热压工艺对SiC纤维增强TB8复合材料组织影响研究

通过箔-纤维-箔法制备了SiC纤维增强TB8复合材料,采用光学电子显微镜(OM)、扫描电镜(SEM)和电子探针(EPMA)对复合材料的微观组织进行表征与分析,研究了真空热压复合时压力、温度和时间工艺参数对SiC纤维增强TB8复合材料微观组织的影响规律。结果表明:压力对复合材料基体与基体以及纤维与基体的结合有着显著影响,而温度对纤维与基体界面反应层影响较大。通过热压工艺的优化,可以有效控制界面反应层厚度,获得组织优良的SiC f/TB8复合材料。     

SiC纤维增强TB8复合材料层合板力学性能研究

通过箔-纤维-箔法制备了SiC纤维增强TB8复合材料,利用光学电子显微镜(OM)、扫描电镜(SEM)和力学性能试验机对SiC纤维增强TB8复合材料层合板的微观组织、断口形貌与力学性能进行表征与分析,研究了铺层方式对SiC纤维增强TB8复合材料层合板力学性能的影响。结果表明:880℃/50 MPa/2 h的热压工艺下,SiC纤维增强TB8复合材料层合板复合效果良好,纤维排布均匀并与设计方向基本一致。通过对单层SiC纤维布铺设角度、铺层顺序的设计可实现对SiC纤维增强TB8复合材料不同方向力学性能的调整与改进。单向SiC纤维增强TB8复合材料的纵向性能最佳,室温抗拉强度达1362.20 MPa,■层合板在部分牺牲复合材料纵向强度的同时,提升了其横向强度。当钛基复合材料多向受力时可考虑采用■层合板;当钛基复合材料构件受力状态确定时,可采用■或根据实际情况确定的其他角度层合板。     

连续SiC纤维增强钛基复合材料横向强度分析

连续SiC纤维增强钛基复合材料(SiCf/Ti)具有良好的综合性能,但其横向性能低于钛合金基体,为了准确地预测SiCf/Ti复合材料的横向强度,提出一种基于界面脱粘强度的计算模型。采用SiCf/Ti复合材料十字拉伸试件来测试复合材料的纤维/基体界面脱粘强度,并分析了热处理工艺对界面脱粘强度影响规律,以及不同纤维之间界面脱粘强度的差别。复合材料横向拉伸试件采用箔-纤维-箔方法制备,每个试件的纤维层数为10层,纤维百分数为30%左右。在不同温度条件下测试复合材料的横向拉伸强度,拉伸温度分别为室温、300,400,550℃,通过对比实验结果和模型预测结果,模型预测的结果与实验结果的误差不超过5%。     

SiC/Ti_3Al复合材料原位合成及其界面反应动力学研究

利用TC4,Al廉价材料,通过磁控溅射物理气相沉积技术制备SiC先驱丝,利用热等静压工艺,在温度1423 K,压力170 MPa条件下进行复合,反应时间为1 h,通过原位反应生成Ti3Al基体,从而制备SiC纤维增强Ti3Al基复合材料。通过扫描电镜(SEM)和能谱分析(EDS)观察SiC纤维增强Ti3Al基复合材料基体与界面的微观组织形貌及界面元素分布,利用透射电镜(TEM)分析复合材料基体的物相结构,并对SiC纤维增强Ti3Al基复合材料的界面反应进行动力学分析。结果表明,利用TC4,Al制备的SiC先驱丝,通过原位反应可生成Ti3Al基体,属于六方晶系,组织为等轴晶,晶粒尺寸约为1μm。通过磁控溅射和热等静压工艺制备SiC纤维增强Ti3Al基复合材料,可缩短工艺流程,节约成本。根据SiC纤维增强Ti3Al基复合材料界面反应层生长动力学分析,得到界面反应层生长动力学方程:δ=2.73×10-6exp(-257.09×103/RT)t1/2,可准确预测连续碳化硅纤维增强Ti3Al基复合材料在制备和使用过程中界面反应层的生长规律,为其应用提供理论依据。     

