NiCrAlFe精密电阻合金中的L12有序结构研究

有序结构的形成是决定NiCrAlFe精密电阻合金电学性能的关键因素。本文利用第一性原理赝势平面波方法,计算了合金处于无序固溶体结构和形成L12型有序结构时的结合能、态密度、晶格常数等参数,并利用高分辨透射电子显微镜（HRTEM）对合金进行了结构表征,还测试了固溶态和时效态的电阻率。从结合能来看,该合金形成L12有序结构时比无序固溶体更加稳定;态密度以及部分态密度计算结果则表明,在L12有序结构中,Ni、Cr、Al、Fe会强烈成键而使得整个合金体系变得稳定;HRTEM分析结果证明固溶态合金经过和时效处理后出现了L12有序结构,而且该有序结构的晶格常数与计算值基本一致。对比无序固溶体与L12型有序结构费米能级处的态密度值发现,当形成L12有序结构时合金的导电能力较无序固溶体下降,电阻率升高,与实际测试结果吻合。     

Ordering tendencies in Pd-Pt,Rh-Pt,and Ag-Au alloys

First-principles quantum-mechanical calculations indicate that the mixing enthalpies for Pd-Pt and Rh-Pt solid solutions are negative, in agreement with experiment. Calculations of the diffuse-scattering intensity due to short-range order also exhibits ordering tendencies. Further, the directly calculated enthalpies of formation of ordered intermetallic compounds are negative. These ordering tendencies are in direct conflict with a 1959 prediction of Raub that Pd-Pt and Rh-Pt will phase-separate below ~760 °C (hence their mixing energy will be positive), a position that has been adopted by all binary alloy phase diagram compilations. The present authors predict that Pd_1-xPt_x will order in the L1₂, L1₀, and L1₂ structures ([001] superstructures) at compositionsx = 1/4, 1/2, and 3/4, respectively, while the ordered structures of Rh_1-xPt_x are predicted to be superlattices stacked along the [012] directions. While the calculated ordering temperatures for these intermetallic compounds are too low to enable direct growth into the ordered phase, diffuse-scattering experiments at higher temperatures should reveal ordering rather than phase-separation characteristics (i.e., off-F peaks). The situation is very similar to the case of Ag-Au, where an ordering tendency is manifested both by a diffuse scattering intensity and by a negative enthalpy of mixing. An experimental reexamination of PdPt and Rh-Pt is needed.     

Ordering tendencies in Pd-Pt, Rh-Pt, and Ag-Au alloys

First-principles quantum-mechanical calculations indicate that the mixing enthalpies for Pd-Pt and Rh-Pt solid solutions are negative, in agreement with experiment. Calculations of the diffuse-scattering intensity due to short-range order also exhibits ordering tendencies. Further, the directly calculated enthalpies of formation of ordered intermetallic compounds are negative. These ordering tendencies are in direct conflict with a 1959 prediction of Raub that Pd-Pt and Rh-Pt will phase-separate below ~760 °C (hence their mixing energy will be positive), a position that has been adopted by all binary alloy phase diagram compilations. The present authors predict that Pd_1-xPt_x will order in the L1₂, L1₀, and L1₂ structures ([001] superstructures) at compositionsx = 1/4, 1/2, and 3/4, respectively, while the ordered structures of Rh_1-xPt_x are predicted to be superlattices stacked along the [012] directions. While the calculated ordering temperatures for these intermetallic compounds are too low to enable direct growth into the ordered phase, diffuse-scattering experiments at higher temperatures should reveal ordering rather than phase-separation characteristics (i.e., off-F peaks). The situation is very similar to the case of Ag-Au, where an ordering tendency is manifested both by a diffuse scattering intensity and by a negative enthalpy of mixing. An experimental reexamination of PdPt and Rh-Pt is needed.     

