Mechanism of Effects of Rare Earths on Microstructure and Properties at Elevated Temperatures of AZ91 Magnesium Alloy

By using real-space recursion method,the energetics of the undoped and Al and/or RE atoms doped 7（1450）〈0001〉 symmetric tilt grain boundaries（GBs）in AZ91 alloys were investigated.Similar calculations were performed on undoped and doped bulk α Mg for comparison.The results showed that Al atoms segregated at GBs in AZ91 alloys.When RE atoms were added,they also segregated at GBs,and their segregation is stronger than Al atoms＇.Therefore,RE atoms retard the segregation of Al atoms.Calculations of interaction energy indicated that Al atoms repelled each other,and could form ordered phase with host Mg atoms.On the contrary to the case of Al,RE atoms attracted each other,they could not form ordered phase with Mg,but could form clusters.Between RE and Al,there existed attractive interaction,and this attractive interaction was the origin of Al11RE3 precipitation.Precipitation of Al11RE3 particles with high melting point and high thermal stability along GB improves high temperature properties of AZ91 alloys.     

An AES Study of Initial Oxidation of Ce-La Alloy at Room Temperature and Low Oxygen Pressure

Auger Electron Spectroscopy was used to characterize the initial stages of the oxidation of Ce-5% La alloy in an oxygen atmosphere at low pressure( ～ 10-6 Pa) and room temperature after the surface is cleaned by Ar ion bombardment.It is shown that exposure of clean cerium to oxygen causes the appearance and development of three new Auger peaks at 97,662 and 676 eV, which steadily grow during oxidation of cerium.Upon oxygen dose less than 20 L,a semi-protective layer of oxide forms on the surface of cerium and its growth follows a logarithmic relationship.With further exposure of oxygen, the oxide film grown in the previous stage becomes thicker and the uptake of oxygen reaches saturation at oxygen exposure of 25 L,and the oxide film mainly consists of Ce2O3.     

Structural heat-resistant β-NiAl + γ′-Ni<Subscript>3</Subscript>Al alloys of the Ni–Al–Co system: II. Oxidation

The heat resistance of the β + γ′ alloys with 28–29 at % Al, 10 at % Co, and 0.25–0.4 at % Re in air at 1300°C is studied. The structures of the scale and the subscale layers that form during oxidation for 2 and 100 h due to the interdiffusion of aluminum and oxygen are investigated. Alloying with 10 at % Co is shown to increase the heat resistance in the absence of chromium and a low content of the elements tht are active to oxygen (La). The heat resistance of the β + γ′ NIAL1 and NIAL2 alloys at 1300°C, which was estimated from the surface unit mass increment in 100 h, is at level of the heat resistance of the γ′ + γ VKNA (VIN) alloys at 1200–1250°C.     

Effect of Yttrium on Microstructures and Preparation and Structure of Mg2-xRExNi (RE=La,Ce,Pr,Nd,Y) Ternary Alloys

A series of Mg2-xNdxNi(x=0.05,0.1,0.2,0.3)alloys and Mg1.95RE0.05Ni(RE= La,Ce,Pr,Nd,Y)ternary alloys were prepared by ball milling of mixted powder of Mg,Ni,RE and sintering under the protection of argon.XRD analysis shows that Mg2-xNdxNi(x=0.05,0.1)and Mg1.95RE0.05Ni consist of single phase with the same crystal structure as Mg2Ni.While three-phase alloys including Mg2Ni,NdNi and NdMgNi4 were formed in Mg1.8Nd0.2Ni and Mg1.7Nd0.3Ni alloys respectively.The lattice constants of Mg2Ni in those ternary alloys were calculated.The decomposition of Mg2Ni occurs in the milling process of Mg2Ni and Mg1.95RE0.05 Ni alloys respectively.For the latter,another earlier reaction occurs in milling process,which means that atoms of RE are separated from crystal structure of Mg2Ni and form relevant oxides by combination with oxygen existed in argon atmosphere.     

