两相Fe-Cu合金的硫化腐蚀特性

研究了Ｆｅ－２５Ｃｕ、Ｆｅ－５０Ｃｕ和Ｆｅ－７５Ｃｕ在硫压高于二组元硫化物分解压条件下的高温硫化，并着重于硫化反应产物结构特征．各合金的腐蚀速率均低于纯铁和铜，其中Ｆｅ－２５Ｃｕ最慢而Ｆｅ－５０Ｃｕ最快．合金形成复杂的硫化膜结构：其外层为两种二元复合硫化物（Ｃｕ５ＦｅＳ４和ＣｕＦｅＳ２）的细微混合层；其内层含未被硫化的金属态α（Ｆｅ）相粒子和源于β（Ｃｕ）的内硫化物Ｃｕ５ＦｅＳ４．由于金属向外迁移的结果，该区域常有大量孔洞形成．硫向合金内的渗透速率随铜含量和温度的升高而增加．此外，在外／内硫化膜界面上形成一些纯金属铜颗粒，它们或呈粒状并被硫化物所包裹、或呈胡须状突出于硫化膜之外．就双相合金腐蚀区别于固溶体合金的特性，对所得实验结果进行了讨论．     

Fe－25Cr－9Mn三元合金高温硫化特性

研究了Ｆｅ－２５Ｃｒ－９Ｍｎ合金在８００℃、１０－３─１Ｐａ硫分压的Ｈ２－Ｈ２Ｓ混合气体中的硫化行为，并与Ｆｅ－２５Ｃｒ合金进行了对比。结果表明：Ｍｎ的加入提高了Ｆｅ－２５Ｃｒ合金的抗硫化性能，但作用并不显著。在Ｆｅ－２５Ｃｒ－９Ｍｎ合金的多层结构硫化层中形成了较厚且独立的α－（Ｍｎ．Ｆｅ）Ｓ层，但它并没有效地阻挡Ｆｅ２＋和Ｃｒ３＋向外的扩散。文中讨论了这种现象的原因以及硫化层分层对铁铬合金硫化行为的影响。     

Co—15Ce合金在S—O双重氧化剂中的腐蚀

研究Ｃｏ－１５Ｃｅ（质量分数,％,下同）合金在Ｓ－Ｏ双重氧化剂作用下的腐蚀特征。结果表明,在６００及７００℃下该合金均形成了复杂的腐蚀产物膜,包括外层单一的Ｃｏ的硫化物、中间层Ｃｏ的硫化物与Ｃｅ的化合物的混合物区及内层Ｃｅ的内腐蚀区。且Ｃｏ－１５Ｃｅ合金在６００及７００℃氧化－硫化混合气氛中的腐蚀速度低于相同温度、相同Ｏ,Ｓ分压下的纯氧化与纯硫化。     

Fe50Mo在不同硫压下的高温硫化行为

用ＴＧＡ、ＸＲＤ、ＳＥＭ观察分析了Ｆｅ５０Ｍｏ合金在９００℃、１０～５０ｋＰａ的硫蒸气中的高温硫化动力学曲线和硫化产物层的组成及结构。发现硫化动力学基本不受硫压的影响，但高硫压下合金发生较严重的硫化，其产物层由低硫压时的一、二层变为类似于Ｆｅ４０Ｍｏ产物层的三层结构：外层ＦｅＳ／中间层ＭｏＳ２／内层Ｆｅ、Ｍｏ的复杂硫化物。内层虽然在硫化后期生成，但发展速度比中间层快，密度也较低。中间层是阻止合金进一步硫化的主要产物，但仍允许Ｆｅ２＋通过，使外层ＦｅＳ得以继续生长，合金进一步硫化。     

