Investigation on diffusion bonding characteristics of SiC particulate reinforced aluminium metal matrix composites (Al/SiCp-MMC)

Joining characteristics of SiC particulate reinforced aluminium metal matrix composites (Al/SiC_p-MMC) were investigated by vacuum diffusion bonding process. The joining performances of the similar and dissimilar composites were studied, and the influences of SiC_p volume percentage and the insert alloy layer on bonding quality and properties of the bonded joints were also estimated. The experimental results indicate that the strength of vacuum diffusion bonded joints decreases with increasing SiC_p volume percentage, and obtaining satisfactory bonding quality in the diffusion bonded joints of the dissimilar Al/SiC_p-MMC is much more difficult than that of the similar Al/SiC_p-MMC. Moreover, the results still manifest that the diffusion bonding either for the similar or for the dissimilar Al/SiC_p-MMC, the suitable insert alloy layer can improve evidently the joining quality of joints, and the strength of diffusion bonded joints corresponding to using the insert alloy layer is apparently higher than that of no insert layer.     

SiC_P/Al基复合材料在等径角挤扭变形中的界面原子扩散行为

为了研究金属基复合材料在剧烈塑性变形(SPD)过程中增强颗粒与金属基体的界面连接机制,通过等径角挤扭(ECAP-T)工艺在较低温度下制备块状10wt%SiCP/Al基复合材料,并对经过1、2和4道次ECAP-T变形的SiC颗粒与纯Al之间的界面反应以及元素扩散进行了研究。通过TEM和XPS研究了界面和元素扩散,结果表明:即使在较低的外界制备温度下,Al和SiC颗粒表面的SiO2层也能够发生反应,形成主要由Al2O3组成的界面层。相比理论计算值,ECAP-T变形可以将Al的扩散系数提高约1016倍,增强扩散的原因主要是ECAP-T变形促使界面温度升高,且在铝基体内产生空位、位错和晶界等高密度晶格缺陷。     

连续分布界面相对SiCp/Al复合材料热导率影响的数值模拟

采用有限元方法对SiCp/Al复合材料的导热性能进行了数值模拟, 建立了含界面相颗粒增强铝基复合材料测试模型, 研究了不同界面相种类、厚度对复合材料热导率的影响。结果表明: 当界面相与SiC/Al结合理想时, 且界面相在颗粒表面呈连续分布时, 复合材料热导率随着界面层热导率的增加而增大, 但增加的幅度由快变慢; 复合材料热导率随界面层厚度的变化取决于界面层厚度t与颗粒粒径a的比值, 当t/a很小或t/a较大时, 热导率随界面层厚度的变化很小, 当t/a较小时, 热导率随界面层厚度的变化则与界面层热导率有关。     

A review on conventional and nonconventional machining of SiC particle-reinforced aluminium matrix composites

Among the various types of metal matrix composites, SiC particle-reinforced aluminum matrix composites (SiC_p/Al) are finding increasing applications in many industrial fields such as aerospace, automotive, and electronics. However, SiC_p/Al composites are considered as difficult-to-cut materials due to the hard ceramic reinforcement, which causes severe machinability degradation by increasing cutting tool wear, cutting force, etc. To improve the machinability of SiC_p/Al composites, many techniques including conventional and nonconventional machining processes have been employed. The purpose of this study is to evaluate the machining performance of SiC p/Al composites using conventional machining, i.e., turning, milling, drilling, and grinding, and using nonconventional machining, namely electrical discharge machining (EDM), powder mixed EDM, wire EDM, electrochemical machining, and newly developed high-efficiency machining technologies, e.g., blasting erosion arc machining. This research not only presents an overview of the machining aspects of SiC_p/Al composites using various processing technologies but also establishes optimization parameters as reference of industry applications.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00313-2     

Heat treatment and wear characteristics of Al/SiCp composites fabricated by duplex process

This study was undertaken to investigate the effects of alloying elements and heat treatment on the microstructures, wear resistance, and heat resistance of Al–Si–Cu–Mg–(Ni)/SiC_p composites fabricated by a duplex process that consists of squeeze infiltration (1st step) followed by squeeze casting (2nd step). This duplex process produces a homogeneous distribution of SiC_p in Al alloy. The hardness of the composites increased with decrease in SiC_p size, and also with Ni addition in both the as-cast and the as-aged specimens. Compared with 5 and 10 μm SiC_p reinforced Al composites, the aging time to obtain the peak hardness was shortened for 3 μm SiC_p reinforced Al composite, because of higher density dislocations on the periphery of SiC_p in the matrix. However, the Al composite reinforced with 10 μm SiC_p was found to have the lowest wear amount as compared with 3 and 5 μm SiC_p composites. The amount of wear in Al/SiC_p composites decreased with increase of the sliding speed because abrasive wear occurred under low sliding speed and block-type wear debris occurred under high sliding speed.     

