热处理对SiC/Ti-6Al-4V复合材料力学性能的影响

测定了经过900℃不同时间热处理的SiC/Ti-6Al-4V复合材料的拉伸强度,并采用全局载荷分配模型计算了复合材料的强度。发现长时间热处理后,复合材料强度的计算值与实测值吻合很好,但该模型对未经热处理的制备态试样的预测值偏高。扫描电镜和透射电镜微观分析表明,随着热处理时间的延长,SiC/Ti-6Al-4V复合材料的界面反应区增厚而SiC纤维的C涂层逐渐消耗,复合材料的界面结合强度逐渐增加但抗拉伸强度逐渐下降。界面反应形成的反应产物主要为TiC,在C涂层消耗完的区域还形成了Ti5Si3。界面反应是使复合材料力学性能变差的主要原因。     

SiCf/SiC复合材料表面Si/Yb2Si2O7双层涂层结合强度分析

目的 通过选择合适的复合材料拉伸方向和涂层制备工艺,在SiCf/SiC复材上获得高结合强度的Si/Yb2Si2O7双层涂层.方法 采用真空等离子喷涂技术在2.5D编织的SiCf/SiC复合材料表面制备Si涂层、Si/Yb2Si2O7双层涂层.采用金相、XRD、SEM和EDS对试样进行表征,采用拉伸试验测试涂层的结合强度...     

Designing the microstructure of squeeze-cast Al composites

Retaining their high strength and stiffness up to 350°C, SiC fiber-reinforced aluminum composites are lightweight alternatives to titanium or steel parts. By combining filament winding and squeeze-casting, components of fairly complex shapes can be produced. Both Nicalon and Tyranno “hybrid” SiC fibers (that is, continuous fibers with SiC particles distributed between the fibers) were used to reinforce pure aluminum and alloy 357 matrices. Their longitudinal properties appear much more dependent on alloying elements and processing conditions than on fiber types, but hybridization is effective in raising transverse properties significantly. Failure modes can be related to microstructural features, including interfaces, fiber-to-fiber contacts, second-phase bridges between fibers and fiber damage through processing. Provided some basic rules for microstructural design are followed for the manufacture of actual parts, squeeze-cast SiC fiber aluminum composites offer great potential for defense and aerospace applications.     

Process for dense 2D SiC fiber-SiC matrix composites

A new process using SiC fiber fabrics and SiC tapes to produce dense 2D SiC fiber-SiC (SiC/SiC) composites is demonstrated. The strategy for fabricating the SiC/SiC composites involves: (i) alternately stacking the SiC fiber fabrics and SiC tapes at room temperature, (ii) pyrolyzing of the stacked composites, and (iii) hot-pressing the pyrolyzed composites. By controlling the hot-pressing temperature, it is possible to obtain dense 2D SiC/SiC composites with relative densities of >98%. The 2D SiC/SiC composites show no degradation of the SiC fibers and a higher mechanical strength.     

SiCp/Al合金复合材料时效强化的综合模型

以颗粒强化和时效强化理论为基础,结合铝合金时效动力学研究了SiCp／Al合金复合材料中增强体尺寸、体积分数以及时效制度对屈服强度的影响．分析不同时效制度下复合材料屈服强度与时效参数的关系,建立了一个SiCp／Al合金复合材料的时效强化综合模型,利用该模型可以预测复合材料屈服强度随增强体体积分数和尺寸以及时效时间的变化规律,将模型应用于SiC颗粒增强2XXX铝合金复合材料,结果显示模型预测值与实验数据吻合很好．     

单向碳化硅短纤维增强玻璃陶瓷材料弯曲断裂行为的研究

制备了单向短碳化硅纤维增强玻璃陶瓷的复合材料。研究了复合材料的弯曲断裂行为，以及相关的增强机制。结果表明．短碳化硅纤维可以有效提高玻璃陶瓷的断裂强度，纤维体积分数为30％时，沿纤维方向的平均弯曲断裂强度是基体材料的3倍：短碳化硅纤维增强玻璃陶瓷基复合材料的弯曲应力-挠度曲线、以及断裂行为具有与长纤维复合材料类似的特征．其断裂方式为非灾难性断裂。单向短碳化硅纤维增强玻璃陶瓷基复合材料的主要增强机制为纤维脱粘、纤维滑移、纤维桥接、纤维断裂与纤维拔出。     