含Ti,Mn或Nb的Fe—25Cr合金在800℃的H2—H2S混合气氛中的硫化

研究了含４％Ｔｉ、９％Ｍｎ和８％Ｎｂ的Ｆｅ２５Ｃｒ合金在８００℃、１０－３～１Ｐａ硫分压范围内Ｈ２Ｈ２Ｓ混合气氛中的高温硫化,硫化动力学均基本遵循抛物线规律。当硫化层开裂或者与基体分离时,硫化增重—时间曲线出现转折。对比Ｆｅ２５Ｃｒ合金,３种元素的加入均不同程度地降低了硫化速度,但未根本改变硫化层结构。讨论了Ｆｅ２５Ｃｒ基三元合金的硫化过程及３种合金元素的作用。     

Fe-Cu纳米涂层在700与800℃空气中的氧化

利用磁控溅射技术制备了Ｆｅ含量（质量分数，％）分别为２５和５０的两种Ｆｅ－Ｃｕ纳米涂层，并研究了该涂层在７００与８００℃空气中的氧化，结果表明，Ｆｅ－７５Ｃｕ涂层氧化后形成了外层为氧化铜和内侧为氧化铁的复合氧化膜，而Ｆｅ－５０Ｃｕ发生了Ｆｅ的单一外氧化，其氧化特征均有别于同成分的铸态合金，这种氧化机制在于晶粒尺寸细化显著扩展了Ｆｅ在Ｃｕ中的溶解度，同时大量的晶界也为组元扩散提供了短路通道，晶粒尺寸     

纯Y和Co—Y合金在800℃不同硫压下的硫化—氧化

研究了纯Ｙ和Ｃｏ－Ｙ合金在８００℃Ｈ２－ＣＯ２混合气中的腐蚀,以检验添加Ｙ对纯Ｃｏ耐硫－氧混合气腐蚀中影响。给定温度下纯Ｙ的腐蚀膜具有保护性。并有助于降低纯Ｃｏ的腐蚀速率,１０＾０２Ｐａ硫压下,合金表面形成的腐蚀产物为多层、以为硫化钴,中间层为由两金属化合物怕成分复杂的混合物层,最内层是由氧和硫引起的Ｙ的内腐蚀区;在１０＾－３Ｐａ硫压下,合金没有形成外层硫钴,仅在表面形成较薄的Ｙ的硫氧化物,其下为Y的内氧化区。在Y含量较高条件下未发生Y的选择性外硫化/氧化,这与Y在基体金属中的有限固溶度以及合金中出现富Y的金属间化合物相有关。     

硫压对Fe40Mo高温硫化行为的影响

观察分析了Ｆｅ４０Ｍｏ合金在１０￣５０ｋＰａ的硫蒸气中的高温硫化动力学规律和硫化产物层结构变化。结果表明，硫压对Ｆｅ４０Ｍｏ的硫化动力学规律和硫化速度有一定影响，５０ｋＰａ时比１０ｋＰａ硫化还慢些；高硫压及较高温度下合金硫化由其中Ｆｅ的硫化控制，而不象低硫压时只受Ｍｏ的硫化控制。这些表现与Ｆｅ２０Ｍｏ的相近，表明在高温和高硫压的苛刻环境中，合金中添加Ｍｏ的作用被削弱了。合金硫化动力学表现与产物层结     

Co-15Ce合金在800℃不同硫压下的硫化

研究了含15wt%Ce的Co-Ce合金在800℃、H2-H2S气体中的硫化腐蚀行为,硫分压分别为10-2Pa及10-3Pa.Co-15Ce合金在800℃硫压为10-2Pa时的腐蚀速度很快,几乎与纯Co相当,而在硫压为10-3Pa时,因其硫压在硫化钴的平衡分解压之下,故其腐蚀速度很慢.该合金硫化腐蚀后形成复杂的腐蚀产物膜,在硫压为10-2Pa时其腐蚀产物膜的最外层为纯Co的硫化物层,其下为Ce的硫化物与Co的硫化物的混合物层,内层为Ce的硫化物与金属Co的混合物层;在硫压为10-3Pa时其腐蚀产物膜仅为Ce     

