两种粒径颗粒混合增强铝基复合材料的导热性能

选用粒径为20μm 和60μm 的SiC 颗粒, 采用挤压铸造方法制备了基体分别为工业纯铝L2 、LD11(Al-12 %Si) 和AlSi20 (Al-(18～21) %Si) 的复合材料, 研究了材料的导热性能。在等比表面积的基础上, 提出了等效颗粒直径的概念, 解决了两种粒径颗粒混合增强铝基复合材料导热率的预测问题。结果表明, SiC_P/ Al 复合材料具有较为优异的导热率, 且LD11 基与AlSi20 基复合材料的导热率大于基体合金的导热率, 这与颗粒的等效直径大于临界粒径且颗粒导热率大于基体导热率有关;但复合材料的导热率随着基体中Si 含量的增加而降低。     

高体积分数SiC_p/Al-Si复合材料的微观组织与导热性能

通过对SiC颗粒进行表面改性处理,并向Al基体中添加Si元素合金化采用热压烧结方法制备了Al-10Si-50%(质量分数)SiC复合材料,研究了复合材料的微观组织和导热性能。结果表明,复合材料中SiC颗粒在基体中分布均匀,复合材料组织致密;SiC-Al界面清晰、平直,无过渡层和其它附加物,复合材料界面结合良好;复合材料导热性能优异,其热导率可达189W/(m·K),能够满足电子封装材料的日常使用要求。     

颗粒增强Al基复合材料的制备工艺及凝固过程

着重研究了颗粒增强Al基复合材料的搅拌法制备工艺及凝固过程。 通过对熔体搅拌法制备颗粒增强金属基复合材料的工艺优化进行探讨,最终用最简单的工艺过程制备出组织致密、颗粒分布均匀、界面结合良好的SiC、Al_2O_3、SiO_2颗粒增强Al-4％Mg复合材料。 SiC、Al_2O_3、SiO_2颗粒增强Al-4％Mg复合材料在等轴晶凝固条件下,颗粒被等轴晶排斥,出现颗粒推移,晶粒直径越大,颗粒分布越不均匀。在试验分析基础上,提出了颗粒推移的强烈程度由晶粒与颗粒的质量比决定的观点:同种颗粒,其直径越大,颗粒推移越不强烈;同样直径不同种类的颗粒,其密度越大,颗粒推移越不强烈。 AlO_3颗粒增强 Al-4％Mg复合材料的凝固组织中的显微缩孔是由颗粒加入导致熔体粘度增加、颗粒堵塞枝晶间的补缩流动通道以及颗粒与基体合金的热膨胀系数的差异三种因素引起的。由于气孔易在SiC颗粒表面形核,或者SiC颗粒与基体结合较弱,使得SiC颗粒增强Al-4％Mg复合材料比Al_2O_3颗粒增强Al-4％Mg复合材料易形成显微缩孔。对SiO_2颗粒增强Al-4％Mg复合材料来说,SiO_2颗粒与基体间发生了界面反应,一定量的Si溶入了基体,增大了基体的凝固潜热,从而提高了基体合金凝固时的补缩流动能力,所以SiO_2(P)/Al-4％Mg复合材料的凝固组织比同样条件下Al_2O_3(P)     

增强体含量对Sip/LD11复合材料热物理性能影响

为研究增强体含量对电子封装用Si颗粒增强铝基复合材料热物理性能的影响,采用挤压铸造法制备了以高纯Si粉为增强体,LD11铝合金为基体,体积分数分别为55%、60%和65%的3种复合材料.利用金相显微镜、热膨胀分析仪、热导率测试仪等多种手段对复合材料的微观组织及热物理性能进行了研究,并对试验结果进行数值模拟.显微组织观察表明,复合材料的铸态组织均匀、致密.通过改变复合材料增强体的含量,复合材料的热膨胀系数介于(8.1～12)×10-6/℃之间可调,热导率大于87.7 W/m·℃,满足电子封装用材料的要求.Sip/LD11复合材料的热膨胀系数介于Rom模型和Turner模型之间,Kerner模型能够更好地预测Sip/LD11复合材料的热膨胀系数.热导率计算结果均大于测试值.     

Sip/Al复合材料导电性能研究及理论计算

摘要：采用挤压铸造专利技术制备了电子封装用Sip/LG5、Sip/LD11、Sip/Al-Si2O,3种可回收再利用的、高体积分数环保型复合材料，探讨了Sip/Al复合材料导电性能的影响因素，并采用理论模型对复合材料电导率进行了理论计算。结果表明，Sip/Al复合材料导电率可达4．42MS/m；Si-A1界面平直、干净、没有反应物产生；基体合金相同时，复合材料的电导率随着增强体颗粒含量增加而下降；颗粒含量相同时，电导率随着基体中合金元素量增加而下降；颗粒大小对电导率影响不明显；复合材料经过退火处理后电导率有所升高。与复合材料电导率的实测值相比较，P.G模型的计算结果和测量值比较接近。     

电子封装用SiCp/Al复合材料的组织与性能

本文选用粒径为20μm和60μm的SiC混合颗粒,采用挤压铸造方法制备了体积分数为70%的SiCp/LD11(Al-12%Si)复合材料.材料组织致密,颗粒分布均匀.复合材料具有低膨胀、高导热的特性和十分优异的力学性能,并且可以通过退火处理进一步降低其热膨胀系数.采用化学镀方法,在复合材料表面涂覆镍层,以其做为底座的二极管满足器件的可靠性测试要求.     

