Processing and interfacial bonding strength of 2014 Al matrix composites reinforced with oxidized SiC particles

The SiC powder with a SiO₂ protective layer is used as the reinforcements for 2014 Al/SiC_p composites to suppress the reaction between the Al matrix and the SiC particle. 2014 Al/SiC_p composites were fabricated by vacuum hot pressing (VHP) and subsequent extrusion using 2014 Al powders and the SiC particles covered with a SiO₂ layer. The interfacial product was found to be Mg spinel (MgAl₂O₄) formed mainly by the chemical reactions of the SiO₂ layer covered on SiC particles with the Mg, Al in the 2014 Al alloy matrix. Also the interfacial bonding strength of the composites was investigated using push-out tests of SiC rods with the SiO₂ oxidation layer, which were processed within 2014 Al alloy.     

Microstructure and mechanical properties of aluminum alloy matrix composites reinforced with Fe-based metallic glass particles

Fe-based metallic glass (FMG) particles reinforced Al-2024 matrix composites were fabricated by using the powder metallurgy method successfully. Mechanical alloying result in nanostructured Al-2024 matrix with a grain size of about 30 nm together with a good distribution of the FMG particles in the Al matrix. The consolidation of the composites was performed at a temperature in the super-cooled liquid region of the FMG particles, where the FMG particles act as a soft liquid-like binder, resulting in composites with low or zero porosity. The microstructure and mechanical properties of the composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and compression test. The yield and fracture strength of the composites are 403 MPa and 660 MPa, respectively, while retaining a considerable fracture deformation of about 12%. The strengthening mechanism is associated with the grain refinement of the matrix and uniform distribution of the FMG particles.     

Interactions between tungsten carbide (WC) particulates and metal matrix in WC-reinforced composites

A variety of experimental techniques have been used to investigate the interactions between tungsten carbide (WC–Co 88/12) particulates and the matrix in some new wear resistant cobalt-based superalloy and steel matrix composites produced by hot isostatic pressing. The results show that the chemical composition of the matrix has a strong influence on the interface reaction between WC and matrix and the structural stability of the WC particulates in the composite. Some characteristics of the interaction between matrix and reinforcement are explained by the calculation of diffusion kinetics. The three-body abrasion wear resistance of the composites has been examined based on the ASTM G65-91 standard procedure. The wear behavior of the best composites of this study shows great potential for wear protection applications.     

Properties of near- and sub-micrometre Al matrix composites strengthened with nano-scale in-situ Al2O3 aimed for low temperature applications

Mechanical and electrical properties of in-situ Al–Al₂O₃ metal matrix composites (MMCs) fabricated by powder metallurgy approach using different aluminium powders of particle size 0.8–21 µm and purity 99.8–99.996% were examined. Hot working powder consolidation by vacuum hot pressing at 270 °C and direct extrusion at 425 °C and reduction ratio of 7:1 were applied. Subsequently, extruded composite rods with the diameter of 7.5 mm were cold worked by groove rolling and rotary swaging to the wires with the diameter of 1.1 mm. Detailed microstructural characterization of composite materials was carried out. Stress-strain characteristics of composite wires were measured at 77 and 300 K. In addition, resistivity of all wires were measured by four-probe method between 25 and 300 K and eddy current losses at frequency 72 Hz and temperatures between 18 and 77 K. Obtained results clearly showed that properly designed Al–Al₂O₃ MMC materials can be utilized at low temperatures e.g., for the thermal stabilization of superconducting wires.     

Microstructure and mechanical properties of Al/Al2O3 MMC produced by anodising and cold roll bonding

Abstract

In the present paper, Al–Al₂O₃ composite strips are produced by the cold roll bonding process of anodised aluminium strips. This technique has the flexibility to control the volume fraction of metal matrix composites by varying the oxide layer thickness on the anodised aluminium strip. Microhardness, tensile strength and elongation of composite strips are investigated as a function of quantity of alumina and the applied production method. It is found that higher quantities of alumina improve microhardness and tensile strength, while the elongation value decreases negligibly. Furthermore, prerolling annealing is found to be the best method of producing this composite via the cold roll bonding process. Finally, it is found that both monolithic aluminium and aluminium/alumina composite exhibited a ductile fracture, having dimples and shear zones.     

Fabrication of aluminium matrix composites reinforced by submicrometre and nanosize Al2O3 via accumulative roll bonding

Abstract

Aluminium matrix composites reinforced with submicrometre and nanosize Al₂O₃ particles were successfully manufactured in the form of sheets through eight cycles of accumulative roll bonding process. The mechanical properties of the produced composite are compared with accumulative roll bonded commercially pure aluminium. It is shown that only 1 vol.-% of submicrometre or nanosize alumina particles as reinforcement in the structure can significantly improve the yield and ultimate tensile strengths. Scanning electron microscopy revealed that particles have a random and uniform distribution in the matrix especially in the less volume fraction of alumina particles, and strong mechanical bonding occurs at the interface of the particle matrix. According to the results of the tensile tests, it is observed that with less alumina content, the composite reinforced by nanosize particles has higher strength than that by submicrometre size particles. However, more reinforcement up to 3 vol.-% of submicrometre particles, as a result of including fewer microstructural defects, leads to better mechanical properties in comparison to the nanoparticle composite.     

