Al2O3 Short Fiber Research Articles

Effect of Al2O3 fiber on twin intersections-induced dynamic recrystallization in fine-grained TiAl matrix composite

Dynamic recrystallization (DRX) is of great significance for the thermomechanical processing and microstructural regulation of TiAl intermetallics. However, the underlying DRX mechanism remains poorly understood. In this study, an Avrami kinetics model for DRX was established, which was capable of predicting the DRX fraction accurately. In addition, the effect of Al2O3 short fiber on the DRX mechanisms of TiAl matrix composite during the isothermal compression was investigated for the first time. The results showed that other than inhibiting DRX by particles in the TiAl matrix composites, the addition of Al2O3 short fiber accelerated a novel DRX process, which was induced by twinning and twin intersections (TDRX). Thus, this composite exhibited a higher DRX rate than that of the as-cast TiAl monolithic alloy. The origin of the twin intersection and TDRX for the composite was revealed. The stress concentration near the Al2O3 fiber was above the critical shear stress for twinning and thus was favorable for the formation of twinning and twin intersections. The high stored strain energy at the regions of twins and twin intersections provided the driving force for TDRX. TDRX accelerated the grain refinement in the TiAl matrix near the Al2O3 fiber. The present findings would provide a new perspective on DRX mechanisms, and provide the scientific guidance for optimizing the microstructures of TiAl matrix composites.

Interfacial reaction in Al2O3 fiber reinforced TiAl matrix composite

Al2O3 short fiber (containing 28 vol.% SiO2) reinforced TiAl matrix composite was prepared by spark plasma sintering (SPS). The interfacial reaction mechanism was clarified by thermodynamic and kinetic analyses. The main interfacial phase was Ti5Si3, originated from Ti element of TiAl matrix and Si element of Al2O3 fiber. The activation energy of interfacial layer was 285.1 kJ/mol. In addition, the matrix around the interfacial region was composed of γ-TiAl phase due to the consumption of Ti element in the process of interfacial reaction. However, the formation of mullite phase occurred in the heat-treated Al2O3 fiber and as-sintered composite due to the chemical reaction between γ-Al2O3 and amorphous SiO2 phases.

Processing and oxidation response of Cr2AlC MAX-phase composites containing ceramic fibers

Three different ceramic matrix composites (CMCs) were produced using Cr2AlC as a matrix, and carbon, SiC and Al2O3 short fibers as a secondary phase. Cr2AlC powders were synthesized by solid-state reaction, followed by mixing with the fibers, and full densification using a field-assisted sintering technique. Of the three different fiber types, Carbon fibers reacted strongly with Cr2AlC, while the reaction with SiC fibers was more limited and alumina fibers didn’t show any reaction. Oxidation tests of the monolithic Cr2AlC and the composites were performed by thermogravimetric analysis. An alumina layer formed at 1000 ​°C on every sample, well attached and worked as a good oxidation barrier. Under realistic conditions using a burner rig for cyclic oxidation at 1200 ​°C for 500 cycles, the oxidation resistance of the alumina fiber CMC is good, as no defects or degradation are visible and the alumina layer is well attached.

Powder Injection Molding of Oxide Ceramic CMC

Ceramic Matrix Composites (CMC) offer improved mechanical properties, especially higher toughness, preferably at elevated temperatures. Fields of application are, for example, highly hot stressed components of aero engines.Processing of Ceramic Matrix Composites by powder injection molding offers attractive economic benefits, however, it represents a considerable challenge. Development of a process chain for the ceramic injection molding of Al2O3 short fiber CMC had started by feedstock preparation and characterization. Fiber content varied between 10 to 50 vol.% whereas for binder a well-examined system from KIT was chosen. The fiber content showed a minor effect on the rheological properties but fiber orientation depended strongly on the apparent shear profile. The sintering behavior was affected as well, i.e. higher densities were achieved.

Stress-induced damage evolution in cast AlSi12CuMgNi alloy with one- and two-ceramic reinforcements

Two composites, consisting of an as-cast AlSi12CuMgNi alloy reinforced with 15 vol% Al2O3 short fibres and with 7 vol% Al2O3 short fibres + 15 vol% SiC particles, were studied. Synchrotron computed tomography disclosed distribution, orientation, and volume fraction of the different phases. In-situ compression tests during neutron diffraction in direction parallel to the fibres plane revealed the load partition between phases. Internal damage (fragmentation) of the Si phase and Al2O3 fibres was directly observed in CT reconstructions. Significant debonding between Al matrix and SiC particles was also found. Finally, based on the Maxwell scheme, a micromechanical model was utilized for the new composite with two-ceramic reinforcements; it rationalizes the experimental data and predicts the evolution of all internal stress components in each phase.