基于界面结构调控硅粒子/聚偏氟乙烯复合材料介电性能

为降低硅粒子/聚偏氟乙烯(Si/PVDF)复合材料体系的介电损耗(tanδ)及提高其击穿强度(E_b),采用高温氧化及聚苯乙烯(PS)包覆法,制备出两种分别具有SiO₂单壳及SiO₂@PS双壳的Si@SiO₂和Si@SiO₂@PS核壳结构粒子。采用FTIR、XRD和TEM分析测试了核壳粒子的壳层结构。分析测试证明,Si粒子表面存在SiO₂和PS壳层。结果表明,相比未改性Si/PVDF复合材料,SiO₂外壳显著降低和抑制了Si@SiO₂/PVDF复合材料的tanδ和漏导电流;PS层改进了Si/PVDF复合材料的界面相容性,促进其在基体中均匀分散。双壳结构Si@SiO₂@PS/PVDF复合材料呈现出最低tanδ和最高E_b。Si@SiO₂/PVDF和Si@SiO₂@PS/PVDF复合材料介电性能的改善归因于Si表面SiO₂及SiO₂@PS绝缘界面层有效阻止了半导体Si粒子间的直接接触,极大抑制了损耗。此外,Si/PVDF复合材料相界面缺陷减少及界面相容性改善均有效降低了局部电场畸变,提高了体系的E_b。Si@SiO₂@PS/PVDF复合材料在1 kHz下介电常数高达48,tanδ低至0.07,E_b约为6 kV/mm,在微电子器件及电力设备领域具有潜在的应用价值。      

CVD SiC fiber-reinforced barium aluminosilicate glass—ceramic matrix composites

Unidirectional CVD SiC (SCS-6) monofilament reinforced BaOAl₂O₃2SiO₂(BAS) glass—ceramic matrix composites have been fabricated by a tape lay-up method followed by hot pressing. The glass matrix flows around fibers during hot pressing resulting in nearly fully dense (95–98%) composites. Strong and tough composites having first matrix cracking stress of 250–300 MPa and ultimate flexural strength as high as 900 MPa have been obtained. Composite fracture surfaces showed fiber pullout with no chemical reaction at the fiber/matrix interface. From fiber push out, the fiber/matrix interfacial debond strength and the sliding frictional stress were determined to be 5.9 ± 1.2 MPa and 4.8 ± 0.9 MPa, respectively. The fracture surface of an uncoated SiC (SCS-0)/BAS composite also showed fiber/matrix debonding, fiber pullout, and crack deflection around the fibers implying that the SiC fibers may need no surface coating for reinforcement of the BAS glass-ceramic. Applicability of micromechanical models in predicting the first matrix cracking stress and the ultimate strength of these composites has also been examined.     

Determination of interface properties from experiments on the fragmentation process in single-fiber composites

This paper attempts to quantify the fracture properties (strength and toughness) of the fiber–matrix interface in composites, using the fragmentation process and debonding growth for HI-Nicalon™ SiC single-fiber and T300 carbon single-fiber epoxy (Bisphenol-A type epoxy resin with triethylenetetramine (TETA) as curing agent) composite systems. This method is based on the numerical modeling for the microscopic damage and fragmentation process in single-fiber composite (SFC) tests, with a cohesive zone model (CZM). For the HI-Nicalon™ SiC single-fiber epoxy composite in which the major damage near a fiber break is interfacial debonding, interface properties were reasonably determined as (T_II,max, G_IIc) = (75 MPa, 200 J/m²). In contrast, for T300 carbon single-fiber epoxy composite, we could not determine unique interfacial properties, since the variation of the cohesive parameters hardly affects the microscopic damage process due to the transition to the damage pattern dominated by matrix cracking.     

