Fiber Reinforced Aluminum Matrix Composites Research Articles

Tensile properties and thermal expansion behaviors of continuous molybdenum fiber reinforced aluminum matrix composites

The tensile properties and thermal expansion behaviors of continuous molybdenum fiber reinforced aluminum matrix composites (Mo f/Al) have been studied. The Mo f/Al composites containing different volume percents of Mo fibers were processed by diffusion bonding. The strengths of unidirectional Mo f/Al composites were close to the rule-of-mixtures. The strengths of 0°/90° dual-directional composites increased with fiber content, while those of 45°/135° composites remained relatively low. The coefficients of thermal expansion (CTEs) of the composites decreased as the fiber content increased, close to the values of Mo fibers. With increasing temperature, the CTEs of unidirectional composites increased, while those of dual-directional composites decreased due to large accumulated thermal stresses. The CTEs of 45°/135° composites were lower than those of 0°/90° composites because of contraction effect. At temperatures above 250 °C, the CTEs of the dual-directional composites gradually increased due to matrix yielding and interfacial decohesion.

Effect of thermal?mechanical cycling on thermal expansion behavior of boron fiber-reinforced aluminum matrix composite

The thermal expansion behavior of boron fiber-reinforced aluminum matrix composite subjected to thermal–mechanical cycling (TMC) was studied. Experimental results showed that TMC affected greatly the thermal expansion behavior of the composite. Using a simple analysis model of internal stress in the fibers, the stress change during the thermal expansion coefficient measurements of the composite subjected to TMC was calculated. The results indicated that TMC could induce the interfacial degradation of the composite, and the more the numbers of TMC cycles, or the higher the applied stress level of TMC, the more serious the interfacial degradation of the composite became. The proposed one-dimensional analysis model was proved to be a simple and qualitative approach to probing the interfacial degradation of unidirectional fiber-reinforced metal matrix composites during TMC.

Thermomechanical fatigue of short fibre reinforced aluminium matrix piston alloy

The technical potential of short fibre reinforced aluminium matrix composites lies in their higher stiffness and higher strength at elevated temperatures compared with unreinforced matrix alloys. In the present investigation, thermal cycling creep tests were conducted on the piston alloy AlSi12CuMgNi reinforced with 20% Saffil (Al2O3) short fibres, to simulate the cold start conditions of combustion engines. After processing of the metal matrix composite (MMC) by direct squeeze casting, four heat treatment conditions were produced. Specimens under constant load were thermally cycled between 50 and 300°C, whereby a heating and cooling speed of 12.5 K s1 was achieved. Series of up to 5000 cycles at tensile stresses between 20 and 80 MPa were executed, comparing reinforced specimens and unreinforced matrix material. The results of these experiments showed that the creep properties of the alloy, especially minimum creep rate and lifetime to fracture, were improved by the reinforcement. Furthermore, the creep rate of the MMC was essentially independent of the heat treatment condition, whereas the minimum creep rate was increased significantly for the matrix material by overaging. It can be concluded that precipitation strengthening influenced the creep properties of unreinforced specimens only, which is in good agreement with theoretical considerations. An analysis of fibre length revealed that the majority of the fibres broke at between 50 and 75% of the lifetime, just before the beginning of tertiary creep. Metallographic investigations using a scanning electron microscope did not show fibre pullout, but multiple fracture of fibres along the whole specimen. Micromechanical models for isothermal creep in short fibre reinforced aluminium alloys confirm the above results, since tertiary creep is assumed to be a consequence of fibre fracture.

Interfacial reactions in aluminosilicate short fiber-reinforced aluminum matrix composites

Aluminosilicate short fibers are one of the less expensive reinforcements used for the fabrication of metal matrix composites (MMCs). The present investigation evaluates the interfacial characteristics of Al-7Si-0.4Mg (356) alloy reinforced with 10 wt pct aluminosilicate short fibers using optical microscopy, electron microscopy, and X-ray analysis. The fibers used are standard- and zirconiagrade aluminosilicate short fibers. The interfacial analysis has shown the formation of MgAl2O4 and Si in both grades of fibers. In addition, ZrAl3 formation is observed in the zirconia-grade fiber because of the interaction between the matrix and the dispersoid. The zirconia-grade fiber is more susceptible to interfacial reaction than the standard-grade fiber because of the presence of the highly reactive ZrO2 phase and a lower amount of the Al2O3 phase, which provides resistance to the reaction.