Fabrication and Characterization of 5 vol.% (Al2O3)p+ 8 vol.% (Al2O3)f/A336 Hybrid Micron and Nano-Composites

Hybrid composites are fabricated by adding two reinforcements into matrix materials so that the expected excellent properties can be achieved through the combined advantages of short fibres, and different size particles (micron or nano), which provide a high degree of design freedom. In this paper, hybrid preforms were produced with the different size reinforcement of the Al2O3 particles and short fibres. The Al-Si alloy-based hybrid composites reinforced by 5 vol. % Al2O3 particles and 8 vol. % Al2O3 fibres were fabricated by preform-squeezing casting route. The structure and performance of composite materials were studied with Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). The results show that the reinforcements, both particles and fibres, distribute homogeneously in the matrix materials, and the properties of composites are found to improve in comparison with the matrix Al-Si alloy.

An Evaluation on Processing of Metal Matrix Composites (Al<sub>2</sub>O<sub>3</sub>/AC8A) by Low-Pressure Infiltration

At present many researches are about low density and high strength material, Metal Matrix Composite (MMC) is one kind of high performance material which is very popular and can fit that condition very well. In this study, matrix material is Al alloy and Al2O3 short fiber is reinforcement, volume fractions of Al2O3 short fiber is 10, 15 and 20 %. Manufacture by a low-pressure infiltration method. And the performance is evaluated by microstructure observation, porosity ratio and relative density. It is found that the porosity ratio can be effectively adjusted by the infiltration temperatures and the loads of Al2O3 short-fibres, exhibiting a minimum of 2 for 10% loading at 700°C. Meanwhile, the relative density of composites reached to be a maximum of 98% for 15% loading at 700°C. The low porosity ratio and high density of composites are reasonably attributed to the proper processing techniques.

Heat Treatment Effects on the Mechanical Properties and Microstructure of Preform-Based Squeeze Cast Aluminum Metal Matrix Composites

Many aluminum alloys are used in the production of metal matrix composites (MMCs). Historically the matrix alloy’s thermal treatment parameters (solution heat treatment temperatures and times, and aging temperatures and times) have been adopted for the MMCs containing that alloy. Previous MMC work indicates that solution heat treatment parameters have a significant effect on the strength and ductility of the cast composite. The current study investigates the effects of solution times on the tensile properties of Al-MMC composites containing two different reinforcement types, SiCp and Al2O3 short fiber, and volume fractions in two different matrix alloy chemistries, A359 and modified A319. Study goals are to optimize the matrix-reinforcement interface strength and thereby maximize tensile strength and elongation of these Al-MMC composites. Scanning Electron Microscopes (SEM) analysis and tensile data analysis conclude that the solution treatment times must be changed for each composite from the time suggested for conventional alloy heat treatment parameters.

Enhanced Young’s Modulus of Al-Si Alloys and Reinforced Matrices by Co-continuous Structures

In the present work, the elastic behavior of different hypoeutectic and hypereutectic Al-Si alloys and different Al2O3 short fiber and SiC particle reinforced materials (SFRM and PRM, respectively) is studied. The effective Young’s modulus (E) of materials was experimentally measured and compared with the different theoretical predictions of Hashin-Strikman, Tuchiniskii, shear lag, and the rule of mixtures (ROM). The unreinforced alloys present an interconnected lamellar Si structure after fast solidification, which increases the Young’s modulus up to that of the Tuchiniskii prediction for interpenetrating skeletal structures. On the other hand, alloys presenting isolated and coarse Si particles (after spheroidization treatment at 540°C) are well described by the lower bound of the ROMs. Similarly, the interconnected Si-SiC structure observed in 10 and 70 vol% SiC reinforced AlSi7Mg and AlSi7 matrices in the as cast condition is responsible for the higher stiffness of the composite, if compared with that of Al99.5 or spheroidized AlSi7 matrices. An analogous behavior is observed in the SFRMs in the as cast condition, where the Si lamellae bridge the Al2O3 fibers, increasing the Young’s modulus of the composites, if compared with the conditions of spheroidized Si. Furthermore, the primary Si particles produce an improvement in the Young’s modulus by connecting several fibers in the case of a short fiber-reinforced hypereutectic AlSi18 matrix.