Electronic structure of Au-Cu alloys

By studying the correlativity between energy, volume and electronic structure of characteristic crystals and bound conditions of OA theory, the potential energy function, atomic volume interactive function and electronic structure of Au-Cu alloys have been determined. Then following the general Vegard‘s law in characteristic theory, the electronic structure and properties of disordered continue solid solution and three ordered alloys with the maximum ordering degree are calculated. It is found that the non-bonding electrons and near-free electrons in outer shell will transform to covalent electrons during alloying. By analyzing the variation of electronic structure and cohesion of ordering and disordered alloys, the transformation of order-disorder transition Au-Cu alloy has been studied.     

Ordering kinetics evaluation of FeAl powders

In this study, time resolved X-ray diffraction experiments using synchrotron X-ray radiation have been performed to get insight on the time and temperature dependent atomic ordering of an intermetallic Fe-40Al (at.%) ball-milled powder. The target of the present study is to gain knowledge on the rapid heating processes occurring during Thermal Spray coating processes. Present results show that in the temperature range 400 °C - 550 °C, the evolution of the order can be followed and modelled by fitting the powder diffraction patterns collected within the first minutes after fast heating. Reasonable refinements have been obtained by assuming the presence of two domains corresponding to the ordered and disordered lattices. The lattice constant changes from 0.29165 nm in the ball-milled powder at room temperature to 0.29281 nm in the ordered phase after 3000 s at 550 °C. The growth of the ordered phase is proposed to be a vacancy-related process with an activation energy of 1.04 eV. Above 550 °C, the ordering kinetics appears too fast to be resolved using the few seconds time scale of the present experiments which is in agreement to thermal spray results conditions.     

Controlling stress and diffusion for the low-temperature-ordering of L1<Subscript>0</Subscript> ordered FePt films

Low-temperature-ordering of L1₀ ordered FePt films have been extensively studied in recent years due to its potential for future application on magnetic perpendicular media. The predominant issue of the ordering process is the diffusion of iron and platinum atoms from a disordered to an ordered phase. The diffusion can be enhanced by adjusting diffusivity, providing extra energy, or reducing energy barriers. In addition to reducing the ordering temperature of FePt, (001)-oriented granular films require perpendicular media because the magnetic easy axis of the ordered phase is [001]. Atomic-scale multilayer deposition is proposed to achieve designed film structures.     

Fe3Al金属间化合物的价电子结构与其力学性能的关系

对长程有序金属间化合物Fe3Al(Fe-28Al)进行淬火处理(有序度截留)研究，处理后获得的B2结构对Fe3Al的力学性能产生了极大的影响，实验结果表明，处理后Fe3Al的硬度和强度有明显的下降。运用固体与分子经验电子理论(EET)对比研究了Fe3Al金属间化合物的两种结构(DO3型和B2型)价电子结构与其力学性能的关系，发现价电子结构与力学性能之间有很好的相关性。     

Fe-Ti二元体系的热力学重新优化(英文)

为提高Fe-Ti二元系外推到三元或多元体系的能力,应用CALPHAD方法重新优化了该二元系。与前人的优化工作相比,重点放在对两个二元金属间化合物Fe2Ti和FeTi的热力学描述上。因目前普遍采用双亚点阵模型来描述C14_Laves相,所以采用双亚点阵模型来描述Fe2Ti相。通过检验包含Fe-Ti二元系的三元体系Fe-Ti边界上Fe2Ti相的均匀化范围进一步证实了Fe2Ti相的相边界。FeTi相具有BCC_B2晶体结构,因而将其处理成为BCC_A2相的有序相,并且用统一的Gibbs 能函数来描述有序和无序相。另外一个特别关注的方面就是重现这两个化合物的实测热容。计算结果与有关相图和热力学性质实验结果的广泛对比显示两者符合得很好,从而证明了所得热力学描述的有效性。     

AP-FIM STUDY ON THE MICROSTRUCTURES OF TiAl INTERMETALLIC COMPOUNDS FXBRICATED BY INGOT METALLURGY AND CENTRIFUGAL SPRAY DEPOSITION

