混料时间和挤压对SiC增强纯Al基复合材料显微组织和力学性能的影响

采用粉末冶金法制备SiC颗粒增强工业纯Al基复合材料,研究混料时间和挤压对复合材料显微组织和力学性能的影响。研究表明:机械混粉过程存在最佳的混料时间,混料时间为16 h时SiC颗粒分布均匀,复合材料的密度高、力学性能好。挤压可以改善复合材料的界面结合强度、减少孔洞的数量,从而提高材料的致密度和力学性能。烧结态复合材料的断裂机制以基体的脆性断裂以及增强相与基体的界面脱粘为主。挤压态复合材料的断裂以基体的韧性断裂以及SiC颗粒的脆性断裂为主,伴随着少量的基体与SiC颗粒的界面脱粘。     

热等静压法制备SiC_p/Al复合材料的组织及性能研究

采用热等静压法制备SiC颗粒增强铝基复合材料,研究其显微组织和力学性能,分析复合材料的断口形貌及断裂机制,测定了其热膨胀系数。结果表明:热等静压后,复合材料中的SiC颗粒会出现颗粒团聚,形成硬质的SiC骨架。对于20%SiC_p/6061Al(体积分数)复合材料,其抗拉强度能达到304 MPa,而20%SiC_p/2024Al(体积分数)的抗拉强度为276 MPa,两种复合材料的抗拉强度都达到或超过其他制备方法的水平。复合材料的断裂方式为基体的韧性断裂、SiC颗粒的解理断裂、SiC颗粒与基体的界面脱粘3种方式并存的混合断裂形式。对比复合材料热膨胀系数的实际测量值和Turner、Kerner模型理论值,Turner模型理论值更接近实测值。     

高压扭转制备SiC_p/Al复合材料的断裂行为

为了研究大塑性变形对颗粒增强复合材料断裂行为的影响规律,在不同高压扭转工艺(high-pressure torsion,HPT)工艺参数下制备SiC_p/Al复合材料,测量试样真应力-应变曲线和观察试样的断口形貌,并分析SiC-Al界面的EDS谱。在分析各参数下材料断口形貌和界面原子扩散的基础上,讨论颗粒增强复合材料的断裂机理。研究发现:SiC_p/Al复合材料包含韧性断裂和脆性断裂2种性质的断裂,断口韧窝的大小和数量与材料的工艺参数有关;HPT变形可以有效改善SiC颗粒与Al基体的界面连接强度,提高该类材料的断裂性质。基体内气孔和颗粒与基体间孔隙的连接是金属基复合材料的主要断裂机制。     

高硅铝合金及颗粒增强铝基复合材料组织性能的探究

采用真空热压烧结工艺制备Al-30Si合金、30%Sip/Al、30%SiCp/2024Al、30%SiCp/6061Al(均为体积分数)复合材料,测定其热膨胀系数及力学性能。利用扫描电镜(SEM)、能谱仪(EDS)对其微观组织结构及断口形貌进行表征,探究了高硅铝合金及颗粒增强铝基复合材料的组织与性能,分析了材料的断裂机制。结果表明:SiCp/2024Al复合材料中SiC颗粒分布均匀,组织致密,综合性能好,热膨胀系数(CTE)为13.69×10-6/K,硬度达到134 HB,极限抗拉强度达353 MPa。SiCp/6061Al复合材料中SiC颗粒分布较均匀,界面结合较好,组织不够致密,有少许孔隙,性能较好。SiCp/6061Al和SiCp/2024Al复合材料的断裂方式都是界面基体的撕裂结合SiC颗粒的断裂。Sip/Al复合材料中Si颗粒分布较均匀,断裂方式为界面脱开,性能较差。Al-30Si合金在烧结过程中形成大量板条状的Si相,性能最差,断裂方式以合金撕裂为主。     

SiC颗粒预处理对SiC_p/Al-Si复合材料组织及性能的影响

采用高温焙烧加水洗工艺对SiC颗粒进行处理,用真空热压法制备SiC颗粒增强Al-Si基复合材料,研究了SiC预处理对复合材料微观组织和抗拉强度的影响。结果表明,经预处理的SiC颗粒增强Al-Si基复合材料界面结合良好,孔隙减少,相对密度和抗拉强度显著提高。     