Interpenetrating Hybrid Reinforcement in Al2O3 Short Fiber Preforms Infiltrated by Al-Si Alloys

In this work, the effect of the Si content and its morphological features on the mechanical properties of different short fiber-reinforced Al-Si matrices is studied. Al-Si alloys with Si contents of 7 wt pct and more contain a percolating Si network in the as-cast condition. The addition of alumina fibers into these Al-Si matrices increases the mechanical properties by forming an interconnected Al2O3-Si network. Both elastic modulus and maximum strength (from tensile and compression tests) increase with increasing Si content, which reinforces the interpenetration. However, Si diffuses toward the fibers’ surface during solution treatment forming coarse Si particles, reducing considerably the connectivity of the Al2O3-Si-hybrid network and thus the mechanical properties of the composites. The mechanical properties of the Al2O3-Si network itself are studied by means of compression tests on extracted hybrid reinforcement samples and are related to the global behavior of the composites. The strength vs true strain curves depict a strain-controlled softening of the composite material, which proceeds the faster, the higher the interconnectivity of the hybrid reinforcement, due to the propagation of damage of the Al2O3-Si network.

Mechanical Properties of Az91 Magnesium Alloys

Commercial magnesium alloys AZ91 were reinforced with Al2O3 short fibres. The composites were prepared by different fabrication routs (powder metallurgy technique, squeeze casting and casting followed by extrusion). Some specimens of the AZ91 alloy were prepared using equal channel angular pressing. The values of the yield stress and the maximum stress of specimens deformed at temperatures between 20 and 300 °C were determined. The test temperature strongly influences the mechanical properties of the AZ91 alloy and its composites.

Mechanical spectroscopy of Mg reinforced with Al2O3 short fibers and C nanotubes

Magnesium matrix composites have been developed, in which the high damping magnesium matrix has been reinforced either with multi-wall carbon nanotubes or with Al 2 O 3 SAFFIL short fibers (40–100 μm), the interface of which was modified by chemical vapor deposition of carbon nanotubes before their infiltration with magnesium. In this case, it was found that the addition of the carbon nanotubes increases the high temperature (500 K) shear modulus of the composite by about 20%. A thermal hysteresis is observable in the mechanical loss spectra, which may be associated with the transitory effects generally observed in the metal matrix composites. These transitory effects are strongly reduced when the reinforcements are carbon nanotubes only, because their small size generates smaller interface thermal stresses.

Interface stress relaxation in magnesium matrix composites studied by mechanical spectroscopy

Mechanical spectroscopy has been used to study magnesium matrix composites reinforced either by long SiC fibres or randomly distributed Al2O3 (Saffil) short fibres. It is well known that, in metal matrix composites, thermal stresses can be built up at the interface due to the mismatch between the thermal expansion coefficients of matrix and reinforcements. In magnesium matrix composites, these thermal stresses are relaxed by dislocation motion in the matrix. This mechanism of thermal stress relaxation yields an extra transient component in the mechanical loss spectrum, which depends on the heating/cooling rate and disappears in isothermal condition in the behaviour of the shear modulus G with temperature has been observed during thermal cycling between 100 K and 500 K. The intensity of this phenomenondepends on the spatial distribution of the reinforcements in the matrix. In particular, composites reinforced with long fibres exhibit a more pronounced anomaly. This is interpreted by the modification of the interface strength when temperature is changed.

Creep resistance in magnesium alloys and their composites

A considerable improvement in the creep properties of magnesium alloys can be potentially achieved by non-metallic reinforcement (metal matrix composites - MMCs). This paper provides a comparative report on experiments which were conducted on the two representative magnesium alloys (AZ91 and QE22) and their composites in order to evaluate the creep properties and to clarify the direct and indirect strengthening effects of reinforcement in creep. A comparison between the creep characteristics of squeeze-cast AZ91 and QE22 magnesium alloys reinforced with 20 vol.% Al2O3 short fibres and unreinforced matrix alloys shows that the creep resistance of the reinforced materials is considerably improved compared to the monolithic alloys. By contrast, the investigations of the creep behaviour of a particulate QE22-15 vol.% SiC composite prepared by powder metallurgy and the squeeze-cast hybrid QE22 matrix composites have revealed no substantial increase in the creep strength of the composite compared to the matrix alloy and AZ91 matrix composites. These results indicate a paramount importance of the choice of the composite matrix alloy and the reinforcement used.

Creep processes in magnesium alloys and their composites

A comparison is made between the creep characteristics of two squeeze-cast magnesium alloys (AZ 91 and QE 22) reinforced with 20 vol pct Al2O3 short fibers and the unreinforced AZ 91 and QE 22 matrix alloys. The results show the creep resistance of the reinforced materials is considerably improved by comparison with the unreinforced matrix alloys. It is suggested that creep strengthening in these short-fiber composites arises primarily from the existence of a threshold stress and the effect of load transfer. By testing samples to failure, it is demonstrated that the unreinforced and reinforced materials exhibit similar times to failure at the higher stress levels. A detailed microstructural investigation by transmission electron microscopy (TEM) reveals no substantial changes in matrix microstructure due to the presence of the reinforcement. This suggests that direct composite strengthening dominates over indirect effects.

