Showing papers on "Metal matrix composite published in 1993"

Documentation of damping capacity of metallic, ceramic and metal-matrix composite materials

Abstract: High-damping materials allow undesirable mechanical vibration and wave propagation to be passively suppressed This proves valuable in the control of noise and the enhancement of vehicle and instrument stability Accordingly, metallurgists are continually working toward the development of high-damping metals (hidamets) and high-damping metal-matrix composites (MMCs) MMCs become particularly attractive in weight-critical applications when the matrix and reinforcement phases are combined to provide high-damping and low-density characteristics In selecting the constituents for an MMC, one would like to have damping capacity data for several prospective component materials Based upon data which have been published in the scientific literature, a concise documentation is given of the damping capacity of materials by three categories: (a) metals and alloys, (b) ceramic materials, and (c) MMCs

Enhanced Mechanical Properties of TiNi Shape Memory Fiber/Al Matrix Composite

Abstract: A design concept of shape memory TiNi fiber reinforced/Al metal matrix composite (SM-MMC) was proposed. Mechanical tensile properties such as stiffness and yield strength, were improved by the strengthening mechanisms: back stress in the Al matrix induced by stiffness of TiNi fibers and the compressive stress in the matrix caused by shape memory shrinkage of TiNi fibers. Damping capacity of the composite was also increased. These results suggest that this composite with prestrain can be applicable and is suitable for machinery, especially engine components where the material becomes stronger at higher temperatures owing to the shape memory effect

Diamond/Al metal matrix composites formed by the pressureless metal infiltration process

Abstract: Diamond particles are unique fillers for metal matrix composites because of their extremely high modulus, high thermal conductivity, and low coefficient of thermal expansion. Diamond reinforced aluminum metal matrix composites were prepared using a pressureless metal infiltration process. The diamond particulates are coated with SiC prior to infiltration to prevent the formation of Al4C3, which is a product of the reaction between aluminum and diamond. The measured thermal conductivity of these initial diamond/Al metal matrix composites is as high as 259 W/m-K. The effects of coating thickness on the physical properties of the diamond/Al metal matrix composite, including Young's modulus, 4-point bend strength, coefficient of thermal expansion, and thermal conductivity, are presented.

Mechanical properties of aluminium alloy 6061–Al2O3 composites

Abstract: One of the most beneficial property improvements that can be realised using metal matrix composite technology is the ability to increase the relatively low stiffness and hardness of aluminium alloys by the addition of high modulus particles such as Al2O3 The stiffness and hardness of the resulting composites increase with increasing volume fraction of particles Unfortunately, these increases are accompanied by corresponding reductions in the ductility Because of this compromise in properties with increasing volume fraction, a balanced combination of tensile strength, ductility, creep resistance, toughness, and fatigue resistance must be achieved for successful industrial application In this regard, mechanical testing of a cast and extruded 6061 aluminium alloy containing 0, 10, or 20 vol-%Al2O3 particles has been carried out with emphasis on measuring the properties which would be the most important for an application such as steam turbine blading In addition to an increased room temperature

Computational modeling of metal matrix composite materials. I: Isothermal deformation patterns in ideal microstructures

Abstract: The mechanical behavior of particulate reinforced metal composites, in particular an SiC reinforced Al-3 wt% Cu model system, was analyzed numerically. The Computational micromechanics approach was taken, i.e. a detailed representation of microstructure in which the material was characterized by a finite deformation, thermo-elastic-viscoplastic crystallographic theory. Individual matrix grains and reinforcing particles were represented, in the context of two dimenssional repeating unit cell models. The performance of the microstructure under variation in microstructural parameters such as (1) reinforcement volume fraction, (2) morphology and (3) matrix strain hardening properties was investigated, as was the effect of change in loading state. In this, the first in a series of four articles, the isothermal microstructural deformation behavior is examined in detail. Localization of plastic deformation is seen to be a natural part of the deformation process and evolves according to patterns, which develop from the onset of yield and are determined for the most part by the positions of the reinforcing particles. This is in contrast to the microscale behavior of single phase polycrystals where deformation patterns only emerge at larger overall strains. Localization intensity depends strongly on reinforcement volume fraction and morphology and less significantly on matrix hardening properties. Results for tensile and compressive loading histories are compared showing differences that depend on particle position and finite geometry changes during deformation.