Fatigue properties of particle-reinforced metal-matrix composites

Fatigue-lifetime behaviour has been examined for extruded 6061 aluminium alloy composites reinforced with 15 vol% SiC and 10 vol% Al₂O₃ particles. The peak particle sizes are at about 4.5 and 6 μm. Within measured S- N curves the fatigue lifetime at given stress amplitudes of SiC_p/AA6061 is superior to that of Al₂O_3p/AA6061 in the low-cycle fatigue region as well as in the high-cycle fatigue region. These results are discussed by consideration of theoretically evaluated crack propagation curves.     

无压浸渗法制备氧化态SiC颗粒增强铝基复合材料

研究了SiC颗粒在1000~1200℃的氧化行为, 其氧化增重率与保温时间符合抛物线规律, 氧化增重受扩散过程控制, 氧化激活能为219 kJ/mol. 采用预氧化处理的SiC颗粒为增强体, 含Si、Mg的铝合金为基体, 通过无压浸渗方法制备了SiC_p/Al复合材料, 分析了复合材料的微观组织与界面形貌, 探讨了无压浸渗机理. 复合材料中颗粒分布均匀, 无偏聚现象. 材料制备过程中存在界面反应, SiC颗粒表面的氧化层与铝合金中的Mg、Al反应形成了一定数量的MgAl₂O₄. 界面反应的存在提高了润湿性, 促进了无压自发浸渗.     

FABRICATION AND CHARACTERIZATION OF Cu-SiCp COMPOSITES FOR ELECTRICAL DISCHARGE MACHINING APPLICATIONS

Cu-SiC_p composites made by the powder metallurgy method were investigated. To avoid the adverse effect of Cu-SiC_p reaction, sintering was controlled at a reaction temperature less than 1032 K. Electroless plating was employed to deposit a copper film on SiC_p powder before mixing with Cu powder in order to improve the bonding status between Cu and SiC particles during sintering. It was found that a continuous copper film could be deposited on SiC_p by electroless copper plating, and a uniform distribution of SiC_p in Cu matrix could be achieved after the sintering and extrusion process. The mechanical properties of Cu-SiC_p composites with SiC_p contents from 0.6 to 10 wt% were improved evidently, whereas electrical properties remained almost unchanged as compared with that of the pure copper counterpart. In the electrical discharge machining (EDM) test, the as-formed composite electrodes exhibited a character of lower electrode wear ratio, justifying its usage. The optimum conditions for EDM were Cu-2 wt% SiC_p composite electrode operating with a pulse time of 150 μsec.     

Composite strengthening in 6061 and Al-4 Mg alloys

Metal matrix composites using prealloyed 6061 Al (containing 1% Mg) and elemental blend Al-4 Mg alloys with 10 vol% SiC particulate reinforcements were fabricated using powder metallurgy techniques. The consolidation of the powders was effected by the section rolling process recently developed at the Defence Metallurgical Research Laboratory. This process involves the successive steps of cold isostatic pressing, vacuum sintering and special canning followed by section rolling. This resulted in a high-integrity composite product. An interfacial layer containing magnesium-rich precipitates observed in both the composites is suggested to be the major reason for the low (compared to the value predicted by the rule of mixtures) modulus and strength values in these composites. This layer also appeared to promote interfacial failure at the alloy/SiC interface. The Al-4 Mg alloy, which is known to be non-heat treatable, was found to respond to precipitation hardening heat treatment in the composite. The enhanced generation of dislocations due to the presence of SiC, promoting a more homogeneous precipitation of the second phase and the possibility of an inhomogeneous distribution of magnesium (as a result of elemental blending) are suggested to be the major factors responsible for rendering the Al-4 Mg alloy amenable to the precipitation hardening heat treatment.     

Corrosion behavior of Al–60 vol.% SiCp composites in NaCl solution

In this study, corrosion behavior of pure Al and Al–4 wt.% Mg alloy matrix composites, comprising 60 vol.% SiC particles, has been investigated. Composites were produced by pressure infiltration technique at 750 °C. The corrosion tests were carried out in 3.5 wt.% NaCl environment up to 28 days. The weight loss of the composites increased with increasing duration time up to 3–5 days then remained constant. Scanning electron microscopy (SEM) analysis showed that Al–4 wt.% Mg alloyed matrix composite exhibited higher corrosion resistance than pure Al matrix composite although potentiodynamic polarisation measurements showed higher i_corr values of Al–4 wt.% Mg alloyed matrix composites than pure Al matrix composites. Experimental results revealed that precipitation of Mg₂Si as a result of reaction between Al–Mg alloy and SiC particle has a beneficial effect on corrosion resistance of Al–4Mg alloy matrix composites due to interruption of the continuity of the matrix channels within the pressure infiltrated composites.     

