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71.
《Intermetallics》2014
In this work, first principles calculation of structural, electronic magnetic and elastic properties of the half-metallic ferromagnetic Heusler compound Co2MnSi are presented. We have applied the full-potential linearized augmented plane waves plus local orbitals (FP-L/APW+lo) method based on the density functional theory (DFT). For the exchange and correlation potential generalized-gradient approximation (GGA) is used. The computed equilibrium lattice parameters agree well with the available theoretical and experimental data. Elastic constants and their pressure dependence are also calculated. The calculated total magnetization of 5 μB is in excellent agreement with recent experiments. We also presented the thermal effects using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. Temperature and pressure effects on the structural parameters, heat capacities, entropy, thermal expansion coefficient, and Debye temperatures are determined from the non-equilibrium Gibbs functions. 相似文献
72.
The effect of titanium additions on the formation of primary TiAlSi intermetallics and resulted cast microstructure in Al–Si alloys has been studied. The precipitation temperature, growth kinetic and morphology of TiAlSi intermetallics as well as the solubility limit of Ti in Al–Si alloys were experimentally evaluated. The impact of primary TiAlSi intermetallic particles on the casting process related problems was investigated on the large scale of industrial production. The influence of Ti in the occurrence of feeding blockage and wormhole defect during ingot casting was described. The perspectives of Ti addition in Al–Si cast alloys were discussed. It is proposed that the Ti level in the most Al–Si cast alloys should be controlled within 0.10 wt.%. 相似文献
73.
利用蒸发法和机械合金化法制备纳米Fe-Al金属间化合物 总被引:1,自引:0,他引:1
利用两种方法制备了纳米Fe-Al金属间化合物:一种是利用氢电弧等离子体法在自制的设备中以Fe-28Al-5Cr块体材料为原料,利用电弧高温蒸发制备出纳米Fe-Al基金属间化合物,该方法制得的纳米粒子呈球形,平均粒度30 nm,为B2相结构。在600℃真空退火1 h后,纳米粒子发生了B2→DO3相转变;第二种是利用机械合金化方法,将氢电弧等离子体法制备的纳米金属铁、铝单质置于球磨罐中混合湿磨,发现湿磨10 h形成了Fe-Al金属间化合物。 相似文献
74.
大晶粒NiAl超塑性变形及其机理的研究 总被引:1,自引:0,他引:1
为解决本质脆性NiAl金属间化合物超塑性加工问题,研究了在高温条件下大晶粒度等原子比NiAl的超塑性变形行为及其机理.结果表明在1 000和1 100℃下,应变速率为1.67×10-4s-1~1.67×10-2s-1,该材料表现出超塑性行为.拉伸延伸率普遍超过200%,应变速率敏感性指数大于0.30.对拉伸试样的金相及TEM分析表明,在高温变形过程中,位错的运动包括滑移和攀移两种方式,超塑性是由动态回复及再结晶过程来实现的. 相似文献
75.
Naren Noolu Nikhil Murdeshwar Kevin Ely John Lippold William BaeslackIII 《Journal of Electronic Materials》2004,33(4):340-352
Gold-aluminum ball bonds were thermally exposed at constant elevated temperatures, and the resultant phase transformations
studied in detail. The as-bonded microstructure of a Au-Al ball bond essentially consisted of a reaction zone (termed “alloyed
zone” (AZ) in the as-bonded condition) between the Au bump and the bonded Al metallization. It is the growth of the reaction
zone between the Au bump and the bonded Al metallization and also the nonbonded Al metallization during thermal exposure that
gave rise to the various phase transformations. Au4Al, Au8Al3, and Au2Al are the predominant phases that grew across the ball bond until the bonded Al metallization is available to take part in
the interdiffusion reactions. After the complete consumption of the bonded Al metallization, the Au-Al phases reverse transformed
resulting in the formation of the Au4Al phase in the entire reaction zone across the ball bond (RZ-A). The lateral interdiffusion reactions resulted in the nucleation
and the growth of all of the Au-Al phases given by the phase diagram. Kidson’s analysis and Tu et al.’s treatment were extended
to a five-phase binary system to explain the phase transformations in thermally exposed Au-Al ball bonds. It is possible for
all of the Au-Al phases to grow across a ball bond uninhibited as long as the bonded metallization is available. However,
the supply limitation of the bonded metallization gives rise to reverse transformations where Al-rich phases transform to
Au-rich phases and eventually result in the formation of the Au4Al phase in the entire RZ-A. If infinite time is allowed, Au4Al would dissolve; the extent of which is dependent on the solubility of Al in Au. No supply of Au lateral to the bond causes
the reverse transformation of the Au4Al phase, giving rise to the lateral growth of the remaining Au-Al phases. If infinite time is allowed, the lateral phase
transformations would result in the formation of a phase that is dependant on the relative proportion of Au and Al present
in the nonbonded metallization (NBM) and Au4Al below the void line. Hence, the presence of a phase in a particular location of a ball bond is dependent on the time and
temperature of thermal exposure. 相似文献
76.
