Extrusion Deformation Texture of SiC_W/Al Composites

The interface orientation relationships betweenSiC whiskers and matrix have been studied byX-ray diffraction and crystallite orientation distri-bution functions (CODFs) analysis.The distribu-tion of SiC whiskers in Al matrix of the as-castSiC_w/Al composite was nearly unperfect isotropic.Both matrix and SiC whisker in as-extrudedSiC_w/Al composite were〈111〉fiber texture.Itis suggested that there are certain interfaceorientation relationships between the SiC_w and theAl matrix.     

Microstructure Characteristics of Interaction Layer of Zn-Al Eutectic Alloy with Al_2O_3p/6061Al Composites

The interaction between Zn-AI eutectic alloy and Al203p/6061AI composites in the vacuum furnace was investigated. Great attention has been paid to the elements diffusion, the microstructure and formation of the interface between Zn-AI eutectic alloy and Al2O3p/6061AI composites. Experimental results show that Zn-AI eutectic alloy has a good wetting ability to Al2O3p/6061 Al composites and the wetting angle decreases with increasing the temperature in vacuum. After the interaction, an interaction layer forms between Zn-AI alloy and Al2O3p/6061 Al composites. The phases in the interaction layer mainly consist of α-AI(Zn), Al2O3 and CuZn5 resulted from the diffusion of elements from the Zn-AI alloy. Several porosities distribute in the region near the interface of the Zn-AI alloy/interaction layer. The amount of shrinkage voids in the interacting layer is relevant to the penetration of Zn element into Al2O3p/6061Al composites which is a function of temperature. So it is necessary to lower heating temperat     

Effect of Interfacial Bonding on the Toughening of Al_2O_3/Ni Ceramic Matrix Composites

The main Iimitation to the toughening of the α-Al2O3/Ni composite is the poor bonding atthe interface. which causes the nickel particles to be pulled-out during crack propagation with-out obvious plastic deformation. A proper control of oxygen content at the Al2O3-Ni interfacecan promote wetting at the intedece, and produce a mechanically interlocked and chemically strengthened intedece, causing most of the nickel particles to be stretched to failure and to expe-rience severe plastic deformation during crack propagation in the composite. Fracture toughnesstesting using a modified double cantilever beam method with in situ observation of crack prop-agation in a scanning electron microscope shows that the composite with the strengthenedinterface has a more desirable R-curve behaviour and a higher fracture toughness value than thenormal composite.     

Effects of Solution Temperature on Tensile Properties ofSiC_w/2024Al Composite

The effects of solution (quench) temperature on the properties of SiCw/Al composite have been investigated using tensile tests. The experiments indicate that the solution temperature of the composite fabricated by P/M technique can be raised to 560℃. The tensile strength of the composite is obviously dependent on solution (quench) temperature and the composite solutionized at 540℃ exhibits a maximum of tensile strength and elongation-to-failure. These results can be accounted for by the variation of the dislocation density in the composite.     

Microstructure-Property Correlation in AI_4C_3 Dispersion Strengthened Al Composite

The microstructure and tensile properties of Al_4C_3 dispersion strengthened Al composite fabricatedby reaction milling technique were investigated.It is indicated that the rod-like Al_4C_3 dispersoidshaving a diameter of 0.02-0.03 μm and a length of 0.1-0.3μm are formed by reaction of C with Al,and uniformly distributed in the Al matrix.The interface between Al_4C_3 and Al is clean and theinterfacial bonding is good.The matrix consists of the subgrains which have the size of 0.3-0.4μm,and most of the Al_4C_3 dispersoids are distributed on the subgrain boundaries.The 11 vol.-%Al_4C_3/Al composite exhibits an UTS (ultimate tensile strength) of 400 MPa and anelongation-to-failure of 8.0%.     

