Observations of glide and decomposition of a⟨101⟩ dislocations at high temperatures in Ni-Al single crystals deformed along the hard orientation

Ni-44 at.% Al and Ni-50 at.% Al single crystals were tested in compression in the hard d001 ¢orientation. The dislocation processes and deformation behaviour were studied as a function of temperature, strain and strain rate. A slip transition in NiAl occurs from a?111? slip to non-a?111? slip at intermediate temperatures. In Ni-50 at.% Al single crystals, only a?010? dislocations are observed above the slip transition temperature. In contrast, a a?101?{101} glide has been observed to control deformation beyond the slip transition temperature in Ni-44 at.% Al. a?101? dislocations are observed primarily along both ?111? directions in the glide plane. High-resolution transmission electron microscopy observations show that the core of the a?101? dislocations along these directions is decomposed into two a?010? dislocations, separated by a distance of approximately 2 nm. The temperature window of stability for these a?101? dislocations depends upon the strain rate. At a strain rate of 1.4 210^?4 s^?1, a?101? dislocations are observed between 800 and 1000 K. Complete decomposition of a?101? dislocations into a?010? dislocations occurs beyond 1000 K, leading to a?010? climb as the deformation mode at higher temperatures. At lower strain rates, decomposition of a?101? dislocations has been observed to occur along the edge orientation at temperatures below 1000 K. Embedded-atom method calculations and experimental results indicate that a?101? dislocations have a large Peierls stress at low temperatures. Based on the present microstructural observations and a survey of the literature with respect to vacancy content and diffusion in NiAl, a model is proposed for a?101?{101} glide in Ni-44 at.% Al, and for the observed yield strength versus temperature behaviour of Ni-Al alloys at intermediate and high temperatures.     

脉冲磁控溅射MoS2-Ti涂层常温及高温真空摩擦磨损性能

利用脉冲磁控溅射法,以铝青铜合金(C63200)和硅片为基底,制作不同Ti含量的MoS₂-Ti复合涂层。通过XRD、SEM、EDS、光学显微镜、多环境摩擦试验机等表征了涂层的结构成分和摩擦性能。结果表明：随Ti含量的增加,涂层致密度提升,S、Mo原子比上升。Ti的掺入使涂层由高度结晶态向非晶态转变。Ti含量增加,涂层摩擦磨损性能先上升再下降,常温真空下含3%Ti的涂层拥有稳定和低至0.015的摩擦系数,23%Ti的涂层失去润滑性。温度升高到400℃,涂层摩擦系数由0.015~0.04上升至0.07~0.1,含13%Ti的涂层高温真空下在800s后润滑失效。磨痕形貌显示,含3%Ti的涂层磨痕最窄,温度升高宽度增加不大,含13%Ti的涂层磨损严重,400℃真空环境下很快磨穿,纯MoS₂和13%Ti涂层摩擦时发现大量磨粒和破碎磨屑。     

溶胶-凝胶法制备Pb(Zr1?xTix)O3复合梯度薄摸以及介电与热释电特性

"在Pt/Ti/SiO2/Si基片上用溶胶-凝胶法生长制备了PZT(Pb(Zr1-xTix)O3)复合梯度铁电薄膜． 薄膜最终结构由6层组成,"向上"梯度薄膜在Pt底电极上的第一层从PbZrO3开始,顶层是PZT(50/50),即第一层是PbZrO3,第二层PZT90/10 (10%Ti),第三层是PZT80/20,第四层PZT70/30,第五层PZT60/40,第六层PZT50/50．每一层与此相反的是"向下"梯度PZT薄膜．用X射线衍射、俄歇电子能谱和阻抗分析来研究梯度薄膜的结构与介电特性．600     

Nature of the temperature dependence of plasticity in the polycrystalline intermetallic compound Ni3Al