钼镧合金表面FeCrAl涂层耐腐蚀性能

采用非平衡磁控溅射工艺在Mo–La合金表面沉积FeCrAl涂层,研究所制备涂层的耐腐蚀性及涂层的腐蚀机理。结果表明：FeCrAl涂层样品在360℃、18.6 MPa、纯水的高压釜中腐蚀72 h,平均腐蚀速率为3.8 mg·dm_?²,低于同条件下锆合金以及未沉积涂层的钼镧合金的腐蚀速率,且涂层中的Al与外界环境介质中的氧发生反应,在涂层表面形成致密的Al₂O₃薄膜,在一定程度上减缓了涂层的腐蚀速度,有效保护了基体材料。FeCrAl涂层样品在1200℃、0.1 MPa的高温水蒸气环境下腐蚀8 h,Al₂O₃氧化膜厚度在4.0μm左右,涂层维持保护效果,钼镧合金基体未暴露在腐蚀环境中;经淬火后,Al₂O₃氧化膜厚度减小至2.5μm左右,涂层依旧维持结构完整性,没有出现贯穿性脱落,满足Mo–La合金表面耐腐蚀性的使用要求。     

Rare earth application for heat-resisting alloys

High-temperature oxidation resistance of Al2O3-and Cr2O3-forming heat-resisting alloys with rare earths(yttrium-implanted FeCrAl,-added FeCrAl,-added FeCrAlPt alloys,Y2O3-or CeO2-coated NiCrSi,yttrium-or lutetium-added NiCr and NiCrSi) was studied in oxygen at high temperatures,by mass gain measurements,mass change measurements,amount of spalled oxide,observation of surface appearance,X-ray diffraction(XRD),scanning electron microscopy(SEM),electron probe X-ray microanalysis(EPMA) and transmission electron microscopy(TEM).After oxidation at 1573 K for 18 ks in oxygen,oxide scale on FeCrAl alloy spalled from the entire surface,however,yttrium-implanted FeCrAl alloys showed good oxide adherence.After oxidation at 1473 K for 18 ks in oxygen,mass gain of FeCrAlY alloys decreased with increasing yttrium of up to 0.1 wt.% follwed by an increase with the yttrium content,and the mass gain of FeCrAl0.005Pt0.05Y alloy with appropriate additions of platinum and yttrium was lower than that of FeCrAl0.1Y alloy.Yttrium-added FeCrAl alloys showed good oxide adherence.TEM analysis revealed that the alumina/alloy interface of FeCrAl0.005Pt0.05Y alloy showed good coherency.The scale surface of FeCrAl alloy was rough,however,those of FeCrAlY and FeCrAlPtY alloys were smooth.Cyclic oxidation of NiCrSi,Y2O3-or CeO2-coated NiCrSi alloys was studied up to 10 cycles(1 cycle:300 s) at 1523 K in oxygen.Mass change of NiCrSi alloy increased up to 3 cycles and then decreased up to 10 cycles because of oxide spallation during cooling.On the other hand,mass change of Y2O3-or CeO2-coated NiCrSi alloy increased up to 10 cycles,and these alloys showed good oxide adherence.Granular Cr2O3 particles on Y2O3-coated NiCrSi alloy were in size smaller than these on CeO2-coated NiCrSi alloy.This result suggested that oxidation rate of Y2O3-coated NiCrSi alloy was lower than that of CeO2-coated NiCrSi alloy.After oxidation at 1473 and 1573 K for 18 ks in oxygen,mass gain of yttrium-or lutetium-added NiCr and NiCrSi alloys decreased.Oxide scales on NiCrS     

稀土Y离子注入对形成不同类型氧化膜合金的高温抗氧化性能的影响

：研究了稀土Ｙ离子注入对ＦｅＣｒ,ＦｅＣｒＡｌ及ＮｉＣｒ合金高温抗氧化性能的影响。结果表明,对于主要形成Ｃｒ２Ｏ３膜的ＦｅＣｒ和ＮｉＣｒ合金,通过离子注入Ｙ可以明显提高其高温抗氧化性能,但对形成Ａｌ２Ｏ３膜的ＦｅＣｒＡｌ合金,离子注入对合金抗氧化性能没有影响,添加稀土Ｙ则使ＦｅＣｒＡｌ合金抗氧化性能大大提高。分析了氧化前、后氧化膜结构变化,认为早期形成的Ｙ２Ｏ３膜对高温氧化时金属离子的扩散有不同的影响     

