An analysis of the mechanical behavior of Al-Al3Ni composites

Commercial purity Al-Al₃Ni eutectic composites have been prepared by directional solidification at growth rates ranging from 9.63 x 10^-3 to 1.0 mm/s. The composites were tested in tension and in compression and the results were analyzed using a simple model taking into consideration the difference in Poisson’s ratio of the phases, interfiber spacing, and discontinuity and premature fracture of fibers. The theoretically predicted values of the tangent modulus and strength in tension and compression were shown to closely fit the experimental results up to a growth rate of about 0.3 mm/s. Beyond this value, the excessive misalignment of the fibers caused some deterioration in the mechanical properties and a change in the mode of fracture. It has been concluded that the elastic constrained matrix exerts considerable effect on the mechanical properties thus providing an effective means of improving them by increasing the surface area of the fiber-matrix interface.     

Yield criteria and strain-rate behavior of Zr57.4Cu16.4Ni8.2Ta8Al10 metallic-glass-matrix composites

We have examined the yielding and fracture behavior of Zr_57.4Cu_16.4Ni_8.2Ta₈Al₁₀ metallic-glass-matrix composites with a small volume fraction (∼4 pct) of ductile crystalline particles under quasi-static uniaxial tension and compression and dynamic uniaxial compression. The yield stress of the composite is the same for quasi-static tension and compression, consistent with a von Mises yield criterion. The measured average angle between the shear bands and the loading axis in quasi-static compression is 47±2 deg, significantly larger than the value of ∼42 deg typically reported for single-phase metallic glasses. Finite element modeling (FEM) shows that the measured value is consistent with both the von Mises criterion (48±4 deg) and the Mohr-Coulomb criterion (46±5 deg). The fracture surface angles, however, are 41±1 deg (compression) and 54±2 deg (tension), in good agreement with observations of single-phase metallic glasses. At low strain rates (<10⁻¹ s⁻¹), the yield stress is independent of strain rate, while at higher strain rates (>10⁰ s⁻¹), the failure stress decreases with increasing strain rate, which again is similar to the behavior of single-phase glasses. These results indicate that while the presence of the particles has a significant effect on the yield behavior of the composites, the fracture behavior is largely governed by the properties and behavior of the amorphous matrix.     

Structure and strength of Al,Cu-Al3Ni directionally solidified composites

A series of Al₃Ni fiber reinforced composites with a matrix composition varying from pure aluminum to Al-3.3 wt pct Cu were prepared by directional solidification of Al-Ni-Cu alloys. The solidification conditions were kept constant in all cases atG/R ≃ 10⁴ °C · s/mm² (G is the temperature gradient andR is the growth rate). The mechanical properties of the composites were studied in the as grown and in the heat treated conditions and the results were discussed in terms of the structure and composition. With the techniques used, it was possible to preserve the Al-Al₃Ni eutectic composite structure while strengthening the matrix by copper addition. The addition of 1 wt copper to the matrix caused a considerable increase in the mechanical strength, especially after heat treatment, without affecting the ductility. Strength values of the order of 530 MN/m² were reached in the heat treated composites which is higher than predicted by the rule of mixtures. This is attributed to the high work hardening capacity of the matrix especially in the presence of θ’ phase. Massive Al₃Ni rods and dendrites caused premature fracture and reduction in the strength of the composites containing 2 and 3 wt pct copper. Eliminating these defects by using higherG/R values can produce composites with exceptionally high strength.     

An analysis of the fatigue behavior of Al-Al3Ni composites

Commercial purity Al-Al₃Ni eutectic composites have been prepared by directional solidification at growth rates ranging from 9.63 x 10^-3 to 1.0 mm/s. The composites were tested under rotating bending fatigue conditions and the results were analyzed using a model taking into consideration the difference in Poisson’s ratio of the phases, interfiber spacing and premature fracture of fibers. The calculated fatigue lives were shown to be in good agreement with the experimental results at all stress levels. Both the experimental results and calculations show that the composite fatigue life is not sensitive to large changes in the growth rate. The fatigue limit was also found to be insensitive to the mode of fatigue loading and notches. At high stress levels, however, smooth specimens tested under reversed bending exhibited longer lives than notched specimens tested under cyclic tension-tension conditions.     