Cf/SiC复合材料的氧化及抗氧化技术研究进展

连续碳纤维增强碳化硅陶瓷基复合材料（C_f/SiC）因其具有高比强、高比模、耐磨损、良好热稳定性以及耐高温等突出性能,成为航空、航天、高性能武器装备等高尖端领域极具潜力的热结构材料。但高温氧化是其工程应用上的弱点,会造成C_f/SiC复合材料性能的下降,直接影响到材料的使用寿命和安全性。分析C_f/SiC复合材料的氧化影响因素,从界面相、基体和表面涂层3个方面综述C_f/SiC复合材料高温抗氧化技术的研究进展,结果表明:不同的温度区间内C_f/SiC复合材料的氧化行为不同,而界面改性、涂层抗氧化和基体改性相结合是实现材料抗氧化的关键。     

Microstructure and mechanical properties of 3D fine-woven punctured C/C composites with PyC/SiC/TaC interphases

The 3D fine-woven punctured C/C-(P_yC/SiC/TaC) composites, composed of P_yC/SiC/TaC interphases and pyrocarbon (PyC) matrix, were synthesized by isothermal chemical vapor infiltration (ICVI) methods. The alternating layers and the structure of these composites were examined by polarized light microscopy (PLM), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). It is found that the P_yC matrix has rough laminar (RL) structure, the TaC layer has NaCl-type cubic structure, and the SiC layer has few wurtzite type 10H-SiC besides β-SiC structure. The effects of fiber coating and the bulk density on the tensile and flexural properties of composites along X or Y and Z direction were investigated. It is shown that fiber coated 3D woven punctured C/C composites have good tensile and flexural strength, and the maximum of flexural strength is 375 MPa in X or Y direction at density of 1.89 g/cm³, which is about three times higher than that of samples without TaC/SiC fiber coating. The flexural strength and bending strength increase with increasing the density of the composites. The analysis of fracture surfaces reveals that fibers and fiber bundles are pulled out in composites, indicating that the composite exhibits a non-linear failure behavior through propagation and deflection of the cracks.     

C/Ti/Cu interfacial reaction in SiC<Subscript>f</Subscript>/Cu composites

Continuous SiC fiber reinforced copper matrix(SiCf/Cu) composites were prepared by fiber coating method,and Ti6Al4V interlayer was introduced as an interfacial modification coating to improve the interfacial bonding strength.The interfacial reaction characteristics were investigated by transmission electron microscopy(TEM).The results show that nearly all the titanium atoms reacted with the carbon coating of SiC fibers to form two layers of TiC.Also,a thin copper layer that is sandwiched between these two layers was detected.No Ti-Cu interfacial reaction product was observed.The formation process of the interfacial reaction along with its mechanism was discussed.     

Effects of dip-coated BN interphase on mechanical properties of SiCf/SiC composites prepared by CVI process

BN interphase was successfully synthesized on SiC fiber fabrics by dip-coating process using boric acid and urea as precursors under N₂ atmosphere. The morphology of BN interphase was observed by SEM, and the structure was characterized by XRD and FT-IR spectra. The SiC_f/SiC composites with dip-coated BN interphase were fabricated by chemical vapor infiltration (CVI) process, and the effects of BN interphase on the mechanical properties of composites were investigated. The results show that the SiC fibers are fully covered by BN interphase with smooth surface and turbostratic structure (t-BN), and the thickness is about 0.4 μm. The flexural strengths of SiC_f/SiC composites with and without BN interphase are about 180 and 95 MPa, respectively. Compared with the as-received SiC_f/SiC composites, the composites with BN interphase exhibit an obvious toughened fracture behavior. From the microstructural analysis, it can be confirmed that the BN interphase plays a key part in protecting the fibers from chemical attack during matrix infiltration and weakening interfacial bonding, which can improve the mechanical properties of SiC_f/SiC composites remarkably.     

Multiscale modeling of failure in metal matrix composites

A multiscale approach to composite failure, in which detailed information on small-scale micromechanics is incorporated approximately yet accurately into larger-scale models capable of simulating extensive damage evolution and ultimate failure, is applied to the deformation and failure of a Ti–matrix composite. The composite is reinforced with SiC fibers under conditions of matrix yielding and interfacial sliding via Coulomb friction. Specifically, a fully three-dimensional finite element model is employed to investigate the load transfer from broken to unbroken fibers as a function of applied stress and interface friction coefficient. With a von Mises matrix yield criterion, constraint effects permit the matrix to carry some of the transferred load near the fiber break, a feature not captured in previous composite models. The single-break results for stress concentrations are then used as the discrete Green's functions for load transfer in the full composite, and the predicted load transfer around a seven-fiber-break cluster is shown in good agreement with finite element results. The Green's function model is then used to predict overall damage evolution and composite failure for an IMI-834 Ti/SCS-6 SiC system for various interface friction coefficients. The composite tensile strength is rather insensitive to the friction coefficient and, for values of μ comparable to those measured experimentally, the predicted tensile strength is in excellent agreement with the measured value. Analytic models for scaling of the tensile strength to very large sizes are then shown to agree well with strengths obtained from simulations. These results suggest that the hierarchical coupling approach used here may be useful for approaching a wide variety of damage and failure problems in fiber composites.     

