颗粒增强2024Al复合材料的微屈服性能研究

为了明确亚微米颗粒增强铝基复合材料微塑性变形行为的规律和机制，利用微屈服强度测试和透射电镜分析，研究了亚微米级Al2O3颗粒增强2024Al复合材料的微屈服性能及尺寸稳定化热处理工艺对微屈服性能的影响。研究结果表明：复合材料的显微组织在稳定化热处理前后均呈现位错稀少的特点，有助于材料微屈服强度的提高；复合材料中尺寸细小，密集分布的S′相和亚微米颗粒本身对位错运动的有效阻碍也能改善材料的微屈服强度；时效后采用不同的冷热循环处理工艺，使得复合材料基体中S′相的尺寸和分布都发生一定的改变，进而呈现出不同的微屈服性能。     

Al2O3 reinforced Al/Ni intermetallic matrix composite by reactive sintering

An aluminium-nickel reinforced Al₂O₃ particulate composite was fabricated by a powder metallurgy route, where 35wt% aluminium and 30wt% nickel powders were mixed with 35wt% Al₂O₃ particles and compacted at 548 MPa. Sintering was carried out at 850 °C, where the synthesis reaction was sustained by the transient liquid phase resulting from the exothermic reaction associated with the formation of intermetallic compounds, i.e. reactive sintering. The resultant microstructure was studied using X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). It was found that the initial distribution of individual constituent powders affect the outcome of the reactive sintering and that the inward diffusion of aluminium in nickel was responsible for nickel aluminide formation.     

Al2O3·SiO2颗粒增强铝基复合材料的摩擦磨损特性

对用挤压铸造法制备出的Al2O3@SiO2颗粒增强铝基复合材料在不同条件下的摩擦磨损特性进行了研究.结果表明:Al2O3@SiO2颗粒的加入可提高复合材料的耐磨性,复合材料同基体铝合金相比摩擦因数也较低.在较低载荷和滑动速度下,该复合材料的耐磨性明显优越于基体铝合金,摩擦因数也稳定地低于基体铝合金;而在较高载荷和滑动速度下,同基体铝合金相比,复合材料耐磨性的改善有所降低,但摩擦因数仍可以保持较低的水平.这是由于随着载荷和滑动速度的变化,复合材料的磨损机制发生了转化.对Al2O3@SiO2颗粒在摩擦磨损过程中所起到的作用进行了分析.     

Synthesis,microstructure and mechanical properties of Al2O3 reinforced Ni3Al matrix composite

A new method to synthesize alumina reinforced Ni₃Al intermetallic matrix composites has been described. The powder mixture of nickel and aluminium was mechanically alloyed. The powder mixture was excessively heated during mechanical alloying and then exposed to atmosphere for oxidation. The oxidized powder mixture was transformed into alumina reinforced nickel aluminide matrix composite on subsequent pulse current processing. Alumina reinforcements were generated in the nickel aluminide matrix by in situ precipitation. The microstructure of the composite showed that the alumina reinforcements were 50–150 nm in size. The fine alumina reinforcements were homogeneously distributed in the matrix phase. The mechanical properties of the alumina reinforced nickel aluminide matrix composite fairly exceeded the nickel aluminide alloys. This novel synthesis approach allowed the rapid and facile production of high strength alumina reinforced Ni₃Al matrix composites.     

Mechanical behaviour of Al2O3–ZrO2 minicomposite reinforced glass matrix optomechanical composite

Abstract

To understand the effect of a 'mesh-structured reinforcement' on the optical and mechanical properties of optomechanical composites, a unidirectional Al₂O₃ fibre–ZrO₂ matrix minicomposite reinforced glass matrix optomechanical composite has been fabricated. By regular alignment of the minicomposites in the glass matrix as part of the 'mesh structure' a high degree of optical transparency is obtained in the composite; this transparency is proportional to its 'optical window' regions. The mesh structured reinforcement composed of millimetre order widely spaced minicomposites is effective in improving the fracture resistance of the resulting composites primarily through an intact minicomposite bridging mechanism. Use of the minicomposite type of reinforcement is one possible means of improving the mechanical properties of brittle matrix optomechanical composites.     

