行为,并探讨水蒸气和温度对其应力腐蚀开裂敏感性的影响规律。方法 采用慢应变速率拉伸试验方法研究了TP439不锈钢在400~600 ℃水蒸气环境中的应力腐蚀开裂行为,利用SEM和EDS分析试样断口区域的形貌及元素分布。结果 同一应变速率(2×10^‒5 s^‒1)下,随着温度在400~600 ℃范围内升高,TP439不锈钢在空气和水蒸气环境中的屈服强度、抗拉强度和断裂能均逐渐降低,延伸率逐渐增大。400 ℃和500 ℃时,试样在水蒸气环境中的抗拉强度较空气环境中有所降低,而延伸率较空气环境中增大。600 ℃时试样在水蒸气环境中的力学性能较空气环境中无明显差别。试样在400、500、600 ℃水蒸气环境中的应力腐蚀开裂敏感性指数分别为0.7%、1.2%和‒2.8%,应力腐蚀开裂敏感性较低。试样在400~600 ℃水蒸气环境中的断口均呈现韧性断裂特征,断口形貌整体由韧窝和微孔组成,颈缩现象显著,断口附近未发现二次裂纹。温度在400~600 ℃范围内升高时,断口的韧窝特征更加明显,颈缩程度逐渐增大,600 ℃时断口侧面的氧化膜表面Cr含量明显降低,主要由Fe的氧化物形成。结论 水蒸气对TP439不锈钢的应力腐蚀开裂行为起促进作用。基于应力腐蚀开裂敏感性指数和断口的分析,在应变速率为2×10^‒5 s^‒1的400~600 ℃水蒸气环境中,TP439不锈钢的应力腐蚀开裂敏感性较低。     

Thermal Oxidation of Metallic Niobium by Water Vapor

The behavior of metallic niobium in pure water vapor (without added oxygen) was studied between 800 and 1000°C. Linear kinetics curves were observed (except for a short initial period) with a homographic influence of H₂O pressure. Hydrogen additions in the gas phase largely modified the reaction rates. The oxide formed (NbO₂) is different from that predicted by thermodynamics (Nb₂O₅). Taking into account all these experimental observations, a mechanism is proposed in which the limiting step is oxygen incorporation into the oxide lattice.     

Increasing the Upper Temperature Oxidation Limit of Alumina Forming Austenitic Stainless Steels in Air with Water Vapor

A family of alumina-forming austenitic (AFA) stainless steels is under development for use in aggressive oxidizing conditions from ~600?C900 °C. These alloys exhibit promising mechanical properties but oxidation resistance in air with water vapor environments is currently limited to ~800 °C due to a transition from external protective alumina scale formation to internal oxidation of aluminum with increasing temperature. The oxidation behavior of a series of AFA alloys was systematically studied as a function of Cr, Si, Al, C, and B additions in an effort to provide a basis to increase the upper-temperature oxidation limit. Oxidation exposures were conducted in air with 10% water vapor environments from 800?C1000 °C, with post oxidation characterization of the 900 °C exposed samples by electron probe microanalysis (EPMA), scanning and transmission electron microscopy, and photo-stimulated luminescence spectroscopy (PSLS). Increased levels of Al, C, and B additions were found to increase the upper-temperature oxidation limit in air with water vapor to between 950 and 1000 °C. These findings are discussed in terms of alloy microstructure and possible gettering of hydrogen from water vapor at second phase carbide and boride precipitates.     

等离子喷涂-物理气相沉积7YSZ热障涂层的高温氧化行为

以纳米团聚烧结的ZrO2-7%Y2O3(7YSZ)粉末为原料,采用等离子喷涂-物理气相沉积(PS-PVD)工艺及大气等离子喷涂工艺(APS)在镍基高温合金表面制备了柱状热障涂层(C-TBC)和层状热障涂层(L-TBC),并进行1 000℃的恒温氧化试验,采用X射线衍射仪、扫描电镜、电子探针、能谱分析等检测手段表征热障涂层的微观结构和高温氧化行为。结果表明:C-TBC涂层在氧化初始阶段快速生成TGO层,氧化50h后TGO层生长速率减慢,氧化动力学曲线符合五次方抛物线规律,而L-TBC涂层氧化动力学曲线符合常规二次方抛物线规律。C-TBC涂层氧化速度快于L-TBC涂层,但抗氧化剥落性能优于L-TBC涂层。     

Vapor-Phase-Mediated Phenomena Associated with High Temperature,High Water Content Oxidation of MCrAlX Bond Coats

Oxidation of MCrAlX (M = Ni and Co; X = Y or Re) bond coats was carried out at 1,125 °C in a range of N₂–O₂–H₂O environments. A three-step process of (1) oxidation, (2) taper-polishing, and (3) re-oxidation was used to evaluate steady state development of thermally grown oxide (TGO). During initial oxidation, transient (Ni,Co)(Al,Cr)₂O₄ spinel formed above α-Al₂O₃. Following taper-polishing, no new spinel grew during 1–200 h of re-oxidation in any water vapor environment; spinel growth at the TGO surface by a steady state mechanism—owing to Al-depletion of the bond coat, as predicted elsewhere—was deemed unlikely. Observations of transient spinel volatilizing in wet environments were supported by measurements of nickel volatilizing from pre-fabricated NiAl₂O₄ spinel pellets as a function of humidity. In some cases, following volatilization, water promoted vapor phase-redeposition of spinel onto adjacent specimen surfaces. Spinel-related conclusions from past humid oxidation experiments for which volatilization phenomena were not considered—and especially for which Al-depletion of the bond coat is cited as the cause for spinel growth—should be reevaluated.     

