ONE-CELL-STATE METHOD FOR DETERMINATION OF ELECTRONIC STRUCTURE OF INTERMETALLIC COMPOUNDS

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An innovative joint interface design for reducing intermetallic compounds and improving joint strength of thick plate friction stir welded Al/Mg joints

Friction stir welding of dissimilar Al/Mg thick plates still faces severe challenges, such as poor formability, formation of thick intermetallic compounds, and low joint strength. In this work, two joint configurations, namely inclined butt(conventional butt) and serrated interlocking(innovative butt), are proposed for improving weld formation and joint quality. The results show that a continuous and straight intermetallic compound layer appears at the Mg side interface in conventional butt joint, and the maximum average thickness reaches about 60.1 μm.Additionally, the Mg side interface also partially melts, forming a eutectic structure composed of Mg solid solution and Al_(12)Mg_(17) phase.For the innovative butt joint, the Mg side interface presents the curved interlocking feature, and intermetallic compounds can be reduced to less than 10 μm. The joint strength of innovative butt joint is more than three times that of conventional butt joint. This is due to the interlocking effect and thin intermetallic compounds in the innovative joint.

Crystallographic Characteristic of Intermetallic Compounds in Al-Si-Mg Casting Alloys Using Electron Backscatter Diffraction

The Al-Si-Mg alloy which can be strengthened by heat treatment is widely applied to the key components of aerospace and aeronautics. Iron-rich intermetallic compounds are well known to be strongly influential on mechanical properties in Al-Si-Mg alloys. But intermetallic compounds in cast Al-Si-Mg alloy intermetallics are often misidentified in previous metallurgical studies. It was described as many different compounds, such as AlFeSi, Al8Fe2Si, Al5（Fe, Mn）3Si2 and so on. For the purpose of solving this problem, the intermetallic compounds in cast Al-Si alloys containing 0.5% Mg were investigated in this study. The iron-rich compounds in Al-Si-Mg casting alloys were characterized by optical microscope（OM）, scanning electron microscope（SEM）, energy dispersive X-ray spectrometer（EDS）, electron backscatter diffraction（EBSD） and X-ray powder diffraction（XRD）. The electron backscatter diffraction patterns were used to assess the crystallographic characteristics of intermetallic compounds. The compound which contains Fe/Mg-rich particles with coarse morphologies was Al8FeMg3Si6 in the alloy by using EBSD. The compound belongs to hexagonal system, space group P6_2m, with the lattice parameter a=0.662 nm, c=0.792 nm. The β-phase is indexed as tetragonal Al3FeSi2, space group I4/mcm, a=0.607 nm and c=0.950 nm. The XRD data indicate that Al8FeMg3Si6 and Al3FeSi2 are present in the microstructure of Al-7Si-Mg alloy, which confirms the identification result of EBSD. The present study identified the iron-rich compound in Al-Si-Mg alloy, which provides a reliable method to identify the intermetallic compounds in short time in Al-Si-Mg alloy. Study results are helpful for identification of complex compounds in alloys.

Structure of the Intermetallic Compound Ni_3Al Synthesized under Compression of the Powder Mixture of Pure Elements Part Ⅰ: Phase Composition and Microstructure of Main Phase

It was shown by TEM and X-ray analysis that there are four types of grains of the main Ni3Al phase in the structure of the intermetallic obtained by the self-propagation high temperature method (SHS). Every type of grains has its own domain and dislocation structure. There are mono- and polydomains with and without dislocations. The grains of the main phase of monoand polydomains without dislocations and polydomains with dislocations were formed by diffusion in the solid phase. In these conditions NiAl3 phase is located on the grain boundary of the main phase. The Ni2Al3 phase is located at the triple joints of the main phase.

Structure of the Intermetallic Compound Ni_3Al Synthesized under Compression of the Powder Mixture of Pure Elements Part Ⅱ: Influence of Alloying by Boron on the Phase Composition and the Microstructure of Grains of the Main Phase

The Ni_3B phase was formed when boron (0.5 at. pct B) was added to the intermetallic of sto- ichiometric and off-stoichiometric (Ni-24 at. pct Al) compounds. In the alloy of stoichiometric composition the particles of Ni_3B phase has the size around 0.1μm and is located on the grain boundary of the main phase. The decreasing of concentrations of Al in the ofF-stoichiometric alloy leads to increase in the degree of the long-range order parameter, increasing the concen- trations of boron in the solid solution and decreasing its localization on the grain boundary. Microalloying of boron leads to increasing in the fraction of grain monodomains with disloca- tions up to 0.7 in the alloy of the off-stoichiometric composition and up to 1 in the alloy of the stoichiometric composition. It was established the correlation between the degree of the concentration inhomogeneity, average density of the dislocations and the average long range-order parameter.

