A new austenitic alumina forming alloy: an aluminium‐coated FeNi32Cr20

The FeCrAl alloys owe their low oxidation rate to the formation of a slow growing α‐aluminium oxide scale. Therefore they are used, for example, as a substrate material in metal‐supported automotive catalytic converters. Increasing exhaust gas temperatures mean that, in addition to the oxidation properties, high temperature mechanical properties should also be improved. Compared to the ferritic FeCrAl alloys, austenitic alloys possess the required high mechanical strength at higher temperatures. However for most commercially available materials the oxidation resistance is not sufficient due to a low aluminium content. High aluminium contents are avoided in austenitic alloys, since they cause severe workability problems, even at aluminium contents, which are below the necessary amount to get a pure alumina scale. The newly developed material Nicrofer 3220 PAl (coated FeNiCrAl) consists of an austenitic FeNi32Cr20 alloy coated with aluminium on both sides. It combines the outstanding oxidation resistance of an alumina forming FeCrAl alloy with the advantage of the high temperature strength of an austenitic alloy. Additionally the oxidation is even lower than the oxidation of the commercial grade Aluchrom YHf (FeCr20Al6)—conventional homogenous FeCrAl. Aluminium coated FeNiCrAl can easily be formed into its final shape. Prior to service, an in situ heat treatment is recommended in order to optimize the properties.     

激光熔敷钴基稀土合金的组织与性能

在２Ｃｒ１３钢表面激光熔敷钴基稀土合金,对稀土元素的添加方式及其对敷层组织与性能的影响进行了系统研究。试验结果表明：采用Ｃｒ－Ｙ,Ｃｏ－Ｙ中间合金的方式,将稀土元素钇加入到钴基合金敷层中是可行的,且以采用Ｃｒ－Ｙ中间合金尤为适宜。钇的加入,细化了激光熔敷层的组织,提高了敷层的硬度,耐磨性及抗高温氧化性能。     

Ce对Ni—Cr—Cu合金抗氧化性的影响

作者研究了添加0.1％和0.8％Ce的Ni—Cr—Cu合金在空气中1200℃100小时等温氧化和500小时循环氧化。Ni—Cr—Cu合金中添加微量Ce后,显著降低了氧化速率,增加了氧化膜的剥落抗力。氧化速率降低是添加Ce后各种效应综合作用的结果。它们是:(1)由于Cr的扩散加快,富Cr保护膜更迅速形成;(2)聚集在膜/合金界面附近的含Ce氧化物与空位复合,减少了膜/合金界面的空洞;(3)固溶于氧化膜中的含Ce氧化物阻碍了Cr~(3+)沿氧化物晶界的短程扩散。 提高耐剥落抗力主要原因是:(1)添加Ce使氧化膜晶粒变细,从而改善了塑性变形和适应热应力的能力;(2)0.8Ce合金中稀土氧化物“钉扎”(Keying)作用改善了膜与合金粘附性,并改变了热应力的分布状态。     

混合稀土对金银铜合金组织及硬度的影响

为研究混合稀土元素在金银铜合金内部的分布状态以及混合稀土元素的添加对金银铜合金硬度的影响,使用真空中频感应炉制备了Au-35Ag-5Cu、Au-35Ag-5Cu-1RE合金,并对铸态合金进行不同变形量的轧制加工,探讨了稀土元素的添加、变形量对合金组织及维氏硬度的影响。使用EDS进行了稀土元素分布检测、DSC分析固液相线温度并进行维氏硬度的测量等。结果表明,稀土元素La、Ce、Pr、Nd占据了Au、Ag元素的位置,改变了AuAg两种元素的分布,与Cu固溶效果较好,对Cu元素分布没有显著影响。稀土元素的添加降低了Au-35Ag-5Cu的液相线温度和固相线温度,增大了液相线温度和固相线的温度差。混合稀土元素的添加有助于提高铸态及轧制态金银铜合金的耐磨性。     

Al对HK40合金高温抗氧化行为的影响

研究了含Al量不同的HK40合金在工业纯Ar气氛中的高温抗氧化性能,用SEM、XRD等方法检查了氧化膜的形貌、结构与成分．结果表明,加入铝后合金表面在高温下形成均匀的Al2O3膜,从而提高了合金的高温抗氧化性能;Al加入量为6mass％时,合金的高温抗氧化性能最好．在1100℃时加Al的合金氧化增重遵从抛物线规律,且随...     

