粉末增塑挤压制备Al_2O_3/Fe复合型蜂窝材料的组织与性能

为制备性能优良的Al_2O_3/Fe复合型蜂窝材料,首先以316L合金粉末、Al_2O_3粉末和黏结剂为原料,通过粉末增塑挤压及在1 200℃氩气气氛中烧结2h获得了Al_2O_3/Fe复合型蜂窝材料;然后,借助SEM、XRD及万能试验机研究了添加Al_2O_3对Al_2O_3/Fe复合型蜂窝材料组织与性能的影响。结果表明:金属粉末颗粒在烧结过程中结合形成γ-Fe基体网状组织,表面有呈多边形几何状形态的Cr_2O_3形成;添加少量的Al_2O_3可以抑制Cr从基体中析出,降低表面Cr_2O_3的含量,使金属颗粒烧结结合更为紧密,组织表面更加光滑;随着Al_2O_3含量的增加,蜂窝材料表面与催化活性涂层的结合能力增强,复合型蜂窝材料的抗压强度先升高后降低;在Al_2O_3含量为5.0wt%时,抗压强度达26 MPa。所得结论表明5.0wt%Al_2O_3/Fe复合型蜂窝材料力学性能最佳,表面涂覆性能优良。     

Synthesis of an Al2O3/Al co-continuous composite by reactive melt infiltration

The route for the fabrication of an Al₂O₃/Al co-continuous composite by reactive melt infiltration was investigated using scanning electron microscopy, energy dispersive X-ray microanalysis and X-ray diffraction analysis. It was found that in the process of molten aluminium infiltration into the SiO₂ preform, the chemical reaction of 3SiO₂ + 4Al → 2Al₂O₃ + 3Si occurred at the infiltration front, and generated a transition zone containing a new type of continuous porosity about 100 μm in width. The reaction continued with further infiltration of molten aluminium alloy into this porosity which reacted with the residual SiO₂ until all the SiO₂ was transformed into Al₂O₃. A comparison was made between this route and that by direct infiltration of molten aluminium alloy into the open porosity of an Al₂O₃ preform. As a result of the increased wetting ability of the molten aluminium alloy by the chemical reaction, reactive melt infiltration took place at a higher rate for the SiO₂ preform than that for the direct infiltration of the Al₂O₃ preform. A fracture surface examination demonstrated a toughening effect provided by the continuous aluminium alloy in the composite.     

Evaluation of microstructure and mechanical properties of Al/Al2O3/SiC hybrid composite fabricated by accumulative roll bonding process

In this investigation, a new kind of metal matrix composites with a matrix of pure aluminum and hybrid reinforcement of Al₂O₃ and SiC particles was fabricated for the first time by anodizing followed by eight cycles accumulative roll bonding (ARB). The resulting microstructures and the corresponding mechanical properties of composites within different stages of ARB process were studied. It was found that with increasing the ARB cycles, alumina layers were fractured, resulting in homogenous distribution of Al₂O₃ particles in the aluminum matrix. Also, the distribution of SiC particles was improved and the porosity between particles and the matrix was decreased. It was observed that the tensile strength of composites improved by increasing the ARB passes, i.e. the tensile strength of the Al/1.6 vol.% Al₂O₃/1 vol.% SiC composite was measured to be about 3.1 times higher than as-received material. In addition, tensile strength of composites decreased by increasing volume fraction of SiC particles to more than 1 vol.%. Scanning electron microscopy (SEM) observation of fractured surfaces showed that the failure mechanism of broken hybrid composite was shear ductile rupture.     

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.     

Microstructure and physical properties of Al/diamond composite fabricated by pressureless infiltration

Abstract

The Al/diamond composite was fabricated using a pressureless infiltration method. The microstructure and physical properties of the composite were investigated. The composite has a very low coefficient of thermal expansion (CTE) of 3·9 × 10^?6 K^?1. The thermal conductivity (TC) of the composite is 12% higher than that of the Al alloy matrix. The lower TC of the composite than the expected value was attributed to the existence of interfacial low conducting phases and the porocity of the composite.     

Synthesis of Al2O3-WC composite powder by SHS process

Al₂O₃-WC composite powder was synthesized by self-propagating high-temperature synthesis using Al powder as a reducing agent. WC, W₂C and Al₂O₃ were concurrently formed in WO₃-Al-C system. It was found that the complete reaction was achieved with excessive addition of carbon and appropriate processing parameters such as degree of dilution, particle size of aluminum, pellet compaction pressure and carbon source. The final product which was leached by 50% 1 : 4 HNO₃ + HF diluted solution was consisted of Al₂O₃-55wt%WC having 2–3 m of mean particle size.     