Interface structure and fractography of a magnesium-alloy, metal-matrix composite reinforced with SiC particles

Abstract: The interfacial structure in SiC-particle-reinforced, as-cast and heat-treated magnesium-alloy-matrix composites was investigated using analytical electron microscopy. No extensive chemical reactions were observed between the magnesium and the SiC particles or the SiC and the eutectic phase. However, most of the eutectic phase appeared to nucleate at the surface of the SiC particles. In addition to the lamellar eutectic, a fine eutectic and Mg2Si particles have been identified at the SiC surface using nanoprobe micro-analysis. As with the aluminium base composite, precipitation was observed to take place on dislocations, and dense precipitation was found to occur in the stress fields around the SiC particles. Examination of the fracture surface indicated that the bonding between the SiC/eutectic is stronger than between the SiC/magnesium matrix. Intergranular cracks have been observed both in the fracture surface and also in a polished and etched section. The fracture surface tends to exhibit a more brittle morphology in the composite than is observed in the alloy.

Model studies of fibre breakage and debonding in a metal reinforced by short fibres

Abstract: F or a metal reinforced by short, brittle fibres the development of damage by fibre cracking or decohesion is studied, taking into account the interaction between these two types of damage. The metal matrix composite, containing a periodic array of aligned fibres, is represented in terms of a cell model, and solutions for the stress and strain fields are determined numerically. Failure at the interface is modelled in terms of a cohesive zone model that accounts for decohesion by normal separation as well as by tangential separation, whereas fibre fracture is simply represented by a critical value of the average tensile stress on a cross-section. The effect of various material parameters and of the macroscopic stress state on the two types of damage is investigated, together with the subsequent mode of void growth.

Light armor improvement

Abstract: A structural armor assembly including a superplastically formed sandwich member having on one side one face sheet of high toughness, high-strength titanium alloy material, and on the other side a second face sheet made of non-superplastically formable metal matrix composite abrasive material. Abrasive materials in the form of "KEVLAR"® or "SPECTRA"® are provided inside cells in the sandwich member to serve as a "catcher's mitt" to absorb part or all of the energy of the ballistic fragments after they have been abraded by the material of the second face sheet.

Mode I fatigue cracking in a fiber reinforced metal matrix composite

Abstract: The mode I fatigue crack growth behavior of a fiber reinforced metal matrix composite with weak interfaces is examined. In the longitudinal orientation, matrix cracks initially grow with minimal fiber failure. The tractions exerted by the intact fibers shield the crack tip from the applied stress and reduce the rate of crack growth relative to that in the unreinforced matrix alloy. In some instances, further growth is accompanied by fiber failure and a concomitant loss in crack tip shielding. The measurements are compared with model predictions, incorporating the intrinsic fatigue properties of the matrix and the shielding contributions derived from the intact fibers. The magnitude of the interface sliding stress inferred from the comparisons between experiment and theory is found to be in broad agreement with values measured using alternate techniques. The results also indicate that the interface sliding stress degrades with cyclic sliding, an effect yet to be incorporated in the model. In contrast, the transverse fatigue properties are found to be inferior to those of the monolithic matrix alloy, a consequence of the poor fatigue resistance of the fiber/matrix interface.

Strengthening of Metal Matrix Composite by Shape Memory Effect

Abstract: The strengthening of a metal matrix composite (MMC) by the shape memory effect of dispersed TiNi particles was theoretically studied. An analytical model was constructed for the prediction of the Young's modulus (E), yield stress σ y ) and work-hardening rate E TC ), on the bases of the Eshelby's equivalent inclusion method. The analysis was performed on the TiNi particle/Al metal matrix composites with varying volume fractions and prestrains of the particle. The present analysis has shown that E, σ y and E TC increase with increasing the volume fraction of the particles, and σ y increases with increasing prestrain while E and E TC are independent of prestrain

Chemical reaction strengthening of Al/TiC metal matrix composites by isothermal heat treatment at 913 K

Abstract: The effect of solid state heat treatment at 913 K on extruded XD Al/TiC metal matrix composite with 0.7 and 4.0 /nm particle sizes has been investigated. The interfaces between Al and TiC after extrusion were atomically abrupt, as observed by HRTEM. On holding at 913 K, the composite with submicron particle size showed substantial changes in the phases present due to reaction between Al and TiC at 913 K. The stable reaction products are Al3Ti and A14C3. A substantial increase in Young's modulus occurs. The room and elevated temperature strength and hardness of the composite with submicron particles also increase significantly with time of heat treatment, but at the expense of ductility. The effect of heat treatment over the time range investigated is limited to the interfaces for the 4.0 /xm TiC particle size composite due to longer diffusion paths.

