Al-SiC Metal Matrix Composites Research Articles

Role of Mg and Mg+Si as external dopants in production of pure Al–SiC metal matrix composites by pressureless infiltration

Metal matrix composites have been produced by pressureless infiltration of pure Al into Mg doped SiC preforms after 1 h at 900°C. Aluminium has been found to infiltrate preforms containing between 2 and 14 wt-%Mg, however Al did not infiltrate a preform containing 1 wt-%Mg. Preforms doped with 1 wt-%Mg and Si did result in infiltration. Increasing the Mg content or increasing the Si content in the preform resulted in more extensive infiltration. The effect of Mg and Mg mixed with Si on pressureless infiltration of pure Al, microstructure of MMC as well as mechanical properties are discussed. Although the dopant was uniformly distributed throughout the preform microstructural analysis and hardness measurements indicate that the resultant composite may not be uniform due to infiltration inwards from the edge to the centre of preform.

Temperature dependent strength analysis of short fiber reinforced Al–Si metal matrix composites

Abstract Metal matrix composites (MMCs) were produced by a pressure infiltration technique, using Saffil ( δ -Al 2 O 3 ) alumina short fiber preforms as the reinforcement, and the alloy Al–12 wt% Si (LM 13) as the matrix material. The matrix alloy and the composites were subjected to a standard T6 heat treatment and consequently tensile tested. The room temperature strength of the composites were seen to increase up to 15 vol.% fiber and then deviated sharply from the linear behavior and decrease continuously as the fiber volume increased. As the test temperature was raised, all composites showed excellent retention of strength up to 300°C. Furthermore, the experimental results of tensile strength were compared to a modified rule of mixtures (ROM). The high temperature strength analysis showed that the strength of planar-randomly oriented short fiber reinforced material can be explained through combined effects of load transfer, dispersion strengthening, and dislocation strengthening. The reinforcement behavior of these type of composites is seen to be controlled by the elevated temperature properties of the matrix alloy. The theoretical tensile strength values, calculated with a temperature dependent modified rule of mixture equation, showed an excellent agreement with experimental data at room temperature and also at elevated temperatures of up to about 200°C.

Cutting applications of DLC, hard carbon and diamond films

Abstract Due to their high hardness and low friction coefficient, diamond-like carbon (DLC), amorphous hard carbon (HC), and diamond coatings have great potential for dry cutting operations. The main differences between these coatings can be found in their hardness (respectively 2500, 5000–8000 and 10 000 HV), morphology (DLC and HC: amorphous and diamond: crystalline) and their thermal stability (DLC: 250 °C, HC: 600 °C and diamond: 700 °C). DLC, HC and CVD diamond-coated hard inserts and end-mills were evaluated for the dry turning of Al–SiC metal matrix composites and for the dry milling of Al malleable alloys, where turning of Al–SiC metal matrix composites and for the dry milling of Al malleable alloys, where hard carbon coatings are known to have good anti-sticking properties with respect to aluminium. In cases where the DLC and HC coatings did not improve the tool lifetime in any of our proofs, CVD diamond-coated tools were found to be a good alternative to PCD tipped tools for the dry machining of Al–SiC metal matrix composites. The coatings were characterized by Raman spectroscopy and Vickers hardness measurements. The wear analyses were performed using scanning electron microscopy (SEM).

Micromechanical modeling of processing-induced damage in Al–SiC metal matrix composites synthesized using the disintegrated melt deposition technique

Porosity of a few percent by volume can often be found in particulate-reinforced metal-matrix composites (MMCs) produced by any of the solid, liquid, or solid–liquid phase processes. Like the voids nucleated within the ductile matrix of the composite during loading, processing-induced voids also have an effect on the mechanical response of the composite. However, unlike nucleated voids, processing-induced voids affect the elastic and initial plastic behavior of the composite, as they are present from the onset of loading. In this study, an axisymmetric finite element model was used to investigate the influence of processing-induced voids on the deformation behavior of silicon carbide particulate-reinforced aluminum metal-matrix composites synthesized by the disintegrated melt deposition technique. A limited parametric analysis of the effect of reinforcement content on the deformation response of the composite is discussed. The numerical predictions are compared with experimental measurements.

Stereological unfolding of the trivariate size-shape-orientation distribution of spheroidal particles with application

A new stereological method is presented which enables the unfolding of joint size-shape-orientation distribution of spheroidal particles in opaque materials. It is shown that this trivariate problem can be decomposed into a series of two simpler problems. The sampling is based on a vertical uniform random planar section. Besides the theoretical integral equations between distributions of planar and spatial parameters, a numerical solution is also described in detail. The method is applied to the study of damage initiation in Al-Si metal matrix composites. Weibull modelling of particle cracking is briefly discussed.