The effect of temperature on the plasticity, the type of failure, and the fractions of brittle intercrystallite and viscous transcrystallite failure of the intermetallic compound Ni-24 at. % Al have been studied with boron and without boron. A method is proposed for determining the cohesive strength of the grain boundaries by using the parameters of the flow curve and taking account of the local plastic deformation at the tip of the crack. It is shown that the cohesive strength of the grain boundaries is quite high in Ni₃Al and it is not the cause of the low-temperature embrittlement. The temperature dependence of the plasticity in the Ni-25 at. % Al alloy with boron and without boron in the region of the anomalous temperature dependence of the flow limit is determined by the change in the deformational hardening coefficient and at higher temperatures by a lowering of the cohesive strength of the grain boundaries.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk University. Institute for Strength and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 80–89, November, 1994.     

铜镍合金的表面张力温度系数的蒙特卡罗模拟

本文采用面心立方体结构合金的嵌入原子模型和蒙特卡罗方法,通过计算平衡液态合金体系的内聚功求得铜镍合金的表面张力温度系数,并对模拟方法和结果进行了分析和探讨,给出了三种组分条件下的铜镍合金的表面张力与温度的关系。     

深过冷Ni-15％Sn合金熔体表面张力研究

在电磁悬浮下实现了Ni-15％Sn合金的深过冷，最大过冷度为265K(0.16T_L)，结合悬浮液滴振荡法实验测定了Ni-15％Sn合金在1368—1915K范围内的表面张力.实验表明，在所测量温度范围内，表面张力随温度增加，连续线性递减，函数关系式为σ_Ni-15%Sn=1316.7—1.01(T-T_L)mN／m.根据表面张力的实验数据，理论计算了该合金的黏度系数和扩散系数，并在此基础上研究了合金的扩散激活能E_D和黏液活 关键词： 深过冷 电磁悬浮 表面张力 黏度系数 扩散系数     

Mössbauer spectroscopic study of a low temperature magnetic transition in ordered Fe-doped NiAl

Mössbauer spectroscopic (MS) measurements at ambient and cryogenic temperatures on powdered Fe-doped NiAl materials (Ni-40Al-9Fe and Ni-50Al-9Fe) exhibited paramagnetic behavior down to 17 K, with one Fe-site in the hosts. At 4.2 K, Ni-40Al-9Fe (Al deficient) remained paramagnetic, while Ni-50Al-9Fe (Ni deficient) displayed a magnetic transition, resolved in terms of one Fe environment. The internal magnetic field of the magnetically split site of Ni-50Al-9Fe was 185?±?8 kOe determined from a field distribution model. This shows that electronic and magnetic interactions in ordered Fe-doped NiAl depend on Fe site preference tendencies. The single Fe site observed at 4.2 K for the Ni-deficient alloy shows that its Fe distribution or site occupancy is not random but ordered. The interactions leading to the development of internal magnetic field in the Ni-deficient ordered alloy is temperature dependent being absent above 17 K based on MS measurements from ambient to 4.2 K.     

Strength and microplasticity of biocarbons prepared by carbonization in the presence of a catalyst

The microdeformation has been investigated under uniaxial compression of beech-derived biocarbons partially graphitized during carbonization in the presence of a Ni- or Fe-containing catalyst. The strength and ultimate fracture strain have been determined at different temperatures of carbonization of the samples in the absence or in the presence of a catalyst. It has been shown using high-precision interferometry that the deformation of biocarbon samples under uniaxial loading occurs through jumps (in magnitude and rate of deformation) with axial displacements in the nanometer and micrometer ranges. The use of a catalyst leads to a decrease in the size of nanometer-scale jumps and in the number of micrometer-scale jumps. The standard deviations of the strain rate on loading steps from the smooth average dependence of the strain rate on the displacement have been calculated for micrometer-scale jumps. A similar characteristic for nanometer- scale jumps has been determined from the distortion of the shape of beats in the primary interferogram. It has been shown that the variation in the standard deviation of the strain rate with a change in the carbonization temperature is similar to the corresponding dependence of the ultimate fracture strain.     

