Kinetics of absorbing hydrogen of Al melt

1　ＩＮＴＲＯＤＵＣＴＩＯＮＨｙｄｒｏｇｅｎｉｎＡｌｍｅｌｔｍａｉｎｌｙｃｏｍｅｓｆｒｏｍｗａｔｅｒｖａｐｏｒ[1] .ＩｔｉｓｔｈｅｗａｔｅｒｖａｐｏｒａｂｓｏｒｂｅｄｂｅｔｗｅｅｎｔｈｅｏｘｉｄｅｌａｙｅｒａｎｄｔｈｅＡｌｍｅｌｔ,ｂｕｔｎｏｔｔｈｅｇａｓｅｏｕｓｗａ ｔｅｒｖａｐｏｒｔｈａｔｒｅａｃｔｓｗｉｔｈｔｈｅｌｉｑｕｉｄｍｅｔａｌ,ｂｅｃａｕｓｅｔｈｅｒｅｉｓａｌｗａｙｓａｔｈｉｎｏｘｉｄｅｌａｙｅｒｏｎｔｈｅｓｕｒｆａｃｅｏｆｔｈｅＡｌｍｅｌｔ.Ｆｏｌｌｏｗｉｎｇｉｓｔｈｅｉｒｃｈｅｍｉｃ…     

定向金属氮化纯铝熔体表面Mg蒸气传质行为

从热力学角度分析并模拟了Mg蒸气在定向金属氮化法制备AlN材料中的相转变过程,证实了在高纯氮气气氛下Mg蒸气层的存在.按照气体扩散传质动力学原理,求出了Mg蒸气层的厚度关系式.研究表明:熔液距坩埚上沿距离、反应前沿的氧分压和初始Mg含量均影响着Mg蒸气层厚度.氧分压降低,初始镁含量的增加,Mg蒸气层厚度增加,有利于铝熔液的渗透氮化.     

Mg-9Al-0.5Zn-0.3Be熔体表面氧化行为

在Mg 9Al 0 .5Zn合金中添加 0 .3%铍 ,镁合金液抗氧化性能得到极大提高 ,可以直接暴露在大气中熔炼。X射线衍射表明 ,合金表面有结构远较氧化镁致密的氧化铍生成 ,从而导致整个氧化膜致密程度提高。利用俄歇电子能谱 (AES)进行氧化膜元素深度剖析发现 ,在含 0 .3%铍的镁合金液表面生成的氧化膜可以分为 3个亚层 :最外层为氧化镁层 ;中间层为致密复合层 ,由氧化铍、氧化镁和氧化铝组成 ;内层为氧化膜向基体的过渡层。热力学分析表明 ,氧化膜中的这种分层结构同镁的高蒸汽压以及自由能变化吻合。     

SURFACE REACTION OF Ni_3Al WITH WATER VAPOR OR OXYGEN

1.IntroductionManyresearcheshavedem0nstratedthatthebrittlefractureandpoorductilityatambienttemperature0fsomeintermetallicc0mp0undsarecausedbytheatmosphereofen.ir0n.entIl-4].Forexample,theel0ngationofFe3Alanditsalloystestedinairwasmuchlowerthanthatinvacuum0roxygenl516].Ni3Al-basedall0yswith0utbor0nandwitha1owcontent0fboronweresh0wnt0bequiteductilewithel0ngati0nof15-25%wl1entestedinvacuum0rpllreoxygen,whi1etheyexhibitedp0orductilityof4-10%inai,[7'8].Thisphenomen0nisbelievedtobeahydrogenembritt…     

Influence of water vapor on the oxidation behavior of aluminized coatings under low oxygen partial pressure

FeCrNi alloy after aluminizing was oxidized at 1000 °C in dry and humid (2.23 vol.% water) H₂. Experimental results showed that H₂ promotes the formation of θ alumina and its transformation to α alumina. The morphology of surface alumina coating does not change significantly, but the oxidation rate of the aluminized layer accelerates by the addition of water vapor. As a result, more cracks are found beneath the alumina layer when water vapor is present. The addition of water vapor seems having a favorable effect on the selective oxidation of Al and concentration of oxygen vacancy in the aluminized alloys.     