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。     

用Ni＋Ti粉坯热压反应烧结连接SiC

用Ni＋Ti粉坯作为焊料，采用热压反应烧结连接法连接SiC陶瓷，研究了焊接温度、保温时间、连接压力和压坯厚度对试样连接强度的影响规律。在本文所述试验范围内，确定的最佳工艺为：连接温度1100℃，保温时间20min，焊接压力12．7MPa，焊料压坯厚度0．3mm，所得连接件的相对抗弯强度为53％。微观结构和XRD物相分析表明：在Ni＋Ti粉坯与sic陶瓷接合界面处，发生了元素的互扩散和界面反应，在适当的工艺条件下，接头界面具有在NiTi、Ni3C、Ni16Ti6Si7混合物的基体中弥散分布TiC相的微观组织，借助于主要基体相NiTi的韧性和与母材SiC晶格匹配良好的TiC可以实现有效的界面结合。     

双尺度SiC颗粒增强铝基复合材料制备工艺研究

通过粉末冶金真空热压烧结法制备双尺度(纳米、微米)混杂SiC颗粒增强铝基复合材料,研究不同烧结温度和压力对复合材料的组织、密度、硬度及耐磨性的影响。试验结果表明:SiC颗粒在复合材料基体中分布均匀,基体与增强体界面结合较好。随着烧结温度和压力的增高,复合材料的致密度、硬度、耐磨性均先增大后减小,最佳烧结温度和压力分别为460℃和30 MPa,微纳米混杂颗粒增强、单一微米颗粒增强、单一纳米颗粒增强复合材料的硬度分别是76.6 HV、70.7 HV、62.75 HV,比基体分别提高52.4%、40.6%、24.8%,耐磨性分别是基体的2.22倍、1.71倍、1.42倍。     

SiC纤维增强Ti/Ti_2AlNb叠层复合材料制备及界面行为研究

以SiC纤维、Ti箔、Ti_2AlNb箔为原材料,采用箔-纤维-箔方法,通过真空热压技术制备了SiCf/Ti/Ti_2AlNb叠层复合材料。利用扫描电子显微镜(SEM)、能谱分析仪(EDS)和X射线衍射仪(XRD)对复合材料相组成和微观组织进行了分析。结果表明,当真空热制造参数为920℃/40 MPa/30 min时,SiC纤维与韧性金属Ti实现良好冶金结合,界面反应产物主要为TiC,界面反应层厚度为0.8μm,C涂层厚度为1.3μm;韧性金属Ti层与金属间化合物Ti_2AlNb层通过Ti,Al,Nb 3种元素相互扩散方式形成固相扩散连接,界面平直,复合材料呈现出理想叠层结构。制备态的SiCf/Ti/Ti_2AlNb叠层复合材料主要由α-Ti,β-Ti,SiC,TiC,O相和B2相构成。在Ti与Ti_2AlNb固相扩散连接过程中,由于Al原子的扩散速率大于Nb原子,且Al是α稳定元素,Nb是β稳定元素,从而导致在Ti/Ti_2AlNb界面区域依次形成α+β双相组织和富B2相。在真空热压实验中,韧性金属Ti层与金属间化合物Ti_2AlNb层固相扩散连接过程依次为:物理接触/α+β双相区形成/富B2相区形成/富B2相区增厚。     

粉体粒径级配比对粉末冶金SiC_p/6061Al复合材料组织与性能的影响

选择不同粒径的6061Al粉末和SiC颗粒,采用真空热压法制备含35%SiC体积分数的SiCp/6061Al复合材料,研究不同级配比对复合材料显微组织和抗拉强度的影响。结果表明:复合粉末的粒径级配比可影响复合材料的微观组织和力学性能;当增强体颗粒粒径为15μm时,随基体6061粉末与SiC颗粒粒径比降低,SiC颗粒在复合材料中的分布越来越均匀,抗拉强度提高;当基体6061Al粒径为10μm时,随SiC颗粒粒径减小,复合材料微观组织的均匀性降低,但抗拉强度提高。并建立了理想的复合粉末颗粒分布模型,模型的理论计算结果与Slipenyuk公式计算结果接近。     

高硬度Mg基复合材料及其制备

本文采用球磨／热压工艺制备了Ni-Ti长纤维增强镁基复合材料。将镁合金切屑在无水乙醇的保护下进行球磨，XRD分析显示镁合金粉末经过球磨没有被氧化。热压后的NiTi纤维增强镁基复合材料密度十分接近镁合金铸态的密度值，经过球磨工艺的复合材料硬度明显提高。复合材料经OM和SEM分析发现基体组织均匀。纤维／基体界面结合较好。     

