First-principles phonon calculations of thermodynamic properties for ductile rare-earth intermetallic compounds

The thermodynamic properties of ductile rare-earth intermetallic compounds YAg and YCu with CsCl-type B2 structure have been studied by performing density-functional theory (DFT) and density-functional perturbation theory (DFPT). To judge that our computational method is reasonable, NiAl has also been investigated in comparisons with experimental data and previous theoretical results. Phonon dispersions and density of states are studied, and it is found that the density of states is mostly composed of Y states both in YAg and YCu at high frequencies. The temperature dependence of various quantities such as the thermal expansion, the isothermal bulk modulus, and the heat capacity is computed under the quasi-harmonic approximation (QHA), and the variation features of these quantities are discussed in detail. From these results, we demonstrate that the intermetallics with better ductility have larger thermal expansions.     

First-principle study on structural,elastic and electronic properties of rare-earth intermetallic compounds: TbCu and TbZn

Structural, elastic and electronic properties of TbCu and TbZn have been studied using the full-potential augmented plane waves plus local orbital (APW + lo) within density functional theory (DFT). Results on elastic properties are obtained using both the local density approximation (LDA) and generalized gradient approximation (GGA) for exchange correlation potentials. The equilibrium lattice parameter, bulk modulus and its pressure derivative have been obtained using optimization method. Young’s modulus, shear modulus, Poisson ratio, sound velocities for longitudinal and shear waves, Debye average velocity, Debye temperature and Grüneisen parameters have been calculated. Taking elastic moduli (calculated from first-principle approach) as reference values at 0 K, temperature variation of elastic moduli has also been calculated using electrostatic and Born repulsive potentials and taking interactions up to next nearest neighbours. Calculated structural, elastic and other parameters are consistent with available data. From electronic calculations, it has been found that electronic conductivity in TbCu and TbZn is attributed to 3d-orbital electrons of Cu and Zn.     

Hydrogen ordering in rare-earth intermetallic (Er, Tb)Fe2 compounds with giant spontaneous magnetostriction

X-ray diffraction studies of rare-earth intermetallic Er_{1 ? x} Tb _x Fe₂ compounds (with 0 ≤ x ≤ 0.6) and their hydrides were performed at room temperature. As the terbium content (x) in Er_{1 ? x} Tb _x Fe₂ increases, the sign of the magnetostriction constant λ₁₁₁ was shown to alternate from positive to negative. The lattice parameters, amount of incorporated hydrogen, and sizes of interstices were found to increase with increasing terbium content. The sizes of interstices accessible for occupation with hydrogen atoms were calculated for all alloys and their hydrides. Spontaneous anisotropic magnetostriction related to the rare-earth atoms was found to make no determining contribution to the resulting crystal lattice distortion caused by the incorporation of hydrogen atoms.     

Nanomechanics of Mg-Al intermetallic compounds

Cold spraying of pure Al powder on a pure Mg substrate together with subsequent post-spray annealing treatment produced Mg₁₇Al₁₂ (β-phase) and Mg₂Al₃ (γ-phase) intermetallic layers on the surface of the substrate. These layers showed significantly better nanomechanical properties, including the reduced elastic modulus and nanohardness, which were determined using nanoindentation, than commercial purity Mg and AZ91 alloys. Combined with their improved corrosion resistance, it is believed that both the γ-phase and the β-phase layers can provide effective protection of Mg alloys from wear and corrosion. The effect of post-spray annealing process on the formation of thick, uniform and dense intermetallic layers on pure Mg substrate was also investigated.     

The thermodynamic properties of calcium intermetallic compounds

The thermodynamic properties of calcium alloys have been measured by emf (an original pin-point method) and calorimetry in recent years. A review of experimental results obtained for 15 binary (Ca,M) systems is presented (with M Ni, Pd, Pt, Cu, Ag, Au, Mg, Al, Ga, Si, Ge, Sn, Pb, Sb, Bi), and numerical optimization is performed for some of them. Application to the ternary (Ca,Sn,Pb) system of industrial interest, allowed calculation of the phase diagram for x(Ca) 0.25.     