Fabrication of 5052Al/Al2O3 nanoceramic particle reinforced composite via friction stir processing route

In this research, microstructure and mechanical properties of 5052Al/Al₂O₃ surface composite fabricated by friction stir processing (FSP) and effect of different FSP pass on these properties were investigated. Two series of samples with and without powder were friction stir processed by one to four passes. Tensile test was used to evaluate mechanical properties of the composites and FSP zones. Also, microstructural observations were carried out using optical and scanning electron microscopes. Results showed that grain size of the stir zone decreased with increasing of FSP pass and the composite fabricated by four passes had submicron mean grain size. Also, increase in the FSP pass caused uniform distribution of Al₂O₃ particles in the matrix and fabrication of nano-composite after four passes with mean cluster size of 70 nm. Tensile test results indicated that tensile and yield strengths were higher and elongation was lower for composites fabricated by three and four passes in comparison to the friction stir processed materials produced without powder in the similar conditions and all FSP samples had higher elongation than base metal. In the best conditions, tensile strength and elongation of base material improved to 118% and 165% in composite fabricated by four passes respectively.     

原位纳米Al2O3颗粒增强铝基复合材料的制备与微结构研究

开发了新型反应体系,以硼砂( Na2B4O7·10H2O)和K2ZrF6粉剂为原料采用熔体直接反应法,在铝熔体中成功制备了原位纳米Al2O3颗粒增强铝基复合材料.借助于扫描电镜( SEM)、X射线衍射(XRD)、透射电镜(TEM)等测试方法,对复合材料的相组成和微观组织进行了分析,结果表明反应生成了纳米级γ-Al2O3...     

Tensile properties and thermal stability of ZnO-coated aluminum borate whiskers reinforced 2024Al composite

ZnO-coated aluminum borate whiskers reinforced 2024Al composite was fabricated by squeeze casting. Interfacial microstructures and tensile properties of the composite in as-cast and after thermal exposure were investigated. Fracture mechanisms of the composite in as-cast and after thermal exposure were also investigated. The results show that ZnO coating of the whiskers reacts with molten 2024Al and MgAl₂O₄ forms at the interface during squeeze casting. On the one hand, the interfacial reaction between ZnO and 2024Al can improve the wettability of the whiskers by molten 2024Al, increasing the tensile properties of as-cast composite. On the other hand, during thermal exposure, MgAl₂O₄ at the interface can effectively hinder serious interfacial reactions between the whiskers and magnesium in the matrix of 2024Al, improving the thermal stability of the composite at high temperatures.     

Preparation and mechanical properties of high-purity Al2O3 fibre/Al2O3 matrix composite

Al₂O₃ matrix composites with unidirectionally oriented high-purity Al₂O₃ fibre with and without carbon coating, were fabricated by the filament-winding method, followed by hot-pressing at 1573–1773 K. The composite with non-coated Al₂O₃ fibre exhibited a bending strength (594 MPa) comparable to that of monolithic Al₂O₃ (589 MPa). While the composite with a carbon-coated fibre had lower strength (477 MPa), it showed improved fracture toughness (6.5 MPa m^1/2) compared to the composite with an uncoated fibre (4.5 MPa m^1/2) and monolithic Al₂O₃ (5.5 MPa m^1/2). This toughness enhancement was explained based on the increased crack extension resistance caused by the fibre pull-out observed by SEM at the notch tip. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of Al2O3 particle size on vacuum breakdown behavior of Al2O3/Cu composite

In order to clarify the effect of Al₂O₃ particle size on the arc erosion behavior of the ceramic-reinforced Al₂O₃/Cu composite, Al₂O₃/Cu composites with different sizes of Al₂O₃ particles were prepared by powder metallurgy, the effect of Al₂O₃ particle size on the characteristics of arc motion was studied, and the mechanism of arc erosion of Al₂O₃/Cu composites was discussed as well. The results show that with decrease in the size of Al₂O₃ particles, the erosion area increases significantly and the erosion pits become shallower. The vacuum breakdown is preferred to appear in the area between Al₂O₃ particle and the copper matrix. Based on the experimental results and theoretical analysis, a particle partition arc model is proposed.     

