Crofer22 APU铁素体不锈钢的氧化行为研究

 Crofer22 APU铁素体不锈钢是固体燃料电池连接体的备选材料之一。通过增重法研究了Crofer22 APU铁素体不锈钢在800℃空气中的抗高温氧化动力学,并结合X射线衍射（XRD）、扫描电镜（SEM）、能谱分析（EDS）等手段,对氧化膜的形貌和组成进行了分析。结果发现,Crofer22 APU 铁素体不锈钢在800℃下 0~100h 的平均氧化速率为0.032g/（m2·h）;100~450h的平均氧化速率为0.0091g/（m2·h）;450~550h的平均氧化速率为50×10-4g/（m2·h）。氧化膜分为内外两层,内层主要是含SiO2的氧化物,外层主要是含Cr2O3的氧化物。     

铝对HP40合金高温抗氧化性能的影响

 采用增重法研究了w(Al)=5%~10%的HP40合金在1 200 ℃×30 h空气中的抗氧化性能。结果表明,铝可显著提高合金的高温抗氧化性能,而且合金的高温抗氧化性能随铝含量增加而提高。1 200 ℃时,合金氧化增重与氧化时间的关系呈抛物线规律,氧化速率随氧化时间延长而逐渐下降。加入铝,改变了合金氧化膜层的物相组成和致密度,含铝合金的氧化层中含有Al2O3,而且Al2O3量随铝加入量增加而增多。     

Fe-Cr合金的钝化膜和点蚀发展模型

本文采用AFS和FPMA以及旋转圆盘-圆环电极等方法,对三种Fe-Cr合金在3.5%NaCl溶液中的钝化和点蚀行为进行了研究,考察了铬的作用和溶解机理,并据此提出了两种点蚀发展模型。     

Cr含量对2.25Cr-1Mo钢蒸汽氧化性能的影响

对第四代核电主体结构材料2.25Cr-1Mo钢中铬含量对蒸汽氧化性能的影响进行了研究.完成了500 ℃/0.1 MPa下600h的高温蒸气氧化实验,并利用分析天平测量氧化增重,采用扫描电镜、X射线能谱和X射线衍射仪表征氧化膜的结构特征和物相.实验结果表明,Cr质量分数为1.99％和2.37％的实验钢氧化增重曲线都符合立...     

钼对耐蚀软磁合金抗蚀性及磁性能的影响

 Fe Cr系软磁合金是一种抗蚀软磁材料。在Fe 13%Cr和Fe 17%Cr中添加不同含量的钼，对合金的抗点蚀、盐雾腐蚀、浸泡腐蚀以及大气腐蚀的能力和相应的磁性能进行了系统、全面的研究。结果表明，在这两种软磁合金中加入质量分数为20%和30%的钼，可明显提高合金的耐蚀能力；合理控制钼含量和采用相应的热处理工艺对合金磁性能的影响并不明显。     

Effect of process parameters on the microstructure and mechanical properties of vacuum hot-press sintered Co-50 mass% Cr alloys

In the present research, two different compositions of submicron-structured cobalt (800?±?45?nm) and chromium (700?±?50?nm) powders are mixed to fabricate Co-50 mass% Cr alloys by the vacuum hot-press sintering technique. This study imposes various hot-press sintering temperatures (1150, 1200, 1250 and 1300°C) and pressures (20, 30, 40 and 50?MPa) while maintaining the sintering time at 1?h, respectively. The experimental results show that the optimum parameters of hot-press sintered Co-50 mass% Cr alloys are 1200°C at 50?MPa for 1?h. Meanwhile, the sintered density reaches 7.73?g?cm^?3, the closed porosity decreases to 0.31%, and the hardness and transverse rupture strength values increase to 80.6?±?0.3 HRA and 1052.9?±?17.5?MPa, respectively. Grain growth is not obviously generated after 1200°C hot-press sintering at 50?MPa for 1?h. Consequently, the optimal solid-phase sintering process effectively improved hot-press sintered Co-50 mass% Cr alloys, which resulted in the good properties.     