稀土元素Ce和La合金化对AM60镁合金腐蚀行为的影响

采用电子探针-能谱分析,场发射扫描电镜X射线衍射等方法研究了稀土元素Ce和La合金化对AM60镁合金结构和耐蚀性能的影响.结果表明,Ce和La的加入可在AM60镁合金中形成了富含稀土元素的γ相（MgAlRE）;能有效抑制析氢,提高镁合金的耐蚀性能;改善镁合金在含Cl-溶液中的耐蚀性能;腐蚀产物膜的晶态主要成分为铝和锰的氧化物,并含有少量的稀土氧化物和氢氧化物.     

Improvement of high temperature oxidation resistance of AISI 316L stainless steel by incorporation of Ce-La elements using intense pulsed plasma beams

It is well documented that adding some active elements (such as Y, Ce, La, Er, others) to austenitic stainless steels helps to improve their high temperature oxidation resistance. In the present work we report preliminary results of incorporation of Ce and La into austenitic stainless steel AISI 316L using a new approach based on high intensity pulsed plasma beams. The characteristic feature of this approach relies upon the fact that incorporation of Ce-La occurs in the transiently melted near-surface layer of the substrate. Improving the near surface layer properties was connected with two facts: (i) material melting and cooling with very high rate and (ii) incorporation Ce-La to the molten phase. Modified samples were oxidized at 1000 °C for 80 h in air at atmospheric pressure. The obtained effects were similar to those observed in chromia-forming alloys doped by other conventional surface treatment techniques: oxide scales formed on the treated samples were more fine-grained, compact and adhered better than those formed on the un-treated samples, whereas the protective layer was produced closer to the surface.     

Factors Affecting Chromium Carbide Precipitate Dissolution During Alloy Oxidation

Ferrous alloys containing significant volumefractions of chromium carbides were formulated so as tocontain an overall chromium level of 15% (by weight) buta nominal metal matrix chromium concentration of only 11%. Their oxidation at 850°C inpure oxygen led to either protectiveCr₂O₃ scale formation accompaniedby subsurface carbide dissolution or rapid growth ofiron-rich oxide scales associated with rapid alloy surface recession, which engulfedthe carbides before they could dissolve. Carbide sizewas important in austenitic alloys: an as-castFe-15Cr-0.5C alloy contained relatively coarse carbides and failed to form aCr₂O₃ scale, whereas the samealloy when hot-forged to produce very fine carbidesoxidized protectively. In ferritic alloys, however, evencoarse carbides dissolved sufficiently rapidly to provide the chromium flux necessary to formand maintain the growth of a Cr₂O₃scale, a result attributed to the high diffusivity ofthe ferrite phase. Small additions of silicon to theas-cast Fe-15Cr-0.5C alloy rendered it ferritic and led toprotective Cr₂O₃ growth. However,when the silicon-containing alloy was made austenitic(by the addition of nickel), it still formed aprotective Cr₂O₃ scale, showing that the principal function of silicon was inmodifying the scale-alloy interface.     

