Effect of fiber characteristics on fracture behavior of Cr／SiC composites

Cr/SiC composites were prepared by precursor pyrolysis-hot pressing, and the effect of fiber characteristics on the fracture behavior of the composites was investigated. Because the heat treatment temperature of fiber T300 (below 1500 ℃ ) was much lower than that d fiber M40JB (over 2000 ℃ ), fiber T300 had lower degree d graphitization and consisted of more impurities compared with fiber M40JB, suggesting that T300 exhibits higher chemical activity. As a resuit, the composite with T300 showed a brittle fracture behavior, which is mainly ascribed to a strongly bonded fiber/matrix interface as well as the degradation d fibers during the preparation d the composite. However, the composite with M40JB exhibits a tough fracture behavior, which is primarily attributed to a weakly bonded fiber/matrix interface and higher strength retention of the fibers.     

Effect of alumina short fiber and air-cooling processing on solidification microstructure and tensile properties of Al2O3/Al-15Si composites

The effect of microstructure variation by addition of alumina short fiber and optimization of tensile properties by air-cooling processing in Al2O3/Al-15Si composites were studied.The results show that in Al-015Si alloy matrix composites with 14% and 30%(volume fraction)fiber,the primary silicon is hardly refined,but the eutectic silicon is effectively refined and granulated.Granulation of some eutectic silicon mainly happens in fiber segregation areas.Refining and granulation of the eutectic silicon are related to the physical constraint arising from the fiber,After the 30%Al2O3/Al-15Si composite was remelted and air-cooled,the number of the eutectic silicon on the surface of the fiber increases,which results in the improvement of fiber/matrix interface and tensile properties for the as-cast composite,Air-cooling processing may be reliable for the optmization of the microstructure and properties of fiber reinforced hypereutectic Al-15Si alloy composites.     

Tensile Behavior of SiC Fiber-Reinforced γ-TiAl Composites Prepared by Suction Casting

The process of preparing SiC fiber-reinforced y-TiAl composites by the conventional methods is difficult and complicated due to the high reactivity,high melting point and poor deformability of y-TiAl alloys.In this work,suction casting,a promising method for preparing SiC_f/TiAl composite,had been attempted.In the process,y-TiAl alloy melt was introduced rapidly into a mold within pre-arranged fibers that were coated with additional layer of titanium alloy.This simple method successfully prevented serious reactions between the alloy melt and the fibers which remained intact during the solidification process.The interfacial reaction layer was observed by optical microscopy,scanning electron microscopy(SEM).The interfacial reaction products were identified by transmission electron microscopy(TEM).Tensile tests of the matrix alloy and composites were performed at room temperature and 800 ℃.The results exhibited that the tensile strength of SiC_f/γ-TiAl composite was higher than that of the matrix alloy at both room temperature and 800 0 C.At room temperature,tensile strength of SiC_f/γ-TiAl composite was increased by about 7%(50 MPa),whereas a double increase in tensile strength 14%(100 MPa)was obtained at 800 ℃.The titanium alloy coating on the fiber not only prevented the serious interfacial reaction between the y-TiAl alloy melt and the SiC fiber,but also played a role in delaying the propagation of cracks in the matrix to the fiber at 800 ℃.The fracture mechanism of the composite was analyzed by fracture metallographic analysis.     

Mechanical Property of M40J_f/5A06Al Composite at Elevated Temperatures

In this work, aluminum alloy with a high concentration of magnesium(5A06) was reinforced with 55 vol% unidirectional ultra-high modulus and highly graphitized carbon fiber(M40J) using pressure infiltration method. The effect of temperature on the bending strength of the Cf/Al composites was investigated from room temperature to 500 ℃. The experimental results showed that the strength of M40Jf/5A06 Al composites was not affected by temperature from room temperature to 200 ℃. The bending strength of the composite at 300 ℃ was decreased by 30% compared with that at room temperature. In order to evaluate the extent of interface weakening, the length of fiber pullout was measured. The results showed that the pullout length reached the maximum at 300 and 500 ℃, which indicated weak interface at the corresponding temperature. The DSC curve presented obvious heat absorption peak at around 300 ℃, which may be attributed to the dissolution of the interfacial product b(Al3Mg2) phases at the C/Al interface. The bending fracture surfaces of the composites after three-point bending tests were observed by SEM, plastic-viscous flow of the matrix were observed at the samples tested at 500 ℃. The predominant mechanisms for high-temperature damage of M40Jf/5A06 Al composites are matrix softening caused by dislocation recovery and interface weakening caused by the dissolution of interfacial products.     