Corrosion properties of excimer laser surface treated Al-SiC metal matrix composite

Indeed, the ultimate goal is to engineer and design metal matrix composites (MMCs) to have good inherent corrosion resistance, however, no significant breakthroughs have been achieved for MMCs that are prone to corrosion. Though, a significant amount of efforts have been spent to understand the corrosion behavior of MMC materials, only few studies were devoted to explore protection methods for improving corrosion resistance of MMCs. Among these, much effort was dedicated to some anodizing and chemical conversion techniques which in many respects have raised environmental concerns. Except a few, little work was found in applying the unique properties of lasers for surface modification of MMC materials with the aim to improve corrosion properties. Among these few, CO{sub 2} lasers were generally used and the unique properties of excimer lasers have not been explored. In fact, intensive research activities on surface treatment of metallic materials and ceramics using excimer laser radiation were only started a few years ago. Since, excimer lasers emit radiation in the ultraviolet (UV) range with an extremely short pulse duration in the range of nanoseconds. Under such a condition, amorphous structures are likely to form, and which by virtue of having no grain boundaries and have the more » likelihood of avoiding any segregation and interfacial precipitates could have a significant effect on the corrosion resistance of excimer laser treated materials. « less

Semi-solid processing of novel MMCs based on hypereutectic aluminium-silicon alloys

This paper reports on the semi-solid processing (thixoforming) of spray-formed Al Si metal matrix composites (MMCs). In these novel MMCs, silicon—in quantities of up to 45 vol.%—was the reinforcing phase, rather than a ceramic. The project investigated all steps in the processing of the materials; mechanical tests on the products were carried out and demonstrator components were manufactured. It was shown that cylindrical billets of the MMCs could be formed in one step into intricate shapes at temperatures well below the liquidus. This confirmed that thixoforming is a safe, clean and practical method for the near net shape forming of components from materials that could be shaped only with difficulty by other techniques. The thixoformed MMCs exhibited very high specific stiffness, low thermal expansion, high specific strengths and high wear resistance.

Industrial scale spray forming of copper alloys : D. Stock, H.R. Müller (Wieland-Werke AG, Ulm, Germany)

This paper reports on the semi-solid processing (thixoforming) of spray-formed AlSi metal matrix composites (MMCs). In these novel MMCs, silicon—in quantities of up to 45 vol.%—was the reinforcing phase, rather than a ceramic. The project investigated all steps in the processing of the materials; mechanical tests on the products were carried out and demonstrator components were manufactured. It was shown that cylindrical billets of the MMCs could be formed in one step into intricate shapes at temperatures well below the liquidus. This confirmed that thixoforming is a safe, clean and practical method for the near net shape forming of components from materials that could be shaped only with difficulty by other techniques. The thixoformed MMCs exhibited very high specific stiffness, low thermal expansion, high specific strengths and high wear resistance.

A finite element model of the effects of primary creep in an Al-SiC metal matrix composite

A two dimensional axisymmetric finite element model has been developed to study the creep behavior of a high-temperature aluminum alloy matrix (alloy 8009) reinforced with 11 vol pct silicon carbide paniculate. Because primary creep represents a significant portion of the total creep strain for this matrix alloy, the emphasis of the present investigation is on the influence of primary creep on the high-temperature behavior of the composite. The base alloy and composite are prepared by rapid solidification processing, resulting in a very fine grain size and the absence of precipitates that may complicate modeling of the composite. Because the matrix microstructure is unaffected by the presence of the SiC paniculate, this material is particularly well suited to continuum finite element modeling. Stress contours, strain contours, and creep curves are presented for the model. While the final distribution of stresses and strains is unaffected by the inclusion of primary creep, the overall creep response of the model reveals a significant primary strain transient. The effects of true primary creep are more significant than the primary-like transient introduced by the redistribution of stresses after loading. Examination of the stress contours indicates that the matrix axial and shear components become less uniform while the effective stress becomes more homogeneous as creep progresses and that the distribution of stresses do not change significantly with time after the strain rate reaches a steady state. These results also confirm that load transfer from the matrix to reinforcement occurs primarily through the shear stress. It is concluded that inclusion of matrix primary creep is essential to obtaining accurate representations of the creep response of metal matrix composites.

Effect of sol gel coating on wettability and interfacial reaction in Al-SiC MMC

The control of the interfacial reaction between the matrix and the SiC reinforcement in Al-SiC metal matrix composites (MMCs) is an important production parameter. The reaction causes degradation of the reinforcement, weakening of the interface and a decrease of the mechanical properties of the products. Much recent work has been carried out to characterize the Al/SiC interface and to control the interfacial reaction. The present paper describes and compares the effects of surface coatings on two interface properties, the wettability of SiC in pure A1 and the interface reaction of the same SiC reinforcement particulates in the presence of controlled amounts of Si pre-alloyed in the matrix. The results suggest that a treated particulate with lower wettability has better resistance to molten A1 attack, and that 4 wt% Si in the matrix is sufficient to protect a coated particulate while 7-9 wt% is needed for uncoated SiC particles.