高温超导Ni—W基带的织构研究

涂层超导是目前国际超导界的研究热点和重点，所采用的韧性金属基带多为Ni和NiW合金．本文采用粉末冶金方法制备了Ni-3 at．％W和Ni-5 at．％W合金．利用轧制辅助双轴织构基带（咖TS）技术制备了Ni-W合金基带，系统研究了Ni-W合金形变和再结晶织构转变规律．研究表明：通过大变形量的冷轧和高温再结晶退火，可以得到强立方织构的Ni-W合金基带．     

On the effect of magnetic fields on alloys with isothermal kinetics of martensitic transformation

The effect of magnetic treatment on the isothermal martensitic transformation in the Fe-24% Ni-4% Mn alloy has been investigated. The martensitic transformation in a dc magnetic field at liquid-helium temperature has been analyzed.     

第一性原理计算Mg2Ni氢化物的电子结构及其稳定性分析

对Mg₂Ni及其氢化物的能量和电子结构进行了第一性原理计算,并对Mg₂Ni低温氢化物和高温氢化物的稳定性进行了分析.结果发现:在Mg₂Ni中,Mg与Ni存在较强的相互作用.H原子的加入使得Mg的价电子向Ni的3d轨道转移,并在Ni-3d轨道和Ni-4p轨道间形成了带隙.Ni-4s和H-1s电子之间的成键作用,使得Mg和Ni间相互作用减弱了;从LT-Mg₂NiH₄中去掉一个H原子比HT-Mg_{关键词： 第一性原理 2}Ni')" href="#">Mg₂Ni 2NiH₄')" href="#">Mg₂NiH₄ 结构稳定性     

Superelasticity in Quenched and Aged FeMnAlNiTi Oligocrystals under Compression

Russian Physics Journal - The paper studies superelasticity in a 203–523 K temperature range of the 42.5Fe-34Mn-15Al-7.5Ni-1Ti at.% oligocrystals quenched and aged at 473 K for 3 hours. It is...     

Morphology and crystallography of martensite in Fe-23% Ni-0·38% C alloy induced by plastic deformation of austenite

A tensile deformation at the temperatures between Ms and Md induces in Fe-23% Ni-0·38% C alloy the so-called butterfly martensite, whose morphology is different from that of thermally transformed martensite. The amount of these butterflies increases gradually with deformation and contributes to the transformation — induced plasticity. The difference in morphology corresponds with a different structure, substructure and crystallography and it is caused by the change of transformation mechanism.The author would like to express his thanks to Ing. P.Michalika for his help with metallographic preparation of specimens.     

Ni diffusion in near-equiatomic Ni-Ti and Ni-Ti(-Cu) alloys

Tracer volume diffusion of 63 Ni in Ni-50.07 at.% Ti binary and Ni-48.83 at.% Ti-9.29 at.% Cu ternary alloys have been measured between 783 and 1288 K. The temperature dependence of the diffusion coefficients can be well described by a straight Arrhenius function This illustrates that a diffusional anomaly (typical in some bcc metallic alloys and related to the well-known phonon softening), if there is any in this system, is negligible. On the other hand, the small activation energy (about half the value expected from simulations for the commonly accepted mechanism with thermally activated vacancies) shows that the mechanism of diffusion is probably mediated by structural vacancies.     

非晶态合金的电阻应变系数

本文系统地研究了Pd-,Cu-,Ni-和Fe-基非晶态合金在拉伸过程中的电阻变化以及成分、冷变形和热处理对电阻应变系数k的影响。电阻随应变增大而升高,k为正。合金电阻应变系数总是低于纯组元。硬态试样的电阻应变系数比淬火态的高,比退火态的更高。应用推广的Ziman电阻率理论讨论了非晶态合金电阻应变系数的物理本质及其影响因素。 关键词：     

On the sign of the anomalous hall effect in ferromagnetic alloys

Low temperature experimental data on the anomalous Hall resistivity in some binary Ni- and Fe-based alloys are analysed in terms of contributions depending linearly and quadratically on the impurity concentration. It is demonstrated that both contributions, which can be identified with the mechanisms of skew scattering and side displacement, can have the negative as wel as the positive sign.     