Recycling of aluminum matric composites

Separation of matrix metals in composites was tried on alumina short fiber-reinforced aluminum and 6061 alloy composites and SiC whisker-reinforced 6061 alloy composite for recycling. It is possible to separate molten matrix metals from fibers in the composites using fluxes that are used for melt treatment to remove inclusions. About 50 vol pct of the matrix metals was separated from the alumina short fiber-reinforced composites. The separation ratio of the matrix from the SiC swisker-reinforced 6061 alloy composite was low and about 20 vol pct. The separation mechanism was discussed thermodynamically using interface free energies. Since the flux/fiber interface energy is smaller than the aluminum/fiber interface energy, the replacement of aluminum with fluxes in composites takes place easily. Gases released by the decomposition of fluxes act an important role in pushing out the molten matrix metal from the composite. The role was confirmed by the great amount cavity formed in the composite after the matrix metal flowed out.     

Recycling of aluminum matrix composites

Separation of matrix metals in composites was tried on alumina short fiber-reinforced aluminum and 6061 alloy composites and SiC whisker-reinforced 6061 alloy composite for recycling. It is possible to separate molten matrix metals from fibers in the composites using fluxes that are used for melt treatment to remove inclusions. About 50 vol pct of the matrix metals was separated from the alumina short fiber-reinforced composites. The separation ratio of the matrix from the SiC whisker-reinforced 6061 alloy composite was low and about 20 vol pct. The separation mechanism was discussed thermodynamically using interface free energies. Since the flux/fiber interface energy is smaller than the aluminum/fiber interface energy, the replacement of aluminum with fluxes in composites takes place easily. Gases released by the decomposition of fluxes act an important role in pushing out the molten matrix metal from the composite. The role was confirmed by the great amount cavity formed in the composite after the matrix metal flowed out.     

Creep rupture of a silicon carbide reinforced aluminum composite

The microstructure, texture, and whisker orientations in 6061 Al-20 wt pct SiC whisker composites have been examined using transmission electron microscopy and X-ray diffraction. Tension creep tests of the composite material have also been conducted in the temperature range 505 to 644 K (450 to 700 F). The steady state creep rate of the composite depends strongly on the temperature and applied stress. The stress exponent for the steady state creep rate of the composite is approximately 20.5 and remains essentially constant within the range of test temperatures. The activation energy is calculated to be 390 kJ/mol, nearly three times as high as the activation energy for self-diffusion of aluminum. No threshold stress was observed. Fracture surface examination using scanning electron microscopy shows that the composite fails by coalescence of voids in the aluminum matrix which originate at the aluminum-SiC interface. It is demonstrated that SiC paniculate composites are less creep resistant than SiC whisker composites.     

Microstructure characterization of a pressureless infiltrating oxidized SiCp preform by A1-8Mg

The microstructure of a pressureless infiltrating 55vo1% oxidized SiC preform by Al-8Mg alloy was characterized by transmission electron microscopy (TEM), high resolution TEM (HRTEM), field emission scanning electron microscopy (FE-SEM), and X-my diffraction.The TEM image of the interface between Al and SiC shows that the surface of SiC is covered by a rough nanocrystal layer of MgAl2O4,Al2O3, and Si, produced by the interracial reaction of Al, Mg, and SiO2 on the surface of SiC. The Al-SiC interface is also examined by HRTEM to be better understood how MgAl2O4 and Al2O3 ale produced Dendritic Al2O3 crystals are embedded in the pores of the composite generated from the mutual bonding of SiO2 on the surface of SiC. Columnar AlN crystals of about 250 nm in length are bunched vertically on the SiC particle surface.     

Observation of fatigue damage process in SiC fiber-reinforced Ti-15-3 composite at high temperature

Unnotched SiC (SCS-6) fiber-reinforced Ti-15-3 alloy composite is subjected to a tension-tension fatigue test in a vacuum of 2×10⁻³ Pa at 293 and 823 K with a frequency of 2 Hz and R=0.1. Direct observation of the damage evolution process during the test is carried out by scanning electron microscopy (SEM). Test temperature dependent and independent fatigue damage behaviors are observed. The early stage fiber fractures observed at the polished surface are not influenced by the test temperature; however, matrix crack initiation and propagation behaviors differ greatly with temperature. The evolution of interface wear damage also differs with temperature, becoming more severe at 823 K, and the interface wear damage zone increases with the increase of the number of fatigue cycles. The macroscopic fatigue damage appears as a modulus reduction associated with interface sliding, matrix crack propagation, and plastic deformation of the matrix. The deformation zone of the composite tested at 823 K spreads more than that at 293 K. The fatigue life of the composite tested at 823 K is longer than that at 293 K. This behavior is related to the difference in spread of the damage zone in the matrix.     