Wear behavior of nanostructured Al/Al2O3 composite fabricated via accumulative roll bonding (ARB) process

In the present work, wear behavior of nanostructured aluminum and composite performed by accumulative roll bonding (ARB) process was investigated. The wear characteristics were studied by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). Also, transmission electron microscopy (TEM) and crystallographic texture investigations were performed. The results indicated that the ARB process led to the decrease in wear resistance of the monolithic and composite samples compared with as-received aluminum strip. The adhesive, abrasive and delaminating wear mechanisms occurred in the monolithic and composite samples simultaneously. At higher number of ARB cycles, delamination was the dominant wear mechanism. It was found that the surface damage of the composite was more extensive than that of the monolithic sample due to the occurrence of spalling mechanism. It was suggested that the intense Rotated Cube {0 0 1}〈1 1 0〉 texture component of composite helped to crack nucleation and propagation greatly. The role of delamination and especially, spalling in decreasing the wear resistance of composite was very important such that it eliminated the role of reinforcing particles and grain size on the wear resistance.     

铝基复合材料(Al2O3p/6061Al)过渡液相扩散连接

研究了Al-Si合金中间层Al2O3p/6061Al复合材料过渡液相扩散连接接头的显微结构和连接工艺参数对接头剪切强度的影响。连接区主要由Al-Si合金组成，无Al2O3颗粒，接头裂纹起源于Al-Si合金与Al2O3颗粒界面处，并主要在连接区Al-Si合金中扩展，连接工艺参数对接头剪切强度影响程度依次为Al-Si合金中间层厚度、连接温度、保温时间。选择合适的连接工艺参数，接头剪切强度可达70－80MPa。     

Al( Cr) 2O32Cr(Mo) 陶瓷基复合材料的制备与组织

在Al-Cr₂O₃ 体系中引入稀释剂(Al₂O₃ 、Cr₂O₃ ) 和反应性添加剂(MoO₃ ) 。利用热爆式燃烧合成法成功制备了含有细小棒状金属相共晶体的Al (Cr) ₂O₃-Cr (Mo) 陶瓷基复合材料。探讨了反应体系成分和制备工艺对复合材料微观组织的影响。对燃烧合成熔体施加1. 26 MPa 压力, 致密度可达90 %左右。陶瓷基体具有3 种形态:边界较圆整的块状, 细小的、按一定的取向交叉排列的长条状以及粗大的长条状。金属相以颗粒状分布在陶瓷晶体内或晶界处, 或与陶瓷相形成共晶组织。产物的共晶体呈准规则的结构, 细小棒状的金属相弥散分布在连续的陶瓷基体中。共晶体的分布具有区域性。原位生成的长条状陶瓷晶粒及金属相呈棒状的共晶结构是制得的复合材料的重要组织特征。      

具有催化与渗透汽化双功能的纳米TiO2和Al2O3填充复合膜性能

采用聚丙烯腈(PAN)中空纤维超滤膜作为支撑底膜,经戊二醛(GA)表面交联的聚乙烯醇(PVA)作为渗透汽化层,以及纳米TiO2或Al2O3填充的全氟磺酸树脂(PFSA)作为催化层,制备了催化与渗透汽化双功能复合膜,考察了其亲水性能、对乙酸乙酯塔顶粗酯的渗透汽化分离性能、催化酯化反应性能以及机械性能.实验结果表明:催化与渗透汽化双功能复合膜具有良好的亲水性和机械性能,渗透通量可达到179g/(m2.h),相对应的分离系数为95,渗透物中不含乙酸乙酯,同时可显著缩短酯化反应达到相同转化率的时间.     

Al2O3微粉Y2O3改性对Al基复合材料性能的影响

采用液相包裹法用Y2O3对Al2O3微粉表面进行改性,用挤压铸造法制备表面改性的Al2O3p／6061A1复合材料,研究改性对复合材料的显微组织和力学性能的影响．结果表明,用Y2O3表面改性后,Al2O3微粉在6061Al基体中的分布均匀性明显改善,复合材料的力学性能明显提高．与改性前比较,Al2O3体积分数为25％的复合材料,抗拉强度提高30％,屈服强度提高40％,弹性模量提高20％．其原因是,改性Al2O3微粉表面的Y2O3与Al基体间发生界面反应,使界面润湿性得以改善：界面相Y2Al与Al2O3和Al基体间均形成良好结合的界面。     

Enhancing energy storage density of (Ba, Sr)TiO3 ceramic particles by coating with Al2O3 and SiO2

The dielectric and energy storage properties of Ba_0.4Sr_0.6TiO₃ particles coated by Al₂O₃ and SiO₂ oxide were investigated. Results showed that the dielectric properties and energy storage density were improved apparently. The improvement of the energy storage density can be ascribed to two factors: one was that the breakdown strength was notably improved by the decrease of the porosity and defects; the other was the reduction of the grain size. Furthermore, the optimized composition showed the maximum energy storage density of 5.09 J/cm³, whereas the energy storage density of uncoated Ba_0.4Sr_0.6TiO₃ was only 0.24 J/cm³.     