Anelasticity of Fe3Al intermetallic compounds

Temperature dependent internal friction (TDIF) spectra in Fe–(25–26)at.%Al alloys were studied using different mechanical spectroscopy techniques in a wide range of vibrating frequencies from 0.1 Hz to 1 kHz. Four relaxation peaks are observed (D, S, X, Z peaks), at least two of them (D, X) have not been reported earlier in Fe₃Al intermetallic compounds. The nature of these peaks is discussed. Special emphasis is put in this paper on the instability of the Fe–Al structure with respect to heating during TDIF measurements.     

Stability of intermetallic compounds under extreme actions

Conclusions  

Studies on drilling processes of intermetallic compounds

Intermetallic compounds have high-specific strength, good creep resistance and excellent oxidation and corrosion resistance at high temperatures. Those good mechanical properties make intermetallic compounds very promising structure materials in industries. Ni₃Al and Fe₃Al are two typical intermetallic compounds. This paper focuses on machinability and tool wear mechanism of PVD TiAlN coated cemented carbide tool in drilling of Ni₃Al and Fe₃Al. The influences of cutting speeds on tool wear and machined surface roughness were investigated. The tool wear mechanism was analyzed using scanning electron microscopy (SEM) and EDX analysis. Chips were analyzed by SEM and the machined surfaces were examined by surface roughness measurement instrument. Tool life when drilling of Ni₃Al is shorter than that of Fe₃Al. The built-up-edge (BUE) could be formed on the cutting edge in drilling of Fe₃Al, and no BUE was observed of Ni₃Al at the cutting speed of 29 m/min.     

Structural stability of intermetallic compounds of Mg-Al-Ca alloy

A first-principles plane-wave pseudopotential method based on the density functional theory was used to investigate the energetic and electronic structures of intermetallic compounds of Mg-Al-Ca alloy, such as Al2Ca, Al4Ca and Mg2Ca. The negative formation heat, the cohesive energies and Gibbs energies of these compounds were estimated from the electronic structure calculations, and their structural stability was also analyzed. The results show that Al2Ca phase has the strongest alloying ability as well as the highest structural stability, next Al4Ca, finally Mg2Ca. After comparing the density of states of Al2Ca, Al4Ca and Mg2Ca phases, it is found that the highest structural stability of Al2Ca is attributed to an increase in the bonding electron numbers in lower energy range below Fermi level, which mainly originates from the contribution of valence electron numbers of Ca（s） and Ca（p） orbits, while the lowest structural stability of Mg2Ca is resulted from the least bonding electron numbers near Fermi level.     

Exchange interactions and magnetic properties of intermetallic compounds

1　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｉｎｔｅｒｍｅｔａｌｌｉｃｃｏｍｐｏｕｎｄｓＲＭｎ2 Ｇｅ2 ｃｒｙｓｔａｌｌｉｚｅｉｎｔｈｅｂｏｄｙ ｃｅｎｔｅｒｅｄ ｔｅｔｒａｇｏｎａｌＴｈＣｒ2 Ｓｉ2 ｔｙｐｅｓｔｒｕｃｔｕｒｅ(ｓｐａｃｅｇｒｏｕｐｉｓＩ4 /ｍｍｍ) ,ｗｈｉｃｈｉｓｃｏｎｓｉｓｔｅｄｏｆＲ ,ＧｅａｎｄＭｎｌａｙｅｒｓ ,ｓｔａｃｋｅｄｉｎｔｈｅｓｅｑｕｅｎｃｅＲ Ｇｅ Ｍｎ Ｇｅ Ｒ ａｌｏｎｇｔｈｅｃ ａｘｉｓ[1] .Ｆｒｏｍｔｈｅｍａｇｎｅｔｉｃｐｏｉｎｔｏｆｖｉｅｗ ,ＲＭｎ2 Ｇｅ2 ｃｏｍｐｏｕｎｄｓｈ…     