EFFECTS OF HIGH-ENERGY BALL MILLING ON STRUCTURE AND MECHANICAL PROPERTIES OF L1_2 INTERMETALLIC COMPOUND Al_(67)Mn_8Ti_(25)

１ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｏｒｄｅｒｅｄｉｎｔｅｒｍｅｔａｌｉｃｃｏｍｐｏｕｎｄＡｌ３Ｔｉｉｓｎｏｔｉｃｅａｂｌｅｂｅｃａｕｓｅｏｆｉｔｓｌｏｗｄｅｎｓｉｔｙ（３．４ｇ／ｃｍ３），ｅｘｃｅｌｅｎｔｈｉｇｈｔｅｍｐｅｒａｔｕｒｅｏｘｉｄａｔｉｏ...

Synthesis of Ni/Al System Intermetallic Compound Under the Influence of Pulsating Electric Current

Synthesis of Ni/Al system intermetallic compound under the influence of pulsating electric current is researched.Reactions of Ni/Al system intermetallic compound are analyzed.It is found that solid-state reactions occur at Ni/Al interface and the main way of reactions is atoms diffusing each other under the influence of a high-density pulsating electric current.

Bonding Characteristics of the Intermetallic Compound Al_3Ti+Cr

Based on our structural model and a tight-binding Hamiltonian the eIectronic structure has been calculated by use of a recursion method (RM) for two models of the tetragonal DO22 and the cubic Ll2 crystal structures in Al3Ti+Cr for contrast, from which bonding characteristics have been discussed. The results for the interaction energy (IE) show that Cr prefers to replacing Al site. Cr partly replacing Al can change the IE between the atoms and make the constriction of lattice constant c and the elongation of lattice constant a for the DO22 and thereby may induce the change of crystal structure from DO22 to L12. The results for bond order integral (BOI) and IE between the atoms also show that the strong (110) directional Cr-Ti bondings are existed.Thus, Al3Ti-base intermetallic compounds with addition of the Cr atom still remain brittle.

Effect of intermetallic compound thickness on anisotropy of Al/Cu honeycomb rods fabricated by hydrostatic extrusion process

The effect of intermetallic compound （IMC） thickness on the thermal and mechanical properties of Al/Cu honeycomb rods was investigated. The Al/Cu honeycomb rods were fabricated using repeated hydrostatic extrusions at 200 ℃. During the process, an IMC layer with 1μm in thickness was generated at the Al/Cu interface. Different IMC thicknesses were obtained by post-heat treatment at 420 ℃ for 0.5 to 2 h. The IMC thickness increased to 10.1μm. The IMC layers were identified as Al2Cu （θ）, AlCu （η2）, and Al4Cu9（γ1） phases. The thermal conductivities in the longitudinal direction and cross direction decreased by 11.9% （（268±4.8） to （236±4.4） W/（m·K）） and 10.4% （（210±3.2） to （188±2.8） W/（m＆#183;K））, respectively, with increasing IMC thickness. The ultimate tensile strength and elongation of the Al/Cu honeycomb rod are （103±8.4） MPa and （73±6.2）%, respectively. The ultimate tensile strength increased to （131±6.5） MPa until the IMC thickness reached 7.7μm. It subsequently decreased to （124±3.9） MPa until the IMC thickness reached 10.1μm. The elongation of the Al/Cu honeycomb rod then sharply decreased to （29±2.5）% with increasing IMC thickness.