挤压及热处理对原位合成(Al_3Zr+ZrB_2)_p/6063Al复合材料力学性能的影响规律

采用Al-KBF4-K2ZrF6剂体系,通过熔体反应法成功制备(Al3Zr+ZrB2)p/6063Al复合材料。对复合材料进行热挤压和热处理,并利用正交试验的方法综合分析挤压和热处理参数(固溶温度、时效时间、时效温度)对铝基复合材料的抗拉强度的影响,采用SEM等分析方法于各阶段分析了复合材料的相组成,探讨了热处理对复合材料拉伸性能的影响的微观机制。结果表明,热挤压和热处理均对复合材料的微观形貌和抗拉强度有较大影响,分别提升了6%和20%。正交试验计算所得热处理参数对抗拉强度影响的大小顺序为固溶温度、时效温度、时效时间。优选出最大抗拉强度热处理工艺为固溶温度723 K,固溶时间4 h;时效温度423 K,时效时间4 h。     

(TiZrHf)P2O7: An equimolar multicomponent or high entropy ceramic with good thermal stability and low thermal conductivity

ZrP₂O₇ is a promising material for high temperature insulating applications. However, decomposition above 1400 °C is the bottleneck that limiting its application at high temperatures. To improve the thermal stability, a novel multicomponent equimolar solid solution (TiZrHf)P₂O₇ was designed and successfully synthesized in this work inspired by high-entropy ceramic (HEC) concept. The as-synthesized (TiZrHf)P₂O₇ exhibits good thermal stability, which is not decomposed after heating at 1550 °C for 3 h. It also shows lower thermal conductivity (0.78 W m⁻¹ K⁻¹) compared to the constituting metal pyrophosphates TiP₂O₇, ZrP₂O₇ and HfP₂O₇. The combination of high thermal stability and low thermal conductivity renders (TiZrHf)P₂O₇ promising for high temperature thermal insulating applications.     

硅酸铝短纤维增强AZ91D复合材料的界面微观结构及力学性能

以晶化的硅酸铝短纤维（Al₂O₃-SiO₂ ）_sf为增强体、用磷酸铝为预制体粘结剂,通过挤压浸渗工艺制备了（Al₂O₃-SiO₂ ）_sf /AZ91D镁基复合材料。通过光学显微镜、TEM和HREM分析研究了复合材料的界面微观结构和界面反应产物。结果表明：用挤压浸渗法制备的硅酸铝短纤维增强AZ91D镁基复合材料的界面厚度约为100 nm,界面上除有一定数量的MgO颗粒和少量的MgAl₂O₄和Mg₂Si颗粒外, 还有少量的MgP₄等反应产物存在;硅酸铝增强纤维与镁合金基体之间形成了较强界面结合,界面微观结构比较理想。力学性能测试表明,与AZ91D基体合金相比,复合材料的室温抗拉强度提高了约18%,弹性模量提高了约58%。     

Tribological investigation of Zamak alloys reinforced with alumina (Al2O3) and fly ash

ABSTRACT

In this study, zinc aluminum alloy (Zamak) (ZA-27) composites reinforced by different weight fractions of fly ash, alumina (Al₂O₃), or both particles were produced using compo-casting technique. The composites were subjected to hardness and wear tests. The hardness of the composites increases with increase of the weight fractions of reinforcements. In wear test, the composites were examined under dry sliding conditions using pin on disc apparatus. The wear results revealed that the wear resistance increases with increase of the weight fractions of reinforcements. However, the effect of fly ash particles on the wear resistance of the produced composites is more statistically significant than the effect of Al₂O₃ particles. The morphology of the composites was examined using scanning electron microscopy (SEM) after the test. The SEM images revealed the existence of adhesion and delamination wear mechanism.     

Optical enhancement by back reflector with ZnO:Al2O3(AZO) or NiCr diffusion barrier for amorphous silicon germanium thin film solar cells

Different composite films, including Al, Ag/NiCr/Al and Al₂O₃-doped ZnO (AZO)/Ag/NiCr (AZO)/Al, were utilized as the back reflectors for p-i-n hydrogenated amorphous silicon germanium (a-SiGe:H) thin film solar cells. The experimental results indicated that the AZO leyer between silicon layers and Ag/NiCr/Al back reflector was effect in improving solar cell performance, mainly owing to an increase in short-circuit current density (J_sc) of the solar cells. In addition, the thickness of AZO film could strongly affect the J_sc. The highest solar cell performance was achieved at the AZO thickness of about 90 nm. A nickel-chromium (NiCr) or AZO film was inserted between Ag and Al as a diffusion barrier against mutual diffusion of them, the similar performances of solar cells were achieved. So AZO/Ag/NiCr (AZO)/Al could be utilized as an advanced AZO/metal back reflector for p-i-n a-SiGe:H solar cells.