Evolution of Thermoplastic Shear Localization and Related Microstructures in Al／SiCp Composites Under Dynamic Compression

The localized shear deformation in the 2024 and 2124 Al matrix composites reinforced with SiC particles was investigated with a split Hopkinson pressure bar (SHPB) at a strain rate of about 2.0×103 s-1. The results showed that the occurrence of localized shear deformation is sensitive to the size of SiC particles. It was found that the critical strain, at which the shear localization occurs, strongly depends on the size and volume fraction of SiC particles. The smaller the particle size, the lower the critical strain required for the shear localization. TEM examinations revealed that Al/SiCp interfaces are the main sources of dislocations. The dislocation density near the interface was found to be high and it decreases with the distance from the particles. The Al matrix in shear bands was highly deformed and severely elongated at low angle boundaries. The AI/SiCp interfaces, particularly the sharp corners of SiC particles, provide the sites for microcrack initiation. Eventual fracture is caused by the g     

Corrosion Behavior and Protection Efficiency of 2024Al and SiCp／2024Al Metal Matrix Composite

The corrosion resistance of 2024 Al and SiC particle reinforced 2024 Al metal matrix composite(SiCp/2024Al MMC) in 3.5% NaCl solution was investigated with electrochemical method and immersion test, and the corrosion protection of sulfuric acid anodized coatings on both materials was evaluated by electrochemical impedance spectroscopy.The results showed that the SiCp/2024AlMMC is more susceptible to corrosion than its matrix alloy in 3.5% NaCl.For 2024Al,the anodized coating provides excellent corrosion resistance to 3.5%NaCl.The anodized coating on the SiCp/2024Al provides satisfactory corrosion protection,but it is not as effective as that for 2024Al because the structure of the anodized layer is affected by the SiC particulates.     

Properties of Cast Hiduminium/Corundum Particulate Composites

This paper reports some results obtained in an investigation to see how increasing the corundum dispersoid content from o% to 7% in a matrix of hiduminium alloy affects the tensile and compressive strengths, the hardness and the casting characteristics of the composite. The results show that as the corundum content is increased, ultimate tensile strength (UTS)- compressive strength and hardness increase remarkably, whereas fluidity of the molten composite during casting drops significantly. It was found that just a minute amount of corundum is sufficient to cause a fairly large change in the mechanical properties and the fluidity of the molten material.This drop in castability is one of the reasons why adding corundum beyond 7 percent is not recommended. If other factors are kept constant, the fluidity is seen to slightly improve if the pouring temperature of the molten metal were increased from 670 to 710℃     

Microstructure and Mechanical Properties of Dy-α-sialon/Nano-size SiC Composites

The composite of Dy-α-sialon/10 wt pct nano-size SiC particles has been prepared from precursor powders of Si3N4, AIN, Al2O3, Dy2O3 and nano-size β-SiC. The hardness, toughness and bending strength of the composite at ambient temperature are a little higher than those of Dy-α-sialon.while the bending strength is maintained up to 1000℃ and about 2 times more than that of Dy-α-sialon at the same temperature. The fracture surfaces show that the grain size of the composite is smaller than that of Dy-α-sialon, and both Of them have predominately transgranular mode of fracture. It is believed that the decrease of the bending strength of Dy-α-sialon at elevated temperature is caused by the viscous flow of the grain boundary phase, while the addition of nanosize SiC particles effectively increases the viscosity of the grain boundary phase and therefore prevents the strength loss of Dy-α-sialon/nano-size SiC composites at elevated temperature     

Microstructure and Mechanical Properties of 45 vol.%SiC_p/7075Al Composite

Microstructure and mechanical behavior of high volume content Si Cp/7xxx Al composites have not been explored yet. Therefore, in the present work, 45 vol.% SiC p/7075 Al composite has been prepared by pressure infiltration method. High density dislocations were found around Si C/Al interface in SiC p/7075 Al composite after water-quenching and aging treatment. Fine dispersed nano-η′ phases were observed after the aging treatment. Adverse to other Si Cp/Al composites prepared by the pressure infiltration method,an interface layer was observed between SiC particles and Al matrix. Furthermore, high-resolution transmission electron microscopy(HRTEM) observation indicated that this interface layer was coherent/semicoherent with that of the SiC particles. 45 vol.% SiC p/7075 Al composite demonstrated high tensile strength(630 MPa) and micro-ductility. Compared to aged Si Cp/2024 Al composite, the aged Si Cp/7075 Al composite showed an increase of about 200% in the tensile strain and 90% in the tensile strength, respectively.It is speculated that nano-η′ phases in the Al matrix significantly contributed to the strengthening effect while the interface layer between Si C and Al matrix might be beneficial to the strength and plasticity of Si Cp/7075 Al composite.     

