A transformation-induced reduction in the oxidation rate of ordered Zr3Al

Oxidation experiments in air from 775 K to 1145 K have established that at temperatures of 975 K and above, the peritectoid Ll₂ phase, Zr₃Al, under the influence of oxygen and nitrogen, undergoes the reverse peritectoid transformation Zr₃Al → Zr₂Al + Zr. This decomposition results in the formation of a lamellar Zr₂Al/Zr product beneath the exposed surface. Correspondingly, the shortterm oxidation rate decreases and the oxide film becomes more adherent. The change in character is caused, at least in part, by the preferential oxidation of the αZr phase within the lamellar product, which leads to oxide platelets being held between the unoxidized Zr₂Al lamellae. Formerly of Chalk River Nuclear Labs., Atomic Energy of Canada, Ltd., Chalk River, Ontario     

Fabrication of Al2O3-reinforced Ni3Al composites by a novel in situ route

A novel in situ technique has been used to fabricate an Al₂O₃-reinforced Ni₃Al matrix composite. The composite was prepared by first incorporating a low volume fraction of continuous Al₂O₃ fibers in a Ni₃Al alloy containing 0.34 at. pct Zr. Pressure casting was used to embed the fibers. Casting resulted in partial reduction of the Al₂O₃ fiber by the Zr present in the matrix and the formation of a layer of ZrO₂ on the surface of the fibers. The final composite was then prepared by air annealing the precursor composite at 1100 °C for 10 days. Air annealing led to the formation of networks of Al₂O₃ around the fibers. The matrix in the immediate vicinity of the networks consisted of Ni₃Al particles in a matrix of disordered α-Ni(Al). The Al₂O₃ networks raised the yield and tensile strength of the material by 35 and 18 pct, respectively. The composite had a tensile ductility of 14 pct.     

Al–Cu–Li and Al–Mg–Li alloys: Phase composition,texture, and anisotropy of mechanical properties (Review)

The results of studying the phase transformations, the texture formation, and the anisotropy of the mechanical properties in Al–Cu–Li and Al–Mg–Li alloys are generalized. A technique and equations are developed to calculate the amounts of the S₁ (Al₂MgLi), T₁ (Al₂CuLi), and δ' (Al₃Li) phases. The fraction of the δ' phase in Al–Cu–Li alloys is shown to be significantly higher than in Al–Mg–Li alloys. Therefore, the role of the T₁ phase in the hardening of Al–Cu–Li alloys is thought to be overestimated, especially in alloys with more than 1.5% Li. A new model is proposed to describe the hardening of Al–Cu–Li alloys upon aging, and the results obtained with this model agree well with the experimental data. A texture, which is analogous to that in aluminum alloys, is shown to form in sheets semiproducts made of Al–Cu–Li and Al–Mg–Li alloys. The more pronounced anisotropy of the properties of lithium-containing aluminum alloys is caused by a significant fraction of the ordered coherent δ' phase, the deformation mechanism in which differs radically from that in the solid solution.     

The oxidation of ordered Zr3Al

Weight gain measurements have been made and metallographic examinations have been carried out on the oxidation of ordered Zr₃Al polycrystals in steam at 675 to 925 K and in pressurized water at 575 K. The study shows that the oxidation rate increases exponentially with increasing volume fraction, f _α, of second-phase αZr particles; that a change occurs in the nature of oxidation at 825 to 875 K; that at 675 to 825 K oxidation is characterized by a breakaway to a higher oxidation rate; that weight gain and oxide film thickening kinetics in pressurized water obey quartic to cubic rate laws, at least for times up to 716 days; and that short-circuit mass transport occurs along dislocations and along grain boundaries. The study also shows that in pressurized water and in steam at temperatures ⪝ 725 K, the oxidation resistance of Zr₃Al is greater than that of Zircaloy-2, provided that . The results are interpreted in terms of the microstructure of the alloys and of the oxide films and in terms of the decomposition phase transformation Zr₃Al → Zr₂Al + Zr. Formerly with Atomic Energy of Canada, Ltd., Clark River, Ontario.     