A process model for friction welding of AlMgSi alloys and AlSiC metal matrix composites—I. Haz temperature and strain rate distribution

The present investigation is concerned with the development of an overall process model for the microstructure and strength evolution during continuous drive friction welding of AlMgSi alloys and AlSiC metal matrix composites. In Part I the different components of the model are outlined and analytical solutions presented which provide quantitative information about the HAZ temperature distribution for a wide range of operational conditions. Moreover, a general procedure for modelling the HAZ strain rate distribution has been developed by introducing a series of kinematically admissible velocity equations which describe the material flow fields in the radial, the rotational, and the axial direction, respectively. Calculations performed for both types of materials show that the effective strain rate may exceed 1000 s −1 in positions close to the contact section due to the high rotational velocities involved. Application of the model for evaluation of the response of AlMgSi alloys and AlSiC metal matrix composites to the imposed heating and plastic deformation is described in an accompanying paper (Part II).

A process model for friction welding of AlMgSi alloys and AlSiC metal matrix composites—II. Haz microstructure and strength evolution

The present investigation is concerned with the development of an overall process model for the microstructure and strength evolution during continuous drive friction welding of AlMgSi alloys and AlSiC metal matrix composites. In Part II the heat and material flow models presented in the first paper (Part I) are utilized for prediction of the HAZ subgrain structure and strength evolution following welding and subsequent natural ageing. The modelling is done on the basis of well established principles from thermodynamics, kinetic theory and simple dislocation mechanics. The models are validated by comparison with experimental data, and are illustrated by means of novel mechanism maps. These show the competition between the different process variables that contribute to microstructural changes and strength losses during friction welding of AlMgSi alloys and AlSiC metal matrix composites.

High temperature creep behavior of metal matrix AluminumSiC composites

The tensile creep behavior of AlSiC metal matrix composites has been investigated and analyzed over the temperature range from 230 to 525°C. It is shown that plastic flow in these materials is lattice-diffusion controlled dislocation creep in the aluminum matrix. All data on AlSiC have been assessed by a creep relation developed for creep of metals at constant structure with the added contribution of a threshold stress. The threshold stress for creep in AlSiC composites is not a thermally-activated process and is shown to have a linear dependence with temperature becoming zero at 470°C. The threshold stress is higher for the whisker composites than for the particulate composites. The origin of the threshold stress is not well understood and cannot be explained by contemporary dislocation models involving dislocation bowing or unpinning around particles sites. The observed interparticle-interwhisker spacing is shown to influence the creep rate in the same way as observed for mechanical alloyed (MA) Al base materials.

The effect of quenching on the mechanical properties of powder metallurgically produced AlSiC (particles) metal matrix composites

Several factors contribute to the strengthening in particulate metal matrix composites (MMCs); their interdependence makes the elaboration of an exhaustive explanation of the phenomenon difficult. In the present work, a comparison between different powder metallurgically produced MMCs consistency of an aluminium matrix reinforced with SiC particles, both in the as-extruded state and in the quenched state, is carried out. Data concerning two powder metallurgy processes, four average particle sizes and four volume fractions of the reinforcement are analysed and compared with the unreinforced matrix. Such analysis allows a deeper understanding both about the result of the mismatch in between the thermal expansion coefficients of the matrix and of the reinforcement on dislocation density, and about the AlSiC solid state reaction. These phenomena act on the strengthening mechanism. Their effect is very specific, because it strongly depends on the SiC particle average size and volume fraction. So, the difference between the ultimate tensile strengths of the as-extruded composites and the quenched composites can change case by case. Sometimes, the improvement in mechanical properties is excellent. This gives well-grounded encouragement in study and design of a suitable heat treatment for such MMCs.

39258 Correlation of mechanical and ultrasonic properties of Al-SiC metal-matrix composite : Mott, G.; Liaw, P.K. Metallurgical Transactions A, Vol. 19A, No. 9, pp. 2233–2246 (Sep. 1988)

39258 Correlation of mechanical and ultrasonic properties of Al-SiC metal-matrix composite : Mott, G.; Liaw, P.K. Metallurgical Transactions A, Vol. 19A, No. 9, pp. 2233–2246 (Sep. 1988)

Correlation of mechanical and ultrasonic properties of Al-SIC metal-matrix composite

Test specimens fabricated from a silicon-carbide (SiC) reinforced aluminum metal-matrix composite forging were examined ultrasonically and subjected to fracture testing. A-scans of ultrasonic back-scatter were recorded, and the velocities of longitudinal and shear waves and the mean density were measured from which elastic moduli were computed. Tensile and fracture toughness specimens were made, and respectively subjected to mechanical testing followed by careful metallographic and frac-tographic examinations. Correlation of mechanical test results, fractographic and metallographic evaluations, and observed ultrasonic back-scatter and reflection phenomena indicates that an inho-mogeneous distribution of SiC significantly degrades mechanical properties. Furthermore, nonuni-formity of SiC concentrations is shown to be detectable by ultrasonic examination. The ultrasonic method shows promise for differentiating between regions in a composite sample that has varying mechanical properties.