固体氧化物燃料电池用SUS430-Sr2Fe1.5Mo0.5O6?δ不锈钢-陶瓷复合连接体材料的制备及性能研究

以SUS430不锈钢粉末和Sr₂Fe_1.5Mo_0.5O_6?δ（SFM）陶瓷粉末为原料,通过成形烧结结合涂覆的方法制备了应用于固体氧化物燃料电池（solid oxide fuel cell,SOFC）的SUS430-SFM不锈钢-陶瓷复合连接体材料,并对SUS430和SUS430-SFM两种烧结体试样的显微组织、抗氧化性能和导电性能进行了分析。结果表明,SFM涂层与SUS430基体具有相匹配的热膨胀系数（thermal expansion coefficient,TEC）,两者界面结合良好;在空气气氛中经800 ℃氧化140 h后,SUS430-SFM试样的氧化速率常数（K）约为3.66×10?14 g2?cm?4?s?1,比SUS430试样（2.42×10?14 g2?cm?4?s?1）降低了约50%,其面比电阻（area specific resistance,ASR）则由SUS430试样的81 mΩ?cm2降至SUS430-SFM的2.6 mΩ?cm2,说明SFM涂层能够有效改善SUS430不锈钢基体的抗氧化及导电性能。     

Chromium Extraction <Emphasis Type="Italic">via</Emphasis> Chemical Processing of Fe-Cr Alloys Fine Powder with High Carbon Content

Ferrous alloys are important raw materials for special steel production. In this context, alloys from the Fe-Cr system, with typical Cr weight fraction ranging from 0.45 to 0.95, are prominent, particularly for the stainless steel industry. During the process in which these alloys are obtained, there is considerable production of fine powder, which could be reused after suitable chemical treatment, for example, through coupling pyrometallurgical and hydrometallurgical processes. In the present study, the extraction of chromium from fine powder generated during the production of a Fe-Cr alloy with high C content was investigated. Roasting reactions were performed at 1073 K, 1173 K, and 1273 K (800 °C, 900 °C, and 1000 °C) with 300 pct (w/w) excess NaOH in an oxidizing atmosphere (air), followed by solubilization in deionized water, selective precipitation, and subsequent calcination at 1173 K (900 °C) in order to convert the obtained chromium hydroxide to Cr₂O₃. The maximum achieved Cr recovery was around 86 pct, suggesting that the proposed chemical route was satisfactory regarding the extraction of the chromium initially present. Moreover, after X-ray diffraction analysis, the final produced oxide has proven to be pure Cr₂O₃ with a mean crystallite size of 200 nm.     

Reactions of Fe-Cr and Ni-Cr alloys in CO/CO2 gases at 850 and 950 °C

A series of Fe-Cr and Ni-Cr solid solution alloys was reacted at 850 and 950 °C in CO/CO₂ gas mixtures in which FeO and NiO were unstable. The compctitive tendencies toward the carburization and oxidation of the chromium solute, as compared to a graphical thermodynamic "metastability" criterion, were tested experimentally. Relatively good agreement was found between predictions and experiments for the occurrence of Cr carburization beneath Cr₂O₃ internal oxides or external scales. The chromium contents required for the transition from internal oxidation of Cr to the formation of Cr₂O₃ external scales in CO/CO₂ gas mixtures were established for Fe-Cr and Ni-Cr alloys. The Cr₂O₃ external scales formed on Fe-Cr alloys were found to be relatively impervious to carbon penetration for short (12-hour) experiments. No carburization was observed in the Ni-Cr alloys, but the only alloys that were predicted to carburize were the ones that formed external scales. Formerly Graduate Student, The Ohio State University     

Structural and phase transformations in high-nitrogen austenitic steel 05Kh20AG10N3MF during thermal action

The structural and phase transformations in high-nitrogen austenitic steel 05Kh20AG10N3MF under various thermal actions are studied. The transformations are shown to occur only in the Fe-Cr diffusion couple, and they resemble the phase transformations in an Fe-20% Cr binary alloy. At 1200°C, hightemperature phase separation is detected; at 550°C or below, low-temperature separation is detected; and at 700 and 800°C, ordering with the formation of a Laves phase is observed. The ordering-low-temperature separation phase transition in the steel differs substantially from that occurring in Fe-Cr binary alloys.     