Brazing of Coated Al Foil Filler to AIN CeramicEI北大核心CSCD

The wettabilities of molten metals on ceramics are poor normally. In order to improve the wettability, all existing ceramic brazing methods introduce a compound transition layer formed by the reaction of active metal and ceramic. The transition layer between brazing seam and ceramic however creates negative effect on the properties of brazing joints. Although Al is the scarce metal which can wet some ceramics such as AIN and Al2O without reaction, the difficulty of removing oxide layer on surface prevents it being ceramic brazing filler. This work proposed a kind of coated Al foil filler able to remove its own Al2O3 film and an elevating temperature brazing process to enhance Al/AIN joint strength. Removing Al2O3. film effect of vapor deposited Ni/Al double layer film on Al foil and the effect of brazing temperature on improving joint strength were studied. The results showed that due to buried by Ni/Al double layer film, Al2O3 film on Al foil original surface broken and was swept in Al-1%Ni (atomic fraction) alloy liquid during heating and melting process. As a result, the direct brazing of Al to AIN without interface reaction transition layer was realized. The joint strength was significantly enhanced by elevating brazing temperature. When brazing at 680 degrees C, the joint fractured along the interface between Al seam and AIN and the sheer strength was 79 MPa because of Al liquid not wetting AIN. With the elevating of brazing temperature, the wettability and interface strength of Al/AIN improved. The fracture gradually transferred to brazing seam from interface. The joint strength increased and reached to the maximum value of 146 MPa at 840 degrees C.     

Sr和稀土对铝合金表面氧化膜保护效果的影响

通过X射线衍射、扫描电镜等方法分析了变质元素对A356铝合金表面氧化膜成分及形貌的影响。从添加元素对表面氧化膜致密性、完整性的影响角度出发，考察了Al—10RE中间合金、Sr处理对A356合金熔体氢含量的影响机制。试验结果表明：A356合金经过Al—10RE中间合金处理后，表面氧化膜中形成了大量La2O3与Al2O3的复合氧化物LaAl11O18这种复合氧化物使表面氧化膜更加致密，氧化膜表面非常平整，几乎看不到开裂的现象，有效地阻止了铝与水的反应。而加入Sr后，形成了SrO与Al2O3的复合氧化物SrAl2O4，这种复合氧化物使表面氧化膜致密性变差，氧化膜表面出现大量反复开裂的痕迹，使得新鲜的铝液不断的暴露于空气中，大大促进了铝与水的反应，使熔体氢含量大幅度增加。     

The low-temperature oxidation of calcium by water vapor

The oxidation kinetics of calcium in water vapor have been studied over the temperature range 25–300°C. There is a change in the form of the oxidation kinetics with temperature, from essentially linear at temperatures below 150°C to logarithmic at 300°C. This is coupled with a change in the manner of growth of the oxide layer as well as the chemical composition of the reaction product. In addition, the oxidation rate decreases with temperature, reaching a minimum at about 150°C. At temperatures below 150°C oxidation appears to be a result of the formation of cracks or fissures in the oxide film. Above 150°C no single oxidation mechanism can be deduced.     

铜/钢爆炸复合板浸铝铸件的界面组织

采用扫描电镜技术观察和分析了爆炸复合铜／钢板浸铝铸件的铝／钢界面组织，用面扫描探明了界面组织中主要成份的分布，结合粉末样品的X射线谱确定了界面组织的相组成，用拉剪方法测得了界面的结合强度。结果表明：爆覆在钢板上的铜全部溶入铝液中，界面上出现了Fe2Al5与FeAl3两层连续的中间化合物；同时界面附近还出现了FeAl3颗粒相，这种颗粒相的形成可能和浸铝用钢板的爆炸焊接组织有关。界面的结合强度为80．5MPa。     

The effect of water vapor on the oxidation behavior of Ni-Pt-Al coatings and alloys

Turbines fired with hydrogen or syngas from coal gasification will have significantly higher water vapor contents in the combustion gas than natural gas fired turbines. The effect of increased water vapor on alumina-forming coatings and model alloys was investigated at 1100 °C in furnace cyclic testing. Increasing the water vapor content from 10% to 50 vol.% increased the amount of scale spallation on undoped alumina-forming alloys. Compared to dry O₂, increased spallation was observed for β and γ/γ' phase coatings on the substrates of alloys 142 and N5. In all cases, the addition of water vapor appeared to reduce the formation of alumina whiskers and ridges at the scale-gas interface, but did not significantly change the alumina growth rate. The addition of water vapor may have a detrimental effect on the selective oxidation of Al in γ/γ' alloys and coatings.     