Microstructure and interfacial strength of SiC fiber-reinforced Ti17 alloy composites with different consolidation temperatures

The interfacial reaction and titanium matrix microstructure in continuous SiC fiber-reinforced titanium matrix composite were investigated. By comparison of two samples actuated by 800℃(in α+β dual-phase field)and 920℃(in β single-phase field) consolidation, it can be concluded that tri-layer interfacial reaction regions consisting of fine TiC_x/transition TiC_x/coarse TiC_x are formed in both two samples. In addition, the total thickness of reaction layer for composites prepared at 920℃is thicker than that consolidated at 800℃, while fine TiC_x layer of 920℃sample is thinner than that of 800℃sample, which may be ascribed to the quick growth of PVD-Ti17 grain manufactured at 920℃. In addition, lower interfacial shear strength is obtained in 920℃sample, which can be ascribed to the formation of too thick brittle TiC layer. The research in the work is expected to motivate further exploration for interface adjustment of titanium matrix composites.     

CRYOGENIC PROPERTIES OF Al-SiC COMPOSITES AND EFFECT OF MATRIX CHARACTERISTICS AND REINFORCEMENT TYPE

The tensile tests on the silicon carbide whisker and partieulate reinforced 2124Al and 2024Al alloy composites fabricated by p/m technique were carried out at the tempera-tures ranging from room temperature to-196C,and the fracture surfaces were examined.The cryogenic strength of the composites incredses with the decreasing test temperature.Clean interface is beneficial to the improvement in cryogemc strength of the composites.The effect of the interface characteristies on the particulate composite is less than that on the whisker composite.With the decreasing temperature,the increase in strength of the whisker composite is more than that or the particulatc composite,which could beattributed to different strengthening mechanism.     

TENSILE PROPERTIES AND INTERFACIAL FEATURE OF SiC COATED C/Al COMPOSITE WIRES UNDER ISOTHERMAL HEAT TREATMENT

The effect of different regimes of heat treatment on the tensile strength of SiC coatedcomposite of C fibers reinforced Al wires has been investigated.Their tensile strengthmay increase under treatment either at 500℃ for 2h or 550℃ for 1h,but decreaseover 600℃.After the strength tests of extracted fibers from composite wires,theSiC coating is an excellent protection to C fibers.EPMA and EDAX showed that theC/Al interface of the composite wires is stable under treatment below 600℃,butunstable at 650℃     

Preparation and properties of Cu matrix composite reinforced by carbon nanotubes

Cu matrix composites reinforced by carbon nanotubes(CNTs) were prepared. The effect of carbon nanotubes on mechanical and tribological properties of the Cu matrix composites were investigated. The chemical method for coating CNTs was reported. The morphology of the fracture surfaces and worn surface were examined by SEM.The results show that Cu/coated-CNTs composites have higher hardness, much better wear resistance and antifriction properties than those of the reference Cu alloy (Cu-10Sn) and Cu/uncoated-CNTs composite sintered under the same conditions. The optimal mechanical properties of the composites occurred at 2. 25%(mass fraction) of CNTs. The excellent wear resistance and anti-friction properties are attributed to the fiber strengthening effect of CNTs and the effect of the spherical wear debris containing carbon nanotubes on the tribo-surface.     

Stir casting process for manufacture of Al-SiC composites

Stir casting is an economical process for the fabrication of aluminum matrix composites.There are many parameters in this process,which affect the final microstructure and mechanical properties of the composites.In this study,micron-sized SiC particles were used as reinforcement to fabricate Al-3 wt% SiC composites at two casting temperatures(680 and 850 ℃) and stirring periods(2 and 6 min).Factors of reaction at matrix/ceramic interface,porosity,ceramic incorporation,and agglomeration of the particles were evaluated by scanning electron microscope(SEM) and high-resolution transition electron microscope(HRTEM) studies.From microstructural characterizations,it is concluded that the shorter stirring period is required for ceramic incorporation to achieve metal/ceramic bonding at the interface.The higher stirring temperature(850 ℃) also leads to improved ceramic incorporation.In some cases,shrinkage porosity and intensive formation of Al_4C_3 at the metal/ceramic interface are also observed.Finally,the mechanical properties of the composites were evaluated,and their relation with the corresponding microstructure and processing parameters of the composites was discussed.     

