High-temperature oxidation of Fe-16.7% Mn-2.1% Ni-6.6% Si alloy in SO2

The oxidation of an austenitic Fe-16.7% Mn-2.1% Ni-6.6% Si (by weight) alloy in SO₂ in the temperature range 600–900°C is described. The corrosion products formed on this alloy in this environment below 800°C consist only of oxides, rather than a mixture of oxides and sulfides as is observed for unalloyed Fe or Mn. The kinetics of oxidation of the alloy in SO₂ in this temperature range are similar to those in O₂. It is proposed that these characteristics result from the presence of a thin silicate layer near the scale-metal interface that alters the gradient of oxygen potential within the scale.     

Effects of alloy microstructure on the high temperature oxidation of an Fe-10% Cr alloy

The oxidation resistance of an Fe10%Cr alloy at 600°C in air increased with increasing amounts of cold work in the alloy. Breakaway oxidation could be prevented for at least 2000 h at 600°C by severe cold rolling or by pretreatment to produce 3–7 m diameter grains. These treatments increased the mass of Cr passing into the oxide and also reduced the mechanical stress. The improvement in oxidation resistance could not have been due entirely to the increased oxidation of Cr. It is suggested that the microstructure produced by pretreatment strengthened the alloy so that it resisted the deformation normally produced by growth stresses. This allowed time for diffusion of Cr into the outer layer of the oxide, leading to a permanent reduction of stress.Shot blasting and mechanical abrasion also significantly improved oxidation resistance at 600°C but very little improvement could be achieved at 800°C using the treatments discussed in this paper.     

Effects of alloy microstructure on the high temperature oxidation of an Fe-10% Cr alloy

The oxidation resistance of an Fe-10% Cr alloy at 600°C in air increased with increasing amounts of cold work in the alloy. Breakaway oxidation could be prevented for at least 2000 h at 600°C by severe cold rolling or by pretreatment to produce 3–7 μm diameter grains. These treatments increased the mass of Cr passing into the oxide and also reduced the mechanical stress. The improvement in oxidation resistance could not have been due entirely to the increased oxidation of Cr. It is suggested that the microstructure produced by pretreatment strengthened the alloy so that it resisted the deformation normally produced by growth stresses. This allowed time for diffusion of Cr into the outer layer of the oxide, leading to a permanent reduction of stress.Shot blasting and mechanical abrasion also significantly improved oxidation resistance at 600°C, but very little improvement could be achieved at 800°C using the treatments discussed in this paper.     

不同氧含量的Fe-36Ni因瓦合金的晶间内氧化行为

利用恒温氧化试验,研究了不同总氧含量的Fe-36Ni因瓦合金在1000℃和1100℃下的高温氧化行为,通过SEM分析了两种试样在不同温度下氧化层的截面形貌的差异并比较了两者氧化增重曲线的不同。试验结果表明,氧化温度和钢内总氧含量能显著影响Fe-36Ni因瓦合金的晶间内氧化行为;氧化温度越高,反应物质扩散越快,晶间内氧化层厚度越大,氧化越严重;钢内总氧含量较高时,有利于反应物质沿晶界扩散,从而造成更严重的晶间内氧化现象。     

High temperature oxidation of Ni-20Cr-12.5Al coatings containing 1% dispersed oxides

Oxidation studies were conducted on plasma sprayed coatings of Ni-20Cr-12.5Al containing one of the following: 1% MgO, 1% La₂O₃, 1% Y₂O₃, and 0.8% Y. The alloy powders containing dispersed oxides were prepared by a variety of processes employing attrition and ball milling. The TEM characterization of the plasma sprayed deposits of Ni-20Cr-12.5Al-1Y₂O₃ indicated that the oxide particles ranged from almost pure aluminum oxide to various compounds of aluminum and yttrium oxide. In cyclic tests conducted at 1150 and 1225°C, the coating containing 1% Y₂O₃ appeared to provide the best oxidation resistance. The oxidation resistance appeared to be influenced by the size and distribution of the oxide particles.     