Segregation and Action of Lanthanum in NiCrCoW Alloys

ＴｈｅｐｒｏｐｅｒｔｉｅｓｏｆｈｏｔｄｅｆｏｒｍａｔｉｏｎａｎｄｏｘｉｄａｔｉｏｎｒｅｓｉｓｔａｎｃｅｏｆＮｉＣｏＣｒＷａｌｏｙａｒｅｉｍｐｒｏｖｅｄｂｙａｄｄｉｔｉｏｎｏｆｒａｒｅｅａｒｔｈｅｌｅｍｅｎｔｓ［１～４］ｂｕｔｔｈｅｍｅｃｈａ...     

Surface oxidation behavior of Mg-Y-Ce alloys at high temperature

After the Mg-Y-Ce magnesium alloy was exposed to air at a temperature up to 1173 K for 0.5 hours, the dense and compact oxide film formed on the surface. Accordingly, oxidation and ignition of magnesium alloys at elevated temperature was successfully retarded by the Y and Ce additions. Thermogravimetric measurements in air revealed that the oxidation dynamics curves measured at 673 and 773 K followed the parabolic-line law and the curve investigated at 873 K followed the complicate quartic law. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis indicated that the oxide film on the surface of Mg-Y-Ce alloys exhibited a duplex structure, which agreed with the results of thermodynamic analysis. The oxidation film included two layers: the outer layer was a multiple structure of Ce_0.202Y_0.798O_1.601 and Y₂O₃, and the inner layer mainly consisted of metal Mg and MgO.     

快淬纳米晶/非晶Mg2-xLaxNi (x=0～0.6)合金的贮氢动力学

为了改善Mg2Ni型合金气态及电化学贮氢动力学性能,用La部分替代合金中的Mg,用快淬技术制备了Mg2-xLaxNi(x=0,0.2,0.4,0.6)合金,用XRD,SEM,HRTEM分析了铸态及快淬态合金的微观结构;用自动控制的Sieverts设备测试了合金的气态贮氢动力学性能,用程控电池测试仪测试了合金的电化学贮氢动力学.结果发现,快淬无La合金具有典型的纳米晶结构,而快淬含La合金显示了以非晶相为主的结构,表明La替代Mg提高Mg2Ni型合金的非晶形成能力.La替代Mg明显地改变Mg2Ni型合金的相组成.当La替代量x=0.4时,合金的主相改变为(La,Mg) Ni3+ LaMg3.合金的气态及电化学吸放氢动力学对La含量及快淬工艺敏感,La替代使合金的吸氢动力学降低,但适量的La替代可以明显改善合金的放氢动力学及高倍率放电能力.适当的快淬处理可以提高合金的气态及电化学贮氢动力学,但获得最佳贮氢动力学的快淬工艺与合金的成分密切相关.     

阳极帽合金表面氧化层研究

研究了实验工艺对Ni42Cr6Fe合金表面氧化膜形成的影响.实验结果表明,Ni42Cr6Fe合金表面氧化膜的主要组分为Cr2O3和FeCr2O4,材料表面打毛处理和氧化温度是影响氧化膜的主要原因,晶格缺陷层产生的微观缺陷有利于原子在氧化过程中的扩散.     

Mechanism of splitting of a few Fe-Mn-Ni-base alloys subjected to thermo-mechanical treatment

Splitting or delamination behaviour of four Fe-Mn-Ni base alloy compositions subjected to thermo-mechanical treatments have been investigated. Delamination has been found to occur in tensile as well as charpy-V specimens of the higher Mn-containing alloys after ausforming with fracture surfaces parallel to the rolling plane. No splitting or delamination could be observed in the ausformed higher Ni-alloy. No splitting occurs in all the four alloys after conventional heat treatment. Marforming produces parting of all the four alloys along a surface parallel to the rolling plane. It appears that the ausformed materials split by way of decohesion of grain-boundaries. A boundary film of austenite or segregation of Mn atoms in the boundaries may be responsible for this. Marforming seems to promote some kind of texture-banding which ultimately leads to the delamination.     