Net-shape forming of bi-continuous Al2O3/Al composite by displacement reaction

Displacement reaction constitutes a novel and specialized reaction-induced processing technique which allows the fabrication of a composite in net-shape. Composite containing α-Al₂O₃ and Al, in which both the phases are continuous, were formed by a displacement reaction between silica shapes and molten aluminium isothermally at temperatures between 1173 and 1573 K. Soaking periods varied between 0.2 and 48 h at each of these peak temperatures. The course of reaction was followed by microstructure evaluation of the products as observed at different time intervals of reaction processing. These specimens were analysed for phase evolution by XRD, extent of reaction and microstructure by optical microscopy and composition profile across the reaction zone by electron probe microanalyzer (EPMA). The product obtained on completion of reaction consisted of 74% α-Al₂O₃ and 26% Al (Si) by volume, and the phase were co-continuous. Grain size of % α-Al₂O₃ increased with an increase in forming temperature. The remarkable features of this forming technique are that the product has the same shape as that of the silica preform and it undergoes an isotropic linear shrinkage of barely over 1%. The formation of the composite and the microstructure evolution are discussed. Some properties of the product are presented.     

Fatigue damage development in Al2O3/Al composite

Fatigue damage development in two aluminium matrix (Al7SiO.6Mg and Al5Si-3Cu1Mg) composites reinforced with discontinuous Al₂O₃ fibres has been monitored by means of acoustic emission (AE). The AE signals (RMS) recorded during the tests clearly exhibit three distinct stages which correspond to crack initiation, dominant crack formation and stable propagation. Generally speaking, the cracks initiated at a high load level form close together and a dominant crack forms easily. By contrast, at a low load, initiated cracks are widely separated and the formation of a dominant crack is difficult. If there are large defects in the composite, the first stage is absent, even at low load. In the first stage, little change in microstructure and modulus of the composite is observed; in the second, fibre fracture, interface debonding and matrix cracking occur and there are often sinusoidal cracks in the matrix; in the last stage, the principal characteristic is stable propagation of the dominant crack. The degradation of the elastic modulus of the composite in the last two stages is small.     

Atomic structure of AlN/Al2O3 interfaces fabricated by pulsed-laser deposition

The atomic structure of AlN/Al₂O₃ interface fabricated by pulsed laser deposition is characterized by high-resolution transmission electron microscopy (HRTEM) combined with systematic multi-slice HRTEM image simulations. It is found that the AlN film deposited on a (0001) Al₂O₃ substrate grows epitaxially with the orientation relationship of (0001)AlN//(0001) Al₂O₃ and [ ]AlN//[ ]Al₂O₃, with an atomically sharp interface. The observed interface showed best correspondence with the rigid structural model that AlN is terminated by Al at the interface, while the Al₂O₃ substrate is terminated by O. Detailed structural analysis indicates that Al sites at the interface are coordinated by both oxygen and nitrogen in this model, with similar coordination environment in AlN. This favored coordination state at the interface may stabilize the AlN/Al₂O₃ interface.     

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/Al复合材料的界面结构特征

利用高分辩透射电子显微镜研究挤压铸造法制备的亚微米 Al 2O 3颗粒增强 Al 基复合材料的界面微观结构。结果表明 : Al基体的 (200) 和 (111) 面优先沿 Al 2O 3颗粒表面生长 , 在复合材料界面处 Al 基体与 Al 2O 3颗粒具有 Al (200) ∥Al 2O 3 (101 2) 、Al [011 ] ∥Al 2O 3 [0221 ] 的晶体学位向关系并形成半共格界面 , 且界面存在 Al (111) / / Al 2O 3 ( 1120) 的共格关系。界面干净无任何反应物。接近界面的 Al 基体中出现了柏氏矢量为 b= 1/ 3 [ 111 ] 弗兰克不全刃位错 , 该刃位错引起界面附近基体中明显的晶格应变场 , 位错周围晶格变形场的范围约为 20～30 层原子面宽度 , 而在 Al 2O 3颗粒靠近界面的区域中未观察到位错等缺陷。并从晶体学角度对界面的形成机制进行了分析。     

