【作者】 王韬；

【导师】 李树丰；

【作者基本信息】 西安理工大学 ， 材料物理与化学， 2018， 硕士

【摘要】 高体积分数（40⁷0 vol.%）碳化硅颗粒（Silicon Carbide Particles,SiC_p）增强铝基复合材料（Aluminum Matrix Composites,AMCs）具有高热导率、低热膨胀系数、高强度及低密度等特点,在电子封装领域应用中有着巨大的应用潜力。本文采用粉末冶金法（Powder Metallurgy,P/M）制备高致密度的高体积分数SiC_P增强AMCs,系统研究了SiC_P的体积分数与粒径对AMCs性能的影响。针对SiC_P与Al基体之间润湿性差的问题,采用对SiC_P进行表面处理以及在复合粉体中添加Si元素的方法制备高体积分数SiC_P增强AMCs,并探究其对SiC_P增强AMCs的致密化过程、界面反应、力学性能以及热物理性能的影响。实验采用行星球磨仪（Planetary Ball Milling,PBM）通过湿磨混合工艺制备SiC_P-Al复合粉体,利用放电等离子烧结（Spark Plasma Sintering,SPS）对复合粉体进行烧结制备高体积分数SiC_p增强AMCs。结果表明:采用合适的球磨混粉工艺及烧结工艺,能够获得SiC_p分散良好的复合材料,其相对密度达到99%以上。采用中位径为56μmSiC_P制备的52 vol.%SiC_P/Al试样的平均弯曲强度392 MPa、平均热导率为204 W/mk,25²00°C的平均线膨胀系数为11.50×10^-66 K^-1。通过热力学计算表明:在现有烧结工艺下SiC_P与Al难以进行自发界面反应,对烧结后的52 vol.%SiC_P/Al样品进行XRD物相分析,未发现Al₄C₃峰。当选取中位径为56μm的SiC_P,体积分数在42⁶0 vol.%范围内变化时,试样的弯曲强度随体积分数的增加呈先增大后减小的变化趋势。相比于纯Al而言,SiC_P的添加能够有效提高AMCs的导热率并降低其的热膨胀系数。随着SiC_P体积分数的增加,导热率呈现先增大后减小的趋势,热膨胀系数随体积分数的增加而减小。在体积分数相同的情况下,试样的弯曲强度随SiC_P粒径的减小而增大。从热膨胀性能结果来看,平均热膨胀系数随SiC_P粒径减小而降低。综合考虑,选择中位径为56μm的SiC_P作为增强相较为合适。为改善SiC_P与Al的界面润湿性,实验在不同温度和不同保温时间对SiC_P进行了表面氧化处理。结果表明:随氧化温度的增加及氧化时间的延长,SiO₂的含量不断增加,但试样的相对密度及弯曲强度基本保持不变,SiO₂层厚度最薄的试样平均弯曲强度达到最大值443 MPa,与未处理试样相比提高了13%。相较而言,厚度适中的SiO₂层（1100°C处理2h）对于试样的热扩散速率与热导率影响最小。SiC_P表面少量的SiO₂对复合材料本身的热膨胀性能影响较小。为降低复合材料的热膨胀系数,并抑制在烧结过程中可能产生的不良界面反应。实验采用添加Si元素以制备致密的52 vol.%SiC_P/Al-Si基复合材料。结果表明:随Si含量的增加,试样的相对密度及弯曲强度降低,其中52 vol.%SiC_P/Al-1Si样品的弯曲强度达到427 MPa,与未添加Si元素样品相比提高了10.8%。当Si含量<6 vol.%时,试样在25¹00°C内热导率均大于未添加Si样品。平均热膨胀系数随Si含量的增加而产生明显的下降,52vol.%SiC_P/Al-8Si在25²00°C的平均热膨胀系数下降至9.54×10^-66 K^-1。通过对复合材料断口的SEM照片进行分析,高体积分数SiC_P增强AMCs的断裂机制主要是以SiC_P的脆性断裂与Al基体的韧性断裂相结合的方式。SiC_P与Al基体之间界面结合良好,SiC_P能够有效的承载与传递载荷。随样品中Si含量的增加,基体上的韧窝呈现出减少和变浅的趋势,表明复合材料基体的塑性不断下降。更多还原