Fe-29Ni-17Co合金的热变形行为

在实验温度为900-1200℃,应变率为0.001-1 s-1的条件下,对Fe-29Ni-17Co合金进行热压缩试验。热压缩过程中的动态再结晶导致材料的流变软化。用双曲正弦方程分析材料的流变行为,并确定了相应的材料常数A, n 和α,其中得到的表观活化能为423 kJ/mol。材料的应力峰值与稳态应力对Zener-Hollomon参数显示出简单的指数依赖关系。用Avrami方程分析了动态再结晶动力学,得到相应的指数为2.7,高于文献报道的2,这与连续动态再结晶机制有关。采用Cingara方程搭建峰值流变曲线,得到应变指数c约为0.85,比有关报道的不锈钢的c值0.2高,这点更加强了关于进行Fe-29Ni-17Co合金动态回复或连续动态再结晶研究的想法。     

Kinetics of changes in the saturation magnetization during annealings of the Fe-36% Ni invar alloy subjected to severe plastic deformation

Changes in the saturation magnetization and microhardness of the Fe-36% Ni invar alloy with a nanocrystalline structure, which were caused by annealings at different temperatures, are studied. The nanocrystalline structure was produced by severe plastic deformation. A high-temperature ferromagnetic phase was found to result from the formation of such a structure. The temperature of annealing after which the content of the phase is maximum was determined. When analyzing the kinetics of phase-composition changes, an increase in the diffusive mobility of atoms during the formation of the nanocrystalline state in the material was taken into account.     

Duplex scale formation during high-temperature oxidation of Ni-0.1 wt.% Al alloy

The development of a duplex NiO scale microstructure on a Ni-0.1 wt.% Al alloy at 900°C has been examined, principally using secondary-ion mass spectrometry and analytical transmission electron microscopy. The¹⁸O-tracer distribution following sequential oxidation in¹⁸O₂/¹⁸O₂ showed that the inner NiO layer formed as a result of gaseous-oxygen penetration of the scale. The provision of pathways for oxygen transport as well as the role of Al, Si, and Ce segregation at oxide grain boundaries in influencing the growth rate and spallation behavior of the scale are discussed.     

High temperature corrosion behaviour of a new Ni-30Fe-10Al-Cr-Alloy

The high temperature corrosion behaviour of a new duplex nickel-base alloy containing about 30 mass% iron, 10 miss% aluminium and 8 mass% chromium was determined in both air and hot process gases containing methane/hydrogen, sulphur dioxide and hydrogen sulphide, respectively. It was found that the corrosion resistance against carburisation, sulphidation and oxidation was excellent due to the formation of a dense, protective alumina scale. The adherence of the alumina scale was increased by an addition of 0.1 mass% hafnium. The concentration of chromium was found to have a remarkable impact on the oxidation and high temperature corrosion resistance. Alloys without chromium showed increased corrosion rates in both air and sulphur-containing gas atmospheres due to the initial formation of nickel oxides. In sulphidising SO₂- and H₂S- containing gases at least 4 mass% chromium are required to stabilise the formation of alumina and to prevent the formation of nickel/sulphur compounds.     

Effect of severe plastic deformation on the properties of the Fe-36% Ni invar alloy

Temperature dependences of the magnetization and thermal expansion coefficient of the Fe-36% Ni invar alloy in different structural states obtained upon plastic deformation by torsion under a quasihydrostatic pressure followed by annealing at different temperatures are studied. A decrease in the thermal expansion coefficient of the invar in a temperature range of 20–100°C and the formation of ordered precipitates (with a superstructure) were found to result from severe plastic deformation.     

Fe-30Ni-5NiO alloy as inert anode for low-temperature aluminum electrolysis

Fe-30Ni-5NiO alloy anodes were prepared by a spark plasma sintering process for aluminum electrolysis. NiO nano-particles with the size of ∼20 nm were dispersed in the anodes. The oxidation behaviors of the anodes were investigated at 800°C and 850°C, respectively. The electrolysis corrosion behaviors were tested in a cryolite-alumina electrolyte at a low temperature of 800°C with anodic current densities of ∼0.5 A/cm². The results indicated that the oxidation kinetic of the anodes followed a parabolic law. A continuous Fe₂O₃ film selectively formed on the surface of the anode during the electrolysis process. A semi-continuous Al₂O₃ layer was observed at oxide film/alloy interface, probably caused by an in-situ chemical dissolution process.     