Microstructures and mechanical properties of engineered short fibre reinforced aluminium matrix composites

Aluminium matrix composites have been fabricated by squeeze casting into short fibre preforms modified on the basis of a phase contiguity model to improve mechanical performance. Fibre junctions were created in a planar random alumina fibre array by (a) sintering, (b) phosphoric acid treatment, (c) phosphoric acid/aluminium hydroxide (P/Al) treatment and (d) infiltration with alumina powder and sintering. The microstructures and mechanical properties of these composites were examined systematically. The results indicate that using phosphoric acid solution itself to create inter-fibre bonds in the preform gave rise to very low composite strength and ductility compared with that resulting from the as-received preform. This is mainly due to the severe damage to the fibres caused by chemical reaction. By employing the P/Al binder to create the cross-links, the composites reinforced with laboratory-made preforms yielded higher tensile strength relative to the uniform fibre reinforced composites without any sacrifice to the ductility and elastic modulus.

Nextel™ 610 alumina fibre reinforced aluminium: influence of matrix and process on flow stress

Abstract Continuous alumina fibre reinforced aluminium matrix composites are produced using two different liquid metal infiltration methods, namely direct squeeze casting and gas pressure infiltration. Net-shape fibre performs for longitudinal parallel tensile bars are prepared by winding the Nextel™ 610 alumina fibre (3M, St Paul, MN) into graphite moulds. High purity aluminium, two binary (Al–6% Zn and Al–1% Mg) and one ternary (Al–6% Zn–0.5% Mg) aluminium alloys are used as matrix materials. The composite is tested in uniaxial tension–compression, using unload–reload loops to monitor the evolution of Young's modulus. A linear dependence between Young's modulus and strain is observed; this is attributed, by deduction, to intrinsic elastic non-linearity of the alumina fibre. This conclusion is then used to compare on the basis of the in situ matrix flow curve the influence of matrix composition and infiltration process on the composite stress–strain behaviour.

Continous Fiber Reinforced Aluminum Matrix Composites – Influence of the Alloy Composition on the Mechanical Properties

Continous Fiber Reinforced Aluminum Matrix Composites – Influence of the Alloy Composition on the Mechanical Properties

TEM study of carbon fibre reinforced aluminium matrix composites: influence of brittle phases and interface on mechanical properties

The microstructure of A357 aluminium alloy (7 wt% Si+0.6 wt% Mg) reinforced by 1D-M40J carbon fibres is characterised using different techniques of transmission electron microscopy (diffraction, HRTEM, EDX, EELS). The microstructure of the high modulus PAN based fibre and of the pyrolytic carbon coating (Cp) is fully characterised. Silicon and Mg 2Si grains which determine matrix-reinforcement adhesion are investigated. On the basis of the microstructural features, the mechanical properties of the composites are discussed. The mechanical behaviour of composites prepared with and without Cp interphases corresponds to a brittle matrix reinforced by brittle fibres. In the case of the composite without Cp interphase, the most influent parameter is the high resistance to sliding at the interface between silicon and fibres which leads to a strong fibre-matrix “bonding” and thus, to a weak and brittle material. The interfacial resistance to decohesion and to sliding is lower in the composite with Cp interphase resulting in higher strength and limited pull out. This lower interfacial resistance is due to the successive microporous and layered microstructures of the pyrolytic carbon coating.

Influence of microstructure on axial strength of unidirectional continuous fibre reinforced aluminium matrix composites

Systematic empirical investigations on the relationship between microstructural features and mechanical performance of unidirectionally reinforced continuous fibre Al matrix composites (CFAMCs) carried out by the present authors in recent years are summarised. The employment of a high strength matrix alloy and the development of a strong fibre/matrix interface are beneficial to maximise the strengthening effect of the fibre reinforcement. Processing defects, such as second brittle phases in the matrix, non-infiltration defects, matrix solidification shrinkage voids, excessive interfacial reactions, the presence of reaction products on the interface, weak interfacial binding, and excessively high fibre volume fraction reduce composite strength to different extents via a number of different mechanisms. Criteria for the microstructure design of CFAMCs for optimum fibre strengthening efficiency are proposed.

Mechanical behavior and microstructure of NiAl short fiber reinforced aluminum matrix composite

Mechanical behavior and microstructure of NiAl short fiber reinforced aluminum matrix composite

Load transfer from broken fibers in continuous fiber Al 2O 3-Al composites and dependence on local volume fraction

The load transfer characteristics of a continuous, high volume fraction alumina (Al 2O 3)fiber reinforced aluminum matrix composite are determined by combining high spatial resolution stress measurements and computational micromechanical modeling. The residual stresses in individual fibers and the redistribution of applied load due to fiber failure have been measured using photostimulated Cr 3+ luminescence based piezospectroscopy. From these measurements, the load transfer profiles along broken fibers and the induced stress concentration profiles on their adjacent neighbors have been determined. They are found to depend on the local inter-fiber spacing. They are compared with fiber stress profiles predicted by a shear-lag stress analysis which accounts for the influences of matrix yielding, called the quadratic influence superpositon (QIS) technique, as well as other shear-lag based multifiber composite models. The current study indicates that fiber breaks are accompanied by matrix yielding extending on the order of fiber diameters and which induce significant stress concentrations on neighboring fibers, dependent on the local fiber spacing and extent of plastic yielding. Additionally, the matrix yield strength is dependent on the local fiber spacing and increases with decreasing local fiber spacing. The implications of the micromechanical load sharing characteristics and composite processing on ultimate tensile strength are discussed.