【Abstract】 High volume fraction（40⁷0%）SiCP reinforced Aluminum matrix composites（AMCs）with have great application potential in electronic packaging applications,due to its high thermal conductivity,low thermal expansion coefficient,high strength and low density.In this paper,SiCP reinforced AMCs with high volume fraction was prepared by Powder metallurgy（P/M）.The effect of the volume fraction and particle size of SiC_P on the properties of the composite was systematically studied.In view of the problem of poor wettability between SiC_P and Al,the surface modification of SiC_P and the addition of Si elements in the composites powder are used to prepare high volume SiC_P reinforced AMCs,and the densification process,interfacial reaction,mechanical properties and thermal physical properties of high volume fraction SiC_P/Al composites were investigated.The SiC_P-Al powder was prepared by planetary ball milling（PBM）through a wet milling process,and the high volume fraction of SiC_P reinforced AMCs was sintered by spark plasma sintering（SPS）suing SiC_P-Al powder.The results show that the composites with good dispersion of SiC_P can be obtained with suitable ball milling and sintering process.The relative density of the composites can be over 99%.The thermal conductivity of the 56μm 52vol.%SiC_P/Al composite is 204 W/mk,the average bending strength is 392 MPa,and the average thermal expansion coefficient of 25²00°C is 11.50×10^-66 K^-1.Through the thermodynamic calculation,it is found that the composites is difficult to carry out spontaneous interfacial reaction under the present sintering process.At the same time,the Al₄C₃ diffraction peak was not found in the XRD patterns of the 52 vol.%SiC_P/Al sample.As the median diameter of SiC_P is 56μm and the volume fraction changes in the range of42⁶0 vol.%,the bending strength of the sample increases first and then decreases with SiC_P of volume fraction increases.Compared with pure Al,the addition of SiC_P can effectively improve the thermal conductivity and reduce the thermal expansion coefficient of composites.When the volume fraction of SiC_P increases,the thermal conductivity increases at first and then decreases,but the thermal expansion coefficient always decreases.When the particle size of SiC_P decreases,the bending strength of the composite increases.The average thermal expansion coefficient of composites decreases with the decrease of SiC_P particle size.Through comprehensive consideration,it is more appropriate to choose the SiC_P with a median diameter of 56μm as reinforcements.In order to improve the wettability of SiC_P and Al matrix,the surface oxidation of SiC_P was carried out at different temperatures and holding time.The results show that the thickness of SiO₂ layer increases with the increase of oxidation temperature and oxidation time,and the relative density and bending strength of the specimen remain unchanged.The average bending strength of the SiO₂ layer with the thinnest thickness reaches the maximum value of 443 MPa,which is 13%higher than that of the untreated sample.By measuring the thermal conductivity of the samples,the moderate thickness of SiO₂ layer（1100°C treat 2 h）has the least effect on the thermal diffusion rate and thermal conductivity of the sample.A small amount of SiO₂ on the surface of SiC_P has little effect on the thermal expansion of the composites.In order to reduce the thermal expansion coefficient of the composites and suppress the bad interfacial reaction during sintering,Si element was added to prepare densified 52vol.%SiC_P/Al-Si composites in the experiment.The results showed that the relative density and bending strength of the samples decreased with the rise of Si content.The bending strength of52 vol.%SiC_P/Al-1Si sample reached 427 MPa,which was 10.8%higher than that of Si samples.When Si content is less than 6 vol.%,the thermal conductivity of samples at25¹00°C are greater than the sample without Si.The average thermal expansion coefficient decreases obviously with the increase of Si content,and the average thermal expansion coefficient of 52 vol.%SiC_P/Al-8Si decreases to 9.54×10^-6 K^-1 at 25²00°C.The fracture mechanism of high volume fraction SiC_P reinforced AMCs is mainly based on the combination of brittle fracture of SiC_P and ductile fracture of Al matrix through the analysis to the SEM photos of the composites fracture.The interface between SiC_P and Al matrix is well connected,and SiC_P can effectively carry and transfer load.In the samples,the dimples on the matrix decrease and shrank with the increase of Si content,indicating that the plasticity of the matrix decreases.更多还原