Microstructure of the Ductile Phase in Intermetallic Compound Ni_(50)Al_(20)Fe_(30)

The microstructure of the single hot extruded and annealed Ni50Al20Fe30Y0.003 intermetallic compound alloys has been examined by means of high resolution electron microscopy (HREM). In these extruded and annealed alloys. the ductile phase is of a mixture of the disordered fcc γ matrix and or dered γ' precipitates. This fact well interprets the reason why the degree of annealing treatment can influence the strength and ductility of these alloys. The HREM observation revealed directly that there was some strain concentration at γ'-γ interfaces, due to the presence of more iron atoms in these two phases. The fixed orientation relationship between the γ phase and γ' precipitates was identified to be {001}γ||{00 }γ' and <100 >γ|| < 100 > γ'

APPLICATION RESEARCH ON THE Ni _3 Al INTERMETALLIC COMPOUND IN CISRI

Research work and recent progress made toward the industrial applications of the Ni_3Al in CISRI are discussed in present paper. The development of a Ni_3Al base alloy named MX-246 hardened by carbides and fine dispersion of disordered γ is summaried. This alloy,with higher peak temperature of yield strength and higher strain hardening rate than alloyIC-218,has been successfully used as the material of rolling guider at elevated temperatures and in wear conditions. The Ni3Al base alloy of GH264 has been made into welding electrodes by horizontal continuous casting process, and recently successfully surfacing welded on hydraulic blades as cavitation erosion resistance material. The process of remelting Ni3Al base alloy in air was also developed. The processes of producing welding electrodes and remelting in air set the base of industrial applications of Ni3Al in welding, repairing and casting in mass production and into components of large size. Another application of the compound, manufacturing the jet engine rivets used at about 1300℃ , can be attributed to its excellent oxidation resistance and still keeping high strength up to the melting point.

Superplasticity of a Ti-24Al-14Nb-3V-0.5Mo Intermetallic Alloy

Superplastic properties and microstructural evolution of a Ti-24Al-14Nb-3V-0.5Mo (at. pct) intermetallic alloy were studied. Optimum superplastic properties were obtained for temperatures in the interval 960℃≤5 T≤5980℃. The apparent activation energy in the superplastic regime was determined and the deformation mechanism was also discussed. Based on the studies, a curve panel with three sheets sandwich structure was fabricated successfully. The microstructures corresponding to different strain in the part were also studied.

Electronic Structure Effect on Model Cluster for L1_2 Structure of Al_3Ti Intermetallic Compound with an Addition of Alloying Elements Fe, Ni and Cu

By use of self-consistent field Xα scattered-wave (SCF-Xα-SW) method, the electronic structure was calculated for four models of Ti4Al14X (X=Al, Fe, Ni and Cu) clusters. The Ti4Al14X cluster was developed based on L12 Al3Ti-base intermetallic compound. The results are presented using the density of states (DOS) and one-electron properties, such as relative binding tendency between the atom and the model cluster, and hybrid bonding tendency between the alloying element and the host atoms. By comparing the four models of Ti4Al14X cluster, the effect of the Fe, Ni or Cu atom on the physical properties of Al3Ti-based L12 intermetallic compounds is analyzed. The results indicate that the addition of the Fe, Ni or Cu atom intensifies the relative binding tendency between Ti atom and Ti4Al14X cluster. It was found that the Fermi level (EF) lies in a maximum in the DOS for Ti4Al14Al cluster; on the contrary, the EF comes near a minimum tn the DOS for Ti4Al14X (X=Fe, Ni and Cu) cluster. Thus the L12 crystal structure for binary Al3Ti alloy is unstable, and the addition of the Fe, Ni or Cu atom to Al3Ti is benefical to stabilize L12 crystal structure. The calculation also shows that the Fe, Ni or Cu atom strengthens the hybrid bonding tendency between the central atom and the host atoms for Ti4Al14X cluster and thereby may lead to the constriction of the lattice of Al3Ti-base intermetallic compounds.

Behavior and Mechanisms of Deformation in Intermetallic Compound Al_(66) Mn_9Ti_(25) +La

The influence of lanthanum on the microstructure, deformed behavior, microcrack susceptibility of intermetallic compound Al 66 Mn 9Ti 25 was investigated. Adding lanthanum into intermetallic compound Al 66 Mn 9Ti 25 , the lattice parameters are not changed and the Ll 2 structure is maintained. At the same time, the dendritical grain and fine second phase are obtained, which inhibits the microcrack initiation and intergranular failure. On the other hand, the movability of dislocation is enhanced and the compressive ductility is improved. The mechanism about the role of lanthanum in intermetallic compound Al 66 Mn 9Ti 25 was discussed.