Studies on fiber treatment and fabrication of short ceramic fiber reinforced aluminum matrix composites

Studies on fiber treatment and fabrication of short ceramic fiber reinforced aluminum matrix composites

Compressive strength of continuous fiber reinforced aluminum matrix composites

Aluminum matrix composites can exhibit exceptionally high compressive strength (ε 4 GPa). The main failure mechanism has been identified to be plastic kinking, although an upper bound seems to be attained when the fibers reach their compressive strength. The experimental results are consistent with a plastic kinking model in strain hardening composites. The important parameters controlling the compressive strength are the composite shear modulus, the shear yield strength, the strain hardening rate and the maximum initial fiber misorientation. Interfaces can also play an important role; composites reinforced with weakly bonded fibers have a reduced compressive strength due to their low shear strength in the fiber direction. The results can be used to design composite systems with high compressive strengths; in practice this is done by selecting matrices with high yield strengths and fast hardening rates.

Strength variability in alumina fiber-reinforced aluminum matrix composites

The strength variability of an Al2% Cu alloy matrix reinforced with 65 vol.% Nextel -610 Al 2O 3 fibers has been investigated, with the aim of identifying and separating the contributions associated with the variabilities in both the fiber bundle strength and the fiber volume fraction. Strength distributions have been measured using three test geometries, including three- and four-point flexure and uniaxial tension. The measured distributions are rationalized on the basis of a fiber strength distribution that follows Weibull statistics and a fiber volume fraction distribution characterized by a Gaussian. The fiber bundle strength distribution is found to be extremely narrow, with a Weibull modulus in the range of ∼ 50–60. In addition, the coefficient of variation in the fiber volume fraction distribution is inferred to be ∼ 6%; by comparison, measurements made on relatively large specimens yield a coefficient of variation of ∼ 3%. The differences in these values are attributed to local volume fraction variations which are not detectable by the global measurements. The measured strengths are compared with the predicted values based on the theoretical work of Curtin and co-workers, incorporating the effects of local load sharing between broken fibers and their neighbors. Good correlations are obtained between the experimental data and the model predictions.

Effect of geometry and volume fraction of fibers on creep in short fiber reinforced aluminum alloys

Creep in short fiber reinforced aluminum alloys is a result of three interconnected elementary microstructural processes: (i) loading of fibers by dislocations; (ii) unloading of fibers by a recovery process in which dislocation loops move to the fiber ends; and (iii) fiber breakage. The present work supports this view in showing that a model which is based on this microstructural scenario can successfully predict the creep behavior of short fiber reinforced aluminum matrix composites with different fiber volume fractions. The present work also addresses the influence of the fiber aspect ratio distribution on the creep process.

A combined process of coating and hybridizing for the fabrication of carbon fiber reinforced aluminum matrix composites

A process which combines fiber coating and particles hybridizing has been utilized for the fabrication of carbon fiber reinforced aluminum matrix composite. Ceramic SiC coating was derived by Sol-gel method and SiC particle hybridizing was processed in Sol-gel solution simultaneously. Squeeze-cast process was used to get bulk composite materials. SEM analysis of the material showed a good fiber distribution in the Al matrix by particles hybridizing. HRTEM works indicated the coating to be an effective barrier of the C/Al interfacial reaction and had reduced the interfacial shear strength noticeably. Mechanical properties of the composite were improved especially for the axial strength. C/Al interfacial reaction was also studied which revealed that PAN-based carbon fiber reacted heavily with aluminum matrix. The nucleation and growth of the reactants were dominantly a random process.

The effect of discontinuous fibre orientation on the wear properties of composites