LIQUID PHASE SINTERED METAL MATRIX COMPOSITE MATERIALS

Iron-base and aluminum-base composite materials reinforced with various ceramic particulates have been fabricated via powder metallurgy and liquid phase sintering. The advantage of this manufacturing route is that conventional powder metallurgy processing equipment can be used to fabricate metal matrix/ceramic composites. Furthermore, this approach makes it possible to manufacture these composites to near-net-shape. A number of matrix/ceramic combinations have been examined: Fe-C-Si and Fe-Cu with ZrO₂ additions and a Al-Cu-Si-Mg alloy with SiC or Al₂O₃ additions. The interfacial structures were characterized and found to play a significant role in controlling the properties of the composites. Reinforcement was observed in several systems. However, a glassy interfacial layer forms when Si additions and oxide reinforcements are present; the resultant particle/matrix bond strength is weak and reinforcement.     

Al含量对漂珠/镁合金可溶复合材料组织与性能的影响

采用搅拌铸造法制备了不同Al含量下的漂珠（FAC）/镁合金可溶复合材料。采用金相显微镜、SEM及XRD观察分析了FAC/镁合金可溶复合材料的微观组织、溶解表面形貌及溶解产物的物相组成,采用力学性能试验机研究了复合材料的压缩性能,采用电化学工作站对复合材料进行电化学性能测试,在常温及水浴锅内进行复合材料在不同温度下的KCl溶液中的溶解试验。结果表明：该FAC/镁合金可溶复合材料主要由α-Mg基体相、β-Mg₁₇Al₁₂相、Mg₂Si相和MgO相组成。随着Al含量的增加,FAC/镁合金可溶复合材料的溶解速率先变快后减慢,在80℃的3wt% KCl溶液中,含15wt% Al的FAC/镁合金复合材料溶解速率最快,为56 mg/（h·cm²）。Al-FAC/镁合金可溶复合材料的抗压强度随Al含量的增加先提高后下降,四种合金的抗压强度均大于300 MPa,最高强度达到372 MPa。     

SiC对反应烧结多孔Al2TiO5的物相及组织性能影响

本研究以γ-AlOOH、TiO₂和SiC为原料, 通过无压反应烧结制备了Al₂TiO₅多孔材料, 分析比较了SiC粒度和含量对合成产物的物相组成、显微组织、抗压强度、孔隙率和孔径分布的影响。结果表明: 反应产物的物相组成为Al₂TiO₅、Al₆Si2O₁₃、TiC、SiO₂和Al₂O₃, 还有少量未反应的TiO₂。SiC与TiO₂反应生成TiC和SiO₂, TiC颗粒弥散分布于多孔材料壁面或者骨架中, 而SiO₂进一步与γ-AlOOH分解出的Al2O3反应生成Al₆Si₂O₁₃晶须, 晶须交错分布于Al₂TiO₅颗粒之间或者孔洞中, 与TiC颗粒一起提高复合材料的抗压强度, 特别是采用小粒径SiC时, 对抗压强度的改善效果更加显著; 添加大粒径SiC后, 改变原有颗粒堆积状态, 可提高复合材料的孔隙率。但当SiC含量超过5wt%时, 因为生成较多低熔点的SiO₂, 部分填充于多孔材料的孔隙中, 部分则分布于Al₂TiO₅晶粒之间, 既减小孔隙率, 又降低晶粒间结合强度和试样的抗压强度。     

陶瓷添加物对Ti_3SiC_2基复合材料抗氧化性的影响

为研究陶瓷添加物对Ti3SiC2基复合材料性能的影响,首先,采用反应热压烧结法制备了Ti3SiC2材料及陶瓷添加物含量均为30wt%的SiC/Ti3SiC2、Al2O3/Ti3SiC2和MgAl2O4/Ti3SiC2复合材料。然后,测试了材料的力学性能和导电性,在1 373~1 773K温度范围内对Ti3SiC2基复合材料的抗氧化性进行了研究,并对其烧结试样的物相组成和显微结构等进行了表征。结果表明:Ti3SiC2在高温氧化后的主要产物为TiO2和SiO2;氧化层分为内外2层,内层由TiO2与SiO2这2相混合组成,外层为TiO2;氧化层中存在大量显气孔,结构较为疏松,导致抗氧化性较差。与Al2O3/Ti3SiC2和MgAl2O4/Ti3SiC2复合材料相比,SiC/Ti3SiC2复合材料具有更好的抗氧化性。     