1. IntroductionTitanium aluminide alloys based on the ac-TiAl phase are attractive materials for hightemperature structural application. The strength and ductility of two-phase TiAl alloys aremainly decided on microstructural size and morphologiesll32]. The mechanical propertiesof ac--TiAl alloys can be widely changed by microstructural control with millor alloyingand processing. It will be seen that an advanced processing, centrifugal spray deposition(CSD), can offer alloys with a refined…     

Effect of Al on microstructure and mechanical properties of cast CrCoNi medium-entropy alloy

Cast Cr Co Ni Alx(x=0-1.2) medium-entropy alloys(MEAs) were produced by arc melting and flip cast to investigate the alloying effect of Al addition on the microstructure, phase constituent and mechanical properties. The crystal structure changes from an initial face-centered cubic(FCC) to duplex FCC and body-centered cubic(BCC) and finally a single BCC with increasing Al content. In the duplex region, FCC and BCC phases form under a eutectic reaction in the interdendrite region. In the single BCC region, the dendrites transform to ordered B2 and disordered A2 BCC phases resulting from spinodal decomposition. Corresponding to their phase constituents, yield strength increases accompanied with an elongation reduction with increasing Al addition. A very interesting phenomenon of very weak ordered FCC(001) spots appearing in Al-0.4 alloy was observed, indicating a local ordering of FCC phase. The changes of fracture surfaces after the tensile deformation are also corresponding to the variations in mechanical properties.     

Effect of atomic ordering on environmental embrittlement of （Co,Fe）3V alloy in gaseous hydrogen

The diffusible hydrogen contents in precharged(Co,Fe)3V alloy were measured.It is found that atomic ordering can not promote hydrogen peretration in the(Co,Fe)3V alloy.The ultimate tensile strength(UTS)and ductilities in various condition were also investigated.The results show that the UTS and elongation of disordered alloy are higher than that of ordered one with fixed diffusible hydrogen content and(Co,Fe)3V alloy with ordered structure is highly sus ceprible to the embrittlement in hydrogen gas.The factor which may affect the susceptibility to the embrittlement of (Co,Fe)3V alloy in hydrogen gas in mainly due to that the atomic ordering may accelerate the kinetics of the catalytic reaction for the dissociation of molecular hydrogen into atomic hydrogen.However,it can not be roled out that atomic ordering intensifies planar slip and restricts cross-slip at the grain boundaries and enhances the suscptibility of the alloy to hydrogen embrittlement.     

Laser interference metallurgy—periodic surface patterning and formation of intermetallics

A new kind of surface modification, called ‘laser interference metallurgy’ is reported. It allows the creation of periodic pattern of features with a well defined long-range order on metallic surfaces in the scale of typical microstructures (i.e. from the sub micrometer level up to micrometers). By means of interfering laser beams with sufficient high pulse power a direct structuring in the micro scale with well known metallurgical effects such as melting, recrystallization, quenching, recovery, defect or phase formation can be exploited. Thus, long range ordered arrays of such pattern of phases, defects, grain sizes, textures or stresses could be created. This should open up a remarkable potential to tailor mechanical and other properties by microstructural surface functionalization. The topographic structuring of metallic multilayers as well as the lateral formation of patterns of B2 intermetallic compounds (NiAl and RuAl) and L1₂ intermetallic compound (Ni₃Al) are reported as examples.     

An experimental study of the difference in vibrational entropy between ordered and disordered Fe3A1

The difference in vibrational entropy between disordered and D0₃-ordered Fe₃Al was measured by calorimetry to be (0.10 ± 0.03)k _B/atom at high temperatures, with the ordered alloy having the lower vibrational entropy. Analysis of the vibrational modes of the ordered and disordered alloys with a Born-von Karman model showed that the lower vibrational entropy of the ordered alloy originates from high-frequency optical modes involving the vibration of the aluminum-rich sublattice. These modes are consistent with the large changes in local vibrational amplitudes of Al atoms upon ordering that were measured by extended electron energy loss fine structure spectrometry.     