Structure and strength of Al, Cu-Al3Ni directionally solidified composites

A series of Al₃Ni fiber reinforced composites with a matrix composition varying from pure aluminum to Al-3.3 wt pct Cu were prepared by directional solidification of Al-Ni-Cu alloys. The solidification conditions were kept constant in all cases atG/R ≃ 10⁴ °C. s/mm² (G is the temperature gradient andR is the growth rate). The mechanical properties of the composites were studied in the as grown and in the heat treated conditions and the results were discussed in terms of the structure and composition. With the techniques used, it was possible to preserve the Al-Al₃Ni eutectic composite structure while strengthening the matrix by copper addition. The addition of 1 wt copper to the matrix caused a considerable increase in the mechanical strength, especially after heat treatment, without affecting the ductility. Strength values of the order of 530 MN/m² were reached in the heat treated composites which is higher than predicted by the rule of mixtures. This is attributed to the high work hardening capacity of the matrix especially in the presence of θ′ phase. Massive Al₃Ni rods and dendrites caused premature fracture and reduction in the strength of the composites containing 2 and 3 wt pct copper. Eliminating these defects by using higherG/R values can produce composites with exceptionally high strength.     

An analysis of the fatigue behavior of Al-Al3Ni composites

Commercial purity Al-Al₃Ni eutectic composites have been prepared by directional solidification at growth rates ranging from 9.63 x 10^-3 to 1.0 mm/s. The composites were tested under rotating bending fatigue conditions and the results were analyzed using a model taking into consideration the difference in Poisson’s ratio of the phases, interfiber spacing and premature fracture of fibers. The calculated fatigue lives were shown to be in good agreement with the experimental results at all stress levels. Both the experimental results and calculations show that the composite fatigue life is not sensitive to large changes in the growth rate. The fatigue limit was also found to be insensitive to the mode of fatigue loading and notches. At high stress levels, however, smooth specimens tested under reversed bending exhibited longer lives than notched specimens tested under cyclic tension-tension conditions.     

Failure characteristics of 6061/AI2O3/15ρ and 2014/AI2O33/15ρ composites as a function of loading rate

The effects of loading rate on the toughness and fracture mechanisms of two cast 6061/Al₂O₃/15p and 2014/Al₂O₃/15p composites under the as-worked (AW) and AW + T6 conditions have been examined. The quasistatic bending and high-rate impact tests were conducted over strain rates from 5 X 10^-4 to 1 X 10³ s^-1 using screw-driven or servohydraulic high-rate systems. The results showed that the peak loadP _max, specimen deflectiond, specimen lateral expansion fraction Δw, crack initiation energyE _i, propagation energyE _p, total fracture energyE _t and deformation zone all tended to increase with increasing strain rate. Under quasistatic loading, the composites failed predominantly by ma-trix/reinforcement interface decohesion. As the loading rate increased, reinforcement failure became the major failure mechanism. Differences in the effect of matrix microstructure and stress state on the fracture properties also are discussed. In comparing the fracture modes in the AW and AW + T6 specimens, the latter showed a higher tendency toward particle cracking. Based on mechanical data, the degree of specimen deflection and expansion and fracture modes, the AW composites exhibited a higher strain-rate dependence. The T6 specimens, due to their intrinsicly more brittle nature, appeared to be less influenced by loading rate over the strain-rate range examined.     