琉压对Fe40Mo高温硫化行为的影响￣ 

观察分析了Ｆｅ４０Ｍｏ合金在１０－５０ｋｐａ的硫蒸气中的高温硫化动力学规律和硫化产物层结构变化。结果表明，硫压对Ｆｅ４０Ｍｏ的硫化动力学规律和硫化速度有一定影响，５０ｋＰａ时比１０ｋＰａ硫化还慢些；高硫压及较高温度下合金硫化由其中Ｆｅ的硫化控制，而不象低硫压时只受Ｍｏ的硫化控制。这些表现与Ｆｅ２０Ｍｏ的相近，表明在高温和高疏压的苛刻环境中，合金中添加Ｍｏ的作用被削弱了。合金硫化动人学表现与产物层结构、特别是中间层ＭｏＳ２的厚度和密度有根大关系，当产物层致密、中间层密度高、厚度大时。合金硫化速度较慢。ＭｏＳ２层的分子片层取向垂直于试样表面，有利于通过这一层的传质，是ＭｏＳ２层形成之后ＦｅＳ外层仍继续增厚的原因。     

The Sulfidation of Two-Phase Fe-Cu Alloys in H2-H2S Mixtures at 500-700°C

The sulfidation behavior of three two-phaseFe-Cu alloys containing 25, 50, and 75 wt.% copper hasbeen investigated in H₂-H₂Smixtures at 500-700^°C under gas-phase sulfur pressures, which is significantly abovethose for the dissociation of both FeS andCu₂S. In all cases, the three alloyssulfidized more slowly than both pure metals under thesame conditions. At all temperatures, Fe-25Cu showed the slowestgrowth rates, whereas Fe-50Cu sulfidized more rapidlythan the other two alloys. However, the kinetics curvesfor the three alloys tended to overlap, particularly at the higher temperatures. The scales werecomplex and contained an outer layer composed of amixture of two different Cu-Fe double sulfides,Cu₅FeS₄ and CuFeS₂,plus an inner zone containing a mixture of metalliciron with the double sulfideCu₅FeS₄formed by completesulfidation of the copper-rich phase and partialsulfidation of the iron-rich phase. This region also contained large voids,possibly because of outward diffusion of metal cations,whereas the iron-rich islands were mainly unattacked.The depth of internal attack increased with increasing temperature and/or iron content. Finally,particles of almost pure copper metal, probably formedduring cooling from the reaction temperature, werepresent at the scale-subscale interface, as inclusions in the scale and as whiskers protruding out ofthe external scale surface.     

The Air Oxidation of Two-Phase Fe-Cu Alloys at 600-800°C

The air oxidation of three Fe-Cu alloyscontaining 25, 50, and 75 wt.% Cu has been studied at600-800°C. The oxidation followed the parabolic lawonly approximately with rates lower than those of thepure constituent metals. The scales were alwayscomposed of an inner layer containing a mixture ofcopper metal and iron oxide and of an outer oxide layerwhose composition depended on the copper content of the alloy. For the two alloys richer in ironthe external layer was composed mostly of iron oxideswith some copper-rich particles which oxidized only inthe external-scale zone. For the alloy richest in copper the external layer contained a complexmixture of iron oxides, copper particles and doubleFe-Cu oxides surmounted by an outermost copper-oxidelayer. No significant iron depletion was observed in the alloys beneath the region of internaloxidation. The peculiar scale microstructure observedfor these alloys is considered mainly as a consequenceof their two-phase microstructure and of the limited solubilities of the two components in oneanother.     

Grain size effects on the oxidation of two-phase Cu-Fe alloys

The oxidation behavior of thin layers of two Cu-Fe alloys containing 25 and 50 wt.% Fe, respectively, prepared by magnetron sputtering deposition on cast alloys of the same composition (Cu-Fe coatings) and presenting grain sizes in the nanometer range, was studied at 600-800 °C in air to examine the influence of the reduction in the grain size on the selective oxidation of the most reactive component in two-phase binary systems. A continuous Fe₃O₄ layer formed beneath an external region of copper oxide on the Cu-25Fe coating, whereas an external iron oxide scale mostly composed of Fe₃O₄ free from copper oxides formed on the Fe-50Cu coating. In both cases, an iron-depleted region was present in a subsurface alloy layer. These results differ remarkably from the oxidation behavior of cast Cu-Fe alloys of similar composition but with a large grain size, which formed mixed external scales of iron and copper oxides in air and simultaneous internal and external oxidation of Fe under both high and low oxygen pressures. Therefore, a grain size reduction can effectively promote the selective external oxidation of the more reactive component in binary two-phase alloys due to an increase in the mutual solubility of the two components associated with the method of alloy preparation as well as to the presence of a large density of grain boundaries in the coatings which may act as short-circuit diffusion paths, allowing a faster outward diffusion of iron during oxidation.     