Tests of surface segregation theory: I. The Ni-5Pt alloy

The surface composition of polycrystalline samples of the binary metallic alloy Ni-5Pt (at%) has been studied as a function of temperature. This alloy is of particular interest as it lies in a relatively unexplored quadrant of a plot of binary alloy surface tension ratios versus atomic size ratios. Such plots have been used to predict which component of a binary alloy will surface segregate and solute (Pt) segregation is anticipated in the present case. Mechanically polished specimens were purged of bulk impurities by prolonged heating and exposure to oxygen. Quantitative Auger data, collected from clean equilibrated surfaces after rapid cooling from elevated temperatures in the range 1050 to 1540 K, showed Pt surface enrichment compared to the bulk composition. The surface composition was temperature dependent with a heat of segregation in the range −10 to −30 kJ mol⁻¹. The expected heat of segregation for this alloy was calculated by assuming that segregation was driven solely by the lowering of surface free energy and the relief of bulk lattice strain. If the strain term is neglected, Ni surface enrichement is predicted but, when both terms are included, Pt enrichment with a heat of segregation of −14 kJ mol⁻¹ is predicted for the Ni-5Pt(100) surface. This value lies within the limits of the experimental data for polycrystalline Ni-5Pt surfaces and it is concluded that the simple theory adequately accounts for the main segregation mechanisms in this type of alloy.     

Crystallographic Analysis of FCC ? BCT Martensitic Transformation in the Alloy Fe-22% Ni-0.8% C

The infinitesimal deformation (ID) approach is applied to analyse the crystallography involved in the fcc to bct martensitic transformation for the case of (101)_γ[<formula><overline>1</overline>01</formula>]_γ twinning shear as LIS (lattice invariant shear) system in the alloy Fe-22% Ni-0.8% C. Analytical solutions are derived for habit plane orientation, orientation relationships between austenite and martensite phases, and the magnitude of the total shape deformation, etc. In order to compare numerical solutions with the ID approach and phenomenological crystallographic theory, the corresponding crystallographic parameters are calculated by using the Ledbetter and Dunn (L-D) theory. The numeric values obtained are compared with the predictions of the phenomenological crystallographic theories, and with experimental results.     

相场法模拟NiCu合金非等温凝固枝晶生长

利用相场模型与溶质场、温度场进行耦合计算,以Ni-40.83%Cu合金为例模拟了二元合金枝晶生长过程.系统研究相场模型中相场和温度场耦合强度对枝晶形貌和浓度分布的影响.模拟结果表明:随着耦合强度的增加,相场受温度场的影响加大,界面前沿变得不稳,扰动被放大,主枝上出现了二次枝晶.同时,枝晶尖端的生长速率增大,而枝晶尖端的曲率半径减小,枝晶前沿的溶质富集现象也更严重;另外,计算结果与Ivantsov理论符合较好. 关键词： 相场法 NiCu合金 枝晶生长 Ivantsov理论     

天然焦-H2O气化反应特性

在加压热重分析仪上研究了气化温度和催化剂种类对沛城煤矿天然焦-H2O的气化反应特性的影响,用扫描电镜(SEM)观察不同温度下焦样的孔隙结构,并计算了动力学参数.结果表明,气化温度是影响天然焦-H2O气化反应性的一个主要因素,随着温度的升高,天然焦的孔隙越发达,碳转化率明显增大;K基、Ni基、Fe基三种催化剂均能有效地促进气化反应,其中K基催化剂效果最好,其次是Ni基和Fe基催化剂;天然焦的活化能为Eα=147.25 kJ/mol.