高强高导高软化温度Al2O3p/Cu合金的制备及研究进展

Al2O3p/Cu合金是具有优良物理性能和力学性能的新型结构-功能材料,在现代电子和电工领域有广阔的应用前景。综述了高强高导高软化温度Al2O3p/Cu合金的性能特点及制备方法。简述了国内外研究现状,分析了Al2O3p/Cu合金存在的问题,并展望了其今后的发展方向。     

内氧化-高速压制法制备Al_2O_3弥散强化铜合金的性能研究

以Cu-0.18%(质量分数)Al合金粉末为原料、Cu2O为氧化剂,采用内氧化法制备Al2O3弥散铜合金粉末,采用高速压制(HVC)对粉末进行成形,经氢气中960~1 080℃烧结制备弥散强化铜合金,研究合金粉末的HVC成形效果和烧结温度对合金致密度、硬度、导电率和压缩强度等性能的影响。结果表明,HVC成形Al2O3弥散铜合金粉能获得良好的成形效果,压坯密度达到8.71 g/cm3(98.4%致密度)。与压坯相比,烧结后合金的致密度并无明显变化,但其导电率显著提升,硬度有所降低,压缩强度升高。随烧结温度的升高,合金的导电率有所升高,硬度略有降低,压缩强度基本保持恒定。经1 040~1 080℃烧结制备合金的导电率、硬度分别达到80%IACS和77 HRB以上,压缩强度达到450 MPa,能基本满足点焊电极的实际应用需求。     

40vol%SiC_P/2024Al复合材料的动态压缩性能

利用分离式霍普金森压杆(SHPB)研究了40%体积分数的SiCP/2024Al复合材料和基体材料2024Al在不同应变率下的动态压缩性能。在高应变率动态压缩时该复合材料与2024Al均表现出应变率不敏感,复合材料屈服应力高于2024Al;与2024Al的应变硬化性能不同,复合材料表现出应变软化性能。利用扫描电镜(SEM)观察动态压缩后复合材料试件的微观组织,发现试件内部出现一些孔洞、微裂纹以及一些增强颗粒的破碎等损伤现象,并且在较高应变率下基体呈现出明显的热软化甚至发生局部熔化,由此判断,在高应变率下SiCP/2024Al复合材料宏观应变软化的机制为内部损伤及基体热软化。将SiCP/2024Al复合材料与2024Al经400℃下烧蚀3 h后自由冷却至室温,利用SHPB再次进行测试,与烧蚀前的测试结果相比,2024Al的性能明显下降,而复合材料的性能变化较小,表现出比基体材料更好的抗高温稳定性能。     

Cu-Al2O3复合材料的高温塑性变形

用Gleeble-1500热模拟实验机研究了弥散强化型Cu-Al2O3复合材料的高温变形行为及其对材料组织结构及性能的影响。结果表明,由于Al2O3粒子对位错运动的阻碍作用,复合材料与纯Cu和Cu-A1合金相比具有更高的高温抗压强度;在复合材料的σ-ε曲线上,流变应力在一突降后稳定;稳定的Al2O3粒子可显著提高复合材料的再结晶温度,高温变形未发生明显的再结晶,动态回复是主要的软化机制;Cu-Al2O3复合材料的高温变形机制是位错滑移和晶界滑移相协调;高温变形对复合材料的显微组织和性能均有显著影响。     

纳米Al_2O_3强化铜基ODS 20的组织与性能

研究了铜基ODS的组织与性能。结果表明,采用内氧化方法生产的铜基ODS 20,在纯铜基体上原位生成弥散、10nm左右的-γAl2O3微粒。该材料导电率约90%IACS,比纯铜导电率约降低10%。加工状态的室温强度可达到610MPa,在1173K保温1.5h,硬度达到室温硬度的86%,表明软化温度高于1173 K。经1273K+1.5h退火,晶粒平均直径小于1μm,Al2O3微粒不发生熔解、聚集、长大等现象。     