AlTiB中间合金中的化合物形态

研究了原料与Ａｌ５Ｔｉ１Ｂ 中间合金组织形态之间的联系, 结果表明：在一定熔炼工艺条件下,用纯Ｔｉ 颗粒法可制备出含有颗粒状ＴｉＡｌ３（３ ～１５ μｍ） 和颗粒状ＴｉＢ２（０ ．１ ～１ ．２ μｍ） 的Ａｌ５Ｔｉ１Ｂ 中间合金; 用氟盐法可以制备出含有块状与片状形态ＴｉＡｌ３（１０ ～１００ μｍ） 和条状与颗粒状ＴｉＢ２（０ ．２ ～３ ．０ μｍ）的Ａｌ５Ｔｉ１Ｂ 中间合金。理论分析认为：原料对Ａｌ５Ｔｉ１Ｂ 中间合金化合物的影响是通过改变化学反应体系和熔体结构状态来实现的。     

Environmental corrosion resistance of porous TiAl intermetallic compounds

Porous TiAl intermetallic compound, as a novel substitute for current inorganic porous material, offsets the shortages of both ceramics and metals. The environmental corrosion resistance of porous TiAl intermetallic compound was investigated. The kinetic equation for the cyclic oxidation of porous TiAl alloy at 600 ℃ is determined to be Δm2=1.08×10-5t. After total oxidation of 140 h, porous TiAl intermetallic compound shows more stability of pore structure and the mass gain of TiAl alloy is 0.042 g/m2, which is only 10.6% that of porous 316L stainless steel. The kinetic equation for the cyclic corrosion behavior of porous TiAl alloy in hydrochloric acid with pH=2 at 90 ℃ is determined to be Δm2=5.41×10-5t-2.08×10-4. After 50 h exposure, the mass loss of TiAl alloy is 0.049 g/m2, which is only 14.8% and 5.57% that of porous Ti and stainless steel, respectively. The kinetic equation in hydrochloric acid with pH=3 is determined to be Δm2=2.63×10-6t-3.72×10-6.     

Zn-2Ni合金金属间化合物的细化

利用金相、扫描电镜观察及能谱分析研究了Ti、Al及Al-RE合金作为细化剂对Zn-2Ni合金中Zn-Ni金属间化合物的细化效果。结果表明:在Zn-2Ni合金中加入微量(≤0.20%)的Ti、Al及Al-RE均可对合金凝固组织中的金属间化合物粒子产生细化作用;以Ti为细化剂时,组织中会出现较大的Zn-Ni-Ti三元板条状粒子;以纯Al为细化剂时,出现-δNiZn8相依附-γNi2Zn5相生长的大粒子和以枝晶状NiAl相为核心较细小的-δNiZn8相粒子共存于凝固组织中;以Al-RE为细化剂时,将获得分布均匀且细化的-γNi2Zn5相粒子,且Al-RE合金细化效果明显优于Ti和Al,其最佳的加入浓度为0.05%~0.10%。     

无铅焊点金属间化合物的纳米压痕力学性能

研究Sn3.0Ag0.5Cu/Cu界面处的IMC在150℃下等温时效的生长情况,时效时间分别为100,300,500,1000 h.拟合出IMC的厚度与时效时间的关系,采用纳米压痕仪进行纳米压痕试验,发现Cu6 Sn5与Cu3 Sn的变形机制不同.Cu6Sn5为非连续性塑性变形,表现为压痕过程中的锯齿流变;Cu3 Sn的压痕曲线比较平滑.随Cu6Sn5厚度的增加,Cu6 Sn5的弹性模量和硬度没有太大变化.对时效100,500 h后的Sn3.0Ag0.5Cu/Cu界面处的过渡区进行纳米压痕试验,发现Cu,Cu3Sn,Cu6 Sn5和Sn3.0Ag0.5Cu的硬度大小顺序为Cu6 Sn5＞ Cu3 Sn＞ Cu＞ Sn3.0Ag0.5Cu.     

Reactivity and deuterium retention properties of titanium-beryllium intermetallic compounds