粉末热挤压SiC_p/2024铝基复合材料的显微组织和力学性能

利用粉末热挤压工艺制备SiCp/2024铝基复合材料,研究所制备复合材料的挤压态和热处理态的显微组织及力学性能,分析复合材料的断口形貌和断裂类型。结果表明:大部分SiC颗粒和析出的大量细小第二相粒子均匀地分布在基体合金中,部分区域的SiC颗粒存在轻微团聚现象,晶粒沿挤压方向被显著拉长,刚性的SiC颗粒长轴平行于挤压方向分布,形成热加工纤维组织。对复合材料进行T6(490℃固溶75 min+170℃时效8 h)热处理后,复合材料的晶粒比较细小,抗拉强度达470 MPa,主要的析出强化相为S′(Al2CuMg)。挤压比的提高有利于提高SiC颗粒和基体合金的界面结合强度。粉末热挤压法制备的SiCp/2024铝基复合材料热处理后的断裂方式主要有3种:SiC颗粒断裂、SiC颗粒与基体合金的剥离和基体合金的韧性断裂,该复合材料的断裂机制为韧性断裂和脆性断裂共存的混合断裂。     

颗粒尺寸对15%SiC_p/2009Al复合材料断裂韧性的影响

采用粉末冶金+挤压工艺制备了含不同粒径SiC颗粒(3.5, 5.0, 10.0和15.0μm)的15%SiC_p/2009A1复合材料挤压棒材,利用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)和万能试验机研究了SiC颗粒尺寸对15%SiC_p/2009Al复合材料力学性能的影响。结果表明, SiC颗粒尺寸对复合材料强度和韧性的影响效果十分显著。随着SiC颗粒从3.5μm增大至15μm,复合材料的强度逐渐减小,而延伸率则逐渐增大。SiC颗粒尺寸为5.0μm时,复合材料的强度和塑性最佳,抗拉强度(R_m)、屈服强度(R_(p0.2))分别为582, 382 MPa,延伸率(A)为10%,断裂韧性(K_(IC))为33.7 MPa·m~(1/2)。SiC颗粒尺寸为3.5μm时,复合材料的断裂以SiC颗粒周围的铝基体韧性撕裂为主, SiC颗粒尺寸超过5.0μm时,复合材料断裂方式为SiC颗粒周围的铝基体韧性撕裂和SiC颗粒脆性断裂的共同作用,由于SiC-Al界面结合较好,未发现SiC-Al界面脱粘的失效形式。     

无压浸渗法制备SiCp/Al复合材料的微观组织与力学性能

采用无压浸渗方法制备了SiC颗粒增强铝基复合材料，研究了材料的微观组织和力学性能。结果表明，复合材料浸渗完全，SiC颗粒分布均匀，无偏聚现象。铸造态复合材料中存在界面反应，经过透射电镜观察和XRD分析确认该界面反应物为MgAl2O4。界面反应的存在提高了润湿性，促进了无压自发浸渗。高温热暴露处理可以提高复合材料的布氏硬度，热暴露处理后的界面反应物呈块状弥散分布，但是反应物的数量略有增加。     

SiC颗粒尺寸对高压扭转制备SiCp/Al基复合材料金相组织和显微硬度影响

采用高压扭转法制备不同增强颗粒尺寸的SiCp/Al基复合材料,利用金相观察、显微硬度测试,分析研究不同增强颗粒尺寸对SiCp/Al基复合材料组织和硬度的影响。研究结果表明:SiC颗粒尺寸较小时,在高的静水压力和剪切作用下,颗粒分布均匀性增强。SiC颗粒尺寸增大时,有效的剪切作用易致使自身存在缺陷的SiC颗粒发生断裂破碎,颗粒分布均匀性降低。同一扭转半径处,随着颗粒尺寸的增大,复合材料显微硬度降低。     

粉末冶金制备SiC/6061Al复合材料的显微组织和力学性能研究

采用粉末冶金法制备了体积分数为35%的SiC_p/6061Al基复合材料,研究了复合材料的显微组织和基体与增强体颗粒界面对复合材料力学性能的影响。结果表明:SiC颗粒在基体中分布均匀,基体与增强体之间的界面结合情况较好,复合材料致密度高,抗拉强度较高。     

