Effect of SiC volume fraction and particle size on the fatigue resistance of a 2080 Al/SiC p composite

The effect of SiC volume fraction and particle size on the fatigue behavior of 2080 Al was investigated. Matrix microstructure in the composite and the unreinforced alloy was held relatively constant by the introduction of a deformation stage prior to aging. It was found that increasing volume fraction and decreasing particle size resulted in an increase in fatigue resistance. Mechanisms responsible for this behavior are described in terms of load transfer from the matrix to the high stiffness reinforcement, increasing obstacles for dislocation motion in the form of S’ precipitates, and the decrease in strain localization with decreasing reinforcement interparticle spacing as a result of reduced particle size. Microplasticity was also observed in the composite, in the form of stress-strain hysteresis loops, and is related to stress concentrations at the poles of the reinforcement. Finally, intermetallic inclusions in the matrix acted as fatigue crack initiation sites. The effect of inclusion size and location on fatigue life of the composites is discussed.     

金属基复合材料增强体体积含量检测方法概述

金属基复合材料的增强体体积含量是表征其性能的一个重要指标。简要介绍了金属基复合材料增强体体积含量的检测方法以及标准化进展。对显微镜法、图像分析仪法和基体溶解法的适用范围、方法原理、试验设备、试样制备和试验方法进行了系统的总结,并对3种检测方法的优缺点进行了比较分析。分析了金属基复合材料增强体体积含量检测方法的国家标准现状,并对未来体积含量国家标准的制定进行了展望。     

溶解法测定铝基复合材料中碳化硅增强体体积含量

对于金相显微镜下难以区分增强体和基体组织的铝基复合材料而言,国家标准方法GB/T 32496—2016难以准确测量铝基复合材料中的增强体体积含量。实验以HCl(1+1)、HF和H₂O₂为溶解液消解铝基体,再采用砂芯坩埚和滤纸两种方法收集SiC,采用溶解法测定铝基复合材料中SiC增强体体积含量。实验探讨了溶解液对SiC增强体的腐蚀行为。结果表明:依次加入10~20mL HCl(1+1)、3~5mL HF和3~6mL H₂O₂可将Al基体组织溶解完全。精密度试验表明,待测SiC体积含量的相对标准偏差(RSD)均不大于0.1%(n=9),能满足铝基复合材料中SiC体积含量的检测要求。相比砂芯坩埚抽滤法,滤纸法较经济且结果稳定。推荐采用滤纸法进行铝基复合材料中SiC体积含量测试。采用滤纸法分析铝基复合材料样品,测定值与理论值吻合良好。     

电子封装用高体积分数SiCp/Al复合材料的制备

采用粉末注射成形制备SiC预成形坯和Al合金无压熔渗相结合的工艺,用单一粒度的粉末成功地制备出了致密度为98．7%的60% SiCp/Al高体积分数复合材料．SEM分析表明,所制备的复合材料增强体和基体分布均匀,组织致密,热膨胀系数在100℃到400℃范围内介于(7．10-7．75)×10^-6K^-1之间,室温热导率为170W·m^-1·K^-1,能够完全满足电子封装的技术要求．     

SiC和Si混合颗粒增强铝基复合材料的研究现状

SiC颗粒增强含Si铝基复合材料在制备过程中由于Si颗粒的析出,使其成为SiC和Si混合颗粒增强铝基复合材料。SiC和Si混合颗粒增强铝基复合材料具有比强度和比刚度高、耐磨性和耐疲劳性好、尺寸稳定性强、轻质等性能,广泛应用于航空、航天、电子电器等工业领域。主要介绍了SiC和Si混合颗粒增强铝基复合材料的研究现状及几种制备工艺,分析了其显微组织中存在的缺陷及复合材料性能的影响因素;展望了SiC和Si混合颗粒增强铝基复合材料的应用前景。     

Influence of reinforcement volume fraction and size on the microstructure and abrasion wear resistance of hot Isostatic pressed white iron matrix composites

The changes in the microstructure and wear resistance of a powder metallurgical high-Cr white iron after the incorporation of TiC particles were studied in the present work. Various reinforcement volume fractions and sizes were used in order to examine their influence on the three-body abrasion wear resistance. The experiments were carried out at three different austenitizing temperatures. The most important observation after a microstructural examination was the increased amount of martensite in the composites subjected to identical heat treatment procedures with the unreinforced alloy. The austenite-to-martensite transformation in the composites increased with the TiC volume fraction and with the austenitizing temperature. This indicates that the two parameters have a key role in the transformation mechanism, which seems to be mechanically induced. The increasing of martensitic transformation with the TiC content in the composites enhanced continuously the supporting ability of the iron alloy matrix to the TiC particles, which in turn increased the wear resistance of the composites. The abrasion wear resistance increased with the TiC volume fraction until the onset of spalling. However, in composites containing coarse reinforcements, spalling occurred earlier in the wear process. This decreased wear resistance significantly because spalled TiC particles contributed additionally to wear.     