C/SiC复合材料应力氧化失效机理

研究了干氧和湿氧两种气氛、疲劳和蠕变两种应力下C／SiC复合材料在1300℃的应力氧化行为．试验结果和断口形貌SEM分析表明：C／SiC复合材料在疲劳应力下比在蠕变应力下具有更强的抗氧化能力和更长的持续时间；干氧环境中的蠕变试样以C纤维氧化失效为主；水蒸气的存在加剧了SiC基体的氧化，并且使受蠕变应力的C／SiC复合材料以SiC基体氧化失效为主.     

SiCp/Al复合材料的SPS烧结及热物理性能研究

采用纯粉末，通过SPS烧结制备了组织均匀、致密且体积分数高的SiC，／Al电子封装材料．通过对SPS烧结现象的研究，认为该复合材料的SPS烧结过程属于反应性烧结，大部分收缩在极短时间内完成；另外对SiC体积分数和SiC颗粒尺寸对热导率、热膨胀系数的影响进行了研究，发现SiC体积分数越高，复合材料的热导率和热膨胀系数越低；SiC颗粒粒径增大，复合材料的热导率增高，而热膨胀系数减小．     

无压浸渗制备的SiC/Al复合材料的微观组织研究

利用SRD,OM,SEM,TEM等微观结构分析手段,对无压浸渗制备的SiCp/Al复合材料的微观结构进行了研究。结果表明,SiCp/Al复合材料中存在SiC,Al,MgAl2O4,Si和Mgi2Si诸相。在组织中没有粗大的铝硅共晶体针条,铝基体被众多SiC颗粒分割,成为细小的连续的空间网络。在铝基体中分布着Si相及Mg2Si相。透射电子显微镜高分辨像表明,在SiC与铝合金的界面上存在镁铝尖晶石（MgAl2O4）相,没有出现Al4C3相。     

铝基复合材料的制备和组织分析

讨论在制备复合材料过程中颗粒与金属基体之间的润湿性，温度控制以及压力等因素对制备工艺的影响，并结合Al／Si复合材料压力熔渗法制备工艺，通过理论计算与实际实验相结合，确定了合理的制备工艺参数，采用该工艺参数制备的复合材料内部自由孔隙和硅颗粒的分布均匀，基体中的共晶组织可依附在颗粒表面形核生长；同时研究了Al／Si复合材料的特性和断裂行为，通过显微组织分析和断口观察表明，复合材料的断裂行为主要是由于硅颗粒的脆裂性而引起的，并且由此向材料内部延伸最后导致复合材料断裂失效。     

Liquid-phase impact diffusion welding of SiCp/6061Al and its mechanism

Liquid-phase impact diffusion welding (LPIDW) technique was used to join the aluminum matrix composite SiC_p/6061Al. The composite joints welded successfully, gave tensile strength up to 260 MPa and radial deformation below 3%. Analysis of the microstructure and tensile strength of the welded joints showed: (i) the achievement of prominent joint interface between SiC particles and the matrix; (ii) the change of pernicious contact-state from reinforcement (SiC)/reinforcement (SiC) to reinforcement (SiC)/matrix/reinforcement (SiC) of the reinforcement particles; (iii) the disappearance of the harmful microstructure/brittle phase of Al₄C₃ from the welded joint; (iv) the density of dislocation in the matrix next to the interface being higher; (v) the sign of intensively mutual entwisting of dislocation; and (vi) the deformation mainly taking place in the matrix grain. Furthermore, the rapid thermal pressing offered a denser nucleus area for matrix crystal and their deforming matrices around SiC particles engendered intensive aberration, which was favorable for forming nano-grains and for improving the properties of the welded composite joints.     

Microstructure and thermo-physical properties of a SiC/pure-Al composite for electronic packaging

A preform comprised of 70 vol% SiC particles was infiltrated with commercially pure aluminium to produce the electronic packaging composite. A dense and uniform microstructure was found in the composite. The incorporation of high volume fraction of SiC particles led to a reduction of coefficient of thermal expansion while maintaining a relatively high thermal conductivity. The correlation between the microstructure features and thermo-physical properties was discussed. The performance of the electronic assemblies using the composite baseplate was evaluated. After 80 thermal shocks (–55 to 150 °C), the thermal resistance kept almost constant, demonstrating the potential application of this composite in the electronic packaging.     