Ultrasonic reflectivity technique for the characterization of fiber‐matrix interface in metal matrix composites

Abstract: An ultrasonic plane wave reflected by a cylindrical fiber embedded in a homogeneous isotropic matrix is modeled. The model calculates the ‘‘back‐reflection’’ coefficient by taking in to account the properties of the fiber and the matrix, the ultrasonic wavelength, the angle of incidence, and a coefficient called ‘‘shear stiffness coefficient’’ which characterizes the elastic behavior between the fiber and the matrix. Results obtained from the theoretical analysis for a model metal matrix composite system are shown. The theory developed in this paper and some of the results obtained are equally applicable in ceramic matrix fiber reinforced composites.

High strain rate tensile properties of an (Al2O3 particles)-(Al alloy 6061-T6) metal matrix composite

Abstract: The metal matrix composite materials consist of 10, 15 and 20 vol.% alumina particles in an aluminium alloy 6061-T6 matrix. Specimens were taken from hot-extruded rods and the tensile tests were carried out at various strain rates. High strain rate tests were performed by the split-Hopkinson-bar method. The fracture surfaces were observed with a scanning electron microscope to understand the fracture mechanisms. From the results, it can be concluded that: (1) the alumina-reinforced composites are more sensitive to strain rate than the unreinforced material, (2) the strain rate sensitivity of the ultimate tensile strength of these composites increases with increasing temperature and (3) the addition of alumina particles will reduced the ductility of aluminium alloy 6061-T6, irrespective of the strain rate and temperature.

Local Approach to Damage in Elasto- Plastic Metal Matrix Composites

Abstract: Damage is incorporated along with plastic deformation in this model for the analysis of fiber-reinforced metal matrix composite materials. In the formulation, a micromechanical composite model is used in the sense that the matrix and fiber local con- stitutive damage relations are treated separately and then linked to the overall response through a certain homogenization procedure. In this process, two local damage tensors M and M are introduced where M accounts for the damage in the ductile matrix such as nucleation and growth of voids, while the tensor M reflects the damage in the fibers such as fiber fracture. The problems of debonding and delamination can be conveniently represented by either M or Mor a combination of both depending on the extent of complexity that is desired of the final constitutive model. A von Mises type yield criterion with an associated flow rule is first assumed for the undamaged matrix material. It is shown that the resulting overall yield function for the damaged composite is of the anisotropic type, while the derived overall flow rule is nonassociative due to the presence of damage. In addition, an overall kinematic hardening rule is obtained for the damaged composite system that is a combination of a generalized Ziegler-Prager rule and a Phillips-type rule. Finally, an elasto-plastic stiffness tensor is

Inelastic deformation of metal matrix composites

Abstract: A theoretical model capable of predicting the thermomechanical response of continuously reinforced metal matrix composite laminates subjected to multiaxial loading was developed. A micromechanical model is used in conjunction with nonlinear lamination theory to determine inelastic laminae response. Matrix viscoplasticity, residual stresses, and damage to the fiber/matrix interfacial zone are explicitly included in the model. The representative cell of the micromechanical model is considered to be in a state of generalized plane strain, enabling a quasi two-dimensional analysis to be performed. Constant strain finite elements are formulated with elastic-viscoplastic constitutive equations. Interfacial debonding is incorporated into the model through interface elements based on the interfacial debonding theory originally presented by Needleman, and modified by Tvergaard. Nonlinear interfacial constitutive equations relate interfacial tractions to displacement discontinuities at the interface. Theoretical predictions are compared with the results of an experimental program conducted on silicon carbide/titanium (SiC/Ti) unidirectional, (O4), and angle-ply, (+34)(sub s), tubular specimens. Multiaxial loading included increments of axial tension, compression, torque, and internal pressure. Loadings were chosen in an effort to distinguish inelastic deformation due to damage from matrix plasticity and separate time-dependent effects from time-independent effects. Results show that fiber/matrix debonding is nonuniform throughout the composite and is a major factor in the effective response. Also, significant creep behavior occurs at relatively low applied stress levels at room temperature.

Computational modeling of metal matrix composite materials—III. Comparisons with phenomenological models

Abstract: The mechanical behavior of particulate reinforced metal matrix composites, in particular an SiC reinforced Al-3 wt% Cu model system, was analyzed numerically and analytically. In this, the third article in a series, the results of the computational micromechanics are compared with those of simpler and more approximate analytical/numerical models. The simplerapproaches considered use phenomenological theories of plasticity and power-law strain hardening. Models that predict overall composite behavior make use of a result, valid for incompressible materials in small strain, that both pure matrix material and composite harden with the same hardening exponent. Results of micromechanical simulations, with power-slip system hardening, show that in a very approximate sense over restricted strain regions, power-law slip hardening is preserved with the power-law exhonent tending to increase with volume fraction. The results of the computations presented in the previous article are compared with the predictions of one such analytical/numerical model, where the matrix hardening function is fitted to the unreinforced poyycrystal stress-strain response. This model employs the self-consistent method to quantify strengthening. There is good agreement between the computed and predicted results. Simulations are performed using existing reinforcement geometry but replacing the physically based crystal plasticity theory with the phenomenologically based J2 flow theory. The results are in good qualitative agreement with those of the original crystal plasticity simulations at both the microscale and the macroscale. Deformation patterns in the J2 flow theory composites are smoother and tend to be less localized than those in the crystal plasticity composites; however, these features depend strongly on volume fraction and morphology. The J2 flow theory composites display power-law exponents whose dependence on overall strain, volume fraction and morphology are much more easily characterized than in the crystal plasticity case.