The effect of high temperature low cycle fatigue on the corrosion resistance of austenitic stainless steels

The effect of high temperature (650 °C) low cycle fatigue on the corrosion behavior of five austenitic stainless steels (Types 304, 316L, 321, and Incoloy Alloys 800 and 800H) has been investigated. For comparison, corrosion tests were also performed on samples of as-received material as well as material which had been solutionized and material which was sensitized at 650 °C. It was observed that cyclic loading at high temperature reduces the corrosion resistance to a much greater extent than does just the exposure of unstressed material to elevated temperatures. Formation of chrome carbides during cycling and depletion of chromium from the matrix is responsible for the decrease in corrosion resistance. Of the alloys tested, Type 304 exhibited the lowest corrosion resistance. Superior corrosion resistance of the other alloys was due to the following: (a) a lower carbon content, (b) a higher chromium content, and (c) the presence of a strong carbide forming element (stabilized material).     

Thermodynamics of inclusion formation in Fe-Cr-Ti-N alloys

The thermodynamics of titanium in Fe-Cr alloys and of inclusion formation in Fe-Cr-N-Ti alloys was investigated. A metal-nitride-gas equilibration technique was used to measure the activity of titanium. The equilibrium titanium content of the metal that is in equilibrium with pure solid titanium nitride and nitrogen gas at 1 atm was determined. The activity coefficients of titanium it(f_Ti) relative to 1 wt pct standard state in Fe were calculated for Fe-Cr alloys from the experimental results. The first-order interaction coefficient between titanium and chromium, e _Ti ^Cr , was determined to be 0.024 at 1873 K. The solubility of nitrogen in Fe-Cr alloys was measured and was found to increase with chromium content, which is in agreement with previous work. Thermodynamic calculations were made in order to predict under what conditions titanium nitride will form in 409 stainless steel and was compared with inclusions found in plant samples. The inclusion stability diagrams for 304 stainless steel and Fe-18 pct Cr and Fe-9 pct Cr alloys were computed.     

Thermodynamic properties of solid alloys of chromium with nickel and iron

The thermodynamic properties of chromium have been determined in the Ni-Cr and Fe-Cr binary systems and in the Fe-corner of the Fe-Ni-Cr system. These properties are based on experimental measurements using solid oxide electrolyte cells of the type: Cr, Cr₂O₃ I ThO₂-Y₂O₃Cr (alloy), Cr₂O₃. In the Ni-Cr system, between 900 and 1300°, the activity of chromium exhibits negative deviation from ideality up to about 25 at. pct chromium. For alloys higher in chromium content, the activity of chromium exhibits positive deviation from ideality. In the Fe-Cr system, between 900 and 1200°, and 0 and 63 at. pct Cr, the chromium activity when referred to solid pure chromium exhibits positive deviation from ideality in both the γ and α phases, approaching ideality with increasing temperature. The nickel and iron activities in these two respective binary systems were calculated by a Gibbs-Duhem integration. The activity of chromium, referred to solid pure chromium, was measured between 900 and 1200° in solid Fe-Ni-Cr alloys with chromium concentrations of 9, 20, and 30 at. pct and Ni concentrations of 8, 18, and 30 at. pct. Additions of nickel to Fe-Cr alloys in the above concentration range are found to increase the chromium activity. The effect of nickel in increasing the chromium activity is greater at both greater chromium contents and lower temperatures. Formerly Graduate Student at The University of Michigan, is Staff Associate, Gulf Energy and Environmental Systems, LaJolla, California. This paper is based on a portion of a thesis submitted by F. N. MAZANDARANY in partial fulfillment of the requirements for the degree Doctor of Philosophy at The University of Michigan.     