Fabrication characteristics and tensile strength of novel Al2024/SiC/red mud composites processed via stir casting route

The stir casting technique was used to fabricate aluminum 2024 matrix hybrid composites reinforced with SiC (5%, mass fraction) and red mud (5%–20%, mass fraction) particles. The developed composites were characterized by using scanning electron microscopy (SEM) and electron dispersive spectrum (EDS) techniques. Further, Taguchi's approach of experimental design was used to examine the tensile strength of the hybrid composites (with minimum number of experiments). It was found that the reinforcing particles were well dispersed and adequately bonded in the hybrid composites. The density and porosity of the hybrid composites were reduced with the increase in reinforcement content. The tensile strength of the composites increased with the increase in the red mud content and the ageing time. The developed model indicated that the red mud content had the highest influence on the tensile strength response followed by the ageing time. Overall, it was found that Al2024/SiC/red mud composites exhibited superior tensile strength (about 34% higher) in comparison to the Al2024 alloy under optimized conditions.     

Effects of volume fraction of SiC particles on mechanical properties of SiC/A1 composites

SiC particle reinforced pure aluminum composites were fabricated using a powder metallurgy method. The effect of the volume fraction of the SiC particles on the mechanical properties of the composites was studied by both model simulation and experiment. The results indicate that the yield strength and tensile strength increase, but the elongation decreases with the increase in the volume fraction of the SiC particles. Both the modified shear lag model and the multi-scale model predicted yield strength and normalized elongation show similar evolution trends with the experimental data. However, the modified shear lag model underestimates the yield strength due to the ignorance of the strengthening mechanisms caused by grain refinement and dislocations interaction by the introduction of the SiC particles, and the multi-scale model overestimates the normalized elongation due to the ignorance of the pores distributed in the matrix.     

Life prediction of titanium MMCs under low-cycle fatigue

Low-cycle fatigue failure in titanium metal matrix composites is caused by two separate damage mechanisms: fatigue crack growth in the Ti matrix and fiber breakage. Here, a coupled numerical model for predicting both crack growth and fiber breakage is developed and applied to predict low-cycle fatigue lives in a SiC-fiber reinforced Ti matrix composite. A three-dimensional finite element model containing a matrix crack, nucleated on the first loading cycle in the reaction layer around a fiber, that is bridged by SiC fibers is used to calculate both the matrix crack tip stress intensity factor and the local fiber stress concentrations due to the matrix crack, as a function of the crack size. The crack tip stress intensity factor is used in a Paris-law model for the growth rate of the matrix crack. The local stress distributions in the fibers are used as the effective “applied” load within a three-dimensional Greens Function method that simulates the fiber damage process at any fixed fatigue crack size. Fiber failure preferentially occurs within the matrix crack region, where the fiber stresses are comparatively high, and composite failure occurs when the damage in this region is sufficient to drive fiber failure throughout the remainder of the composite in a crack-like fracture mode. A fatigue life threshold is predicted at about 80% of the quasistatic tensile strength, where the fiber bundle can survive even with a matrix crack extending throughout the entire cross-section. Predictions for the low-cycle fatigue of Ti-matrix (IMI834) reinforced with SCS-6 SiC fibers compare well with available experimental data at high stresses using pristine fiber strengths and no adjustable parameters. Using literature values for the fatigued fiber strength beyond 10⁴ cycles and no adjustable parameters, the experimental data are also well matched at lower stresses. The model demonstrates that fatigue life can be dependent on actual composite size and can be very sensitive to initial fiber damage.     