镁锂基复合材料界面结构及热力学分析

制备了碳纤维及ＳｉＣ晶须增强的Ｍｇ８Ｌｉ１Ａｌ基复合材料。利用透射电镜,高分辨电子显微镜研究了Ｍｇ８Ｌｉ１Ａｌ／ＳｉＣｗ复合材料的界面结构,发现ＳｉＣ晶须与基体合金界面结合良好,没有明显的反应物。     

Mechanical properties of 2014Al/SiC composites with oxidized SiC particles

Metal-matrix composites (MMCs) are known to have wide applications in parts of transportation devices such as automobiles and aircraft. Al-matrix composites using SiC particles as reinforcements are especially spotlighted because of their low cost, superior specific modulus, specific strength, wear resistance, and high-temperature stability. However, Al₄C₃ formed by the interfacial reaction between Al and SiC weakens the interfacial bonding strength. It is also known to be unstable in the water-soluble atmosphere. In this study, the passive oxidation of SiC powder is used as a protective layer against the reaction between the Al matrix and the SiC particles. We investigated the changes in interfacial product of the composites, and mechanical properties such as interfacial bonding strength and tensile strength, in terms of the oxidized-layer thickness of the reinforcement.     

Processing,microstructure, and mechanical behavior of cast magnesium metal matrix composites

Magnesium metal matrix composites (MMCs) have been receiving attention in recent years as an attractive choice for aerospace and automotive applications because of their low density and superior specific properties. This article presents a liquid mixing and casting process that can be used to produce SiC particulate-reinforced magnesium metal matrix composites via conventional foundry processes. Microstructural features, such as SiC particle distribution, grain refinement, and particle/matrix interfacial reactions of the cast magnesium matrix composites, are investigated, and the effects of solidification-process parameters and matrix alloys (pure Mg and Mg-9 pct Al-1 pct Zn alloy AZ91) on the microstructure are established. The results of this work suggest that in the solidification processing of MMCs, it is important to optimize the process parameters both to avoid excessive interfacial reactions and simultaneously achieve wetting, so that a good particle distribution and interfacial bonding are obtained. The tensile properties, strain hardening, and fracture behavior of the AZ91/SiC composites are also studied and the results are compared with those of the unreinforced AZ91 alloy. The strengthening mechanisms for AZ91/SiC composite, based on the proposed SiC particle/matrix interaction during deformation, are used to explain the increased yield strength and elastic modulus of the composite over the magnesium matrix alloy. The low ductility found in the composites is due to the early appearance of localized damages, such as particle cracking, matrix cracking, and occasionally interface debonding, in the fracture process of the composite.     

Tailoring interfacial shear strength of SiC fiber-reinforced brittle matrix composites

The interfacial shear strength of Nicalon SiC fiber-reinforced glass-ceramic matrix composites was aimed to be tailored via two methods: (1) varying of the thickness of the carbon-rich interfacial layer between the fiber and the matrix by controlling hot pressing period and (2) formation of the secondary interfacial layer, TaC, at the carbon/matrix boundary by doping the Ta₂O₅ matrix addition. In the series of composites with varying carbon-rich layer thickness, fiber/matrix debonding mostly occurred at the carbon/matrix boundary and hence the increase in the carbon-rich layer thickness did not cause any apparent changes in the interfacial shear strength. In the TaC formed series of composites, the interfacial shear strength was affected considerably by the presence of the TaC phase at carbon/matrix boundary. The Ta₂O₅ addition to control the quantity of the TaC phase has shown to be a useful method to tailor the interfacial shear strength of SiC fiber/glass-ceramic composites.     

Transverse strengths and failure mechanisms in Ti3Al matrix composites

Transverse mechanical properties have been measured, and damage mechanisms identified, in three Ti₃Al matrix composites with different interface compositions and residual stress states. Two of the composites contained SiC fibers with weak interfaces. Large improvements in transverse strength and rupture strain were found in one of these composites, in which brittle reaction products in the matrix around the fibers had been avoided by coating the fibers with Ag and Ta before consolidation. The third composite contained sapphire fibers that were strongly bonded to the matrix. Different damage mechanisms were observed in the strongly and weakly bonded composites. Insight into the damage mechanisms and their dependence on residual stress fields and interface properties is gained from comparison of the observations with analytical solutions of elastic stresses. The conditions for optimum transverse properties are discussed; the results indicate that strong interfacial bonding does not necessarily lead to optimum transverse strength of the composite.     