Mechanical-stress relaxation in magnesium-based composites

In metal matrix composites (MMCs), the metal matrix is exposed to plastic deformation and damage accumulation in the region close to the reinforcements, following mechanical or thermal stresses. Mechanical spectroscopy has been used to study interface stress–relaxation in Mg–2%Si based MMC reinforced with either C aligned long fibers or Al2O3 short fibers. In the Al2O3/Mg–2%Si composite, the damping capacity is low; the mechanical stresses are relaxed by damage accumulation at interfaces. The elastic shear modulus decreases until rupture, when the composite is cycled at high vibration amplitude. On the contrary, the damping capacity is high in the C/Mg–2%Si composite and the interface stresses are relaxed by reversible motion of dislocations in the matrix, leading to a strong increase in fatigue resistance.

Computer Simulation of 3-D Random Distribution of Short Fibers in Metal Matrix Composite Materials

In this paper, the microstructure of “Saffil”-Al2O3 short fiber reinforced Al-Mg5.5 metal matrix composite material is simulated by computer. In the simulation it is taken into account of that the lengths, diameters, orientations, and locations of short fibers, etc. For the 3-D randomly distributed short fibers in composite materials, the typical distributions of short fiber microstructures on different planes are obtained for different short fiber volume fractions. The microstructural effects of average fiber length, diameter and their standard deviations on the overall strength of metal matrix composite materials are analyzed. From the short fiber microstructural distribution in metal matrix composite materials, the short fiber diameter coefficient ξd and short fiber length coefficient ξ1 are obtained for different standard deviations σd and σl, respectively. The short fiber orientation coefficient ξa is obtained, also. The results of these coefficients may be useful to the manufacture and use of short fiber reinforced composite materials. Considering these coefficients ξa ξd and ξl, the improved formula is given for the direct calculation of overall strength of short fibers reinforced composite materials. The improved formula may reflect the microstructural characteristics of short fibers reinforced composite materials.

Grinding Characteristics of Directionally Aligned SiC Whisker Wheel. Comparison with Al2O3 Fiber Wheel.

One of the authors invented a unique SiC whisker wheel in which the whiskers were aligned normally to the grinding wheel surface. In this paper, grindabilities of the SiC whisker wheel are investigated and compared with those of other wheels of SiC grains, Al2O3 grains, as well as Al2O3 long and short fibers which were also aligned normally to the grinding wheel surface, respectively. The main research contents grinding characteristics of a directionally aligned SiC whisker wheel such as material-removal rates, wheel-wear rates, integrity of the ground surfaces, grinding ratios and grinding efficiency. Furthermore, grinding wheels of whiskers and fibers have a common disadvantage : they tend to load easily. The authors introduced a simple method of loading-free grinding to overcome this propensity and investigate some related grinding characteristics under loading-free grinding conditions.

６０６１アルミニウム合金基複合材料切削時の工具摩耗機構

To clarify the tool wear mechanism in cutting fiber reinforced metal (FRM), turning three kinds of FRM were carried out. They are two kinds of SiC whisker reinforced Al (A6061) and Al2O3 short fiber reinforced Al (A6061). In cutting them, it is known that severe tool wear is observed. So, the tool wear mechanism in cutting them was investigated. Tool materials were five kinds of cemented carbides, two kinds of ceramics and the sintered diamond. In comparison in the cemented carbides, there is the difference of the tool wear by the Co content, the hard grain of the tool and the grain holding strength of the binder. And there is the difference of the wear mechanism in comparison in the three work materials. In cutting SiC whisker reinforced Al (A6061) with the cemented carbide, the tool wear seems to progress due to both of the simple abrasive wear and the falling off of the hard grains. This falling off is produced so that the binder is cut away by the very thin whisker. On the other hand, that in cutting Al2O3 short fiber reinforced Al (A6061) seems to progress due to only the simple abrasive wear. In cutting with two ceramic tools, the severe tool wear is observed in spite of the high hardness. In the diamond tool, the tool wear is very small and this is the most suitable tool in cutting FRM.

The Choice of the Initial Form of δ- Al2O3 Short Fibers to Reinforce the Al-4.5 Cu Alloy Prepared From Elemental Powders

The Choice of the Initial Form of δ- Al2O3 Short Fibers to Reinforce the Al-4.5 Cu Alloy Prepared From Elemental Powders