Oxidation at High Temperature Under Three-Point Bending Considering Stress-Diffusion Coupling Effects

Stress-diffusion coupling effects during oxidation have attracted extensive attention. In this work, an analytical model is developed for oxidation kinetics and stress evolution considering stress-diffusion coupling effects for three-point bending tests under high temperature. With the oxide thickening, growth strain can be generated and induces compressive stress in the oxide. The total stress in the oxide is estimated by superimposing the stress caused by oxidation and the applied load. The oxidation kinetics and stress evolution at typical locations where maximum tensile or compressive stress occurs are discussed. The theoretical analysis reveals that tensile stress accelerates the oxidation rate, while compressive stress would decelerate it. The model prediction for the parabolic rate constant of the oxidation kinetics is consistent with experimental observation, which validates this analysis. In addition, the influence of the applied load on oxidation kinetics is investigated.     

微观组织结构对NiCrAlY涂层抗高温氧化性能的影响

利用低压等离子喷涂(LPPS)和超音速火焰喷涂(HVOF)分别制备出具有两种典型组织的Ni Cr Al Y涂层,分别为层片状组织和粉末颗粒堆积结构。两种涂层的耐高温氧化性能试验在空气条件下进行,1 100℃分别保温5、10和20 h,以及在1 200℃和1 300℃分别保温10 h。结果表明,在1 100℃等温氧化条件下,层片状结构的LPPS涂层的抗高温性能优于颗粒堆积结构的HVOF涂层,并且随着保温时间的增加,氧化增重呈现抛物线形式增长。在1 200℃和1 300℃变温氧化过程中,颗粒堆积结构的HVOF涂层的抗高温氧化性能高于LPPS涂层。     

晶粒尺寸对耐热钢在高温水蒸汽中的氧化行为的影响

从氧化动力学、氧化膜相组成及微观结构方面,研究了晶粒尺寸对18Cr-8Ni耐热钢在700 ℃下的高温水蒸汽中氧化行为的影响。结果表明：晶粒细化提高了耐热钢的抗水蒸汽氧化性能,降低了其氧化增重,推迟了失稳氧化的发生;晶粒细化改变了耐热钢氧化膜的微观结构,减小了“弹坑”区的尺寸且促进了“弹坑”区与合金界面上富Cr氧化物层的形成;晶粒细化对耐热钢抗水蒸汽氧化性能的改善主要归因于其对氧化物的形核和Cr向氧化膜/合金界面扩散的促进作用。     

Al对高温合金高温抗氧化性能的影响

通过加入Al改善高温合金氧化膜的稳定性,并辅以微量强化元素Nb与合理的热处理工艺来提高高温合金抗氧化性。在真空感应熔炼炉中熔炼合金,利用扫描电镜、X射线衍射仪研究了Al元素对高温抗氧化性能的影响。结果表明:Al的加入提高了钢的抗氧化性,但含5%Al试样的氧化膜表面出现大量裂纹;合金氧化膜主要是由Cr2O3和具有尖晶石结构的FeCr2O4、Fe3O4以及少量Al3Fe5O12组成。     

Pt-Pd-Rh合金的高温氧化

用ＴＧ 热重仪测定Ｐｔ－ Ｐｄ － Ｒｈ 合金的挥发失重曲线, 用Ｘ 光电子能谱（ＸＰＳ） 和溅射剥离技术确定其氧化态表层及次表层组元化学状态和浓度。结果表明合金挥发失重曲线遵循： Δｍ ＝ Ｋ０ｔｎ ———直线失重规律。合金组元化学态为Ｐｔ０ 、Ｐｄ０ 、Ｒｈ０ 、Ｒｈ２Ｏ３ , 次表层为Ｐｔ０ 、Ｐｄ０ 、Ｒｈ０ 、ＲｈＯ２ , Ｐｄ０ 相对富集于表层。讨论了Ｐｄ 及少量Ｒｕ 、Ｃｅ 对Ｐｔ － Ｐｄ － Ｒｈ合金挥发失重曲线和表层结构的影响     

Effect of Water Vapor on the High-Temperature Oxidation of Pure Ni

The high-temperature oxidation behavior of pure Ni in air and Ar with and without 30?vol%H₂O at 1,000?°C was investigated to understand the effects of water–vapor on the resulting oxidation kinetics and scale structures. It was found that water–vapor significantly affected the morphology and scale structure of NiO. A duplex NiO scale with a powder-like outer and dense inner NiO layer developed when the Ni was oxidized in atmospheres containing water–vapor. The grain size of the dense inner NiO layer was much smaller than that formed in dry atmospheres. The growth of the powder-like NiO required outward diffusion of Ni and its continued formation occurred at the interface between the powder and dense NiO layers. The dense inner NiO layer grew outward and incorporated the powder-like NiO particles and the resulting grain size of the inner layer was smaller in the presence of water–vapor. The water–vapor is speculated to have prevented sintering of NiO particles during growth of the NiO scale.     

Pd-Ni-Al涂层的高温长期氧化行为

利用TGA，XRD，SEM／EDS等方法，研究了Pd改性铝化物涂层在900—1100℃的长期高温氧化行为．结果表明，在900-1100℃下，与简单铝化物涂层相比，β-(Ni，Pd)Al涂层具有较好的抗高温氧化性能．添加改性元素Pd加速了涂层表面的θ-Al2O3向α—Al2O3转变，有利于形成致密的保护膜；另外，Pd还促进了合金基体中Ti元素向涂层的表面以及氧化膜中扩散．