Microstructural investigation of the oxidation of an Fe-3 pct Cr alloy

The microstructure and microchemistry of the oxide scale on an Fe-3 wt pct Cr alloy have been investigated after oxidation in the temperature range 700 to 800 °C. Transmission and scanning electron microscopy along with energy dispersive X-ray analysis and Auger electron spectroscopy techniques were used for the investigation. Multilayered scales are observed which vary in composition and structure; the innermost oxide is an Fe-Cr spinel of the type Fe(Fe_2•xCr_x)O₄. The intermediate layer and the outer oxide layer are both α-Fe₂O₃ hematite. The outer hematite layer is nonadherent and wrinkling is observed. Spallation occurs readily at the inner hematiteJspinel interface and at the spinel oxideJalloy interface. The poor oxidation resistance of the alloy is discussed in terms of these observations.     

Effect of carbon addition on the strength and creep resistance of FeAl alloys

We investigated the effect of carbon content (0.05, 0.12, and 0.2 wt pct C) and heat-treatment temperature (1100°C and 1300°C for 2 hours and air cooled) on the tensile and the creep properties of Fe-24 wt pct Al alloy. The increase of carbon content increased the yield strength without affecting the tensile ductility of the alloys. Carbon content appears to be beneficial in suppressing the hydrogen embrittlement at the grain boundary, because the fracture mode changes from predominantly intergranular failure in a low carbon (0.05 wt pct C) alloy to a predominantly transgranular cleavage failure in a high carbon (0.2 wt pct C) alloy. With the increase of carbon content, the anomalous yield strength peak shifted to a higher temperature possibly due to the interaction between carbon and vacanies. Significant improvements were noted in the tensile and the creep properties of medium (0.12 wt pct C) and high carbon (0.2 wt pct C) alloys after heat treating at 1300°C. The improvements in the tensile and the creep properties were attributed to the synergetic effect of retained vacancies and fine carbide precipitates present in the alloys after 1300°C heat treatment. However, the improved strength and creep properties associated with 1300 °C heat treatment were lost when the heat-treated alloys were further subjected to a vacancy removal annealing. Our results suggest that the retained vacancies present in the FeAl alloys after high-temperature heat treatment and air cooling are effective in improving the creep resistance at 700°C, and yield strength up to 800°C. The creep resistance of the present high carbon FeAl alloy is comparable to or better than several grades commercial heat-resistant Fe-based and Ni-based alloys. The work was carried out when the authors were with Chrysalis Technologies Inc., Richmond, VA. This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint Committee on Mechanical Behavior of Materials.     

Effects of Chromium Addition on Preparation and Properties of Bulk Cementite

Bulk cementites with the Cr contents of 0,3.01,6.03,8.22,and 11.51mass% were prepared by mechanical alloying(MA)and spark plasma sintering(SPS).The results indicated that when the Cr content was low(3.01mass%),the phases were composed of cementite with a small amount ofα-Fe at a sintering temperature of 1 173 K,but the microstructure became single-phase alloyed cementite as the Cr content was further increased.It showed that microaddition of Cr was beneficial for promoting the formation of cementite.Furthermore,the mechanical performance of cementite can be greatly affected by the variation of Cr content.The hardness,elastic modulus and elastic recovery presented a remarkably increasing tendency with the addition of Cr,and the maximum micro-hardness and elastic modulus values reached 1 070.74 HV and 199.32 GPa,respectively,which were similar to the precipitation phase(cementite)obtained by melting and casting techniques.Moreover,when the Cr content was below 11.51mass%,the crystal structure of Fe_3C-type cementite would not change with increasing the Cr content.A Cr atom replaced an Fe atom in the lattice of the cementite,and voids appeared when Cr was doped into the cementite at content of about11.51mass%,causing the relative density to decrease.     