Oxidation of Two Ternary Fe–Cu–5 at.% Al Alloys in 1 atm of Pure O2 at 800°C

The oxidation of two two-phase ternary Fe–Cu–Al alloys containing about 5 at.% aluminium, one Fe-rich and one Cu-rich, has been studied at 800°C under 1 atm O₂. The Fe-rich alloy (Fe–15Cu–5Al) shows two parabolic stages, with a large decrease of the parabolic rate constant after about 2 hr. The presence of 5 at.% Al reduces significantly the oxidation rate of this alloy with respect to a binary Fe-Cu alloy of similar composition by forming an external alumina scale. Moreover, the addition of 15 at.% Cu is able to reduce the critical aluminium content needed to form alumina scales with respect to binary Fe–Al alloys. On the contrary, the Cu-rich Fe–85Cu–5 Al alloy presents a single parabolic stage and forms a thick and porous external scale composed of an outermost layer of copper oxides and an inner region containing a mixture of copper and Fe–Al oxides, coupled to the internal oxidation of iron and aluminium. As a result, the oxidation of the Cu-rich ternary alloy at 800°C is much faster than that of the Fe-rich ternary alloy.     

The air oxidation of two-phase Cu-Ag alloys at 650–750°C

The corrosion of three two phase Cu-Ag alloys containing 25, 50, and 75 wt% Ag has been studied at 650 and 750°C. In all cases the alloys formed external scales of copper oxides. At the same time, an internal precipitation of Cu₂O within a silver matrix was also produced, with an oxide volume fraction larger for the alloys richer in Cu. Beneath this mixed layer a region of single-phase solid solution of Cu in silver formed for Cu-50Ag and especially for Cu-75Ag. Silver metal remained in the metal-consumption zone, acting essentially as an inert marker, except for a few particles with were incorporated into the growing scales. Both pure Cu and the alloys corroded parabolically, but the rate constants for the alloys decreased with increased Ag content under constant temperature. The various aspects of the corrosion of these alloys are examined by taking into account the possible effects associated with the presence of two metal phases.     

还原性气氛中HCl和H2S导致Fe-Cr合金在700℃的加速失效

研究了Fe-8Cr,Fe-12Cr和Fe-18Cr合金在700℃含氯和两种硫含量还原性气氛中的腐蚀行为.气氛中H2S含量增加导致合金发生加速腐蚀,尤其造成Fe-18Cr合金表面氧化铬膜退化.合金的加速腐蚀与膜中生成的硫化物和氯化物密切相关.合金的腐蚀速率随其Cr含量的升高而降低.通过计算气氛中平衡时的氯势、氧势、硫势预测了合金与气氛可能发生的反应,并解释了腐蚀机制.     

Oxidation at defects in scales on iron-chromium alloys

A prior investigation on the lateral spreading of oxide into defects in Wustite scales on iron was extended to study the same phenomena in Fe-Cr alloys. Included were two Fe-Cr-Mo alloys and an Fe-25Cr-6Al alloy. Three types of experiments were conducted to study flaws introduced to simulate damage to protective oxide layers caused by particle erosion. It was found that outer scales of Wustite on the Cr-Mo alloys spread into flaws in much the same way as Wustite on unalloyed iron. However, inner scales of (Fe,Cr)₃O₄ on the Cr-Mo alloys and the scale formed on the Fe-25Cr-6Al alloy had only a slight tendency to spread into flaws. These results are consistent with the known higher diffusion coefficients and higher defect concentrations in Wustite than in other oxide phases.     