The effect of matrix microstructure on the tensile and fatigue behavior of SiC particle-reinforced 2080 Al matrix composites

The effect of matrix microstructure on the stress-controlled fatigue behavior of a 2080 Al alloy reinforced with 30 pct SiC particles was investigated. A thermomechanical heat treatment (T8) produced a fine and homogeneous distribution of S′ precipitates, while a thermal heat treatment (T6) resulted in coarser and inhomogeneously distributed S′ precipitates. The cyclic and monotonic strength, as well as the cyclic stress-strain response, were found to be significantly affected by the microstructure of the matrix. Because of the finer and more-closely spaced precipitates, the composite given the T8 treatment exhibited higher yield strengths than the T6 materials. Despite its lower yield strength, the T6 matrix composite exhibited higher fatigue resistance than the T8 matrix composite. The cyclic deformation behavior of the composites is compared to monotonic deformation behavior and is explained in terms of microstructural instabilities that cause cyclic hardening or softening. The effect of precipitate spacing and size has a significant effect on fatigue behavior and is discussed. The interactive role of matrix strength and SiC reinforcement on stress within “rogue” inclusions was quantified using a finite-element analysis (FEA) unit-cell model.     

无压浸渗法制备高体分比SiCp/Al

采用粉末注射成形/无压浸渗法成功制备出了SiC体积分数为63%的SiCp/Al复合材料．重点研究了主要工艺参数对SiC骨架及复合材料性能的影响规律．研究表明,采用粉末注射成形制备的SiC骨架经1100℃预烧后,仍具有很高的开口孔隙率,达到总孔隙率的97．9%．SiC颗粒经高温氧化处理后所生成的SiO₂薄膜可明显改善铝合金熔液与SiC颗粒之间的润湿性,显著提高复合材料的密度．通过对工艺参数的优化可使铝液较好地润湿SiC骨架,获得最高相对密度可超过97%的复合材料．     

The influence of buoyant forces and volume fraction of particles on the particle pushing/entrapment transition during directional solidification of Al/SiC and Al/graphite composites

Directional solidification experiments in a Bridgman-type furnace were used to study particle behavior at the liquid/solid interface in aluminum metal matrix composites. Graphite or siliconcarbide particles were first dispersed in aluminum-base alloysvia a mechanically stirred vortex. Then, 100-mm-diameter and 120-mm-long samples were cast in steel dies and used for directional solidification. The processing variables controlled were the direction and velocity of solidification and the temperature gradient at the interface. The material variables monitored were the interface energy, the liquid/particle density difference, the particle/liquid thermal conductivity ratio, and the volume fraction of particles. These properties were changed by selecting combinations of particles (graphite or silicon carbide) and alloys (Al-Cu, Al-Mg, Al-Ni). A model which considers process thermodynamics, process kinetics (including the role of buoyant forces), and thermophysical properties was developed. Based on solidification direction and velocity, and on materials properties, four types of behavior were predicted. Sessile drop experiments were also used to determine some of the interface energies required in calculation with the proposed model. Experimental results compared favorably with model predictions. BRU K. DHINDAW Visiting Scholar with the Solidification Laboratory at the time this work was performed.     

热挤压对SiC/2024Al复合材料性能的影响

采用冷压烧结工艺制备35%Si C/2024Al基(质量分数)复合材料,对烧结后的试样进行热挤压二次成形。利用金相显微镜、透射电镜(TEM)观察热挤压前后材料的微观组织,检测复合材料的物理和力学性能,研究热挤压前后Si C颗粒的分布特征、基体晶粒变化情况以及复合材料的强化机理。结果表明:挤压后的Si C颗粒偏聚现象减少,分布更加均匀,具有一定的"流向"性;挤压后的基体晶粒发生明显的细化;复合材料的致密度和抗拉强度得到明显的提高。     

铝基体类型对铍铝复合材料均匀流变特征的影响

在变形温度450~600℃、应变速率0.1~10 s-1条件下, 采用Gleeble-3800热模拟试验机和扫描电镜研究了铝基体类型对铍铝(Be/Al)复合材料流变曲线、应变硬化指数(n)及压缩试样宏微观组织结构的影响。结果表明: 纯铝基复合材料在相对较小的应变下易发生断裂失效; 6061Al基复合材料在发生不稳定变形之前的均匀变形能力高于纯铝基复合材料, 具有更好的均匀变形能力。     

Acoustic emission during fatigue crack propagation in SiC particle reinforced Al matrix composites

The acoustic emission (AE) behavior during fatigue propagation in aluminum 6061 and aluminum 6061 matrix composites containing 5, 10, and 20 wt pct SiC particle reinforcement was investigated under tension-tension fatigue loading. The purpose of this investigation was to monitor fatigue crack propagation by the AE technique and to identify the source(s) of AE. Most of the AEs detected were observed at the top of the load cycles. The cumulative number of AE events was found to correspond closely to the fatigue crack growth and to increase with increasing SiC content. Fractographic studies revealed an increasing number of fractured particles and to a lesser extent decohered particles on the fatigue fracture surface as the crack propagation rate(e.g., †K) or the SiC content was increased. This article is based on a presentation made in the symposium entitled “Creep and Fatigue in Metal Matrix Composites” at the 1994 TMS/ASM Spring meeting, held February 28–March 3, 1994, in San Francisco, California, under the auspices of the Joint TMS-SMD/ ASM-MSD Composite Materials Committee.     