Synthesis of Al2O3/TiCN-0.2%Y2O3 Composite by Hot Pressing

Al2O3/TiCN composites were synthesized by hot pressing.The influences of components and HP temperature on mechanical properties,such as bending strength,breaking tenacity and Vickers hardness were investigated.The results showed that the mechanical properties of Al2O3/TiCN composite increased with temperature when hot pressing temperature is below 1650 ℃.The mechanical properties reached their maximums when the composites were sintered at 1650 ℃ for 30 min under hot pressing pressure of 35 MPa,the value of bending strength,breaking tenacity and Vickers hardness was 1015 MPa,6.89 MPa·m1/2,and 20.82 MPa,respectively.When hot pressing temperature was above 1650 ℃,density decreased because of decomposition with increased temperature,and mechanical properties dropped because of rapid growth of grains in size at high temperature.Microstructure analysis showed that the addition of Y2O3 led to the formation of YAG phase so as to inhibit the growth of crystals.This helped to improve breaking tenacity of the composites.TiCN particles with diameters of 1 μm dispersed at Al2O3 grain boundaries,inhibited grain growth and enhanced mechanical properties of the composites.SEM study of the propagation of indentation cracks showed that the bridge linking behavior between matrix and strengthening phase might lead to the formation of the coexisted field of crack deflection,branching and bridge linking.The mechanism of this phenomenon was that the addition of Y2O3 improved the dispersion of TiCN particles so as to enhance the tenacity of the composites.The breaking tenacity was changed from 5.94 to 6.89 MPa·m1/2.     

Mechanical behavior and failure micromechanisms of Al/Al2O3 composites under cyclic deformation

The mechanical behavior under fully reversed cyclic deformation was determined through the incremental step method for two Al alloys reinforced with 15 vol pct A1₂O₃ particulates in the naturally aged and peak-aged conditions. The composites exhibited cyclic strain hardening in all cases, but the hardening was more pronounced in the naturally aged condition. This behavior was reflected by the stress-strain curves in monotonie tension and in fatigue, and the cyclic strain-hardening coefficient was about twice the monotonie one for both materials and tempers. The tensile and cyclic strengths of the materials were very similar, and the dominant failure mechanism under both loading conditions was paniculate fracture, which was very localized around the fracture region in fatigue, but was spread along the specimen length in monotonie tension. In addition, a few A1₂O₃ particulates were broken in compression during cyclic deformation. The final fracture micromechanism was the growth and coalescence of voids in the matrix from broken ceramic particulates. This last stage in the fracture process was fast and started when a critical volume fraction of broken reinforcements (between 30 and 45 pct) was reached in a given section of the specimen. This article is based on a presentation made in the symposium entitled “Creep and Fatigue in Metal Matrix Composites” at the 1994 TMS/ASM Spring meeting, held February 28–March 3, 1994, in San Francisco, California, under the auspices of the Joint TMS-SMD/ASM-MSD Composite Materials Committee.     

Development of a high-performance green Fe–Al2O3 composites using Bayan Obo minerals: Enhancement effects of CeO2

With the deepening understanding for the concept of sustainable development, the utilization of minerals is no longer limited to the traditional way. In this study, an environment friendly method for preparing Fe–Al₂O₃ composites by using natural minerals was investigated. Additionally, the effects of CeO₂ on the properties of composites were studied. The mechanical properties of Fe–Al₂O₃ composites prepared by natural minerals are affected by the brittleness of glass phase. The strength and toughness of the glass phase in the composite are improved successfully by using rare earth oxides, indicating that the natural rare earths in Bayan Obo minerals have an enhanced influence on the properties of composite materials. The results show that the properties of glass phase can be significantly improved by addition of CeO₂. At the optimal addition of 3 wt% CeO₂, the composite achieves the density of 4.21 g/cm³, flexural strength of 401 MPa, Vickers hardness of 13.07 GPa and fracture toughness of 6.58 MPa⋅m^1/2. The composite has excellent mechanical properties, which can be used in engineering as a cheap structural material. This study aims at reducing waste emissions, improving energy efficiencies and avoiding waste of rare earth resources during the preparation of composite materials.     