原位合成法制备Cu-Al_2O_3复合材料及其性能研究

为改善Al2O3颗粒的分散性,提高Al2O3颗粒与Cu基体的结合力,采用原位合成法制备Al2O3弥散强化铜基复合材料,并研究了Al2O3含量变化对复合材料性能的影响。结果表明,复合材料的相对密度和导电性随着Al2O3含量的增加而下降,而硬度随Al2O3的增加而增加。与外加法相比,原位合成法制备的Al2O3弥散强化Cu基复合材料在提高硬度的同时,仍能保持很好的导电性。     

纳米Al2O3p/Cu复合材料的制备及其性能研究

采用高能球磨法制备了纳米Al2O3p/Cu复合材料粉体,复合粉体经过压制、烧结和挤压后成为铜复合材料,采用X射线衍射(XRD)、扫描电镜(SEM)、能谱仪(EDS)、电导仪等测试方法,研究了球磨后的复合粉体和复合材料显微结构、电导率和硬度.实验证明,粉体经过2h以上球磨后,Al2O3相逐渐消失,复合粉体为纳米晶结构,晶粒直径66～87nm.随着Al2O3粉体含量增加,铜复合材料的电导率显著下降.烧结后挤压有利于复合材料导电性能的提高.当Al2O3粉体含量1wt%、球磨6h时,烧结后重新挤压的复合材料试样电导率IACS 76%、硬度HB 83.8.     

原位铝基复合材料的制备及微观组织

提出制备原位合金化和原位反应颗粒共同强化金属基复合材料的概念,并据此制备了原位10％Cu(质量分数,下同）和5．35％α-Al2O3颗粒增强纯铝复合材料（A）以及原位10％Cu,4%Si和15.06%α-Al2O3颗粒共同增强纯铝复合材料（B）。对原位反应过程进行了热力学分析。SEM观察和EDS分析显示,A和B中的原位反应分别生成了合金元素Cu、Cu Si以及Al2O3;原位Al2O3颗粒直径小于0.5μm,在材料中均匀分布。TEM观测显示Al2O3颗粒边角圆滑,与基体结合良好。探讨了原位反应的机理以及在铸造凝固过程中原位颗粒的行为。     

固体酸对介孔氧化铝导电性能影响

在介孔氧化铝(Al2O3)中掺杂固体酸硫酸氢铯(CsHSO4)制备具有高质子导电性能的材料.通过SEM、XRD表征其孔道形貌和晶型特点,采用氮吸脱附测试孔径大小和比表面积等性能参数,运用TG-DSC研究材料的热稳定性及水含量,并应用交流阻抗法测试材料导电率.结果表明,以仲丁醇铝为铝源,通过溶胶-凝胶法合成孔径约为25nm的介孔γ-Al2O3材料,材料具有介孔大小均匀、比表面积大、热稳定性高等特点;掺杂固体酸后,介孔Al2O3的导电率在低温范围提高一个数量级,热分析结果进一步证实固体酸的添加使介孔Al2O3的吸水率提高,从而使质子传导的速率增加,最终提高固体酸掺杂介孔Al2O3的导电率.     

W80/Cu-Al_2O_3复合材料的耐电弧侵蚀性能

采用粉末冶金和熔渗法制备W80/Cu-Al_2O_3复合材料,测试其密度、硬度和导电率,探究Al_2O_3对W80/Cu复合材料耐电弧侵蚀性能的影响。结果表明,添加Al_2O_3对复合材料的致密度和导电率影响不大,硬度有所增加;W80/Cu和W80/Cu-Al_2O_3复合材料在不同电流条件下燃弧时间和燃弧能量基本相同,但W80/Cu-Al_2O_3复合材料的稳定性更高;在30 V、30 A条件下,W80/Cu复合材料在电弧侵蚀过程中发生材料从阴极向阳极转移,加入Al_2O_3增强相后,材料的转移方向为阳极向阴极转移,且材料损耗量降低,喷溅现象减少,电弧侵蚀后触头表面更加平整。     

Toward the β-FeSi2p-n homo-junction structure

β-FeSi₂ thin films were prepared on various substrates, and the influence of the thermal expansion coefficient (TEC) and the softening temperature on the film quality were discussed. It was clarified that a crack-free β-FeSi₂ film could be formed on a glass material substrate with a TEC close to that of β-FeSi₂, and when the softening point of the substrate is close to the crystal growth temperature of β-FeSi₂. A (β-FeSi₂)/(MoSi₂)/(Corning 1737 glass) stacked structure without leak current was prepared to demonstrate the possibility of a MoSi₂ back electrode layer. Furthermore, the (Al-doped p-β-FeSi₂)/(Ni-doped n-β-FeSi₂) homo-junction was also prepared by the vacuum evaporation and thermal diffusion method. We have succeeded in achieving current-rectification to a β-FeSi₂ thin film, although the anode current was small.     