77.
Interface phase transformations in 1 μm aluminum + 1 μm gold thin film couples upon 24-h isothermal annealing at 125, 150 and 175 °C were studied. It is shown that temperature change does not affect the type of phases formed but only alters their growth rates. The layered structures consisting of multiple intermetallics were identified by X-ray diffraction and electron microscopy. Interface tracking using secondary ion mass spectroscopy depth profiling showed that Au is the predominant diffusant in this system. Intermetallic thickness growth measurements were made and the activation energy calculated to be 33.602 kJ/mol. 相似文献
78.
A.V. Morozkin O. Isnard P. Henry P. Manfrinetti 《Journal of Alloys and Compounds》2008,464(1-2):219-226
A neutron diffraction investigation has been performed on the Ho5Si3 and Ho5Ge3 compounds (hexagonal Mn5Si3-type, hP16, P63/mcm) to study their magnetic structure. The results prove that these intermetallic phases show a complex sine-modulated type magnetic ordering, both presenting on cooling two subsequent antiferromagnetic orderings (TN1 and TN2).Between TN1 = 24(2) and TN2 = 16(4) K Ho5Si3 shows a first antiferromagnetic ordering of the sine-modulated type with a propagation vector K1 = [0, 0, ±0.284(1)]; then, below TN2 the sine-modulated type ordering is conserved, but by the two propagation vectors K1 = [0, 0, ±0.2773(7)] and K2 = [±1/5, ±1/5, 0].For Ho5Ge3, between TN1 = 27(2) and TN2 = 18(4) K, the sine-modulated ordering is realized through the propagation vectors K1 = [0, 0, ±3/10] and K2 = [0, 1/2, 0], whilst below TN2 the ordering takes place with propagation vectors K1 = [0, 0, ±3/10], K2 = [0, 1/2, 0], K3 = [0, 0, ±2/5] and K4 = [±1/5, ±1/5, 0]. For both the Ho5Si3 and Ho5Ge3 compounds, the dimensions of the magnetic unit cell are 5a × 5a × 10c times the crystal unit cell of Mn5Si3-type. 相似文献
79.
F.X. Qin X.M. Wang G.Q. Xie K. Wada M. Song K. Furuya K. Asami A. Inoue 《Intermetallics》2009,17(11):945-950
In this study, pure Ti was coated on Zr55Al10Ni5Cu30 bulk metallic glass (BMG) using a physical vapour deposition (PVD) technique with magnetron sputtering. Microstructures of Ti coating, BMG substrate and interface were investigated by conventional and high-resolution transmission electron microscopy (TEM and HREM). The electrochemical behavior of Ti-coated Zr55Al10Ni5Cu30 BMG was studied by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) in Hanks' solution. Scanning electron microscopy (SEM) was used to characterize the surface morphology of the coating after electrochemical testing. HRTEM observation reveals that the sputtering Ti coating consists of α-Ti nano-scale particles with the size about 10 nm. The polarization curves revealed that the open-circuit potential shifted to a more positive potential and the passive current density was lower after Ti coating was applied in comparison with that of the monolithic Zr55Al10Ni5Cu30 BMG. Electrochemical impedance spectroscopy (EIS) measurements showed that the Bode plots of Ti-coated Zr55Al10Ni5Cu30 BMG presented one time constant for 1 h and 12 h immersion and two time constants after 24 h immersion. The good bonding condition between Ti coating and Zr55Al10Ni5Cu30 BMG substrate may be responsible for the high corrosion resistance of Ti-coated Zr55Al10Ni5Cu30 BMG. 相似文献
80.
《Intermetallics》2013
The magnetic properties of CeCo7Mn5 and CeCo8Mn4 compounds have been investigated by combining X-ray photoelectron spectroscopy (XPS) and magnetic measurements in a wide temperature range (4–550) K and magnetic field up to 12 T. X-ray powder diffraction (XRD) measurements showed that CeCo7Mn5 and CeCo8Mn4 compounds are isostructural and crystallize in the ThMn12 structure type. XPS spectra pointed out the intermediate valence state of Ce atoms and that both Co and Mn atoms carry magnetic moments. The complex magnetic structure of CeCo7Mn5 and CeCo8Mn4 is determined by the competition between the ferromagnetic (Co–Co pairs) and antiferromagnetic (Co–Mn and Mn–Mn pairs) interactions. Two different ordering temperatures TN and TC correlated to antiferromagnetic and ferromagnetic coupling of 3d magnetic moments, respectively, are evidenced. Magnetic moments of about 1.6 μB/Co and 3.2 μB/Mn atoms were determined by correlating the magnetic data of the two compounds, in good agreement with the exchange splitting of XPS Co 3s and Mn 3s core levels. 相似文献