La-Ce-Cu复合金属氧化物的结构表征及催化性能

本文用ＮＨ４ＮＯ３共熔法合成Ｌａ－Ｃｅ－Ｃｕ系列样品。用ＸＲＤ分析了ＣｅＯ２在铜酸镧盐中的溶解度,发现大量ＣｅＯ２存在时,Ｌａ２Ｏ３、ＣｕＯ的加入导致原晶体结构发生变形,生成少量铜酸镧盐。ＸＲＦ分析了系列样品组成均为氧缺陷型化合物。ＸＰＳ研究发现,含大量ＣｅＯ２的样品高温焙烧后在ＣｅＯ２表面生成复合金属氧化物Ｌａ２ＣｕＯ４,最表面一层为少量Ｌａ２Ｏ３,并确定了其中Ｏ的属性。利用ＴＥＭ研究了部分样品的表面结构,同时研究了其ＣＯ催化氧化活性。     

新型高硅奥氏体耐热不锈钢TD305B的高温抗氧化性

采用增重法研究了高硅奥氏体耐热不锈钢TD305B(/%:0.05C、3.30Si、0.80Mn、19.50Cr、13.30Ni、0.05N)和传统耐热不锈钢SUS310S(/%:0.05C、0.60Si、0.80Mn、24.60Cr、19.10Ni、0.05N)在500～1 000℃空气中氧化性能,通过扫描电镜及能谱分析(EDS)对试样表面氧化膜的形貌进行了分析。结果发现,在700～1 000℃新型高硅耐热不锈钢TD305B较传统耐热不锈钢SUS310S抗氧化性好,主要是由于TD305B钢除了在高温时基体与氧容易形成FeO·Cr₂O₃和FeCr₂O₄、NiCr₂O₄等保护性氧化膜外,还由于含有一定量的硅,在距表面20μm处形成了一层SiO₂阻止了氧化的进一步加剧,使得TD305B钢具有良好的耐高温氧化性能。     

Effect of Ni/（La＋Mg） Ratio on Structure and Electrochemical Performance of La-Mg-Ni Alloy System

As the alloy with the most suitable Ni/(La+ Mg) ratio has higher capacity and good cycle stability,theeffects of Ni/(La+Mg) ratios on the electrochemical performances of the La0.80 Mg0.20 Nix (x= 3.5 to 5.0) alloys have been investigated to find the most suitable Ni/(La+ Mg) ratio.The results of XRD and SEM observations show that the phase composition of the alloys varies with different Ni/(La+Mg) ratios.When Ni/(La+Mg) is notmore than 4.25,all the alloys contain LaNi5 and (La,Mg)2Ni7 phases,in addition,the LaMg and (La,Mg)Ni3 phases exist in the x=3.5 and 3.75 alloys,respectively.The LaMg2Ni9 phase exists in the x=4.25 alloy.There are the LaNi5 and LaMg2 Ni9 phases in the x= 4.5,4.75,and 5.0 alloys.The phase abundance and cell volume change with different Ni content.When the Ni/(La+Mg) ratio is not more than 4.25,the alloys possess excellent activation capability,however,the activation capabilities of the alloys decrease with a further increase in the Ni/(La+Mg)ratio.With increasing the Ni/(La+ Mg) ratio,the maximum discharge capacities,the medium voltages,and the cycle stabilities of the alloys first increase and then decrease.When the Ni/(La+Mg) ratio is 3.75,the corresponding alloyhas the maximum discharge capacity among all the alloys.However,the cycle stability of the Ni/(La+ Mg)= 4.0 alloy is better than that of the others.     