Study of the interface and its effect on mechanical properties of continuous graphite fiber-reinforced 201 aluminum

The formation of fiber-matrix interfacial reaction zone and its impact on mechanical properties of Gr/201 Al composite (41 vol pct fiber) was evaluated in the as-received condition and after heat treatment in vacuum at 450°C, 500°C, and 545°C temperatures for one day, and at 545°C for one week. After heat treatment the microstructures of matrix and interface were studied by transmission electron microscopy. This study revealed the presence of interfacial constituents Al₄C₃, Al₄O₄C, and TiB₂. The mean fiber-matrix reaction zone thickness showed an increase with increasing heat treatment temperature and time. The effects of heat treatment on interfacial shear strength, monotonic and cyclic tension/compression properties were evaluated. The results show that the interfacial shear strength not only depends on chemical reaction but also depends on the thickness of the reaction zone. An increase in reaction zone size reduces mechanical bonding considerably (thermal induced stresses). The growth of reaction zone was very detrimental to monotonic and cyclic tension/tension fatigue behavior. The mechanism of failure in tension/tension fatigue was the initiation of cracks at the interface and their subsequent propagation in the matrix. It was concluded that the reaction zone was the controlling factor in tension/tension fatigue. In contrast, the results showed that compressional fatigue was matrix dependent and was little sensitive to the size of the fiber/matrix interfacial reaction zone.     

The effect of consolidation temperature on microstructure and mechanical properties in powder metallurgy-processed 2XXX aluminum alloy composites reinforced with SiC particulates

The effects of consolidation temperature on the development of microstructure and resulting mechanical properties of 2XXX aluminum composites were studied in an effort to fabricate composites with enhanced properties. Type 2009 and 2124 aluminum composites reinforced with 15 pct SiC particulates were produced at four different consolidation temperatures, i.e., 560 °C, 580 °C, 600 °C, and 620 °C, followed by extrusion at 450 °C. The 2124 Al-SiC _p composites consolidated at 560 °C showed the most homogeneous and the finest microstructures with the best mechanical properties, which were even better than the whisker-reinforced counterparts. All the results of the tensile tests, hardness tests, in situ scanning electron microscope (SEM) observations of the fracture process, and the apparent fracture toughness indicated that the prominent mechanical property improvement observed in the 2124 Al-SiC _p was associated largely with the reduction of volume fraction of the detrimental coarse and brittle manganese-containing particles, as well as grain refinement. The detrimental manganese-containing particles that were routinely observed in the 2124 Al-SiC composites were very effectively refined by the reduction of consolidation temperature, and they rather contributed to the overall mechanical properties of the composites through Orowan-type strengthening and grain growth inhibition.     

Mechanical properties and failure characteristics of FP/aluminum and W/aluminum composites

Tension and compression properties of continuous FP and W fiber reinforced aluminum composites have been characterized at a nominal strain rate of 10⁻⁴ s⁻¹. Tests were conducted on specimens with fibers oriented at 0 deg, 30 deg, 60 deg, and 90 deg to the specimen axis. Compression properties of these composites were evaluated using specially designed compression jigs. The variables studied include fiber orientation and specimen height to width ratio. In all the tests Wood’s metal pot was used to ensure the alignment of the specimen axis with the loading direction. In addition, a limited number of compression tests were conducted using IIT Research Institute compression fixture for comparison purposes. A test fixture for a tube specimen loaded biaxially was also designed and fabricated. A limited number of biaxial tests were conducted on FP-aluminum tubes to determine the fracture stress and to prove the test technique. Theoretical analyses and metallurgical examinations of test specimens have been performed to understand the strengthening and failure characteristics of these composites.     