On the propagation of localization in the plasticity collapse of hardening-softening beams

This paper is focused on the propagation of localization in hardening-softening plasticity media. Using a piecewise linear plasticity hardening-softening constitutive law, we look at the 1D propagation of plastic strains along a bending beam. Such simplified models can be useful for the understanding of plastic buckling of tubes in bending, the bending response of thin-walled members experiencing softening induced by the local buckling phenomenon, or the bending of composite structures at the ultimate state (reinforced concrete members, timber beams, composite members, etc.). The cantilever beam is considered as a structural paradigm associated to generalized stress gradient. An integral-based non-local plasticity model is developed, in order to overcome Wood’s paradox when softening prevails. This plasticity model is derived from a variational principle, leading to meaningful boundary conditions. The need to introduce some non-locality in the hardening regime is also discussed. We show that the non-local plastic variable during the softening process has to be strictly defined within the localized softening domain. The propagation of localization is theoretically highlighted, and the softening region grows during the softening process until a finite length region. The pre-hardening response has no influence on the propagation law of localization in the softening regime. It is also shown that the “material” time derivative and the “partial” time derivative have to be explicitly distinguished, especially for moving elastoplastic boundaries. It is recommended to use the “material” time derivative in the rate-format of the boundary value problem.     

Zirconium-Induced Softening in Hyperstoichiometric Ni3Al

The room temperature compressive properties and microhardness of Ni3AI alloys doped with Zr were studied. For the hypostoichiometric Ni3AI alloys, the compressive strength and microhardness increased with an increase in Zr content, while softening behavior induced by doping with a certain amount of Zr was observed in hyperstoichiometric Ni3AI alloy. Possible mechanisms for the softening effect were suggested.     

Effect of aggregate shape on the mechanical properties of a simple concrete

The influence of aggregate shape on the fracture energy, tensile strength and elasticity modulus in concrete is considered. For this purpose, eight simple cement-based composites were designed, manufactured and tested, with two purposes: to provide experimental data that can throw some light on this involved problem and help in the design of future cement-based composites, and supply information that can be used as a benchmark for checking numerical models of concrete failure, as this simple composite is amenable to being modelled quite easily. Thirty-six notched beams were tested and values of the fracture energy and elasticity modulus were recorded. The tensile strength was measured from indirect standard tensile tests. Comparison with available experimental data is also included and discussed. Fracture was modelled using a cohesive crack with a bilinear softening function; data of the softening function inferred from the experimental measurements are also provided and discussed.     

Microstructure and mechanical behavior of Mg-5Zn matrix influenced by particle deformation zone

The effect of particle deformation zone(PDZ) on the microstructure and mechanical properties of SiC_p/Mg-5Zn composites was studied.Meanwhile,the work hardening and so ftening behavior of SiC_p/Mg-5Zn composites influenced by PDZ size were analyzed and discussed using neutron diffraction under in-situ tensile deformation.The evolution of FWHM(full width at half maximum) extracted from the diffraction pattern of SiC_p/Mg-5Zn composites was used to interpret the modification of dislocation density during in-situ tension,which discovered the effect of dislocation on the work hardening behavior of SiC_p/Mg-5Zn composites.In addition,the tensile stress reduction(△P_i) values during in-situ tension test were calculated to analyze the effect of PDZ size on the softening behavior of SiC_p/Mg-5Zn composites.The results show that the work hardening rate of SiC_p/Mg-5Zn composites increased with the enlargement of PDZ size,which was attributed to the grain size of SiC_p/Mg-5Zn composites increased with the enlargement of PDZ size.Moreover,the stress reduction(△P_i) values increased continuously during in-situ tensile for SiC_p/Mg-5Zn composites due to the increased stored energy produced during plastic deformation,which provided a driving force for the softening effect.However,the effect of grain size on the softening behavior is greater than that of the stored energy,which led to the tensile stress reduction(△P_i) values of P30(d_PDZ=30 μm)-SiC_p/Mg-5Zn composite were higher than that of P60(d_PDZ=60 μm)-SiC_p/Mg-5Zn composite when the ε_ri were 0.25,0.5,0.75 and 1,respectively.     