Mo-La2O3烧结坯的韧化机制研究

通过扫描电镜，定点探针分析，X射线衍射分析及俄歇电子能谱分析研究了Mo-La2O3烧结坯的韧化机制，结果表明：La2O3的加入提高了烧结钼坯的横向断裂强度和韧性，Mo-La2O3O烧结坯的韧化机制源于间隙杂质在La2O3粒子表面的吸附作用。     

The effect of rare earths on the solidification structure of Fe-36Ni invar alloy

The effect of Ce,La and mischmetal on the solidification structure of Fe-36Ni invar alloy was investigated.The results show that great amounts of high-melting point compounds (Ce2O3,La2O2S and (Ce,La)2O2S) respectively formed in the alloy with the addition of Ce,La or mischmetal.Based on the theory of lattice misfit,the lattice misfit between the (0001) surfaces of Ce2O3,Ce2O2S and La2O2S and (100) surface of Fe-36Ni invar alloy were 6.21%,5.77% and 5.42%,respectively,which are relatively low.Therefore,Ce2O3 ,La2O2S and (Ce,La)2O2S could serve as the core of heterogeneous nucleation,improve the equiaxed grain ratio,reduce the equiaxed grain size and refine the solidification structure of alloy.     

Effects of lanthanum ion-implantation on microstructure of oxide film formed on Co-Cr alloy

Isothermal and cyclic oxidizing behavior of Co-40Cr alloy and its lanthanum ion-implanted samples were studied at 1000 ℃ in the air by thermal-gravimetric analysis （TGA）. Scanning electronic microscopy （SEM） and transmission electronic microscopy （TEM） were used to examine the morphology and structure of oxide film after oxidation. Secondary ion mass spectrum （SIMS） method was used to examine the binding energy change of chromium caused by La-doping and its influence on the formation of Cr2O3 film. laser Raman spectrum was used to examine the stress changes within the oxide film. It was found that lanthanum implantation remarkably reduced isothermal oxidizing rate of Co-40Cr and improved anti-cracking and anti-spalling properties of Cr2O3 oxide film. The reasons for the improvement were mainly that the implanted lanthanum reduced the grain size and internal stress of Cr2O3 oxide and increased high temperature plasticity of the oxide film. Lanthanum mainly existed on the outer surface of Cr2O3 oxide film in the form of fine La2O3 and LaCrO3 spinel particles.     

The high temperature oxidation of Al-4.2 Wt Pct Mg alloy

The high temperature oxidation of Al-Mg alloys is characterized by the rapid formation of thick, micro-crystalline oxide films. The oxidation kinetics of an Al-4.2 wt pct Mg alloy under dry and moist 20 pct O₂/Ar have been measured, and oxide films grown on bulk specimens complementary to the weight gain curves have been characterized using electron optical techniques (TEM, SEM). Initial oxidation takes place by the nucleation and growth of primary crystalline oxides at the oxide/metal interface and by the formation of secondary oxides of MgO by the reduction of the original amorphous over-layer of γ-Al₂O₃ by Mg. Subsequent oxidation is dominated by the further nucleation and growth of primary oxides. The presence of water vapor in the oxidizing environment initially reduces oxidation rates through a modification of the mechanical properties of the amorphous overlayer but does not affect the overall oxidation mechanism. A microstructural model has been developed which describes oxidation of Al-Mg alloys in terms of fracture of the original air-formed film by primary MgO nucleation and growth and modification to this film by the presence of water vapor in the oxidizing environment.     

Hydriding and dehydriding characteristics of nanocrystalline and amorphous Mg20-xLaxNi10（X=0-6） alloys prepared by melt-spinning

In order to improve the hydrogenation and dehydrogenation performances of the Mg2Ni-type alloys, Mg was partially substituted by La in the alloy, and melt spinning technology was used for the preparation of the Mg20-xLaxNi10 (x=0, 2, 4, 6) hydrogen storage alloys. The structures of the alloys were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). It was found that no amorphous phase formed in the as-spun La-free alloy, but the as-spun alloys containing La held a major amorphous phase. When La content x≤2, the major phase in the as-cast alloys was Mg2Ni phase, but with further increase of La content, the major phase of the as-cast alloys changed into LaNi5+LaMg3 phase. Thermal stability of the as-spun alloys was studied by differential scanning calorimetry (DSC), showing that spinning rate was a negligible factor on the crystallization temperature of the amor-phous phase. The hydrogen absorption and desorption kinetics of the as-cast and as-spun alloys were measured using an automatically con-trolled Sieverts apparatus, confirming that the hydrogen absorption and desorption capacities and kinetics of the as-cast alloys clearly in-creased with rising La content. For La content x=2, the as-spun alloy displayed optimal hydrogen desorption kinetics at 200 ℃.