The Effect of Water Vapor on Passive-Layer Stability and Corrosion Behavior of Fe–Al–Cr Base Alloys

Although it has been reported that additions of water vapor to high-temperature corrosion environments accelerate corrosion, the role of water vapor on increasing the corrosion rate of Fe–Al–Cr alloys and coatings is not very well understood. In order to better understand these effects, multiple Fe–Al–Cr base alloys were tested at 500°C for 100 hr in three different multi-component corrosive gases with and without water vapor. The three gases were a sulfidizing gas, a mixed oxidizing/sulfidizing gas, and an oxidizing gas. Thermogravimetric testing showed that the corrosion kinetics increased when water vapor up to 6% was added to the atmospheres. The surfaces of the exposed samples were considered carefully to determine if the addition of water vapor changed the morphology of the corrosion products and, more importantly, affected the passive layer. It has previously been shown that the formation of nodules can be caused by the inability of the passive layer to re-heal itself after the presence of a defect allowing fast growing non-protective corrosion products to externally grow from the surface. In this study, the amount of external nodules that formed on the surface of the alloys was shown to increase with the addition of water vapor. An increase in the amount of external nodules present due to additions of water vapor gives an indication that water vapor accelerates the passive-layer breakdown. It was observed that the scale morphology correlated well with the corrosion kinetics for the exposed alloys, which showed that water vapor increased the corrosion rates of the alloys.     

Oxidation of a Ni-Cr-Al alloy at 850°C in air containing HCl gas

Moist air containing HCl gas caused the oxide formed on a Ni-Cr-Al alloy at 850°C to crack during the early stages of growth, and extensive blistering and spalling occurred on cooling. In dry air containing HCl gas no oxide cracking was observed at temperature although the oxide blistered and spalled on cooling. In dry or moist air free from HCl an adherent protective oxide formed which did not spall on cooling. The oxide cracking at temperature has been attributed to the production of hydrogen by reaction of Cr and Al in the alloy with water vapor and the removal of NiO as NiCl₂ by reaction with HCl gas. Hydrogen produced by reaction of water vapor or HCl with Cr or Al dissolved in the alloy at temperature, but on cooling the hydrogen was released, causing the oxide to blister and spall. Preoxidation of the alloy in HCl-free atmospheres eliminated these effects of HCl gas in short-term isothermal tests.Sandwich course student at Surrey University.     

SURFACE REACTION，HYDROGEN DIFFUSIVITY AND ENVIRONMENTAL EMBRITTLEMENT OF INTERMETALLIC COMPOUNDS Ni_3Al AND Fe_3Al

ＳＵＲＦＡＣＥＲＥＡＣＴＩＯＮ，ＨＹＤＲＯＧＥＮＤＩＦＦＵＳＩＶＩＴＹＡＮＤＥＮＶＩＲＯＮＭＥＮＴＡＬＥＭＢＲＩＴＴＬＥＭＥＮＴＯＦＩＮＴＥＲＭＥＴＡＬＬＩＣＣＯＭＰＯＵＮＤＳＮｉ_３ＡｌＡＮＤＦｅ_３ＡｌＷＡＮＸｉａｏｊｉｎｇ；ＺＨＵＪｉａｈｏｎｇ；...     

Zr-Sn系合金在过热蒸气中的腐蚀吸氢行为

研究第二相大小和种类对Zr-2和Zr-4合金在400℃,10.3MPa过热蒸气中腐蚀吸氢行为的影响。结果表明:吸氢量的多少和耐腐蚀性能的好坏之间并不一定存在严格的对应关系,而是与第二相大小和种类密切相关。在相同腐蚀增重下,含粗大第二相样品的吸氢量均大于含细小第二相样品;第二相比较粗大的Zr-2样品的吸氢量比Zr-4样品大得多;而第二相比较细小的Zr-2和Zr-4样品的吸氢量差别却很小。对Zr(Fe,Cr)2和Zr2(Fe,Ni)金属间化合物及纯锆进行的PCT和吸放氢动力学测试表明,前两者可自由吸放氢,且吸放氢速度快,而纯锆只能吸氢难以放氢。据此,Zr-Sn系合金在400℃,10.3MPa过热蒸气中腐蚀吸氢行为可以用提出的"在金属/氧化膜界面处Zr和OH-反应生成的氢可以优先被镶嵌在金属/氧化膜界面处的可逆吸放氢能力强于Zr的Zr(Fe,Cr)2和Zr2(Fe,Ni)第二相捕获,它们可作为吸氢的优先通道"的吸氢模型得到合理解释。     

电化学测量金属中氢的背景电流问题

为连续监测常温下金属中氢浓度,根据Devanathan-Stachurski电池原理设计了一种新型的双电极电化学氢传感器,采用电镀Ni层作为催化剂,金属氧化物电极作为辅助电极.用电化学方法和SEM研究了背景电流问题.结果表明,电镀过程中产生的氢是测量初期较大背景电流的根本原因.氯碱生产现场实验结果表明,该传感器对大电流电解槽阴极中的原子氢含量变化响应灵敏、迅速.     