热压反应烧结制备ZrB2-SiC复合材料的工艺及性能研究

以二硼化锆、正硅酸乙酯、蔗糖为原料,采用溶胶-凝胶法制备ZrB2-SiC前躯体,然后利用热压反应烧结方法,在1800℃,30MPa压力,流动的Ar气氛条件下,制备出高致密的ZrB2-SiC复合材料。其最大相对密度达到99.6%。ZrB2-SiC复合材料的抗弯强度和断裂韧性都随着SiC含量的增加先增加后降低。当SiC含量为20%时,ZrB2-SiC复合材料断裂韧性最大达到5.1MPa·m1/2。ZrB2-SiC复合材料的最大弯曲强度为272MPa,比报道出的值要低,这可能与过大的ZrB2晶粒有关。但当SiC含量为30%时,由于出现大量气孔而使材料不致密,从而导致其力学性能下降。     

Influence of preparation temperature on the oxidation resistance and mechanical properties of C/SiC coated C/C composites

A C/SiC oxidation resistance coating was prepared on carbon/carbon (C/C) composites by slurry and pack cementation. The microstructure, oxidation resistance and mechanical properties of C/SiC coating prepared from 1773 to 2573 K were investigated. With the increase of the preparation temperature, the oxidation resistance of C/SiC coating increases, however, the flexure strength decreases gradually. The preparation of C/SiC coating on C/C composites results in the fracture behavior of C/C composites changing from pseudo-plastic to brittle failure model. The decrease of flexure strength is mainly attributed to the decrease of C/C matrix’ flexure strength at high temperature.     

Finite Element Analysis of Push-Out Test of SiC Fiber Reinforced Titanium Matrix Composites

Based on the interphase layer model and the spring layer model, an improved interface model was developed to evaluate the interfacial shear strength of Titanium matrix composites(TMCs) and to analyze the effects of various parameters on the interfacial properties. The results showed that the improved interface model is more suitable for calculating the interfacial properties of SiC fiber reinforced titanium matrix composites. The interfacial shear strength of SiC/Timetal-834 predicted is 500 MPa. In additio...     

电子封装用Al/Si/SiC复合材料的显微组织与性能(英文)

采用气压浸渗法制备中体积分数电子封装用 Al/Si/SiC 复合材料。在保证加工性能的前提下,用与 Si 颗粒相同尺寸(13 μm)的 SiC 替代相同体积分数的硅颗粒制得复合材料,并研究其显微组织与性能。结果显示,颗粒分布均匀,未发现明显的孔洞。随着 SiC 的加入,强度和热导率将得到明显提高,但热膨胀系数变化较小,对使用影响也不大。讨论几种用于预测材料热学性能的模型。新的当量有效热导被引入后,H-J 模型将适用于混杂和多颗粒尺寸分布的情况。     

原位反应热压SiCp/MoSi2复合材料的组织与性能

以Mo粉、Si粉和C粉为原料,采用原位反应热压一次复合工艺制备不同含量SiC颗粒增强的SiCp/MoSi2试样,并研究其室温抗弯强度、断裂韧性、相对密度以及显微组织。结果表明,原位反应热压一次复合工艺制备的SiCp/MoSi2复合材料的强韧性比纯MoSi2有了大幅度的提高,当SiC含量为40vol%时,SiCp/MoSi2复合材料的抗弯强度达到最大,为475.2MPa,当SiC含量为50vol%时,复合材料的断裂韧性达到最大,为5.45MPa.m1/2。原位形成的SiC使MoSi2基体晶粒得到明显细化,并减少和消除了脆性的SiO2玻璃相。SiCp/MoSi2复合材料强韧性的提高主要是由于晶粒细化、SiC颗粒弥散强化以及脆性SiO2玻璃相的减少和消除。     

Superplastic behavior of PM SiCp/6061 aluminum alloy composites at high strain rates

The superplastic behavior of a powder-metallurgy processed 6061 Al composite was investigated as a function of SiC content increasing from 0% to 30% at 10% increments over a wide temperature range from 430°C to 610°C. The materials were found to be high-strain-rate superplastic. In the temperature range where grain boundary sliding (GBS) controlled the plastic flow, the strength of the composite was lower than that of the unreinforced matrix alloy even after compensating for grain size and threshold stress. This “particle weakening” was in contrast with the particle strengthening observed in the low temperature range where dislocation climb creep was found to control the plastic flow. In the GBS regime, the strength differential between the materials was a function of SiC content and temperature, which increased with the increase in SiC content and temperature. Strong Mg segregation was detected at interfaces between SiC and Al phases in the composites. Evidence for interfacial reaction reported in the Si₃N₄ reinforced 6061 Al composites could not be detected in the current composites. Extensive formation of whisker-like fibers was observed at the fractured surface of the tensile samples above the critical temperature where particle weakening begins to be exhibited. This result suggests the possibility that partial melting in the solute-enriched region near SiC interfaces is responsible for the particle weakening in the SiC reinforced 6061 Al composite.