Fibre-reinforced aluminium matrix composites possess good mechanical and tribological properties and are applied successfully in the aerospace and automobile industry. Their wear properties and mechanisms have been investigated for several decades. One important aspect of these is the effect of ®bre orientation on the wear properties of composites. For continuous-®bre-reinforced metal matrix composites, it is found in general that the composites with ®bres normal to the wear surface exhibit superior wear resistance to those with ®bres parallel to the wear surface [1±3]. However, different conclusions have been obtained by different studies on the effects of discontinuous ®bre orientation on the wear resistance of composites. Arikan and Murphy [4] concluded that the a-Al2O3y(AlyZn) composites with normal-orientation ®bres exhibited superior wear resistance to those with parallelorientation ®bres. Asanuma and Hirohashi [5] obtain the same conclusion by the investigation on the wear behaviour of SiC whiskers (SiCw)yAl composites under lubricated sliding conditions. However, Pan and Fine [6] found that the wear rate of SiCwyAl alloy 2124 composites is lower when the ®bres are parallel rather than normal to the wear surface. Wang and Rack [7] concluded that the initial wear rates of SiCwyAl alloy 7091 composites depend strongly upon whisker orientation; the highest wear rates were observed on normal-orientation whisker composites. The steady-state wear rates of the composites were, however, generally independent of reinforcement orientation, with the exception of wear at 3:6 m sy1 where the parallel-orientation composites was superior. In the present letter, the effect of discontinuous ®bre orientation on the wear properties of composites was studied by a number of tests and a statistical method. Mullite (3Al2O3 . 2SiO2)-®bre reinforced Al±Si composites were fabricated by squeeze casting. The ®bre, with a mean diameter of 3.0±8.0 im and a mean length of 40±100 im, was obtained from the Luoyang Institute of Refractories Research Ministry (People's Republic of China). The Al±Si alloys used were Al±12 wt % Si±Cu±Mg±Ni. The composites was treated by T6 treatment after casting. The ®bres possess a planar-random distribution in the composites, as shown in Fig. 1. Wear tests under lubricated sliding conditions were carried out on a block-on-ring type of wear apparatus at room temperature. The sliding ring (width, 10 mm; outer diameter, 50 mm) was steel 45 with a surface Rockwell C hardness of 56 HRC. The stationary block was a metal matrix composite (MMC) specimen, 10 mm wide, 10 mm high and 17 mm long. The rectangular faces of the MMC specimens were placed in contact with the sliders. The lubricant used was a grade 20 hydraulic oil, which was continuously sprayed onto the outside surface of the sliding ring during the experiment by a spray gun. The nomal load, sliding velocity and distance were 60 N, 1.5 m sy1 and 3768 m, respectively. Composites with ®bres parallel (face A in Fig. 1) and normal (face B in Fig. 1) were tested 44 times. The detailed data have been given in [8]. Using the Shapiro±Wilk method [9], which is a non-parametric method for data-normality tests, it was found that wear volumes of each kind of ®bre orientation composites agree with the normal

Assessment of overload profiles and interfacial shear strength in unidirectional fibre composites via quantitative fractography

A stereometric method for digitising the fracture surface of unidirectional fibre composites is used to calculate the breaking height differences of each fibre to its six nearest neighbours. From this height distribution the overload profile along the fibres, the critical length, interfacial shear strength, and the characteristic strength of the fibres are derived. This method is applied to ceramic fibre reinforced aluminium matrix composites tested in three point bending.MST/3004

ＳｉＣウィスカおよび粒子強化アルミ合金基複合材料の下限界近傍の疲労き裂成長機構の検討

Fatigue crack propagation properties and fracture mechanisms were examined for three commercially fabricated aluminum matrix composites containing SiC whiskers (SiCw) and SiC particles (SiCp) under rotating bending condition. Fatigue crack propagation rates for SiCw/A2024 and SiCp/A356 composites were lower than those for unreinforced alloys at a given stress intensity factor near fatigue threshold, while the fatigue thresholds for those composites were higher than those for matrix alloys. For SiCp/A357 composite the fatigue crack propagation rates were higher than those for SiCp/A356 composite. Fractography revealed that the fatigue crack would propagate to the whisker/matrix interface following the formation of dimple patterns in the whisker rich zones or formation of striation patterns in the whisker poor zones for SiCw/A2024 composites, while for SiCp/A356 and SiCp/A357 composites the fatigue crack would propagate in the matrix near fatigue threshold . The near final failure crack would be linked to the sub-crack initiated from the particles ahead of the main crack. The fatiguecrack propagation models were proposed for discontinuous fiber reinforced aluminum matrix composites. It is suggested that the silicon carbide whiskers or particles would have a very significant effect on fatigue crack propagation properties near fatigue threshold.

Stainless steel fibre reinforced aluminium matrix composites processed by squeeze casting : relationship between processing conditions and interfacial microstructure

This work investigates the influence of some processing parameters on the extent of interfacial reaction in squeeze cast aluminium matrix composites reinforced with 12 mu m diameter, continuous stainless steel fibres. The average thickness of the reaction layer at fibre/matrix interfaces was measured by image analysis. When casting was made in a die at room temperature, the thickness of the reaction layer was affected on a distance of several mm from the lateral surface or from the bottom of the preform. The results indicate that the major part of the reaction occurs before solidification of the liquid metal. The control of the extent of interfacial reaction can be achieved through optimization of both infiltration parameters and features of the preform such as the volume fraction of the fibres.