W-Cu梯度功能材料的设计、制备与评价

W-Cu梯度功能材料的高W含量侧具有低热膨胀率、高强度和耐热流冲蚀等特点,高Cu含量的另一侧具有高导热性能,而中间过渡层可使内部热应力获得良好的缓和;该材料作为热沉材料、面向等离子体材料以及触头材料等的应用具有非常大的发展潜力,其研究受到广泛的重视。本文作者对W-Cu梯度材料的研究进展进行综合评述,介绍了W-Cu梯度功能材料的设计、制备及评价方法;根据其工作环境,着重对W-Cu梯度功能材料的致密性,热膨胀,热导率,热损蚀和热冲击等性能进行评价,并对W-Cu梯度功能材料的进一步发展作了展望。     

Computer-aided design methods for functionally graded materials showing mesoscopic phenomena

Theoretical principles are given for the computer-aided design of functionally graded materials (FGM) for use under graded loading. The graded property distribution makes itself felt most strongly in wave processes. On shock loading, the FGM gives rise to new types of wave: isoentropic compression waves and soliton-type ones.     

功能梯度材料的制备技术

从工艺原理、特点、材料体系等方面概述了功能梯度材料的制备技术,阐述了功能梯度材料制备技术的应用现状及发展趋势。     

Design and fabrication of W-Mo-Ti-TiAl-Al system functionally graded material

To obtain a kind of functionally graded material (FGM) with a density gradient, the W-Mo-Ti-TiAl-Al system graded material was designed, and the powder metallurgy method was chosen for its fabrication. The sintering of W, W-Mo, and Mo-Ti alloys at low temperature was studied, and then the approximately wholly dense W-Mo-Ti-TiAl system FGM was achieved by one-step sintering at 1473 K for 1 hour under a pressure of 30 MPa. It was found that through sintering at 1473 K, mainly the mechanical mixtures of W and Mo were formed in W-Mo alloys. In Mo-Ti alloys, the newly designed Fe-Al sintering aids not only have an important effect on the densification of the alloys, but also contribute to the formation of the (Mo, Ti) solid solution. However, the solid-solution reaction that occurred in Mo-Ti alloys was still insufficient. During the sintering of Ti + TiAl, the chemical reaction of Ti + TiAl → AlTi₂ was induced within the sintered body. The W-Mo-Ti-TiAl-Al system FGM was finally fabricated by joining of the TiAl side of the sintered W-Mo-Ti-TiAl system FGM to metal Al with an Al-based brazing filler metal, and its density changed quasi-continuously within the large range from 17.15 to 2.70 g/cm³.     

Characterization of Mo-SiO2 functionally graded materials

Mo/SiO₂ functionally graded materials (FGMs) have been prepared by combined slip casting and sedimentation techniques. The final, sintered samples have a gradient in molybdenum content, with a maximum value of ∼20 to 25 vol pct Mo. At one edge, the FGM is a good electrical conductor (for approximately one-third of the total length), while the opposite end is composed mainly of fused SiO₂. The variation of electrical resistivity, hardness, toughness, and thermal expansion along the gradient has been analyzed. The FGMs sintered in vacuum contained a small amount of Mo oxide (∼2 wt pct) as a third phase. The oxide originated from the starting Mo powders and oxidation during presintering. The oxide was in the form of discrete particles and did not appreciably affect the measured properties. The Mo content had the expected effect on the FGM properties; an increase in Mo increases resistivity, thermal expansion, and toughness.     

粉末冶金技术制备功能梯度材料研究进展

功能梯度材料因其所呈现出的优异性能,已成为材料领域的研究热点之一.本文通过介绍粉末冶金技术制备功能梯度材料的国内外研究动态,对粉末冶金技术制备功能梯度材料的工艺流程进行了系统论述,尤其对功能梯度材料的粉末成形工艺予以重点阐述,并对其发展趋势进行了展望.     

功能梯度材料的设计与制备以及性能评价

阐述了功能梯度材料设计、制备及性能评价的国内外研究现状, 并着重分析了功能梯度材料物性参数预测模型、热应力模拟与计算、梯度组成分布优化设计以及各种制备方法的优劣对比, 最后对功能梯度材料存在的问题及前景进行了探讨。同时指出, 功能梯度材料性能评价需建立合适的评价标准, 随着制备技术的不断完善、应用范围不断扩大, 功能梯度材料在材料科学中广阔的应用前景必将受到应有的重视。鉴于功能梯度材料的制造方法具有很强的目的性、理论性、工艺性及实用性, 研究宜从基础入手, 兼顾其它应用技术, 广泛开展横向联合, 将基础理论研究、材料设计、工艺制造及性能测试很好地结合, 以促进功能梯度材料技术的发展。     

原位扩散形成功能梯度硬质材料的研究进展

功能梯度硬质材料是20世纪80年代将功能梯度材料(FGM)的概念应用于硬质合金和金属陶瓷而发展起来的一类新型材料.本文综述了目前国内外用原位扩散控制方法-氮化工艺制备功能梯度硬质材料的研究进展,详细介绍了冶金学基础、成分体系和梯度结构类型、主要类型梯度结构的制备工艺和形成机理,比较了切削性能,并讨论了今后研究工作的重点.     