Effect of Cr and Ni Contents on the Oxidation Behavior of Ferritic and Austenitic Model Alloys in Air with Water Vapor

Ferritic and austenitic model alloys with various contents of Cr and Ni ranging between 10–20% and 0–30%, respectively, were oxidized in air + 10% water vapor during 1 hr cyclic oxidation at 650°C and 800°C. Depending on the alloy composition and temperature, either a thin protective oxide scale was observed or accelerated attack occurred which sometimes included spallation. For austenitic model alloys, increasing either the Cr or Ni contents delayed the accelerated attack. For lower Cr and Ni contents at 800°C, accelerated attack, including spallation, occurred at short exposure times. No spallation was observed for the ferritic model alloys. However, accelerated attack can occur quickly with low Cr contents. Increasing the temperature delayed the breakaway observed on ferritic alloys whereas it reduced the protective-oxide-growth stage for austenitic alloys.     

Influence of rare earth element Ce and La addition on corrosion behavior of AZ91 magnesium alloy

Two types of AZ91 magnesium alloys containing rare earth element Ce or La were fabricated. Hydrogen evolution and electrochemical tests were carried out to evaluate the corrosion behavior of new AZRE (RE = Ce or La) and AZ91 alloys in 3.5% NaCl solutions (pH 6.50). Various corrosion rate tests indicated that addition of RE obviously enhanced corrosion resistance of AZ91 magnesium alloy. The optimal content of RE was 0.92% for Ce and 0.66% for La. Scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and low‐angle X‐ray diffraction (XRD) were used to characterize the effect of RE addition on microstructure and corrosion product film of AZ91 magnesium alloy. The refined β phase and formation of γ phase in AZRE alloy were observed by SEM, which resulted in the improvement of corrosion resistance due to the depression of microgalvanic couples. Moreover, the enhanced protective effectiveness of corrosion products was another reason for the improved corrosion resistance.     

稀土元素La和Ce对纯铜性能的影响

以中间合金的方式在纯铜中加入不同量稀土元素La和Ce,机械加工成统一尺寸试样后,测试其导电性、强度和硬度.结果表明,稀土添加剂能起到净化基体和细化晶粒作用,改善纯铜的导电性,提高纯铜的强度、硬度.考虑试样的综合性能,得出La和Ce的最佳加入量均为0.02%.通过研究稀土元素对纯铜性能的影响,旨在对高强高导铜合金的进一步研究打下基础.     

The effects of reactive element additions and sulfur removal on the adherence of alumina to Ni- and Fe-base alloys

The effects of reactive element additions to alumina-forming alloys (single-crystal Ni-base and ferritic Fe-Cr-Al alloys) and the effect of hydrogen annealing to remove sulfur on the oxide adherence to these alloys have been studied. The results have shown that desulfurization by hydrogen annealing can result in improvements in cyclic oxidation comparable to that achieved by doping with reactive elements. The results have also shown that there is less stress generation during the cyclic oxidation of Y-doped FeCrAl compared to Ti-doped or desulfurized FeCrAl. This indicates that the growth mechanism, as well as the strength of the oxide/alloy interface, influences the ultimate oxidation morphology and stress state which will certainly affect the length of time the alumina remains protective. It has been shown to be possible to estimate the amount of sulfur available to segregate to the alloy/oxide interface and how this is influenced by reactive element additions or hydrogen annealing. If these calculations can be made more quantitative it should be possible to engineer alumina-forming alloys for optimum resistance to cyclic oxidation e.g. by combining an appropriate desulfurization treatment and choice of reactive element addition.     

High temperature oxidation of iron-manganese-aluminum based alloys

The isothermal oxidation resistance of high purity iron-manganese-aluminum alloys containing from 0 to 40% manganese and from 0 to 15% aluminum was investigated at 600, 800, and 1000°C in pure oxygen at a pressure of 200 torr for periods up to 100 hr. They were subsequently examined using SEM and metallographic techniques, and an oxide map showing the alloy structure and general oxidation behavior at 800°C was produced. Scales formed on alloys which contain insufficient aluminum to form protective alumina have structures which depend largely upon the concentration of manganese in the alloy. Alloys which contain more than 7.5% manganese form manganese rich scales, whereas alloys which contain lower levels of manganese form scales that are composed almost entirely of the oxides of iron. Small manganese oxide nodules grow through the alumina scales which form on alloys containing in excess of 9% aluminum. The most oxidation resistant alloys, having compositions within the range Fe-(5–10)%Mn-(6–10)% Al, develop continuous protective alumina scales and are totally ferritic. Austenite is detrimental to the oxidation resistance of duplex alloys as it promotes the breakdown of preexisting alumina scales and the growth of bulky manganese rich oxides. Small additions of chromium are beneficial and reduce the concentration of aluminum required to form protective alumina scales.     