00Cr25Ni22Mo2N奥氏体不锈钢的高温氧化行为

采用静态增重法研究了00Cr25Ni22Mo2N奥氏体不锈钢在不同温度下的循环氧化动力学曲线.结果表明,00Cr25Ni22Mo2N不锈钢在700℃时的氧化动力学曲线是一条平行于时间轴的直线,这说明其在该温度下氧化反应非常微弱;在800和900℃时的氧化动力学曲线遵循抛物线氧化规律,具有良好的抗氧化性能.利用扫描电镜、能谱分析和X射线衍射对氧化膜的表面形貌、截面形貌和相组成进行研究,发现该钢在3个温度下都生成了致密和黏附性好的保护性氧化膜,700℃生成的氧化膜主要由Cr2O3和Fe2O3组成,氧化膜很薄;800℃生成的氧化膜由Cr2O3、Fe2O3和少量的NiCr2O4、FeCr2O4组成,氧化膜厚度增加;900℃生成的氧化膜由Cr2O3、Fe2O3和NiCr2O4组成,氧化膜厚度进一步增加.认为氧化膜组成和结构是00Cr25Ni22Mo2N不锈钢具有良好抗高温氧化性能的重要原因.     

几种Nb—Ti—Cr—A1合金的微合金强化工艺

Nb—Ti—A1合金是一类在航天航空工业中具有良好发展前景的低密度铌基高温合金。但在该类合金的成分设计中存在两大矛盾制约了该类合金的发展。主要是Nb／Ti比值和cr＋Al含量。高的Nb／Ti比值可以提高合金的使用温度和热强性,但是反过来也增大了合金的密度。较高的cr＋Al含量可以提高合金的抗氧化能力和抗拉强度,但同时也导致合金低温脆性急剧上升。虽然可以通过调整Nb、Ti、Cr、A1四种成分的比值获得最佳的性能,但距离航空航天方面的性能指标尚有一定距离。因此必须对合金采取固溶强化和弥散强化等工艺处理。利用金相分析、XRD和SEM等多种实验方法分析了硼、钨、钼、碳和硅对Nb—Ti—A1合金的微合金化强化后的合金微观组织,并对其强化机理做了初步探讨分析。     

镍对Fe-Cr系软磁合金耐蚀性及磁性能的影响

在实验室熔炼了添加不同量镍的Fe-Cr系软磁合金,研究了其耐点蚀、盐雾腐蚀、浸泡腐蚀以及大气腐蚀的能力,并测量了其磁性能.结果表明,在Cr13系软磁合金中加入质量分数大于1.0%的镍可明显提高其耐蚀能力,但造成磁性能的显著下降;在Cr17系软磁合金中加入质量分数小于2.0%的镍,磁性能没有明显变化.     

High Temperature Materials Based on the Intermetallic Compound NiAl Reinforced by Refractory Metals for Advanced Energy Conversion Technologies

Advanced NiAl‐based high temperature materials are developed and characterized for structural applications in energy conversion systems. The intermetallic compound NiAl with B2 superlattice structure exhibits superior physical and high temperature mechanical properties, and excellent oxidation resistance. Disadvantages of polycrystalline pure NiAl are the lack in plasticity and fracture toughness at room temperature and insufficient high temperature strength at temperatures above 800 °C. The refractory metals Cr, Mo, and Re form with NiAl quasi‐binary eutectic systems which enable to produce metal fibres reinforced NiAl‐based alloys in the as‐cast condition and by performing directional solidification. These in‐situ composites show fine‐grained and thermally stable microstructures possessing high temperature strength, superior creep resistance and sufficient room temperature ductility.