轧膜成形制备W-Cu层状功能梯度材料及其性能研究

以W粉和电解Cu粉为原料,聚乙烯醇缩丁醛(PVB)为粘结剂,通过有机基轧膜工艺制备出3种组成的单层生坯(Cu质量分数分别为25%、50%、75%),再叠层共轧,制备出了具有不同粘结剂含量的W-Cu层状梯度材料生坯,之后在H2气氛中烧结,获得了W-Cu层状梯度材料,考察了粘结剂含量与制备工艺条件对材料显微组织和性能的影响。结果表明,通过单层轧制、叠层共轧共烧可以制得层状梯度W-Cu复合材料;粘结剂含量对W-Cu层状梯度材料的致密度和性能有着明显的影响。当粘结剂质量分数为6%时,轧膜坯有较好的成形性,且成形坯的孔隙率较低;所得多层生坯经1 150℃烧结后相对密度达93.11%;所得梯度W-Cu材料有良好的物理、力学性能。     

Thermal residual stresses in functionally graded and layered 6061 Al/SiC materials

The thermal residual stresses that develop in spray atomized and codeposited functionally graded and layered 6061 Al/SiC metal-matrix composites (MMCs) during cooling from the codeposition temperature to ambient temperature were studied using thermo-elastoplastic finite element analysis. In an effort to investigate the effect of layered and graded structures on the residual stress distribution, the composites with homogeneous distribution of SiC particulates were also analyzed. The effect of SiC volume fraction in the SiC-rich layers and the effect of SiC-rich layer thickness on the residual stresses were investigated. Based on the present study, it was found that the residual stress distribution is very distinct for the aluminum and the SiC-rich layers in the layered materials. As the volume fraction of SiC increases in the SiC-rich layer, the magnitude of residual stresses also increases. The radial stress was found to be tensile in the aluminum layers and compressive in the SiC-rich layers. It was also found that, as the thickness of the SiC-rich layer increases, the magnitude of radial stress in the aluminum layers increases, and that in the SiC-rich layers decreases. In the graded material, the lower region of each layer exhibits tensile radial stress, and the upper region of each layer shows compressive radial stress in order to maintain continuity between layers during cooldown. In general, the layered and the graded materials have greater residual stresses and more complicated stress distribution, as compared with those in the composite materials with homogeneous distribution of SiC particulates.     

超高压力下通电烧结制备钨铁功能梯度材料

采用超高压力下通电烧结技术制备了钨体积分数为0%、25%、50%、75%和100%的钨铁功能梯度材料.研究了材料组分和工艺参数对W/Fe功能梯度材料的显微形貌及力学性能的影响.结果表明:当施加压力为9 GPa,通电功率为11 kW,通电时间60 s时可以获得相对密度大于98%的钨铁功能梯度材料,其组分分布与设计成分保持一致.     

Fatigue crack growth behavior of 2124/SiC/10p functionally graded materials

Powder metallurgy processing involving cold pressing and hot extrusion has been used to fabricate bulk functionally graded materials (FGMs) based on the 2124/SiC/10p composite system. Two forms of single-core bulk FGMs with circular cross section were fabricated. One form (designated 10SiC-2124) had a central core of unreinforced Al-2124 alloy that was surrounded by a 2124/SiC/10p reinforced surface layer: the other (designated 2124-10SiC) had a composite core and an alloy surface layer. These forms enabled the effect of the radial graded core on fatigue to be investigated with fatigue crack propagation from either (1) a ductile core to a more brittle region or (2) a brittle core to a ductile region of the FGM. The fatigue crack growth rate was measured using a constant applied stress intensity factor range (δK=7 MPa ) technique. Two main fatigue crack growth rates were distinguished corresponding to growth in the core and in the surface layer. The results show that FGMs may exhibit good fatigue crack propagation resistance. For example, when the crack propagated from the brittle core to the tough surface layer, the average fatigue crack growth rate in the Al-2124 core (3.9×10⁻⁶ mm/cycle) was significantly lower than for the Al-2124 alloy (1.5×10⁻⁵ mm/cycle) at a similar δK value (7 MPa ), due to the highly tortuous crack path in the 2124/SiC/10p brittle layer. The 2124/SiC/10p brittle layer had a lower fatigue crack growth rate (6.6×10⁻⁶ mm/cycle) than the 2124/SiC/10p conventional composite (7.5×10⁻⁶ mm/cycle) because of the compressive residual stresses in the surface layer. Thus, FGMs could be more acceptable for critical applications than their conventional composite counterparts.     