Combined Effect of Micro Fillers on the Mechanical and Fracture Behavior of Polyamide 66 and Polypropylene (PA66/PP) Blend

The combinative effect of Micro fillers on the 80/20 wt% of Polyamide 66 and Polypropylene blend (PA66/PP) is studied. Three composites prepared by reinforcing micro fillers of Molybdenum disulphide (MoS₂) (PA66/PP/MoS₂), Silicon carbide (SiC) (PA66/PP/MoS₂/SiC) and Alumina (Al₂O₃) (PA66/PP/MoS₂/SiC/Al₂O₃) of, having different geometric shapes. The mechanical properties studied are tensile strength, flexural strength, impact strength including the hardness of the blend micro composites as per ASTM methods. The fracture toughness at different temperatures of the composites is studied as per ASTM. Results reveal that the combined effect of hybrid micro fillers decreases the mechanical behavior of PA66/PP blend composites. The poorest mechanical properties are obtained when SiC is incorporated into the MoS₂ filled blend PA66/PP composites. The appreciable increase in the mechanical properties is noticed by the addition of Al₂O₃ into the hybrid filled PA66/PP blend composites. Though the effect of SiC addition to PA66/PP/MoS₂ composites increases the impact strength appreciably but decreasing trend is also observed due to the hybrid effect of three fillers. But the differently shaped micro fillers exhibit a synergic effect on the tensile and flexure properties of PA66/PP based composites respectively. The density of the studied blend increases due to denser nature of micro fillers. The hardness of the blend is increased by 18 % by the addition of micro fillers as against the blend PA66/PP. The increase in fracture toughness by 188 % is exhibited by the hybrid effect of micro fillers as against the neat blend at room temperature. Among these micro composites, PA66/PP/MoS₂/SiC/Al₂O₃ has shown superior mechanical properties when compared to individual effect of the fillers on the blend. The fractured surfaces are studied by using scanning electron microscope photographs.     

Work of fracture in aluminum metal-matrix composites

The effect of isothermal exposure and thermal cycling on the toughness of B/Al (1100), B/Al (6061), and A1₂O₃/A1 composites has been investigated. In B/Al (1100), isothermal exposure at 773 K for 45 × 10⁴ s (125 hours) reduced toughness, measured by the work of fracture, from 76 kJm^-2 to 10 kJm^-2, and a similar reduction occurred after equivalent thermal cycling. The corresponding reduction in toughness after isothermal exposure in B/Al (6061) was from 44.5 kJm^-2 to 8 kJm^-2; however, the effect of thermal cycling was less detrimental. In the FP-A1₂O³/A1 composite, the work of fracture was insensitive to both forms of thermal treatment. Changes in the toughness of the B/Al composites have been correlated with and analyzed in terms of modifications to matrix, fiber, and interface properties, in particular, matrix softening, interface reaction products, and fiber notch sensitivity. The latter currently on The latter currently on     

Fracture toughness of discontinuously reinforced Al-4Cu-1.5Mg/TiB2 composites

The effect of particle size, particle volume fraction, and matrix microstructure on the fracture initiation toughness of a discontinuously reinforced aluminum composite was examined. The composites were Al-4 wt pct Cu-1.5 wt pct Mg reinforced with 0 to 15 vol pct of TiB₂ having an average particle diameter of 1.3 or 0.3μm producedin situ by the XD process. The room-temperature plane-strain toughness measured using compact tension specimens ranged from 19 to 25 MPa . Toughness was adversely affected by increases in TiB₂ volume fraction. The fracture toughness of all composites was affected by changes in the matrix microstructure produced by aging. The response of the composites to artificial aging deviates from that of the matrix. Fractography revealed that these composites failed in a ductile manner, with voids initiating at the reinforcing TiB₂ particles. The experimentally measured plane-strain toughness properties of Al-4Cu-l .5Mg composites with well-dispersed, 1.3-μm TiB² reinforcements agree with the Rice and Johnson model.     