Comparison of Nb- and Ta-effectiveness for improvement of the cyclic oxidation resistance of TiAl-based intermetallics

High-temperature cyclic oxidation resistance of Ti–45.2Al–7.2Nb and Ti–44.8Al–6.6Ta (in at.%) alloys is studied. The alloys were oxidized at 800–1000 °C for up to 380 h and oxidation kinetics was expressed as a function of weight gain versus time. Both as-cast and oxidized alloys were examined by optical and scanning electron microscopy, energy- and wave-dispersion spectrometry, X-ray diffraction and X-ray fluorescence spectrometry. In contrast to previously reported studies, tantalum is found to retard oxidation more effectively than niobium, despite its lower content in the investigated alloy. It also shows a significantly better adherence of oxide scales to the substrate, i.e. a lower tendency to scale spallation, particularly at 1000 °C. Chemical and phase analysis of oxidized alloys reveals considerable differences in element and phase distribution in oxidation-affected zones: 1. Niobium is observed to increase alumina amount in scales more effectively than tantalum. 2. Concentration of tantalum in scales is lower than of niobium. 3. Tantalum causes the occurrence of nitrides both in scales and in metallic substrate, while niobium supports formation of nitrides only in metallic substrate beneath scales. Differences between the investigated alloys are discussed in relation to oxidation mechanism, stability of Ta- and Nb-containing compounds.     

Effects of Silicon on the Oxidation Behavior of Ni-Base Chromia-Forming Alloys

This paper compares and analyzes the oxidation behavior of Ni-base alloys with and without about 2.7 wt.% Si addition. The Ni-base alloys studied were of two types: cast model alloys or wrought commercial alloys. Oxidation testing was conducted at 1000°C in still air. The specific aspects studied were scale spallation resistance, nature by which the silicon oxidized, and the influence of silicon on the subsurface depletion behavior of chromium. From oxidation results of the cast model alloys, Si addition was found to improve oxidation resistance by forming a continuous SiO₂ layer at the alloy/scale interface, which resulted in decreased oxidation kinetics. The cast alloys with Si addition also showed larger average effective interdiffusion coefficients of chromium compared to the cast alloys without Si addition. As a consequence, the Si addition assisted in the establishment and re-formation of a chromia scale during oxidation. In the case of the wrought commercial alloys, a discontinuous distribution of SiO₂ precipitates in the vicinity of the alloy/scale interface was found to be beneficial to cyclic oxidation resistance.     

Effect of La on arc erosion behaviors and oxidation resistance of Cu alloys

Cu with and without La addition was prepared and the effect of a trace amount of La on the arc erosion behaviors and oxidation resistance of Cu alloys was investigated. The results indicate that CuLa alloy exhibits superior oxidation resistance and arc erosion resistance. The contact resistance and temperature rise were obviously improved. The oxidation resistance of CuLa alloy mainly is due to the interface wrapping of La₂O₃ particles and CuLa alloy phase on Cu atoms. Thermodynamic calculation indicated that La₂O₃ could form preferentially in the CuLa alloy, which was beneficial for the protection of the Cu substrate. According to kinetics analysis, the activation energy of CuLa alloy was higher than that of pure Cu, indicating the better oxidation resistance of CuLa alloys.     