Aging Behavior of High Volume Fraction SiC Particles Reinforced 2024Al Composite

2024 Al matrix composite reinforced by SiC particles with 45% volume fraction and 1μm diameter was successfully fabricated by squeeze-exhaust casting method. The aging behavior of SiCp/2024AI composite at four temperatures was investigated and compared to 2024 alloy. It was found that the addition of high volume fraction SiC particles does not alter the aging sequence, but it significantly accelerates the kinetics of precipitation in the composite matrices. Therefore, the aging peak of the composite appears earlier than that of 2024AI alloy. This is attributed to the decrease in the activation energy for the precipitate formation and the increase in the precipitate growth rate due to the high density dislocations in the composite with high volume fraction particles. The high density dislocations, as preferential nucleation sites for precipitates, bring about the tiny and dense precipitates in the composite.     

Fracture Analysis of Composites in High-speed Tension

In this paper the results of a high-speedtension experiment of the SiC_w/Al compositehave been reported and a simplified theoreticalmodel has been developed to study the fracturemechanism of composites in high-speed tension.This theoretical model provides a new explanationfor the increase of dynamic fracture strengthof composites in high-speed tension.     

In-situ Formed AIN Particulates and TiN Whiskers Mixture Reinforced Al Composite

The TiNw-AINp/Al composite has been successfully fabricated by gas-liquid reaction method in an intensive electromagnetic mixing and casting in an appropriate cooling condition. The as-cast samples of the composite exhibit a homogeneous distribution of TiNw and AINp, and the in situ formed TiN whisker has a mean diameter of 0.5 μm and mean aspect ratio of 5.8~7.5, and the diameter of the AIN particulates is less than 5 μm. TEM observation indicates that there exist some submicron and nanometer sized in situ formed TiNw-AINp in α-Al matrix. The formation mechanism of in situ formed TiNw and AINp is also discussed     

Residual Stresses and Deformation Behaviour in a SiC_p/Al Composite

Experiments were conducted to determine theresidual stresses with X-ray diffraction in the ma-trix of a SiC/Al composite after different thermaltreatments,and to investigate the stress-straincharacteristics and fracture behaviour of the com-posite.It was found that there existed a tensileresidual stress in the matrix and both thermal cy-cling between room temperature and 350℃ and lowtemperature treatment in liquid nitrogen reducedthe residual stress.The results of the strengthdifferential effect and Bauschinger effect were con-sistent with the results of residual stressmeasurements.The tensile residual stresses in the Almatrix enhanced the strength differential effect.Themagnitude of Bauschinger effect is greater for a testinitially started in compression than that in tension.     

Modeling of the Microstructure Evolution in Continuously Cast Al—Pb Alloys

A numerical model is presented describing the microstructure evolution of an immiscible alloy under the continuous casting conditions.Calculations are carried out to investigate the microstructure evolution in a vertical strip cast sample of Al 5wt pct Pb alloy.The numerical results show that there exists a peak value for the supersaturation in front of the solid/liquid interface ,and the minority phase droplets are nucleated in a region around this peak.Under strip casting conditions the Marangoni migration dominates the motion of droplets.This leads to an accumulation of the minority phase droplets in front of the solid /liquid interface.     

Influence of α/β interface phase on the tensile properties of laser cladding deposited Ti–6Al–4V titanium alloy

Laser cladding deposited Ti–6Al–4V titanium alloy universally shows more complex microstructures,each of which has significant effect on mechanical properties. Of particular α/β interface phase has been observed in this paper under certain conditions. It demonstrates that the influence of the α/β interface phase on the tensile properties is closely associated with dislocations and twin substructure through comparison experiments. The results show that the α/β interface phase hinders dislocation motion and decreases effective slip length. In addition, the twin substructure has been activated in the α/β interface phase during tensile process and has acted somehow like grain boundaries. Therefore, the strength and the work-hardening rate of the laser cladding deposited Ti–6Al–4V titanium alloy have been significantly improved due to the dynamic Hall–Petch effect. Besides, the α/β interface phase leads to more uniform dislocations distribution, which implies that relative lower local concentrated stress will be produced along the α/β interface phase or colony boundary after the same amount of plastic deformation. Moreover,the twinning-induced plasticity effects in the α/β interface phase further increase the plastic deformation capacity. These results in higher elongation for the laser cladding deposited Ti–6Al–4V titanium alloy.It can be concluded that the current work suggests an effective method to simultaneously improve the strength and plasticity of laser cladding deposited Ti–6Al–4V titanium alloy based on the α/β interface phase.     