Failure of SiC particulate-reinforced metal matrix composites induced by laser thermal shock

Thermal failure of SiC particulate-reinforced 6061 aluminum alloy composites induced by both laser thermal shock and mechanical load has been investigated. The specimens with a single-edge notch were mechanically polished to 0.25 mm in thickness. The notched-tip region of the specimen is subjected to laser beam rapid heating. In the test, a pulsed Nd:glass laser beam is used with duration 1.0 ms or 250 μs, intensity 15 or 70 kW/cm², and spot size 5.0 mm in diameter. Threshold intensity was tested and fracture behavior was studied. The crack-tip process zone development and the microcrack formation were macroscopically and microscopically observed. It was found that in these materials, the initial crack occurred in the notched-tip region, wherein the initial crack was induced by either void nucleation, growth, and subsequent coalescence of the matrix materials or separation of the SiC particulate-matrix interface. It was further found that the process of the crack propagation occurred by the fracture of the SiC particulates.     

Effects of La_2O_3 addition on microstructure development and physical properties of harder ZTA-CeO_2 composites with sustainable high fracture toughness

The influence of La_2 O_3 inclusion(0-3 wt%) on the micro structure,phase formation and mechanical properties of zirconia toughed alumina(ZTA) added with 5.0 wt% CeO_2 was investigated.ZTA CeO_2 composites were sintered at 1600℃ for 4 h.The microstructure,phase formation,density,fracture toughness and hardness properties were characterised through FESEM,Microscopy Image Analysis Software and XRD diffractometer,Archimedes principle and Vickers indentation technique,respectively.The XRD,image processing and FESEM reveal the existence of LaAl_(11)O_(18).The addition of La_2 O_3 incites the sintering,microstructure refinement,densification of ZTA-CeO_2 matrix and phase transformation.Hence,the hardness of ZTA-CeO_2 ceramics is increased rapidly based on refinement of Al_2 O_3 grains,densification of ZTA-CeO_2 composites and porosity reduction.It is observed that the fracture toughness is enhanced through in situ formation of elongated LaAl_(11)O_(18) grains.The addition of 0.7 wt% La_2 O_3 culminated in the achievement of the optimum findings for density(4.41 g/cm3),porosity(0.46%),hardness(1792 HV) and fracture toughness(8.8 MPa·m~(1/2)).Nevertheless,excess La_2 O_3 is proven to be detrimental as it displays poor mechanical properties due to the poor compactness of numerous LaAl_(11)O_(18) grains,coarsening of Al_2 O_3 grains and decline in density.     

The mechanical properties of Al alloys reinforced with continuous Al2O3 fibers

The mechanical properties of aluminum matrix composites unidirectionally reinforced with Al₂O₃ fibers have been measured and characterized in longitudinal and transverse tension, as well as in shear. The flow strengths in transverse tension and shear are found to exceed those of the matrices, although the ductilities are lower. The strengthening is generally consistent with the development of plastic constraint in the matrix around well-bonded fibers, subject to the in situ properties of the matrix being known from independent measurements. The properties in longitudinal tension are found to involve interactions between fibers, such that fiber bundle strengths are not achieved, even when a low strength, pure Al matrix is used. Instead, the strengths are consistent with a crack growth controlled failure mechanism, wherein the strength is governed by the resistance of the material to crack extension from failed fibers.     

Study on Mechanical Properties and Fracture Mechanisms of B4 C-CeB6/A1 Composites

B₄C-CeB₆/Al composites were first fabricated by pressureless infiltration technology. The mechanical properties of B₄C-CeB₆/Al composites were tested. The results show that the density, the flexibility strength and the fracture toughness of B₄C-CeB₆/Al composites were greatly improved compared with those of monolithic boron carbide, but the hardness of it decreased. The analysis of B₄C-CeB₆/Al composites by using the fracture scanning electric microscope and the back-scattering equipment showed that, the fracture way of B₄C-CeB₆/Al composites was intercrystalline rupture. The flexibility strength and the fracture toughness of B₄C-CeB₆/Al composites were greatly improved for two major reasons. Firstly the flexibility strength and the fracture toughness of B₄C-CeB₆ porous perform were improved because for the CeB₆ existing. Secondly the ductility of aluminum was manifested in B₄C-CeB₆/Al composites.