Study on SCS-6/Ti-6A1-4V Composite

COMPARED WITH traditional titanium alloys,titanium matrix composites exhibit much improvedmechanical properties,in terms of specific strengthsand stiffness at ambient and elevated temperatures.From1970's on,much attention has been put ontitanium matrix composite[1~31.Titanium matrixcomposites are divided into two categories:fiber-reinforced and particle reinforced.These twokinds of composites have their own advantageous.AsTSM Company solve the interface interaction betweenSCS-6fiber an…     

Thermal expansion and dimensional stability of unidirectional and orthogonal fabric M40/AZ91D composites

Unidirectional (60%, volume fraction) and orthogonal (50%, volume fraction) M40 graphite fibre reinforced AZ91D magnesium alloy matrix composites were fabricated by pressure infiltration method. The coefficients of thermal expansion (in the temperature range of 20-350 ℃) and dimensional stability (in the temperature range of 20-150 ℃) of the composites and the corresponding AZ91D magnesium alloy matrix were measured. The results show that coefficients of thermal expansion of the composites in longitudinal direction decrease with elevating temperature. The coefficients of thermal expansion (CTE) for unidirectional M40/AZ91D composites and orthogonal M40/AZ91D composites are 1.24×10-6 ℃-1 and 5.71×10-6 ℃-1 at 20 ℃, and 0.85×10-6 ℃-1 and 2.75×10-6 ℃-1 at 350 ℃, respectively, much lower than those of the AZ91D alloy matrix. Thermal cycling testing demonstrates that the thermal stress plays an important role on residual deformation. Thus, a better dimensional stability is obtained for the AZ91D magnesium alloy matrix composites. More extreme strain hysteresis and residual plastic deformation are observed in orthogonally fabric M40 reinforced AZ91D composite, but its net residual strain after each cycle is similar to that of the unidirectional M40/AZ91D composite.     

Evaluation of interface fracture toughness in SiC fiber reinforced titanium matrix composite

The finite element method based on the equivalent domain integral technique was developed to simulate the push out test and evaluate the interfacial fracture toughness of SiC reinforced titanium matrix composites. A special subroutine was introduced while modeling the push-out test to control interfacial failure process. In addition, the residual stresses, Poisson ratio and friction stresses were all considered in the finite element analysis and the interface debonding was described as a continuous process. The results show that the interfacial fracture toughness of SiC/Timetal-834 is about 50 Jim2. Moreover, the effects of various parameters on the interfacial fracture toughness and the variations of energy release rates at both ends of the specimen were analyzed in detail.     

Enhanced mechanical properties in Al/diamond composites by Si addition

Diamond particles reinforced aluminum–silicon matrix composites,abbreviated as Al(Si)/diamond composites,were fabricated by squeeze casting.The effect of Si content on the microstructure and mechanical properties of the composites were investigated.The mechanical properties are found to increase monotonically with Si content increasing up to 7.0 wt%.The Al-7.0 wt% Si/diamond composite exhibits tensile strength of 78 MPa,bending strength of 230 MPa,and compressive strength of426 MPa.Al–Si eutectic phases are shown to connect with Al matrix and diamond particles tightly,which is responsible for the enhancement of mechanical properties in the Al(Si)/diamond composites.     

Shape Memory Alloy-Reinforced Metal-Matrix Composites:A Review

Metal-matrix composites reinforced with shape memory alloys(SMA, including long fiber, short fiber, and particle) are ‘‘intelligent materials' ' with many special physical and mechanical properties, such as high damping property,high tensile strength, and fatigue resistance. In this review article, the fabrication method, microstructure, interface reaction, modeling, and physical and mechanical properties of the composites are addressed. Particular emphasis has been given to(a) fabrication and microstructure of aluminum matrix composites reinforced with SMAs, and(b) shape memory effect on the physical and mechanical properties of the composites. While the bulk of the information is related to aluminum matrix composites, important results are now available for other metal-matrix composites.     

Microstructure and mechanical properties of 2D woven Grf/Al composite

A 2D woven graphite fibers reinforced aluminum matrix composite with 50%Grf （volume fraction） was fabricated by the squeeze-casting technology, and its microstructure and mechanical properties were investigated. The results show that the composite is dense, the graphite fibers are distributed uniformly in the composite. TEM observation indicates the bonding between fiber and matrix is good and little interfacial reaction is found in the Grf/Al composite. This is attributed to the better stability of graphite fiber and the fabrication process minimizing the contact time between fiber with matrix at high temperatures. The 2D woven Grf/Al composite exhibites better mechanical properties with tensile strength, bending strength and elastic modulus of 366.2, 519.7 and 110.7 GPa, respectively.＂ SEM images suggeste that the fracture is irregular and some pulled-out fibers are found, which indicats that the high strength of fiber is not degraded.     