Casting method for metal matrix composite castings

Abstract: The invention discloses an improved method for forming metal matrix composite castings. The method achieves the casting having increased mechanical properties by using a selectively permeable mold in conjunction with pressurized gas. This allows a greater degree of metal infiltration within the interstices of a suspended preform. The method teaches the use of whiskered, fibered and particulated ceramic constituents for use in the preform, as well as various embodiments of casting methods.

Method for making graded composite bodies and bodies produced thereby

Abstract: The present invention relates to the formation of bodies having graded properties. Particularly, the invention provides a method for forming a metal matrix composite body having graded properties. The graded properties are achieved by, for example, locating differing amounts of filler material in different portions of a formed body and/or locating different compositions of filler material in different portions of a formed body and/or locating different sizes of filler materials in different portions of a formed body. In addition, the invention provides for the formation of macrocomposite bodies wherein, for example, an excess of matrix metal can be integrally bonded or attached to a graded metal matrix composite portion of a macrocomposite body.

Effect of thermal and mechanical processing on tensile properties of powder formed 2124 aluminium and 2124 Al-SiC p metal matrix composite

Abstract: The aging responses of 2124 Al-SiC p metal matrix composite (MMC) and unreinforced matrix alloy are studied and related to variations in tensile properties. The MMC is aged from Wo starting conditions: (i) stretched and naturally aged and (ii) re-solution treated. Accelerated aging occurs in both MMC conditions compared with unreinforced alloy. Tensile strengths and elastic moduli are improved in the MMC compared with the alloy, but ductility is reduced. Stretched MMC exhibits higher strength but lower ductility and modulus than re-solutioned MMC. The re-solutioned MMC fails by microvoid coalescence in low aging conditions, and by void nucleation and shear in high aging conditions. Failure of the stretched MMC initiates at the surface at specimen shoulders, illustrating the increased notch sensitivity of this condition, and propagates via a zigzag shear fracture mode. Zigzag facet size increases on gross aging. Particle fracture occurs during tensile failure, but also before testing as a result of the manufacturing process. © 1995 The Institute of Materials.

Effect of melt cleanliness on the properties of an Al-10 wt pct Si-10 vol pct SiC(p) composite

Abstract: An experimental study was conducted to examine the effect of melt cleanliness with respect to the presence of inclusions on the properties of an Al-10 wt pct Si metal matrix composite (MMC) reinforced with 10 vol pct SiC particles. The occurrence of inclusions was controlled by filtra- tion, using ceramic foam filters of 10, 20, and 30 ppi sizes, under gravity and pressure. Test bars obtained from filtered and unfiltered melt castings, prepared from fresh (as-received) and recycled composite materials, were T6-tempered and tensile tested at room temperature. The casting quality was examined using X-ray radiography. The results indicate that various factors influence the casting quality and mechanical properties of the cast composite. The A12O3 films and spinel MgAl2O4 — the main inclusions observed in the present composite — are chiefly responsible for the degradation in the mechanical properties. In addition, SiC sedimentation, Al4C3 formation, the hydrogen level of the melt, and the starting material used can also influence these properties. Fracture studies reveal that the inclusions and associated microvoids act as the crack initiation sites during composite fracture. Simple filtration using 10 ppi ceramic foam filters under gravity serves adequately in removing these inclusions and producing the desired mechanical properties.