Al2O3 陶瓷与Al低温连接工艺研究

采用共晶烧结工艺对Ａｌ２Ｏ３陶瓷进行表面Ｃｕ金属化,并采用乔探钎焊的办法实现了陶瓷与Ａｌ的低熳连接。实验结果表明,钎料与Ａｌ基体和金属化层之间均有良好的冶金作用,能够保证接头的强度,而且钎焊过程不会对金属化层／陶瓷界面造成不良影响。     

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.     

Cyclic Oxidation Behavior of IN 718 Superalloy in Air at High Temperatures

Ni-base superalloy IN 718 was cyclically oxidized in laboratory air at temperatures ranging from 750 to 950 °C for up to 12 cycles (14 h/cycle). The kinetic behaviour as well as the surface morphology, and the oxide phases of the scales were characterized by means of weight gain measurements, cyclic oxidation kinetics, scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD) analysis techniques. The results showed that as the oxidation temperature increased, the oxidation rate, the external scale thickness, and internal oxidation zone increased. It was suggested that the oxidation rate was controlled by the diffusion of substrate elements in the alloy and the inward diffusion of oxygen through the oxide scale. The oxidation kinetics followed a sub-parabolic rate law and, the activation energy of oxidation was 249 ± 20 kJ mol^?1. The scaling process was controlled mainly by the diffusion of chromium, titanium, manganese, and oxygen ions through the chromia scale. IN 718 showed low weight gain and very slow reaction rates of substrate elements at 750 °C. At 850 °C, a continuous and very thin oxide scale was formed. At 950 °C, XRD and EDS-elemental mapping analysis revealed that a complex oxide scale had formed. It consisted of an outermost layer of TiO₂?CMnCr₂O₄ spinels, inner layer of Cr₂O₃, and the inner most layer composed of Ni₃Nb enriched with Nb, Ti and Al oxides underneath the chromia layer. The oxide scale at this temperature seemed to be thicker layer, significant spallation and volatilization had apparently occurred, and greater internal corrosion was identified. The doping effect of titanium was observed, where it was found to be diffused through the chromia scale to form TiO₂ at the oxide-gas interface as well as internally and at the oxide alloy interface. The amount of rutile (TiO₂) at the oxide surface increased with temperature. In view of Mn contents in the alloy, the manganese?Cchromium spinel oxide was inferred to have played an important role in cyclic oxidation behaviour of IN 718, where the change in oxidation kinetic was noted. The Al contents would cause internal Al-rich oxide formation at grain boundaries.     

An Al+Y Coating Process for Improvement of the High-Temperature Oxidation Resistance of a TiAl Alloy

An Al+Y codeposition by a single EB–PVD process has been developed to improve the high-temperature oxidation resistance of a TiAl alloy. The Al+Y codeposited TiAl alloy with various ratios of Al and Y evaporation sources was evaluated by isothermal and cyclic-oxidation tests. The coating layer has a composition gradient because of the difference in vapor pressure between Y and Al. The oxidation resistance can be extensively improved by the formation of an Al+Y codeposition layer and it depends on the ratio of the source material of Al and Y. The best oxidation resistance was obtained from the Al+Y codeposited TiAl alloy with a ratio of Al:2Y. With the proper ratio of Al:Y, the Al+Y codeposition coating forms two layers of the oxides during high-temperature oxidation+the outer (Y, Al)O layer and the inner Al₂O₃ layer, containing small amounts of Y oxide. These oxide layers, which have a fine grain size, act as a diffusion barrier, thus suppressing the rate of inward diffusion of O and may readily relieve thermal stresses.     

Interface phenomena in aluminium–magnesium magnetic pulse welding

Abstract

The morphology and structure of the weld interface in magnetic pulse welding of similar and dissimilar metals were investigated. The interface zone of dissimilar metal couples such as Al–Mg, was studied in comparison to Al–Al welds. It was found that intermetallic phases (IMP) of different compositions are created during welding of the Al–Mg couple by rapid solidification of a thin melted layer at the interface. According to the calculated energy balance of magnetic pulse welding (MPW), there is enough energy to melt a thin interfacial layer and create IMP. Intensive characterisation techniques were used, including the focused ion beam (FIB) method that was used to prepare a cross-section of the Al–Mg interface for TEM characterisation. It was established that the jet action plays an important role in the melting process at the bonding zone.