Characterization of the alumina scale formed on coated and uncoated doped superalloys

To investigate the mechanisms by which Y and La dopants affect the oxidation behavior of Ni-base single‐crystal superalloys, the oxide scales formed on two variants of a commercial X4 alloy, each with and without a MCrAlYHfSi coating were characterized. The alloy systems were oxidized for 100 h at 1100 °C and then examined using analytical transmission electron microscopy. Without a coating, a duplex scale was formed on the superalloy surface comprised of an outer Ni‐rich spinel‐type layer and an inner columnar α‐Al₂O₃ layer. In this case, Hf and Ti were found segregated to the alumina grain boundaries in the outer part of the scale on both alloys but only Hf was detected near the metal–alumina interface. There was no evidence of Ta, Y or La segregation to the alumina scale grain boundaries after this exposure. The scale formed on the alloys with the thermally sprayed coating was primarily alumina, and Y and Hf segregated to the alumina grain boundaries for both alloys. There was evidence of Ti-rich oxides in the outer part of the scale indicating that Ti had diffused through the coating into the thermally grown oxide but La was not found.     

Beneficial Effects of Ce Implantation into Preformed Cr2O3 Scales on the Subsequent Oxidation of Ni–20Cr Alloy

The influence of Ce implantation into preformed Cr₂O₃ scales with a dose of 1 × 10¹⁷ ions/cm² on the subsequent oxidation behavior of Ni–20Cr alloy at 1050°C in air has been investigated. The pre-oxidation was carried out at 1050°C in air for 0.5 and 1 hr respectively Cr₂O₃ and NiCr₂O₄ formed on Ni–20Cr alloy. The oxidation rate was decreased remarkably due to Ce implantation regardless of whether it was implanted into the alloy or into the pre-formed oxide scales, and the beneficial effect decreased with increasing pre-oxidation time, the alloy implanted directly with Ce had the lowest oxidation rate constant. During cyclic oxidation (350 cycles) Ce implantation played a similar benefical effect on the oxide-spallation resistance for blank and pretreated alloys. The result indicates that Ce incorporated into the oxide scale affected the diffusion of the reaction species and also the spallation resistance of the oxide scales. The change of the oxidation process is attributed to the segregation of Ce at the oxide grain boundaries     

Interfacial segregation during oxidation in O2 at 1173 K of CeO2-coated Fe-20Cr alloys

The interfacial segregation of sulphur and carbon during the oxidation in 1 torr O₂ at 1173 K of Fe-20Cr alloy, which was either free of Ce, alloyed with 0.078 wt.% Ce, or sputter-coated with a 4 nm-thick CeO₂ layer, was studied using polyatomic SIMS. Oxidation periods were up to 19 hr. During oxidation, sulphur and carbon accumulated at the alloy-oxide interface region of both uncoated and coated alloys. The amount of segregated sulphur did not vary appreciably with time, whereas carbon increased with time. The total amount of segregants was similar for both uncoated and coated alloys, although the scales formed on the sputter-coated alloy maintained adhesion and were about 10 times thinner than those on the uncoated alloys.     

W、B、Y微合金化高铌TiAl基合金高温抗氧化性研究

使用元素W、B、Y对Ti-45Al-8Nb合金进行了微合金化,研究了微合金化后高铌TiAl基合金在900℃静止空气中的断续氧化行为。结果表明,与Ti-45Al-8Nb合金相比,经过0.2B与0.1Y联合微合金化后合金的氧化增重小,氧化膜与基体的粘附性强,抗氧化性明显改善;经过0.2W与0.1Y微合金化后合金氧化增重明显,氧化膜容易脱落,合金抗氧化性下降;经过0.2B、0.2W、0.1Y联合微合金化后合金抗氧化性没有明显变化。对氧化膜进行的扫描电镜(SEM)、能谱分析(EDS)及X射线衍射(XRD)分析表明,联合添加B、Y促进了合金中的连续致密的Al2O3条带的形成,W、Y联合微合金化的合金中靠近基体处未形成连续的Al2O3条带,并且混合层中形成了较厚的低铌含量的TiO2层。W、B、Y联合微合金促进了混合层中富Al2O3层的形成。