Phase equilibria in the Fe–Rh–Ti system II. CVM calculations

Cluster Variation Method (CVM) calculations of phase equilibria in the bcc Fe–Rh–Ti system were performed in the irregular tetrahedron (IT) approximation including tetrahedron interactions. The energy parameters were obtained from a fit to recent experimental data on phase equilibria at 1000 °C and 800 °C. At these temperatures the ordering between first nearest neighbours dominates leading to large single-phase fields with B2 ordering. At lower temperatures the calculations predict additional ordering between second nearest neighbours of type D0₃. In the Fe–Ti system the second neighbour interactions are of segregation type leading to miscibility gaps between the disordered A2 and the ordered B2 phases extending from the binary Fe–Ti system into the ternary system. Calculated isothermal sections are presented at several temperatures. The complex ordering in the ternary system leads to strong variations of chemical potentials with composition. This is shown by calculated iso-chemical potential contours.     

Co-Ni-Al-Ti系L2_1/L1_2型双相金属间化合物合金热处理显微组织研究

对由 Ｌ２１型（Ｃｏ,Ｎｉ）２ＡｌＴｉ和Ｌ１２型（Ｃｏ,Ｎｉ）３（Ａｌ,Ｔｉ）两种有序相组成的Ｃｏ－Ｎｉ－Ａｌ－Ｔｉ系新型金属间化合物高温结构实验用合金进行了不同制度的热处理,并对相应的显微组织特征进行了分析研究,找到了控制显微组织以优化性能的热处理参数。     

Revisiting the phenomenological model for effect of chemical ordering on diffusion

The recently developed phenomenological model (Helander T, Ågren J. 1999.) in two-sublattice (2SL) formalism for describing the effect of chemical ordering on diffusion in bcc-B2 ordered alloys was carefully re-analyzed and validated to be applicable in ordered bcc-B2, fcc-L1₀ and fcc-L1₂ phases. The model was then extended into one in four-sublattice (4SL) formalism in a thermodynamically consistent way. With the more physically based 4SL model, different ordered structures (e.g., fcc-L1₀ and fcc-L1₂) with respect to the same disordered phase (e.g., fcc-A1) can be simultaneously described. In order to evaluate the reasonable “endmembers” in 4SL model when the first-principles calculations and/or sufficient experimental diffusivities are not available, the “pair activation energy” was proposed in the present work to a first approximation. The suggested phenomenological model in 4SL formalism together with the concept of “pair activation energy” was finally applied to describe diffusion in the ordered fcc-L1₂ phase of the binary Ni–Al system. Several advantages of using the 4SL model over the 2SL model were also demonstrated.     

Effect of long-range order on the cyclic deformation behaviour of Ni3Fe single crystals

Effect of ordering on cyclic deformation in disordered and ordered Ni₃Fe single crystals was investigated focusing on stress–strain response and deformation substructure. The cyclic hardening depended strongly on the long range order. The maximum stress in the disordered crystals increased gradually with increasing number of cycles and then reached a saturation, while ordered ones exhibited cyclic softening after an initial strong cyclic hardening. The cyclic hardening at an early stage of fatigue in ordered crystals may be due to APB tubes and debris which were produced by the intersection between primary and secondary slips. Coarse slip bands were observed in fatigued ordered Ni₃Fe single crystals. In the bands, three-dimensional dislocation structure was formed accompanied by a decrease in the degree of order, which was responsible for the cyclic softening.     

Processes of atomic ordering in microcrystalline ternary alloys based on Ni3Mn

Stable and metastable phases are formed in the production of microcrystalline alloys By quenching from the melt, The atomic ordering of these phases has not been completely studied until recently. In ternary systems with two ordered phases having different Kurnakov temperatures TK (the temperature of the order-to-disorder transition), for example, an intetmetallic compound and an ordinary superstructure, preferential formation of a superstructure with a highT _K is expected and the alloying atoms occupy vacancies in the ordered lattice of the intermetallic compound. The present work concerns neutron diffraction analysis of atomic ordering in the ternary systems Ni₃Mn-Ni₃Al, Ni₃Mn-Ni₃Si, and Ni₃Mn-Ni₃Ti.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 2–4, August. 1995.