Sliding wear of Al2O3P/6061 Al composite

The mild sliding wear behaviour of a 15 vol % Al₂O_3P/6061 Al composite has been investigated by using a pin-on-disc reciprocating sliding machine. The composite has been shown to exhibit an excellent wear resistance as compared to the unreinforced matrix alloy. The wear rate of the composite under dry wear conditions with a 12N load is approximately one tenth of that in the 6061 aluminium alloy. The wear rate of the composite under lubrication with 15W/40 gear oil under a 100N load is only one thousandth ofthat in the 6061 aluminium alloy.The dry wear resistance of an over-aged sample is shown here to be better than a peak aged or under-aged sample when the composite was aged at 160°C. The coefficient of friction of the composite was approximately 0.5–0.6 under dry conditions and 0.07 in lubricated wear experiments.In the initial stage, the worn surface of the composite under dry conditions is primarily composed of ploughed grooves and ductile tear. The composite makes a conducting contact with the steel pin. The worn surface is composed of compacted powder and the contact potential gradually increases when the period of the wear experiment goes beyond 2 h.     

Synthesis of Al2O3 matrix composites by reactive infiltration

Reactive infiltration of a NiO-base blended powder with molten aluminium was attempted at 1673 K in order to obtain Al2O3 matrix composites containing a dispersion of Al3Ni, AlNi and/or AlNi3. The NiO powder was barely infiltrated by the molten aluminium after a 3600 s holding time at 1673 K. A continuous layer of Al2O3 was observed to exist at the infiltration front, which prevented any further infiltration. TiB2 particles were added to the NiO powder in order to absorb the heat of reaction between NiO and aluminium. When the TiB2 particle content in the [NiO+TiB2] powder blend was greater than 20 vol%, spontaneous infiltration occurred completely. Thus, it was shown that the addition of the TiB2 particles assisted in the spontaneous infiltration. The specimens produced by the in situ reaction consisted of Al2O3, TiB2 and Al3Ni. Al3Ni was mainly located between the TiB2 and Al2O3. The effect of the TiB2 addition on the infiltration kinetics was to decrease the maximum attainable temperature caused by the exothermic reaction. This in turn prevented the formation of a continuous Al2O3 film at the infiltration front. This resulted in the production of pathways for the infiltration of the molten aluminium and made possible the complete infiltration. This revised version was published online in November 2006 with corrections to the Cover Date.     

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.     

无压熔渗制备SiCp/Al复合材料的界面改性研究进展

研究表明,SiCp/Al间界面润湿性的好坏是采用无压熔渗法制备高体积分数SiCp/Al复合材料的最关键因素,也是影响复合材料性能的主要因素.本文从界面反应和界面润湿性角度出发,综述了近几年来国内外关于SiCp/Al复合材料的界面研究情况.     

Microstructure and infiltration kinetics of Si3N4/Al–Mg composites fabricated by pressureless infiltration

Si₃N₄/ Al–Mg composites reinforced by ceramic interpenetrating network structure had been fabricated via pressureless infiltration technology. The matrix and the reinforcement phase, form an interconnected interpenetrating network structure. The Al–Mg/Si₃N₄ system exhibits an excellent wettability under moderate conditions. The increasing of Mg content (2–10 wt%) resulted in an increased amount of infiltration, once Mg content beyond 10 wt% has an adverse effect. Light chemical reaction occurs in the interface of Al–Mg/Si₃N₄ system and the reaction productions reduce the surface tension of melt and impulse the advance of infiltration. Infiltration temperature and infiltration time were the key parameters, which turn into the infiltration impetus. The appropriate infiltration temperature is 1050 °C and the corresponding infiltration time is 15 min, prolonging the infiltration time continuously has no significance.     

Nickel aluminide (Ni3Al) fabricated by reactive infiltration

Nickel aluminide Ni₃Al in the single phase form, with grain size 10 m, porosity 5%, tensile strength 425 MPa, modulus 92 GPa and ductility 9.5% at room temperature, was fabricated by reactive infiltration at 800 °C of liquid aluminium into a porous preform containing 78 vol % nickel and made by sintering 3–7 m size nickel particles. Without sintering, the preform contained 58 vol % nickel and reactive infiltration resulted in an aluminium-matrix NiAl₃ particle ( 50 m size) composite and extensive growth of Ni-Al needles from the preform to the excess liquid aluminium around the preform.