Sulfidation of Three Two-Phase Cu-Cr Alloys in H2-H2S Mixtures at 400-600°C

The sulfidation of three Cu-Cr alloys withnominal Cr contents of 25, 50, and 75 wt.% and of thetwo pure metals has been studied at 400-600°C inH₂-H₂S mixtures under sulfurpressures of 10^-12 atm at 400 and 500°C and 10^-10 atm at 500and 600°C, slightly above the Cu-Cu₂Sequilibrium. All the alloys were two-phase, containinga mixture of the solid solution of chromium in copperwith nearly pure chromium. The corrosion rates of the three materialsunder the same conditions were similar and intermediatebetween those of the two pure metals and increased withtemperature and sulfur pressure. The scales had a complex composition, often containing anexternal Cu₂S layer, which becamediscontinuous or even disappeared, in some cases,followed by an intermediate layer of the double Cu-Crsulfide CuCrS₂ and an innermost complex layer, which generallyconsisted of a mixture of the double Cu-Cr sulfideCuCr₂S₄ with the chromium sulfideCrS and also commonly contained unsul fidized chromiummetal particles. No chromium depletion was developed in the alloys beneaththe corrosion-affected region. Moreover, no internalsulfidation of chromium was observed in the alloyrichest in copper and no exclusive external sulfidation of chromium in those richest in chromium, inspite of the large difference in the thermodynamicstabilities of the sulfides of the two pure metals.These peculiar scale features are interpreted by taking into account the special two-phase nature ofthese alloys.     

The corrosion of a Fe-15 wt.% Ce alloy in coal gasification type atmospheres at 600 to 800 °C

The corrosion of a Fe-15 wt.% Ce alloy and of the two pure metals have been studied at 600 to 800 °C in H₂-H₂S-CO₂ mixtures providing high-sulfur and low-oxygen activities that are typical of coal gasification atmospheres. The alloy corrodes more slowly at 600 to 700 °C than pure Fe, more rapidly than pure Ce, while at 800 °C it corrodes at about the same rate as pure Fe. The scaling kinetics of Fe-15Ce are irregular and generally intermediate between linear and parabolic. The scale formed on Fe-15Ce shows a multilayered structure, including an outermost layer of base metal sulfide (FeS), an intermediate complex layer composed of a mixture of compounds of the two metals, and finally an innermost region of internal attack of Ce by both oxygen and sulfur. Ce is not able to diffuse outward in the metal substrate and remains in the alloy consumption region. In the intermediate region, FeS forms a continuous network that allows the growth of an external iron sulfide layer. A Ce content of 15 wt.% is insufficient to prevent the sulfidation of the base metal. These results as well as the scale microstructure are interpreted by taking into account the limited solubility of Ce in Fe and the presence of Ce-rich intermetallic compounds in the alloy examined.     

The corrosion of a Fe-15 wt.% Ce alloy in coal gasification type atmospheres at 600 to 800 °C

The corrosion of a Fe-15 wt.% Ce alloy and of the two pure metals have been studied at 600 to 800 °C in H₂-H₂S-CO₂ mixtures providing high-sulfur and low-oxygen activities that are typical of coal gasification atmospheres. The alloy corrodes more slowly at 600 to 700 °C than pure Fe, more rapidly than pure Ce, while at 800 °C it corrodes at about the same rate as pure Fe. The scaling kinetics of Fe-15Ce are irregular and generally intermediate between linear and parabolic. The scale formed on Fe-15Ce shows a multilayered structure, including an outermost layer of base metal sulfide (FeS), an intermediate complex layer composed of a mixture of compounds of the two metals, and finally an innermost region of internal attack of Ce by both oxygen and sulfur. Ce is not able to diffuse outward in the metal substrate and remains in the alloy consumption region. In the intermediate region, FeS forms a continuous network that allows the growth of an external iron sulfide layer. A Ce content of 15 wt.% is insufficient to prevent the sulfidation of the base metal. These results as well as the scale microstructure are interpreted by taking into account the limited solubility of Ce in Fe and the presence of Ce-rich intermetallic compounds in the alloy examined.