多坯料挤压法制备近全致密W-Cu梯度热沉材料

采用多坯料挤压法制备封接层、中间过渡层和散热层分别为W/Cu20、W/Cu33和W/Cu50的近全致密均厚结构W-Cu梯度热沉材料,梯度层厚度均为0.5 mm,并对工艺过程、致密性能和显微结构进行研究。结果表明:采用多坯料挤压法制备W-Cu梯度预制块时压力仅为0.6 KN,经10 h自然干燥后,预制块外观平整,无开裂;在350℃脱脂1 h、然后在烧结温度1 060℃、压力85 MPa条件下,保温3 h可以获得各层相对密度分别为98.3%、99.3%、99.9%的近全致密的W-Cu均厚结构梯度热沉材料;各层间界面位置清晰,层间为冶金结合界面;各层中Cu相呈网状分布,W颗粒镶嵌于网络结构中。     

WC-Co功能梯度硬质合金研究进展

概述了梯度硬质合金的分类;介绍了WC-Co梯度硬质合金的一些制备方法及应用领域;重点总结了梯度结构的形成机理、驱动力及生长动力学等方面的研究进展;分析了目前存在的不足,展望了梯度硬质合金的发展前景。     

Titanium-titanium boride (Ti-TiB) functionally graded materials through reaction sintering: Synthesis,microstructure, and properties

The study demonstrates an effective method to synthesize titanium-titanium boride (Ti-TiB) functionally graded material (FGM) tiles by exploiting the simultaneous TiB whisker formation in situ and the densification occurring during the reaction sintering process. The macrostructure of the graded material was designed to have a beta-titanium (β-Ti) layer on one side with the composite layers of Ti-TiB mixture having increasing volume fraction of the TiB through the thickness. The approach used an optimized tri-modal powder mixture consisting of α-Ti powder, a master alloy of the β-stabilizing-element powders (Fe-Mo), and TiB₂. The structure and properties of both of these FGMs were systematically characterized by X-ray diffraction, electron microscopy, and microhardness measurements. Interestingly, it has been found that two different kinds of TiB whisker morphologies were observed in the FGMs. The Ti-rich layers were found to have large and pristine TiB whiskers uniformly distributed in the Ti matrix. On the other hand, the TiB-rich layer was found to have a network of interconnected and relatively smaller TiB whiskers appearing as clusters. The layers of intermediate TiB volume fractions were found to consist of both the morphologies of TiB. The effectiveness of the X-ray direct comparison method for the determination of volume fractions of phases in the FGM layers was also demonstrated. The Vickers microhardness level was found to increase dramatically from 420 kgf/mm² in the β-Ti layer to 1600 kgf/mm² in the TiB-rich layer. The elastic residual stresses retained in the graded layers after fabrication were determined based on an elastic multilayer model. The nature of microstructure, the hardness variation, and the distribution of residual stresses in these novel FGMs are discussed.     

Tensile behavior of functionally graded steels produced by electroslag remelting

Tensile behavior of functionally graded steels produced by electroslag refining has been studied. Functionally graded steels containing layers of ferrite, austenite, bainite, and martensite may be fabricatedvia diffusion of alloying elements during electroslag remelting. Tensile strength of the composites depends on the composition and number of layers and those have been modeled based on the tensile behavior of individual phases. The yield stress of each element in the composites is related to the microhardness value of that element. Considering the Holloman relation for the true stress-strain behavior of each element, the tensile strength of an individual element is also related to the microhardness value of that element. By applying the rule of mixtures, the tensile strengths of the composites were determinedvia the numerical method. The obtained results are in good agreement with the experimental results.     

Transformation characteristics of functionally graded steels produced by electroslag remelting

In this work, functionally graded steel has been produced via diffusion of the alloying elements during electroslag refining. As the alloying element diffuses, it creates alternating regions with different transformation characteristics. Thus, it is possible to obtain steel composites with various combinations of ferrite, bainite, martensite, and austenite phases. By choosing the appropriate thickness of the slices used to set up the consumable electrodes and subsequent heat treatment, different functionally graded phases may be produced. The diffusion coefficients of chromium, nickel, and carbon atoms at temperatures just above the melting point of iron were estimated. Also, the thicknesses of the emerging bainite and martensite phases were determined and are in good agreement with the experimental results.     

Fabrication and characterization of Ti-TiB2 functionally graded material system

In this work, a five-layer metal-ceramics Ti-TiB₂ functionally graded material (FGM) system was fabricated using a powder metallurgy route. The fabricated FGM system was found to possess 50 pct more fracture toughness than the conventional monolithic TiB₂ ceramics. The composition and microstructure of the FGM fabricated were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX), and the results are presented and discussed in this article. Vickers hardness and fracture energy of each compositional layer in the FGM were also measured. The significant fracture toughness improvement observed in the FGM system is attributed to the operation of a crack deflection mechanism. The present experimental results were compared with the theoretical predictions reported in the literature on operating crack deflection criteria of layered systems.     

Study on electromagnetic force for preparation of in-situ Al/Mg2Si functionally graded materials by electromagnetic separation method

The aim of this article is to investigate the effects of electromagnetic force on primary particle distribution of in-situ Al/Mg₂Si functionally graded materials (FGMs) by electromagnetic separation method. Experimental results show that there is a critical value of electromagnetic force. The FGMs can be produced only when the electromagnetic force is beyond the critical value. With increasing the electromagnetic force, the particle volume fraction of the particle-packed regions increases, the length of the particle-packed regions decreases, the average gradient of particle volume fraction increases, and the primary particle size become smaller.