Fiber-Matrix interactions in brittle matrix composites

Brittle matrix composites, including carbon-carbon (C-C) and ceramic matrix, offer a new dimension in the area of high-temperature structural materials. Fiber-matrix interactions determine the mechanism of the load transfer between the fiber and matrix and resulting mechanical properties. Composites studied in this work include a C-C composite densified with a chemical vapor infiltration (CVI) pyrolytic carbon, silicon carbide fiber-silicon carbide matrix composite, and carbon fiber-silicon carbide matrix composites densified by the CVI technique. The type of the interfacial carbon in C-C composites was found to control their mechanical properties. The presence of the compressive stress exerted by the matrix on the carbon fibers was attributed to an increase in flexural strength. The transverse matrix cracking in C/SiC composites was believed to cause a lowering in the flexural strength value. Brittle fracture behavior of SiC/SiC composites was correlated with the presence of an amorphous silica layer at the fiber-matrix interface. This invited paper is based on a presentation made in the symposium “Structure and Properties of Fine and Ultrafine Particles, Surfaces and Interfaces” presented as part of the 1989 Fall Meeting of TMS, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Structures Committee of ASM/MSD.     

Fiber and interface fracture in singlecrystal aluminum/SiC fiber composites

Model metal-matrix composite tensile specimens, each containing a single SiC fiber in a single crystal of pure Al, were grown using a modified Bridgman method at two growth rates and with various fiber surface treatments in order to study their effect on fiber and interface strength. Using the load drops in tensile tests, we measured both fiber and interface strengthin situ. Acoustic emission (AE) was monitored to assist in determining the failure mechanisms. Both the fiber surface treatment and growth rate were found to significantly affect the fiber and interface strength. Fibers with carbon-rich outer surfaces had higher fiber strengths but lower interfacial strengths than untreated fibers. These results are discussed in terms of failure mechanisms and interfacial reactions occurring during growth of the composites.     

Interface characterization of duplex metal-coated SiC fiber-reinforced Ti-15-3 matrix composites

The interfacial reaction behavior of duplex metal (Cu/Mo and Cu/W)-coated SiC (SCS-6) fiber-reinforced Ti-15-3 composites, before and after thermal exposure, has been studied. The effect of thermal exposure on the shear sliding resistance of these composites was also obtained using a thin-specimen push-out test. The results are compared to those of an original SiC (SCS-6) fiber-reinforced Ti-15-3 composite. The interfacial reaction behavior is strongly affected by the existence of a coating layer. Both the Cu/Mo and Cu/W coating layers prevent the growth of a reaction layer. However, the coatings could not effectively prevent diffusion of alloying elements; only the W layer exists after the thermal exposure. On the other hand, the interface shear sliding stress minimally depends on the duplex metal coating layers prior to the thermal exposure, and this sliding stress in both the SiC/Cu/Mo/Ti-15-3 and SiC/Cu/W/Ti-15-3 composites decreases slightly relative to that in the SiC/Ti-15-3 composite. After thermal exposure, the interface shear sliding stress increases for the SiC/Ti-15-3 composite. In distinction, the interface shear sliding stress significantly decreases after thermal exposure in both the SiC/Cu/Mo/Ti-15-3 and SiC/Cu/W/Ti-15-3 composites. Theses behaviors are attributed to the decrease of radial clamping stress, which originates from a volume expansion associated with the β → α phase transformation.     

Squeeze Infiltration Processing of Functionally Graded Aluminum–SiC Metal Ceramic Composites

The objective of the present work is on fabrication of functionally graded SiC/Al composite by direct squeeze infiltration of 6061 aluminum alloy using graded SiC porous preform prepared by inorganic porogen technique. Graded SiC preform is synthesized by varying the concentration of inorganic salt mixture and using Al as the binder. The microstructure analysis indicates the graded distribution of SiC particle and the melt has infiltrated completely throughout the preform to form functionally graded materials. The influence of preform and mold temperature, liquid metal superheat, squeeze pressure, and its rate of application plays major role on solidification microstructures and properties of the composites. The macro porous graded SiC preforms and the composites were characterized using SEM, optical microscopy, and XRD. The major interfacial reaction product is MgAl₂O₄ spinel which helps in formation of good interface bonding.