Prediction of dynamic recrystallization condition by deformation efficiency for Al 2024 composite reinforced with SiC particle

Hot torsion test has been carried out for Al 2024 composite reinforced with 8 m SiCp (15 vol.%) to suggest optimum hot working condition for dynamic recrystallization (DRX) at the temperature range of 320 to 520 °C and strain rate range of 0.1 to 3.0/sec. Flow curve and deformed microstructure have been analyzed to identify the hot restoration mechanism of DRX. Processing map showing the variation of the deformation efficiency expressed by [2m/(m + 1)], where m is the strain rate sensitivity, with temperature and strain rate has been described for the composite. The characteristics of domain of DRX and peak efficiency of the composite have been analyzed by observing deformed microstructure. The composite showed 40–50% efficiency at the DRX domain (370–460 °C, 0.1–0.5/sec). Also, the variation of deformation efficiency with Zener-Hollomon parameter (Z = exp(Q/RT)) were discussed to find out optimum hot working condition for DRX of the composite. It is found that the optimum temperature and strain rate condition for DRX of the composite is 430–450 °C and 0.5/sec.     

原位自生TiB2颗粒增强2024-T4铝基复合材料断裂行为数值模拟

利用SEM结合原位观测技术观察了颗粒体积分数为4.17%的原位自生TiB₂颗粒增强2024-T4铝基复合材料（TiB₂/2024-T4）的损伤断裂行为。试验结果表明,TiB₂颗粒偏聚带中的铝合金基体比颗粒稀疏区域中的铝合金基体率先发生断裂。根据这一试验现象建立了三种含随机颗粒偏聚带的二维体胞有限元模型,并施加拉伸载荷和周期性边界条件,推导了平面应力状态下的径向返回算法,结合Rice-Tracey局部失效准则模拟了颗粒偏聚带中微裂纹的萌生及扩展过程。数值分析结果表明：就单个颗粒来说,颗粒两极附近基体损伤最严重。颗粒偏聚导致损伤在颗粒附近基体中迅速累积,并发展成为基体微裂纹,且随着颗粒偏聚程度加剧,材料断裂应变下降。另外,体胞模型应力-应变曲线的非线性部分低于实测曲线,说明除了本文模型反映的载荷传递强化机制外,还需要进一步考虑颗粒对基体的间接强化机制。     

Identification of interfacial parameters in a particle reinforced metal matrix composite Al6061–10%Al2O3 by hybrid method and genetic algorithm

The mechanical behavior of interfaces between matrix and inclusions in composite materials has a strong influence on their mechanical properties such as the strength and the toughness of these materials. To effectively predict the mechanical behavior and investigate the effects of interface properties on the composites, a novel hybrid/inverse numerical method is proposed in conjunction with experimental measurements of real microstructure. This method is based on a combination of hybrid/inverse analysis, finite element method and an improved genetic algorithm (GA). A non-continuum four-node interface element is adopted to simulate the interface behavior of a metal matrix composite whose displacement field has been measured by experiment. By way of the observed failure occurring on the interface in the experiment, a hybrid/inverse analysis for estimating the four unknown mechanical parameters of the interface is carried out by using an improved GA and the interface element model mentioned. Approximate interfacial parameters obtained from the proposed method can reasonably simulate interfacial failure which is in agreement with that observed experimentally. It is found that the proposed hybrid/inverse method is simple and robust for solving complex interfacial problems in composites.     

Determining the effect of flake matrix size and Al2O3 content on microstructure and mechanical properties of Al2O3 nanoparticle reinforced Al matrix composites

In this study, Al2024 matrix composites reinforced with Al₂O₃ nanoparticle contents ranging from 1 to 5?wt% were produced via a new method called as flake powder metallurgy (FPM). The effect of flake size and Al₂O₃ nanoparticle content on the reinforcement distribution, microstructure, physical, and mechanical properties of the composites were studied. SEM analysis was performed to investigate the microstructure of metal matrix and the distribution of nanoparticles. The hot-pressed density increased with decreasing the matrix size. The hardness of the Al2024–Al₂O₃ nanocomposites fabricated by using fine matrix powders increased as compared to the Al2024–Al₂O₃ nanocomposites produced by using coarse matrix powders. It has been found that the FPM method proposed in this study revealed to be an effective method for the production of nanoparticle reinforced metal matrix composites.     