Interfacial characteristics and dynamic mechanical properties of Wf/Zr-based metallic glass matrix composites

Tungsten fiber reinforced Zr41.25Ti13.75Cu12.5Ni10Be22.5 metallic glass matrix composites were fabricated by means of melt infiltration casting. Their dynamic compressive tests were performed using a Hopkinson bar. The relationship between the interfacial characteristics and the dynamic compressive behavior was investigated. The results indicate that the interface characteristics of composites include interfacial diffusion and interfacial reaction, and the interfacial shear strength increases when the interfacial reaction is serious. The dynamic plastic performance are improved obviously if the suitable interface reaction occurs. The failure occurs by shear and the fibers split longitudinally if there is no interface reaction or a little reaction; in contrast, holistic failure occurs if there is too much interface reaction.     

Fabrication and mechanical properties of MWCNTs-reinforced aluminum composites by hot extrusion

Over the past decade,the interest in aluminum composites reinforced with carbon nanotubes has grown significantly.Studies have been carried out to overcome problems with uniform dispersion,interfacial bonding,void formation and carbide formation of the composites.In the present work,multi-wall carbon nanotubes(MWCNTs)aluminum composites were produced.High-energy ball milling with the aim at developing well-dispersed MWCNTs Al composites was followed by cold compaction,sintering,and hot extrusion at 500 ℃.Different amounts of stearic acid as processing control agent(PCA)is used in order to minimize cold welding of the Al particles,and to produce finer particles.Differential scanning calorimetry(DSC),scanning electron microscopy(SEM),transmission electron microscopy(TEM),and X-ray diffraction(XRD)were employed to analyze the MWCNTs,the aluminum powder,and the composites' microstructural behavior.The hardness and tensile properties of the composites are also evaluated.The results showed 500％ increase in yield stress after the addition of 1 wt％ MWCNTs in Al-MWCNTs based composite.The ball-milling time of 4 h is found to be sufficient as excessive milling time destroys a vast number of MWCNTs.     

Effects of whisker surface treatment on microstructure and properties of Al_(18)B_4O_(33w)/6061Al composites

6061Al matrix composites reinforced by ZnO-coated Al18B4O33 whiskers were fabricated by a semi-solid mechanical stirring technique.The effects of ZnO coating on interfacial reaction between whiskers and matrix and the tensile properties of the composites were investigated.Tensile tests on composites were performed at room temperature,and microstructures were observed by scanning electron microscopy(SEM).The results show that the surface treatment of whiskers could reduce interfacial reaction effectively,improve the wettability between whiskers and matrix and enhance the tensile properties of the composites obviously.In addition,semi-solid stirring parameters were also under preliminary study.The stirring parameters were determined by the distribution of whiskers in the composites.The composites with homogeneously distributed whiskers were fabricated by semi-solid stirring at 610 ℃ for 30 min.     

Effect of Rolling on a Warm Compacted Ti_3SiC_2 Particulate Reinforced Cu Matrix Composite

Warm compaction was employed to fabricate a Ti3SiC2 particulate reinforced copper matrix composite for electro-friction application. Copper matrix composite reinforced with 5wt% of copper-coated Ti3SiC2 particulates were prepared by compacting mixed powder with a pressure of 700 MPa at 145 ℃, and then sintered at 1000 ℃ under cracked ammonia atmosphere for 60 min. In order to improve the density, rolling process was applied on the sintered samples, their density, hardness, electrical conductivity, ultimate tensile strength and tribological behaviors were studied. Results showed that the rolled composite with 30% deformation has a density of 8.28 g/cm3, a hardness of 1060 MPa (HB), an ultimate tensile strength of 288 MPa, an electrical resistivity of 7.0 ×10-8 Ω·m and a friction coefficient of 0.17.     

Effect of heat-treatment on microstructure and properties of SiC particulate-reinforced aluminum matrix composite

The effects of solid solution and aging processing on the microstructures and mechanical properties of the multi-layer spray co-deposited 7090Al/SiCp composite were investigated. The experimented results show that fine grains and homogeneous microstructures can be obtained, the average grain size of the as-solid solution treated and as-aged composites after extrusion is under 3.0μm. A large amount of the Cu-rich phase particles form in the as-extruded samples, and solve into the matrix after solid solution treatment. After aging, the size of the precipitate phases, mainly MgZn2 and CuAl2 is less than 1.0 μm, which homogeneously distribute inside the grains and at the grain boundaries. The ultimate tensile strength of the composite treated at T6 state, i.e. solid solution treated at 475 ℃for 1 h then aged at 120 ℃ for 24 h, is up to 765 MPa.