Methane Combustion and TPR/TPO Properties of Pd/CexZr1-xO2/Al2O3 Catalysts

Methane Combustion and TPR/TPO Properties of Pd/Ce_xZr_ 1-xO_2/Al_2O_3 Catalysts     

铝液还原熔盐中ZrO2制备纯铝锆母合金

研究了铝液还原熔盐中ZrO₂制备铝锆母合金的新方法,考察了还原时间对合金中锆浓度的影响.结果表明,铝液还原熔盐中ZrO₂法制备出的铝锆母合金不含有氧化锆和氧化铝夹杂,可制备出更纯净的铝锆母合金.扫描电镜和电子能谱分析结果表明,合金中的Zr主要以Al₃Zr晶须形式存在.铝锆母合金中锆浓度随还原时间的延长而明显增加,当还原4 h后合金中锆质量百分含量为1.5 %,基本达到上限值.      

Effect of Zirconium on Tensile Property,Microstructure and Fracture Behaviour of Cast Ni_3Al Based Alloy

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Oxidation behavior of single-crystal Al2O3-fiber-reinforced Ni3Al-based composites

A series of single-crystal Al₂O₃-fiber-reinforced Ni3Al-based intermetallic matrix composites were fabricated by pressure casting. The matrices employed were binary Ni₃Al, Ni₃Al-0.5 at. pct Cr, and Ni₃Al-0.34 at. pct Zr. The development of microstructure upon oxidation in air at either 1100 °C or 1200 °C was investigated by optical, scanning, and transmission electron microscopy. In air-oxidized binary Ni₃Al, some of the fibers were fully or partially covered with a layer of oxide. A weak fiber/matrix bond in this system, which led to fiber debonding during composite processing, is believed to be responsible for the ingress of O into the composite and oxidation of the matrix in the debonded regions at the fiber/matrix interface. Addition of Cr to Ni₃Al resulted in an almost threefold increase in fiber/matrix bond strength. No oxidation of the interface was observed. A thick layer of oxide was formed around all the fibers when the composite was thermally cycled prior to isothermal annealing. Addition of Zr to Ni₃Al resulted in the formation of a layer of ZrO₂ on the surface of the fibers during composite processing. The ZrO₂ layer provided a fast path for the diffusion of O, which led to the formation of a rootlike oxide structure around the fibers. The rootlike structure consisted of a network of Al₂O₃-covered ZrO₂.     

铝液还原熔盐中ZrO_2制备纯铝锆母合金

研究了铝液还原熔盐中ZrO2制备铝锆母合金的新方法,考察了还原时间对合金中锆浓度的影响.结果表明,铝液还原熔盐中ZrO2法制备出的铝锆母合金不含有氧化锆和氧化铝夹杂,可制备出更纯净的铝锆母合金.扫描电镜和电子能谱分析结果表明,合金中的Zr主要以Al3Zr晶须形式存在.铝锆母合金中锆浓度随还原时间的延长而明显增加,当还原4 h后合金中锆质量百分含量为1.5%,基本达到上限值.     

Solidification behaviour of Al particles embedded in a Zr Aluminide matrix

A hyperperitectic Al-50 wt% Zr alloy has been manufactured by melt spinning, and the resulting microstructure has been examined by transmission electron microscopy. As-melt spun and annealed hyperperitectic Al-50 wt% Zr consist of a Zr aluminide matrix and an Al rich phase distributed in the form of small and large particles with sizes ∼ 15 and ∼ 100 nm, and as an irregular layer at the cell and grain boundaries. Diffraction analysis of the Zr aluminide matrix is consistent with the aluminide having a tetragonal unit cell with a = 4.014 Å and c = 17.32 Å, similar to equilibrium D0₂₃ tetragonal ZrAl₃ but with a different stoichiometry and different atomic ordering on alternate (004) planes. The Al rich particles show a (001)_Al (001)_Matrix; [100]_Al [100]_Matrix orientation relationship with the Zr aluminide matrix. The solidification nucleation kinetics of the Al rich particles have been examined by heating and cooling experiments in a differential scanning calorimeter over a range of heating and cooling rates. Solidification of Al rich particles is nucleated catalytically on the Zr aluminide matrix at an undercooling in the range 0–5 K. Analysis of the solidification nucleation kinetics of the Al rich particles supports the hypothesis that the classical spherical cap model of heterogeneous nucleation breaks down at low undercoolings and small contact angles.     