Drilling studies of an Al2O3-Al metal matrix composite

Comparative drilling studies have been carried out for a 20% Al₂O₃ microsphere reinforced Al metal matrix composite (MMC) using a (a) high speed steel (HSS) drill, (b) tungsten carbide (WC) drill and (c) polycrystalline diamond (PCD) drill. In this part of the paper, the flank wear characteristics of the drills have been presented. It is found that for the HSS drill a flank wear of 1.00 mm is reached in drilling for as little as 12 s. In contrast, under similar conditions for the WC drill, a flank wear of 0.16 mm was observed after drilling for a period of 600 s and in the case of the PCD drill, after 2210 s of drilling a flank wear of only 0.12 mm was observed. The PCD drill, however, showed some signs of chipping in the early stage, but this seemed to stabilize later on. Scanning electron microscopic (SEM) observations of the worn drill tips revealed that in addition to flank wear the HSS exhibited margin wear, the WC drill exhibited both margin wear and chisel edge wear and the PCD drill displayed crater wear.     

Al2O3@Y3Al5O12纳米短纤维对铝合金基复合材料的增强作用

采用一种具有芯-壳结构的复合纳米纤维增强铝合金复合材料,可以在提高抗拉强度的同时增加塑性。通过真空热压烧结技术制备了Al₂O₃@Y₃Al₅O₁₂复合纳米短纤维增强2024铝合金复合材料。研究了纤维添加质量分数对复合材料致密度、硬度、抗拉强度及延伸率的影响;并探究了芯-壳结构在复合材料增韧中的作用。结果表明:Al₂O₃@Y₃Al₅O₁₂纳米短纤维具有良好的分散性,在超声分散及机械搅拌混粉后均匀吸附在铝合金颗粒表面,无分层及团聚现象;经热压烧结后,Al₂O₃@Y₃Al₅O₁₂纳米短纤维以短纤维形态均匀分散在铝合金基体内,少量添加Al₂O₃@Y₃Al₅O₁₂纳米短纤维起到了桥联和孔洞填充作用,使复合材料致密度和硬度提高;添加质量分数为1wt%时,抗拉强度和延伸率取得最大值,由铝合金的249.3 MPa、2.9%增加到299.1 MPa、4.3%。Al₂O₃@Y₃Al₅O₁₂纳米短纤维的添加可以细化晶粒,阻碍裂纹扩展,且在拔出/断过程中Al₂O₃@Y₃Al₅O₁₂纳米短纤维芯-壳结构的塑性变形起到了增强增韧作用。      

Properties of Al2O3 nano-particle reinforced copper matrix composite coatings prepared by pulse and direct current electroplating

Cu–Al₂O₃ nano-composite coatings have high potential for use in applications in which high mechanical properties together with high corrosion resistance are required. In the present study it is intended to produce copper nano-alumina composite coatings with various nano-alumina contents in order to investigate the effect of alumina reinforcement particles on corrosion resistance and mechanical properties such as hardness and wear resistance. The composite coatings were deposited using direct current (DC) and pulse current (PC) plating. The microstructures of the coatings produced from both methods were examined via scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The wear behaviors, micro hardness, coating thickness, corrosion rate and coating porosity were examined using appropriate methods. Compared to DC deposition, PC plating facilitated higher amounts of particle incorporation with more uniform distribution. The results indicated that the mechanical properties of the applied coatings with incorporated nano-alumina reinforcement were far more superior as compared to its own matrix as well as non-composite copper coatings. It was also found out that increasing the amount of nano-alumina content in the coating, led to enhanced general properties of the coatings.     

Hot Working behaviour of AI-AI2O3 particulate reinforced metal matrix composite

Abstract

The hot deformation behaviour of a particulate reinforced metal matrix composite, manufactured via a casting route and consisting of a 2000 series matrix reinforced with 20 vol.-%Al₂O₃ particles, was investigated over a range of temperatures and strain rates. The behaviour was compared with the unreinforced alloy deformed under the same conditions. Both materials exhibited similar hot working behaviour. However, under all deformation conditions the composite exhibited flow stresses higher than that of the alloy, but as the deformation temperature increased and the strain rate decreased, this difference became negligible. The activation energy for deformation was determined using constitutive equations. The value determined for the composite was slightly higher than that for the alloy. This suggested that the ceramic particles in the composite force the matrix to undergo additional strain hardening during deformation. Dynamic recovery was the sole restoration process in both materials. No evidence of dynamic recrystallisation was found.