Kinetics of ferrite formation in low-carbon alloy Fe-9% Cr

Conclusions  1. The formation of ferrite in low-carbon Fe-9% Cr alloys seems to obey the kinetic theory of Khan, which is confirmed by the transformation fromn=4 (nucleation over grain boundaries) ton=1 (growth without the appearance of new centers). 2. The time of the transformation to a specified degreef can be described quite satisfactorily by an equation of the form

XPS and AES studies of the high temperature corrosion mechanism of Fe-30Cr alloy

Fe-30Cr alloy specimens were pre-oxidized at two different oxygen partial pressures (10^?16 and 10^?19 atm) at 900°C and subsequently exposed to environments containing both oxygen and sulfur. The sulfur and oxygen partial pressures were maintained such that Cr₂O₃ was the stable phase. The Cr₂O₃ scales formed during pre-oxidation became rapidly unstable when exposed to an environment whose composition approached the chromium sulfide-chromium oxide phase boundary; but when exposed to a higher oxygen partial pressure with the same sulfur partial pressure, the preformed scales remained intact. For elucidating the sulfidation mechanisms, the reaction products on the surface were analyzed at different stages of sulfidation by X-ray photo-electron spectroscopy and Auger electron spectroscopy. Correlation of the reaction mechanisms with thermodynamic and transport parameters are discussed.     

Formation of metastable phases in a Ni-9.6 wt % Al-6.7 wt % Fe-1 wt % Cr intermetallic alloy

Structural changes and the formation of metastable phase states in an Ni₃Al-based intermetallic alloy after short-term 5-h annealing at a temperature of 1000°C and upon subsequent multiple deformation of the crystal by compression to 38% at room temperature have been analyzed using transmission electron microscopy and neutron diffraction.     

Fe-40%Ni合金的高温氧化行为

采用测定高温下保温不同时间后氧化层厚度的方法讨论分析了Fe-40%Ni合金的高温氧化行为,并通过回归分析得到了预测氧化层厚度的数学模型。结果表明,当温度低于1000 ℃时,合金氧化层增加的趋势相对较缓,超过1000 ℃后显著加快。随保温时间的延长,氧化层厚度以一定的速度增加,并与保温时间呈近似线性的关系,而当温度较高时则逐渐向抛物线型转变。回归分析表明,合金的氧化层厚度(μm)可用h=6700×t^0.44×e^-6870/T计算。     

硼对Fe-36Ni因瓦合金热塑性的影响

用Gleeble-3800热模拟试验机研究了850~1050℃温度范围内B对Fe-36Ni因瓦合金热塑性的影响。结果表明,添加0.01%B可显著提高Fe-36Ni因瓦合金的热塑性,尤其是提高850~1000℃温度范围内的热塑性,断面收缩率均大于80%,拉伸断口均为典型的韧性断裂。热塑性的提高,主要与B元素的晶界偏聚和降低动态结晶开始温度有关。     

Al对Fe-20Cr-35Ni-0.6Nb合金显微组织和抗氧化性的影响

采用增量法研究了不同Al含量(0.5%、1.5%、2.5%,质量分数)的Fe-20Cr-35Ni-0.6Nb含Nb合金在1000 ℃空气条件下的抗氧化。采用SEM、EDS、TEM、拉曼光谱等手段研究了合金的显微组织和氧化膜特性。结果表明,3种含Nb合金组织为单相奥氏体,基体中存在少量弥散分布的NbC沉淀相,氧化前后沉淀相含量和晶粒大小保持不变。添加0.5%和1.5%的Al后,含Nb合金的表面形成多层结构的氧化膜,最外层和第三层为Cr₂O₃,次表层主要为NiCr₂O₄、NiFe₂O₄和Fe₂O₃,最内层为Al₂O₃内氧化层。基体中的NbC析出相和氧化膜中少量Nb的氧化物(Nb₂O₅)加剧了氧化膜的疏松。当Al含量增加到2.5%时,含Nb合金表面形成连续致密的Al₂O₃氧化膜,降低了Fe-20Cr-35Ni-0.6Nb合金的氧化速率,提高了抗氧化性。     