Beryllium intermetallic compounds (beryllides), such as Be₁₂Ti and Be₁₂V, are the most promising advanced neutron multipliers in demonstration (DEMO) fusion power reactors because of higher stability, lower retention, and swelling. The advanced neutron multipliers are being developed by Japan and the EU as a framework of Broader Approach (BA) activities, targeted at broadening the research fields to not only establish fabrication methods but also for their characterization. Our group has proposed a plasma sintering method for the synthesis of beryllides. When the mixed powder was plasma-sintered at the beginning of the experiment, consolidation of the target composition was so insufficient that single-phase beryllides could not be synthesized. In order to obtain single-phase beryllides, an additional homogenization treatment of the sintered beryllides at 1473 K was necessary, resulting in increased porosity. Using the homogenized powder as the starting material, single-phase Be₁₂Ti and Be₁₇Ti₂ intermetallic compounds were successfully synthesized. As experimental results, the hardness of the compounds was relatively low owing to low sintering density. In addition, the oxidation behavior of the beryllides, when exposed to 15% H₂O/Ar at high temperatures, were investigated and the results indicate the presence, gray colored Be oxide formed on the surface in Be₁₂Ti tested at above 1073 K and Be oxide with a small fraction of white colored Ti oxide even tested at 873 K in Be₁₇Ti₂ phase resulting in the bigger increase of the weight gain than Be₁₂Ti. In addition, this oxidation occurring at lower temperature can be reasoned by the assumption that the existence of BeO (=oxygen content) in Be₁₂Ti (1.95%) and Be₁₇Ti₂ (2.95%) may facilitate increased reactivity. Furthermore, thermal expansion of Be₁₇Ti₂ was found out to be bigger than that of Be₁₂Ti because Be₁₇Ti₂ has more complex crystal structure and higher melting temperature. In terms of deuterium desorption and retention properties, the maximum peaks are detected around 600 K in beryllides, while those in beryllium occur at 800 and 980 K. From the comparison of deuterium retention, it was obvious that Be₁₇Ti₂ has a lower retention than Be₁₂Ti, while Be has the highest value.     

Ti-Al系金属间化合物精密加工研究进展

稀有材料Ti-Al系金属间化合物的本征脆性在一定程度上限制了精密加工技术的选择和在航空航天、国防等领域的应用,为促进此类材料精密加工的适应性及获得高质量的表面,本文对Ti-Al系金属间化合物的精密加工技术进行综述。首先对此类材料的特性及精密加工技术进行总体概括;其次从材料的切削性能(材料去除机理、切削力、切削温度、切屑形态和刀具磨损)对其可加工性进行分析,并对材料加工后的表面完整性(表面粗糙度、表面缺陷、残余应力、加工硬化和金相组织)进行总结;最后,对应用于Ti-Al系金属间化合物所采用的超声振动辅助加工技术进行展望,以期为此类材料的加工提供一定的理论依据和技术支撑。     

Types of mechanical relaxation by hydrogen in intermetallic compounds

Hydrogen in polycrystalline intermetallic compounds generally produces extremely broad damping spectra, indicating the presence of short-range as well as long-range relaxation mechanisms. These are discussed on the basis of vibrating-reed results on Zr₆₅Cu_27.5Al_7.5, Zr₆₅Cu_17.5Ni₁₀Al_7.5, and CuZr₂ alloys. A relaxation peak at 270 K observed in all three cases is interpreted as a Zener-type relaxation of hydrogen in the CuZr₂ lattice. The differences found at higher temperatures — a second relaxation peak in the ternary and quaternary alloys but an exponential increase of damping in CuZr₂ — are related to different grain sizes and can be attributed to an ‘intercrystalline Gorsky effect’ due to elastic anisotropy mismatch strains.     

Evolution of AuSnx intermetallic compounds in laser reflowed micro-solder joints

To investigate the effect of Au thickness on evolution of AuSnx IMCs,pads with 0.1,0.5 and 4.0 μm thickness of Au surface finish were utilized.Laser reflowed solder joints were aged in 125℃ isothermal ovens.Results indicated that little IMC formed at the interface of solder and pad with 0.1 μm thickness of Au.Even in condition of 744 hours aging,thickness of IMCs did not increase obviously.As for the joints with 0.5 μm thickness of Au,most of AuSn4 IMCs stayed at the interface and were in needle-like or dendritic morphology.With the increase of aging time,AuSn4 IMCs became flat and changed to a continuous layer.In the joints with 4.0 μm thickness of Au on pads,AuSn,AuSn2,AuSn4 IMCs and Au2Sn phase formed at the interface.As aging time was increased,more Sn rich IMCs formed at the interface,and evolved to AuSn4 IMCs in condition of long time aging.Thickness of AuSn4 IMCs reached about 30 μm.