Electrochemical behaviour and codeposition of Al-Li-Er alloys in LiCl-KCl-AlCl3-Er2O3 melts

The electrochemical behaviour of Al, Li, and Er were investigated by electrochemical techniques, such as cyclic voltammograms, chronopotentiometric, chronoamperograms, and open circuit chronopotentiogram on molybdenum electrodes. The results showed that the underpotential deposition of erbium on pre-deposited Al electrodes formed two Al-Er intermetallic compounds. The codeposition of Al, Li, Er occurred and formed Al-Li-Er alloys in LiCl-KCl-AlCl3 -Er2O3 melts at 773K. Different phases such as Al2Er, Al2Er3 and βLi phase of Al-Li-Er alloys were prepared by galvanostatic electrolysis and characterized by X-ray diffraction (XRD). Scanning electron microscopy (SEM) indicated that Er element mainly distributed at the grain boundary. ICP analyses showed that lithium and erbium contents of Al-Li-Er alloys could be controlled by AlCl3 and Er2O3 concentration and electrochemical parameters.     

Effect of metal doping into Ce0.5Zr0.5O2 on catalytic activity of MnOx/Ce0.5-xZr0.5-xM0.2xOy/Al2O3 for benzene combustion

The research investigated the effect of doping two metals separately or together into Ce0.5Zr0.5O2 on the catalytic activity of MnOx/Ce0.5–xZr0.5–xM0.2xOy/Al2O3 (M=Y, Mn, Y and Mn) for catalytic combustion of benzene. The prepared catalysts were characterized by X-ray diffraction (XRD), surface area analysis, oxygen storage capacity (OSC), and H2-temperature programmed reduction (H2-TPR). Cata-lytic test was performed on a conventional fixed bed flow reactor. The characterization results revealed that Y and Mn ions entered into the ceria-zirconia mixed oxides framework, which improved the textural properties and greatly promoted the MnOx dispersion on the support surface. The complete conversion temperature of benzene on MnOx/Ce0.4Zr0.4Y0.1Mn0.1Oy /Al2O3 was 563 K, and the selectivity of carbon dioxides was 99%. This catalyst could be applied in a wide range of GHSV and wide concentration condition, showing great potential for application.     

原位反应合成致密Al2O3p-TiCp/Al复合材料

采用高能球磨细化晶粒、原位反应合成及热压技术制备了致密的Al2 O3 p TiCp/Al复合材料 ,并用XRD、SEM、以及EDAX等手段分析了复合材料的相组成、显微组织。结果表明 :Al TiO2 C三元体系在热压反应烧结后 ,可制得致密度较高的Al2 O3p TiCp/Al原位复合材料 ,其显微组织中Al2 O3 和TiC颗粒尺寸为 1μm左右 ,分布均匀。高能球磨有利于增强颗粒细化及弥散分布和反应。     

The forming of Zr3Al-base alloys

Tubes have been formed from the intermediate phase Zr₃Al (L1₂ type) which is of potential use as a structural element in thermal nuclear power reactors. The procedure is to extrude Zr/Zr₂Al two-phase ingots at temperatures above 1270 K in theβ Zr + Zr₂Al two-phase field and then transform the extruded product at lower temperatures to Zr₃Al via the peritectoid transformation Zr + Zr₂Al → Zr₃Al. For small tubes (⪝ 3.2 cm OD) the extrusion constants at 1375 and 1425 K, respectively, are ≃ 400 and ≃ 300 MN/m² for the conditions chosen. The experimental extrusions indicate no fundamental barriers to forming pressure tubes from Zr-Al alloys containing 7.6 to 9.0 wt pct Al.     