Analysis of Interfacial Coating Effect on Thermal Stress in Composites

A preliminary model for the analysis of thermo-mechanical behaviour of interfacial coatings on thefibers in unidirectional composites have been developed on the solution of thermo-elastic mechan-ics. Thermal stress would be introduced into the composite during cooling because of the mismatchof thermo-mechanical properties among their components. The low modulus coating can effectivelyreduce the interracial stress caused by different thermal expansion coefficient between fibers and ma-trix, no matter how high or low the expansion coefficients of coatings are in CF/Al and SiC/Ticomposite systems, however, high modulus coating can decrease the interfacial compressive stress,only when the thermal expansion coefficient of coating is lower.     

Effect of Ni Content on Mechanical Properties and Corrosion Behavior of Al/Sn－9Zn－xNi/Cu Joints

The effects of Ni content on the microstructure and the wetting behavior of Sn-9Zn-xNi solders on Al and Cu substrates, as well as the mechanical properties and electrochemical corrosion behavior of Al/Sn-9Zn-xNi/Cu solder joints, were investigated. The microstructure of Sn-9Zn-xNi revealed that tiny Zn and coarsened Ni 5 Zn 21 phases dispersed in the β-Sn matrix. The wettability of Sn-9Zn-xNi solders on Al substrate was much better than that on Cu substrate. With increasing Ni content, the wettability on Cu substrate was slightly improved but became worse on Al substrate. In the Al/Sn-9Zn-xNi/Cu joints, an Al4.2Cu3.2Zn0.7 intermetallic compound (IMC) layer formed at the Sn-9Zn-xNi/Cu interfaces, while an Al-Zn-Sn solid solution layer formed at the Sn-9Zn-xNi/Al interface. The mixed compounds of Ni3Sn4 and Al3Ni dispersed in the solder matrix and coarsened with increasing Ni content, thus leading to a reduction in shear strength of the Al/Sn-9Zn-xNi/Cu joints. Al particles were segregated at both interfaces in the solder joints. The corrosion potentials of Sn-9Zn-xNi solders continuously increased with increasing Ni content. The Al/Sn-9Zn-0.25Ni/Cu joint was found to have the best electrochemical corrosion resistance in 5% NaCl solution.     

XRD and TEM Analysis in the Interface of Diffusion Bonding for Fe3Al/Q235 Dissimilar Materials

Phase structure characteristics near the interface of Fe3Al/Q235 diffusion bonding are investigated by means of X raydiffraction (XRD), transmission electronic microscope (TEM) and electron diffraction, etc. The test results indicatedthat obviously a diffusion transition zone forms near the interface of Fe3Al/Q235 under the condition of heatingtemperature 1050~1100℃, holding time 60 min and pressure 9.8 MPa, which indicated that the diffusion interfaceof Fe3Al/Q235 was combined well. The diffusion transition zone consisted of Fe3Al and a-Fe(Al) solid solution.Microhardness near the diffusion transition zone was HM 480~540. There was not brittle phase of high hardness inthe interface transition zone. This is favorable to enhance toughness of Fe3Al/Q235 diffusion joint.     

Plasticity and Interfacial Dislocation Mechanisms in Epitaxial and Polycrystalline Al Films Constrained by Substrates

Stresses in epitaxial and textured Al films were determined by substrate-curvature measurements.It was found that in both cases the flow stresses increase with decreasing film thickness.The flow stresses in the epitaxial Al films are in agreement with a dislocation-based model,while the same model strongly underestimates the flow stresses of textured Al films.In-situ transmission electron microscopy studies indicate that dislocations channeling through epitxial Al films on single-crytalline(0001)α-Al2O3 substrates frequently deposit dislocation segments adjacent to the interface.Furthermore,the Al/α-Al2O3 interface of textured Al films on oxidized sillicon substrates is between the crystalline Al and the amorphous SiOx interlayer.It is speculated that the different nature of the interfaces changes dislocation mechanisms and thus influences the flow stresses.