Effect of particle-size distribution on the properties of high-volume-fraction SiC p -Al-based composites

High-volume-fraction SiC-Al-based composites have been fabricated by squeeze casting. The effect of particle-size distribution and squeeze-cast parameters on the metal-matrix composites (MMCs) was investigated. The results showed that bulk density of the composites was 2.855 to 3.067 g/cm³ with the various component mixtures of SiC particulates, i.e., the SiC volume fraction was 51.6 to 74.4 pct. The young’s modulus of the composites was between 220 and 226 GPa. The maximum four-point bending strength and fracture toughness reached 478 MPa and 9.42 MPa(m)^−1/2, respectively. The coefficient of thermal expansion (CTE) of the composites was from 5 to 8 × 10⁻⁶/K, depending on the volume fraction of SiC.     

不同粒径的SiC体积配比对SiC_p/Al基复合材料显微组织和拉伸性能的影响

为了研究不同粒径的Si C体积配比对SiC_p/Al基复合材料显微组织及拉伸性能的影响,采用高压扭转法(High-pressure torsion,HPT)将3.5μm(小)、7.0μm(大)SiC颗粒体积比分别为4∶1、1∶1、1∶4的SiC颗粒和纯Al粉末混合物制备成10%SiC_p/Al基复合材料(体积分数)。用金相显微镜、万能试验机、扫描电镜等分析2种粒径的Si C体积比对SiC_p/Al基复合材料显微组织和拉伸性能的影响。结果表明,随扭转半径增大,各试样的SiC颗粒分布更加均匀,颗粒团聚、偏聚现象减少,其中小、大SiC颗粒体积比为1∶1的试样性能最优,伸长率、相对密度最高,分别达到14.3%和99.1%,拉伸断裂形式为塑性断裂。     

超细SiC增强纯铝基复合材料显微组织与力学性能的研究

采用平均粒径为800nm的超细SiC颗粒作为增强体,制备含SiC体积分数为15%的铝基复合材料,研究烧结温度和强压处理对复合材料微观组织和力学性能的影响。研究表明,提高烧结温度可有效加速复合材料的致密化,与520℃下烧结制备的复合材料相比,610℃下烧结制备的复合材料具有更高的密度和较低的孔隙度,从而具有更高的硬度。610℃下烧结制备的复合材料的硬度为83.9HBS,远高于520℃烧结制备的复合材料的硬度(53.7HBS)。这主要是由于烧结温度的提高可加速原子扩散,有利于Al粉之间以及Al粉与SiC颗粒之间的结合,并改善界面结合情况。研究还表明,强压处理可以有效提高复合材料的致密度和降低孔隙的体积分数,610℃下烧结制备的复合材料经强压处理以后的密度为2.68g/cm3,接近于理论密度(2.78g/cm3),且硬度可达121HBS,抗拉强度、屈服强度和伸长率分别可达177.6MPa、168.6MPa和3.97%。     

造孔剂含量对SiC/Al复合材料抗弯强度的影响

采用无压熔浸法制备SiC/Al复合材料,并利用颗粒堆积和毛细管力的静力学理论研究造孔剂含量对SiC/Al复合材料抗弯强度的影响.通过扫描电镜对试样的断口形貌进行分析,发现造孔剂含量为20%(质量分数)时,残余孔隙较小,而造孔剂含量为10%和15%时,残余孔隙较大.造孔剂含量对抗弯强度产生影响,随造孔剂含量增加,抗弯强度先增大后减小,造孔剂为20%时,抗弯强度出现最大值343.63 MPa.     

Effect of SiC and graphite particulates on the damping behavior of metal matrix composites

The effect of SiC and graphite (Gr) particulates on the resultant damping behavior of 6061 A1 metal matrix composites (MMCs) was investigated in an effort to develop a high damping material. The MMCs were processed by a spray atomization and deposition technique and the damping characterization was conducted on a dynamic mechanical thermal analyzer. The damping capacity, as well as the dynamic modulus, was measured at frequencies of 0.1, 1, 10 and 30 Hz over a 30 to 250°C temperature range. The microstructural analysis was performed using scanning electron microscopy, optical microscopy and image analysis. The damping capacity of the 6061 Al/SiC and 6061 Al/Gr MMCs, with two different volume fractions of reinforcements, were compared with that of as-received 6061-T6 Al and spray deposited 6061 Al. It was shown that the damping capacity of 6061 Al could be significantly improved by the addition of either SiC or graphite particulates through spray deposition processing. Finally, the operative damping mechanisms were discussed in light of the data obtained from characterization of microstructure and damping capacity.