机械合金化制备Zr50Cu40Ai10非晶合金粉末及其晶化研究

以金属Zr、Cu和Al为原料,通过真空熔炼和气体雾化制备Zr-Cu-Al合金粉末,再经高能球磨得到Zr50Cu40Al10非晶合金粉末。采用氮/氧分析仪、X射线衍射仪(XRD)、扫描电镜(SEM)和热分析仪(DSC)对其非晶形成能力及晶化行为进行研究。结果表明,球磨120h后可获得Zr50Cu40Al10非晶合金粉末,且随球磨时间增加,粉末的颗粒尺寸逐渐减小,90h后达到亚微米级。球磨过程中由于铁的增加,使合金的结构"混乱度"增加、负混合热增大,因而热稳定性增强,其过冷区间ΔTx为62K,约为雾化法制备的非晶合金粉末的2倍。此外,采用非等温晶化方法,用KISSINGER方程计算出机械合金化Zr50Cu40Al10非晶合金的玻璃转变和初始晶化的表观激活能分别为152.6kJ/mol和172.4kJ/mol,远小于相应的气体雾化法制备的Zr50Cu40Al10非晶合金粉末表观激活能,其原因是粉末中氧含量和体系自由能较高。     

Low-field magnetic entropy changes in （Gd1-xYx）3Al2 alloys

The effects of Y substitution on the magnetic properties and magnetocaloric effect of(Gd1-xYx)3Al2(x=0-0.3) alloys were investigated by X-ray diffraction and magnetization measurements.All samples crystallized in single phase with Zr3Al2-type tetragonal structure.The lattice parameters and magnetic transition temperature decreased obviously with increasing Y content.The magnetic entropy change and refrigerant capacity of these alloys were calculated.The adjustable transition temperature and favorable proper...     

Hydrogen Embrittlement Processes and AL／AL2O3 Hydrogen Resistance Coatings of NdFeB Magnets

After analyzing the phenomena and processes of hydrogen embrittlement of NdFeB permanent magnets, RF magnetron sputtering was used to fabricate A1 thin films and then oxidized to form the Al/Al2O3 composite films on the magnets as the hydrogen resistance coatings. SEM and EDS were used to examine the morphology and composition respectively. Hy-drogen resistance performance was tested by exposing the magnets in 10 MPa hydrogen gas at room temperature. The results show that the magnets with 8μm Al/Al2O3 coatings can withstand hydrogen of 10 MPa for 65 min without being embrittledinto powd er. The samples with and without hydrogen resistance coatings have almost the same magnetic properties.     

Zr_(55)Al_(10)Ni_5Cu_(30)非晶态合金的制备与性能研究

采用石墨坩埚浇铸法在真空中频感应熔炼炉中制备Zr55Al10Ni5Cu30合金,并对合金进行了金相、X射线衍射和显微硬度的测试,考察原料纯度、过热度及冷却速率对非晶态合金性能的影响。结果表明,采用工业级原料就可以制备出性能良好的非晶态合金,在低的冷却速率下形成的非晶态合金具有相对较高的硬度,适当提高过热度可以减少微晶的形成。     

Microstructural control of toughness in aluminium-lithium alloys

Investigation of the deformation behaviour of AlLi based alloys containing zirconium as a grain-refining addition shows that the poor toughness properties are attributed to the intense coplanar slip associated with δ' (Al₃Li) precipitation being unimpeded by the grain structure as a result of the pronounced deformation texture present in the sheet product; fracture proceeds via a transgranular shear failure mode which limits toughness. Changes in composition and thermomechanical treatment have been utilised in order to encourage the formation of additional precipitate phases, and, whilst δ' confers the major increment of strength to all AlLi based alloys, widespread precipitation of S phase (Al₂CuMg) within AlLiMgCuZr alloys is shown to influence strongly the deformation behaviour; in particular the propensity towards slip coplanarity is reduced, and significant improvements in toughness are obtained. Additionally, by promoting homogeneous deformation within the grain structure, the presence of S phase causes the material to display isotropic properties even though a strong texture remains in the zirconium-refined sheet product.     

过冷处理对Cu45Zr42Al8Ag5非晶热稳定性及力学性能的影响

采用过冷液体等温处理的方法制备出直径为3 mm的Cu45Zr42Al8Ag5合金圆棒,研究了过冷液体等温处理对铜基内生复合材料的热稳定性和力学性能的影响,研究表明,过冷处理后的试样均为原位自生晶体/非晶复合材料,且其有较好的热稳定性.由铜基非晶合金压缩后的应力--应变曲线可以看出,随保温时间的延长,最大抗压强度逐渐降低...