改性纳米SiO2/硅橡胶复合材料的制备及性能

为提高纳米SiO₂在硅橡胶（SR）基体中的分散性及两相间的界面结合力,设计以羟基硅油（HSO）和γ-甲基丙烯酰氧基丙基三甲氧基硅烷（KH570）为纳米SiO₂的表面封端改性剂,并将改性SiO₂与双组份加成型液体SR复合得到改性纳米SiO₂/SR复合材料。通过一系列表征手段对改性纳米SiO₂的形貌结构及其在乙醇中的分散性等进行分析,研究了改性纳米SiO₂对纳米SiO₂/SR复合材料的断面形貌、力学性能及热稳定性的影响。结果表明:KH570成功接枝到纳米SiO₂表面并与SR基体间形成化学键。当HSO协同KH570改性纳米SiO₂时,可有效改善纳米SiO₂在SR基体中的分散性能及纳米SiO₂与SR两相间的界面结合性能,并显著提高纳米SiO₂/SR复合材料的力学性能和热稳定性。将SiO₂∶HSO∶KH570以质量比为2.0∶0.2∶0.6处理的改性纳米SiO₂粒子,得到的改性纳米SiO₂/SR复合材料起始热分解温度提高了230℃。当SiO₂∶HSO∶KH570质量比为2.0∶0.2∶0.45时,改性纳米SiO₂/SR复合材料的拉伸强度和断裂伸长率分别提高了约1倍。      

Comparison of oxidation behaviors of 3D C/PyC/SiC and SiC/PyC/SiC composites in an O2-Ar atmosphere

Oxidation behaviors of three-dimensional woven C/PyC/SiC and SiC/PyC/SiC prepared by CVI processing were investigated in an O₂-Ar atmosphere at 600 °C, 900 °C and 1200 °C, respectively, by using thermogravimetric analysis. After machining, both composites should be protected by CVD SiC coating, which was demonstrated effectively in improving the oxidation resistance of both composites. The oxidation behavior of SiC/PyC/SiC was different from that of C/PyC/SiC. The oxidation kinetics of C/PyC/SiC was controlled by the rate of the reaction between carbon and oxygen at 600 °C and by the oxygen diffusion through the coating microcracks at 900 °C. The oxidation kinetics of SiC/PyC/SiC at both 600 °C and 900 °C were assumed to be controlled by the oxygen diffusion through channels of coating and matrix defects and looped pipelines instead of PyC interphase. At 1200 °C, the oxidation was controlled by oxygen diffusion through the SiO₂ scale, which took place mainly on the surfaces of both composites.     

Abrasive wear of Al2O3-reinforced aluminium-based MMCs

The effects of volume fraction, Al₂O₃ particle size and effects of porosity in the composites on the abrasive wear resistance of compo-casting Al alloy MMCs have been studied for different abrasive conditions. It was seen that porosity in the composites is proportional to particle content. In addition, process variables like the stirring speed, and the position and diameter of the stirrer affect of the porosity content in a way similar to that observed for particle content. In addition, the abrasive wear rates of composites decreased more rapidly with increase in Al₂O₃ volume fraction in tests performed over 80 grade SiC abrasive paper than in tests conducted over 220 grade SiC abrasive paper. Furthermore, the wear rates decreased with increase in Al₂O₃ size for the composites containing the same amount of Al₂O₃. Hence, it is deduced that aluminium alloy composites reinforced with larger Al₂O₃ particles are more effective against abrasive wear than those reinforced with smaller Al₂O₃ particles. At the same time the results show that the beneficial effects of hard Al₂O₃ particles on wear resistance far surpassed that of the sintered porosity in the compocasting metal-matrix composites (MMCs). Nevertheless, the fabrication of composites containing soft particles such as graphite favors a reduction in the friction coefficient. For this reason graphite and copper were used in the matrix in different amounts to detect their effect on wear resistance. Finally, it was seen that wear rate of the composites decreased considerably with graphite additions.