Ni63W30Co5TiAl合金高温塑性变形行为

采用Gleeble-3800热模拟试验机,在1000～1250℃温度范围,以0. 01～10 s~(-1)应变速率对Ni63W30Co5TiAl合金进行轴向热压缩试验,获得该合金的真应力-真应变曲线,并对Ni63W30Co5TiAl合金不同变形条件下的变形组织进行了系统观察与分析。结果表明,Ni63W30Co5TiAl合金流变曲线表现为典型的动态再结晶软化类型,流变应力随着应变速率的升高和变形温度的降低而逐渐增加;在1150～1200℃温度范围,Ni63W30Co5TiAl合金可获得细小均匀的等轴完全动态再结晶晶粒组织,而当变形温度高于1200℃时,合金的完全动态再结晶晶粒发生长大;另外,计算得到Ni63W30Co5TiAl合金的热变形激活能Q为398. 9403 kJ·mol~(-1),临界应变ε_c和稳态应变ε_s与ln Z近似呈线性增长关系。基于双曲正弦函数模型建立了Ni63W30Co5TiAl合金的峰值应力热变形本构方程。     

四元三相Cu-20Ni-20Cr-5Co合金的高温氧化行为

研究四元三相Cu-20Ni-20Cr-5Co合金在700-900℃、0.1MPa纯氧气中的氧化行为以及添加第四组元Co对三元三相Cu-20Ni-20Cr合金氧化行为的影响。结果表明:合金为三相混合物,其氧化动力学曲线偏离抛物线规律,由几个线段组成,添加5%Co后合金的氧化速率明显降低。Cu-20Ni-20Cr-5Co合金表面形成的氧化膜外层主要是由CuO组成,内层是合金与氧化物组成的混合内氧化区,最终合金内层表面形成一连续的Cr2O3层,阻止合金的进一步氧化。     

添加Nb对Zr-0.75Sn-0.35Fe-0.15Cr合金高温蒸汽氧化行为的影响

本文熔炼了Zr-0.75Sn-0.35Fe-0.15Cr-xNb（x=0、0.15、0.50、1.00,wt.%）合金,并制备成板状样品。采用TG-DSC研究了4种锆合金在模拟LOCA工况下800~1200 ℃的抗高温蒸汽氧化行为和相变行为,利用金相显微镜分析了氧化样品横截面的显微组织。结果表明,4种锆合金的抗高温蒸汽氧化性能并没有随Nb含量的变化呈单一的变化规律,其氧化动力学大多为线性规律,只有添加0.5%Nb的合金在1000 ℃的氧化动力学发生了两次转折,由线性规律转变为幂指数规律再转变为线性规律;锆合金中基体的相转变温度随着Nb含量的增加而降低,而其氧化物的相变行为并没有随Nb含量的变化呈单一变化趋势,这说明Nb含量对锆合金氧化物的相变行为的影响比对合金相变行为的影响复杂。氧化温度为800 ℃、1000 ℃和1200 ℃时,氧化样品截面组织分别为：ZrO2和α-Zr(O),ZrO2、α-Zr(O)和原β-Zr层,ZrO2和α-Zr(O); 800 ℃氧化样品截面各层组织的厚度占比基本不随Nb含量发生变化;1000 ℃氧化样品截面α-Zr(O)层的厚度占比随Nb含量的增加而增大,原β-Zr层的厚度占比正好相反,出现了指状侵入的α-Zr(O)。1200 ℃氧化样品截面显微组织厚度占比随Nb含量的变化比较复杂。这说明Nb有促进β→α-Zr(O)转变的作用。