Fe-Al、Ti-Al和Ni-Al系金属间化合物多孔材料的研究进展

总结Fe-Al、Ti-Al、Ni-Al 3大系金属间化合物的物相结构和基本特性,论述Fe-Al、Ti-Al和Ni-Al 3大类金属间化合物多孔材料的制备方法、孔结构表征以及耐腐蚀性能,并指出孔结构参数的可控性研究、复合材料的制备和焊接性能的提高是金属间化合物多孔材料未来的研究重点。

Ti-Al金属间化合物多孔材料的研究进展

Ti-Al金属间化合物多孔材料兼备陶瓷和金属多孔材料的性能优势,为具有很大发展潜力的新型无机多孔材料。目前,对于Ti-Al金属间化合物多孔材料的研究包括以下3个方面:反应合成Ti-Al金属间化合物多孔材料的制备及孔结构形成过程和机理;偏扩散-反应合成-烧结制备的Ti-Al金属间化合物多孔材料的物理、化学性能;偏扩散-反应合成Ti-Al金属间化合物多孔材料的应用及其潜力。Ti-Al金属间化合物多孔材料包括多孔体、多孔膜和多孔纸型膜等多种形式;Ti-Al金属间化合物多孔材料的性能主要包括膨胀特性、孔结构性能、抗环境腐蚀性能及焊接性能;Ti-Al金属间化合物多孔材料的现有应用范围主要包括过程工业中流体介质的过滤分离净化,以及化学工业中复合钯膜的支撑体。

Ti-Al/TiC陶瓷基复合材料烧结过程的研究

用DTA方法分析了Ti AI/TiC陶瓷基复合材料的烧结过程 ,测定了材料的力学性能 ,分析了不同的烧结制度对材料性能的影响。实验结果表明 :温度升高至 5 0 0℃以上时 ,Ti与Al发生反应Ti+3Al→Al3Ti,Al3Ti+2Ti→ 3TiAl,TiAl+2Ti→Ti3Al,依次生成Al3Ti,TiAl和Ti3Al,这一过程为放热过程。继续升温至 90 0℃以上时 ,体系出现吸热现象。分析认为 ,在最高温度 16 0 0℃ ,压力 30MPa烧结时得到的材料室温力学性能优于在最高温度15 2 0℃ ,压力 17 3MPa烧结时得到的材料的室温力学性能。

二元Ti-Al合金高温氧化机理

研究了Ti－33．3％Al，Ti－48％Al和Ti－52％Al（原子分数）合金在1073和1173K空气中的恒温氢化行为，用X射线衍射仪（XRD）和配有能谱仪（EDS）的扫描电子显微镜（SEM）对氧化层表面的相组成、形貌以及氧化层剖面的显微结构和氧化机理进行了分析结果表明：二元Ti-Al合金的氧化层由一系列薄层组成，其氢化过程可以分为三个阶段，不同阶段氧化层的生长方向及氧化反应的控制步骤略有差别。

Ti-Al系金属间化合物基复合材料的发展

介绍了Ti-Al系金属间化合物基复合材料的研究现状和发展趋势。对近10年来有关Ti-Al系金属间化合物基复合材料制造工艺、界面特性和机械性能研究状况进行了系统的综述。

热处理条件下激光原位合成高铌Ti-Al金属间化合物复合涂层的微结构特征

为了提高钛合金的高温抗氧化性能,推动钛合金在高温和复杂工况环境下的进一步工程应用,利用高能激光束作用下Ti、Al、Nb三种元素混合粉末之间的原位反应在BT3-1钛合金表面制备了高温抗氧化的高铌Ti-Al金属间化合物复合涂层。针对原位反应所制备涂层存在的缺陷,通过自行设计的热处理工艺优化了涂层和界面微观组织。借助光学显微镜(OM)、X射线衍射仪(XRD)、扫描电镜(SEM)分析了热处理前后复合涂层的物相结构及显微形貌。结果表明:热处理前的涂层主要由单质Nb、金属间化合物γ-TiAl、α_2-Ti_3Al、Ti_3Al_2等物相组成;热处理后的复合涂层,单质Nb固溶到γ-TiAl和α_2-Ti_3Al中,同时形成了新相Ti_3AlNb_(0.3),涂层近似为γ-TiAl+α_2-Ti_3Al双相层片状等轴晶组织。此外,涂层中并未观察到减弱抗氧化性的单质Nb颗粒和Ti_3Al_2相,Ti、Al、Nb的宏观偏析得以消除,涂层与基材界面位置的气孔和裂纹均以消失,出现了明显的白亮带冶金结合过渡层,涂层组织也更加均匀致密。热处理对提高钛合金表面Nb的合金化程度和改善Ti-Al金属间化合物的高温抗氧化性能起到了显著的促进作用。