温度及搅拌速度对纳米氢氧化镍性能的影响

采用化学沉淀法制备出片状和棒状混合的纳米β-Ni（OH）_2,将纳米粉体以 8%比例掺入到球镍中制成复合电极,研究了反应温度和搅拌速度对纳米粉体结构、形貌及其复合电极电化学性能的影响,结果表明,反应温度升高,纳米颗粒粒径增大;搅拌速度提高,粒径减小;复合电极的放电比容量随反应温度和搅拌速度提高先增大后减小,当反应温度为 50℃、搅拌速度为 600 r/min时,相应的复合电极放电比容量最大,达到了 263.3 mAh/g,比纯球镍电极放电比容量（239.4 mAh/g）提高了约 10%。研究还显示,复合电极的放电比容量与其粉体的压实密度有直接对应关系,其放电比容量和放电平台均高于纯球镍电极。     

Hardening and softening mechanisms of pearlitic steel wire under torsion

The mechanical behaviors and microstructure evolution of pearlitic steel wires under monotonic shear deformation have been investigated by a torsion test and a number of electron microscopy techniques including scanning electron microscopy (SEM) and transmission electron microscopy (TEM), with an aim to reveal the softening and hardening mechanisms of a randomly oriented pearlitic structure during a monotonic stain path. Significantly different from the remarkable strain hardening in cold wire drawing, the strain hardening rate during torsion drops to zero quickly after a short hardening stage. The microstructure observations indicate that the inter-lamellar spacing (ILS) decreases and the dislocations accumulate with strain, which leads to hardening of the material. Meanwhile, when the strain is larger than 0.154, the enhancement of dynamic recovery, shear bands (SBs) and cementite fragmentations results in the softening and balances the strain hardening. A microstructure based analytical flow stress model with considering the influence of ILS on the mean free path of dislocations and the softening caused by SBs and cementite fragmentations, has been established and the predicted flow shear curve meets well with the measured curve in the torsion test.     

Inverse analysis of the wedge-splitting test

The amount of information which it is possible to retrieve from the wedge-splitting test is investigated. Inverse analysis is undertaken based on the analytical hinge model for various multi-linear softening curves. This showed that the commonly used bi-linear softening curve can be replaced by an up to quad-linear curve, which is reflected by increased accuracy of the test simulation. Furthermore it was demonstrated that the next refinement of the softening curve leads to convergence problems due to problems with local minima. Finally, the semi-analytically obtained results are verified using FEM simulations.     

On the Estimation of Softening of Ablating Heat-Shielding Coatings

A method of analytical estimation of softening of ablating heat-shielding coatings is considered. The softening is evaluated by the coefficient that describes the effect of variation in the modulus of elasticity with increasing temperature on the process of softening and takes into account the pattern of the temperature field determined from the character of the temperature dependence of the heat conductivity coefficient. An acceptable agreement of the calculated and experimental results under conditions of quasi-stationary ablation is shown.     

The influence of Al2O3 particulate reinforcement on cyclic stress response and fracture behavior of 6061 aluminum alloy

The cyclic stress response characteristics and cyclic fracture behavior of aluminum alloy 6061 discontinuously reinforced with particulates of Al₂O₃ are presented and discussed. The 6061/Al₂O₃ composite specimens and the unreinforced 6061 aluminum alloy were cyclically deformed using tension-compression loading under constant total strain amplitude control. Both the composite and the unreinforced alloy exhibited softening to failure from the onset of cyclic deformation. The degree of softening was observed to increase at the elevated test temperature for both the composite and the unreinforced counterpart. The intrisic micromechanisms controlling the stress response characteristics during fully-reversed cyclic straining are highlighted and rationale for the observed behavior is discussed. The cyclic fracture behavior of the composite is discussed in terms of the competing influences of intrinsic microstructural effects, deformation characteristics arising from a combination of mechanical and microstructural contributions, cyclic stress response, and test temperature.