Computational modeling of metal matrix composite materials—II. Isothermal stress-strain behavior

Abstract: The mechanical behavior of particulate reinforced metal matrix composites, in particular an SiC reinforced Al-3 wt% Cu model system, was analyzed numerically using the computational micromechanics approach. In this, the second in a series of four articles, the isothermal overall stress-strain behavior and its relation to microstructural deformation is examined in detail. The macroscopic strengthening effect of the reinforcement is quantified in terms of a hardness increment . As seen in the first article for microscale deformation, inhomogeneous and localized stress patterns develop in the microstructures. These are predominantly controlled by the positions of the reinforcing particles. Within the particles stress levels are high, indicating a load transfer from matrix to reinforcement. The higher straining that develops in the matrix grains, relative to the unreinforced polycrystal, causes matrix hardness advancement . Hydrostatic stress levels in the composite are enhanced by constraints on plastic flow imposed by the particles. Constrained plastic flow and matrix hardness advancement are seen as major composite strengthening mechanisms. The latter is sensitive to the strain hardening nature in the matrix alloy. To assess the effects of constraint more fully, simulations using external confining loads were performed. Both strengthening mechanisms depend strongly on reinforcement volume fraction and morphology. In addition, texture development and grain interaction influence the overall composite behavior. Failure mechanisms can be inferred from the microscale deformation and stress patterns. Intense strain localization and development of high stresses within particles and in the matrix close to the particle vertices indicate possible sites for fracture.

Cast wheel reinforced with a metal matrix composite

Abstract: A light weight cast metal wheel having a disk-shaped wheel disk formed across an annular wheel rim and including a reinforcing layer of a metal matrix composite extending radially across the wheel disk. The reinforcing layer also can extend axially across a portion of the wheel rim. The metal matrix composite layer is formed by securing a preform formed from a reinforcing material within the wheel mold prior to casting the wheel. The use of a preform assures that the resulting reinforcing layer is uniform.

Conventional Machining of an Aluminium Based SiC Reinforced Metal Matrix Composite (MMC) Alloy

Abstract: Metal Matrix Composites (MMC’s) are a new class of materials intended for high performance applications. The paper outlines the results of a series of turning, face milling, drilling, reaming and tapping tests performed on an aluminium 2618 alloy reinforced with 15 vol% silicon carbide (SiC) particulate. High speed steel, cemented tungsten carbide and polycrystalline diamond (PCD) cutting tools were used. Based on a tool life criterion PCD products proved, in general, to be the most effective and the only tool material capable of providing a realistic operating performance. For instance, when using tungsten carbide drills only 48 holes could be made before lip flank wear reached 0.6 mm. PCD tipped drills cut 300 holes with only 0.08 mm of flank wear. In turning and to some extent in face milling operations, changes in cutting speed did not significantly effect flank wear rate. In drilling and reaming feed rate proved to be the key parameter.

Crack closure and residual stress effects in fatigue of a particle-reinforced metal matrix composite

Abstract: A study of the influence of macroscopic quenching stresses on long fatigue crack growth in an aluminium alloy-SiC composite has been made. Direct comparison between quenched plate, where high residual stresses are present, and quenched and stretched plate, where they have been eliminated, has highlighted their role in crack closure. Despite similar strength levels and identical crack growth mechanisms, the stretched composite displays faster crack growth rates over the complete range of ΔK, measured at R = 0.1, with threshold being displaced to a lower nominal ΔK value. Closure levels are dependent upon crack length, but are greater in the unstretched composite, due to the effect of surface compressive stresses acting to close the crack tip. These result in lower values of ΔKeff in the unstretched material, explaining the slower crack growth rates. Effective ΔKth values are measured at 1.7 MPa√m, confirmed by constant Kmax testing. In the absence of residual stress, closure levels of approximately 2.5 MPa√m are measured and this is attributed to a roughness mechanism.

Effect of ceramic particle size, melt superheat, impurities and alloy conditions on threshold pressure for infiltration on SiC powder compacts by aluminium-based melts

Abstract: An instrumented heated pressure vessel has been used to determine the effect of some experimental variables on the pressurized infiltration of SiC powder preforms by a series of Al-based melts Threshold pressure for infiltration of 2014 Al alloy decreased with increasing SiC particle size and increasing melt superheat Decreased purity of unalloyed aluminium and addition of 42 wt% Cu to 99999% pure aluminium increased the threshold pressure while addition of an extra 10 wt% Mg to 2014 alloy lowered it Increasing the melt superheat of 2014 alloy reduced the incidence of entrapped porosity in the compacts which tended to increase in the direction of infiltration There was evidence of partial dissolution of SiC into the liquid during infiltration These findings are discussed in the context of present understanding of metal matrix composite formation via melt infiltration routes

Metal matrix composite

Abstract: A metal matrix composite is made by roll consolidating a sandwich formed from alternating layers of a matrix metal, a brazing alloy, and reinforcing fiber at elevated temperature and pressure. If made in a process using mandrels to impart the pressure and heat, such as a process described in U.S. Pat. No. 5,229,562, the metal matrix composite is kept separate from the mandrels by using a release agent or stop-off such as a layer of boron nitride between the mandrel and layup.