多相复合陶瓷刀具材料残余热应力的有限元模拟

以SiC和(W,Ti)C颗粒增强Al₂O₃多相复合陶瓷刀具材料为基础,运用有限元方法详细研究了材料内部残余热应力的大小与分布形态。计算结果发现,单元模型取法、弥散相颗粒大小、分布及其含量均对多相复合陶瓷刀具材料中的残余热应力有较大影响。基体内不仅存在拉应力区,而且存在不同程度和范围的压应力区,拉、压应力区的结构形式与弥散相颗粒的分布方式密切相关。研究表明,残余热应力的存在与材料的力学性能和微观结构有着密切的关系。     

高体积分数挤压铸造铝基复合材料时效特征

采用挤压铸造法制备40 ％SiC_P/LD2复合材料,并对其在不同温度下的时效特征进行了研究。结果表明,高体积分数SiC颗粒的加入带来的弥散强化作用,可以大幅度提高基体合金的硬度和强度,但区别于基体合金和低体积分数复合材料,复合材料本身时效强化效果不明显。高体积分数复合材料峰时效时间较低体积分数缩短,且随时效温度的提高峰时效时间缩短。低温时效时峰值硬度最高且时效动力学较基体合金提前幅度较大。在时效析出过程中,高体积分数复合材料G.P.区的形成受到完全抑制,而β'相热扩散激活能降低,易于析出。     

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.     

Effect of SiC particle size on the physical and mechanical properties of extruded Al matrix nanocomposites

In this work, the effect of SiC particle size and its amount on both physical and mechanical properties of Al matrix composite were investigated. SiC of particle size 70 nm, 10 μm and 40 μm, and Al powder of particle size 60 μm were used. Composites of Al with 5 and 10 wt.% SiC were fabricated by powder metallurgy technique followed by hot extrusion. Phase composition and microstructure were characterized. Relative density, thermal conductivity, hardness and compression strength were studied. The results showed that the X-ray diffraction (XRD) analysis indicated that the dominant components were Al and SiC. Densification and thermal conductivity of the composites decreased with increasing the amount of SiC and increased with increasing SiC particle size. Scanning electron microscope (SEM) studies showed that the distribution of the reinforced particle was uniform. Increasing the amount of SiC leads to higher hardness and consequently improves the compressive strength of Al–SiC composite. Moreover, as the SiC particle size decreases, hardness and compressive strength increase. The use of fine SiC particles has a similar effect on both hardness and compressive strength.     

Fabrication and thermal shock resistance of HfB2-SiC composite with B4C additives

A HfB₂ based ceramic matrix composite containing 20 vol.% SiC particles with 2 vol.% B₄C as sintering additives was fabricated by hot-pressed sintering. The microstructure and properties, especially the thermal shock resistance of the composite were investigated. Results showed that the addition of B4C improved the powder sinterability and led to obtaining nearly full dense composite. The flexural strength and fracture toughness of the composite were 771 MPa and 7.06 MPam^1/2, respectively. The thermal shock resistance tests indicated that the residual strength decreased significantly when the thermal shock temperature difference was higher than 600 °C. The large number of microcracks on the sample surface was the main reason for the catastrophic failure.     

Thermal conductivity of graphite flakes–SiC particles/metal composites

A new family of high thermal conductivity composites, produced through infiltration of a metallic alloy into preforms of mixtures of graphite flakes and either ceramic or carbon materials (in the form of particles or short fibers), has been recently developed. Composites microstructure roughly consists of alternating layers of flakes and metal-particles composite. The present work focuses on graphite flakes–SiC particles/Al–12 wt%Si composites. The effects that the relative amounts of the components, as well as the average diameter of SiC particles (varied over the range 13–170 μm), have on the thermal conductivity are investigated. The experimental results are analyzed by means of two model microstructures: (i) alternating layers of flakes and metal-particle composite, and, (ii) oriented discs (graphite flakes) randomly distributed in a metal-particle composite matrix. Fitting experimental data by means of these model microstructures leads to reasonable values of the thermal conductivity of graphite flakes along the transversal and longitudinal directions.     

SiCP/AZ31镁基复合材料微弧氧化膜结构与性能分析

采用微弧氧化表面处理技术在SiC颗粒增强AZ31镁基复合材料表面制备保护性陶瓷膜.分析了陶瓷膜的表面形貌、截面组织和相组成,并测量了膜层的硬度、热震和电化学腐蚀特性.结果表明,陶瓷膜由MgO、Mg₂SiO₄和少量同电解液组成元素相关的相所组成,膜内还残留少量SiC_P增强体.膜层的最高硬度可达到HV800,比复合材料基体提高五倍以上.经过100次热循环(500℃→水淬)后膜层与复合材料结合良好,显示该膜层有较好的抗热震性能.微弧氧化处理后,SiC_P/AZ31镁基复合材料的抗腐蚀能力得到较大提高.