Effects of microstructure on the strength and fatigue behavior of a silicon carbide fiber-reinforced titanium matrix composite and its constituents

The results of a systematic study of the effects of microstructure on the strength and fatigue behavior of a symmetric [0/90]_2s Ti-15Al-3Cr-3Al-3Sn/SiC (SCS-6) composite are presented along with relevant information on failnure mechanisms in the composite constituents, i.e., the interface, fiber, and matrix materials. Damage micromechanisms are elucidated via optical microscopy, scanning electron microscopy (SEM), and nondestructive acoustic emission (AE) and ultrasonic techniques. Composite damage is shown to initiate early under cyclic loading conditions and is dominated by longitudinal and transverse interfacial cracking. Subsequent fatigue damage occurs by matrix slip band formation, matrix and fiber cracking, and crack coalescence, prior to the onset of catastrophic failure. However, the sequence of the damage is different in material annealed above or below the β solvus of the Ti-15-3 matrix material. Mechanistically based micromechanics models are applied to the prediction of the changes in modulus induced by fatigue damage. Idealized fracture mechanics models are also employed in the prediction of the fatigue lives of smooth specimens deformed to failure at room temperature. The article highlights the potential to develop mechanistically based predictive models based on simplified mechanics idealizations of experimental observations.     

Microstructure of AI2O3 fiber-reinforced superalloy (INCONEL 718) composites

Composites of INCONEL 718 alloy reinforced with either single-crystal (SAPHIKON) or polycrys-talline (Du Pont's FP) A1₂O₃ fiber were fabricated by pressure casting. Optical and transmission electron microscopy were used to characterize the microstructure of the composites and to determine the nature of the fiber/matrix reaction. The widely dispersed fibers in the SAPHIKON-fiber-reinforced composite had no influence on the solidification of the matrix. Six phases, γ-Ni₃Al, γ'-Ni₃Nb, δ-Ni₃Nb, TiC, NbC, and Laves, were present in the matrix of the composite. The last three phases were formed during solidification and the others precipitated during subsequent cooling. The high density of fibers in the FP-fiber-reinforced composite led to a more uniform microstructure within the matrix. Only three phases,γ″-Ni₃Nb, NbC, and Laves, were identified. Diffusion of Ti into the A1₂O₃ fiber resulted in preferential grain growth in the FP fiber in areas adjacent to the fiber/matrix interface. The fiber/matrix bond strength in shear in the SAPHIKON-fiber-reinforced composite was in excess of 150 MPa.     

Interface characterization of fiber-reinforced Ni3Al matrix composites

The interfacial reaction characteristics of SCS-6, Sigma, and B₄C/B fibers with nickel aluminide (Ni₃Al) matrix have been investigated between 780°C to 980°C for times ranging from 1 to 100 hours. The microstructure and elemental compositions across the reaction zone have been analyzed quantitatively using microscopy and electron probe microanalyses, respectively. The results show that Ni₃Al reacts extensively with SCS-6, Sigma, and B₄C/B fibers to form complex reaction products, and Ni is the dominant diffusing species controlling the extent of reaction. In the SiC/Ni₃Al composite, the C-rich layer on the SiC surface can slow down but cannot stop the inward diffusion of Ni into SiC fiber. When the C-rich layer is depleted, a rapid increase in reaction zone thickness occurs. Diffusion barrier coating on the fibers is required to minimize the interfacial reactions.     

Influence of Si on Interfacial Combination of SiCp/Al-Mg-Si Composite

The scanning electron microscopy (SEM) analysis results of Si distribution in the interface between SiC reinforcements and aluminum matrix of a stir casting SiCp/Al-Mg-Si composite were presented. Results show that there is Si precipitation deposit on the interface of the composite and Si connects with SiC reinforcements in one side and connects with aluminum matrix in the other side. Si phase plays as a connecting bridge, which contributes to the interfacial combination of SiCp/Al composite.