This paper reviews the world wide upsurge in metal matrix composite research and development activities with particular emphasis on cast metal-matrix particulate composites. Extensive applications of cast aluminium alloy MMCs in day-to-day use in transportation as well as durable good industries are expected to advance rapidly in the next decade. The potential for extensive application of cast composites is very large in India, especially in the areas of transportation, energy and electromechanical machinery; the extensive use of composites can lead to large savings in materials and energy, and in several instances, reduce environmental pollution. It is important that engineering education and short-term courses be organized to bring MMCs to the attention of students and engineering industry leaders. India already has excellent infrastructure for development of composites, and has a long track record of world class research in cast metal matrix particulate composites. It is now necessary to catalyze prototype and regular production of selected composite components, and get them used in different sectors, especially railways, cars, trucks, buses, scooters and other electromechanical machinery. This will require suitable policies backed up by funding to bring together the first rate talent in cast composites which already exists in India, to form viable development groups followed by setting up of production plants involving the process engineering capability already available within the country. On the longer term, cast composites should be developed for use in energy generation equipment, electronic packaging aerospace systems, and smart structures.

http://publications.drdo.gov.in/ojs/index.php/dsj/article/download/4336/2539

Metal matrix Composites

Fundamentals of materials processes wherein a reinforcing phase is combined with bulk molten metal are reviewed. Capillary phenomena which govern the incorporation of the reinforcement into the matrix are discussed first, with focus on thermodynamics, mechanics, and chemistry of wetting. Engineering strategies that have been adopted to increase reinforcement wettability are also addressed. Relevant transport phenomena are covered next, with focus on the infiltration process and the rheology of composite slurries. The last section of this review is concerned with solidification of the matrix after it has been combined with the reinforcement, including nucleation and growth of the matrix, and particle pushing by the solidifying metal. This review places emphasis on the physical phenomena that govern the processing and the microstructural development of cast metal matrix composites.

Solidification Processing Of Metal Matrix Composites

The functional requirements for synthetic tissue substitutes appear deceptively simple: they should provide a porous matrix with interconnecting porosity and surface properties that promote rapid tissue ingrowth; at the same time, they should possess sufficient stiffness, strength and toughness to prevent crushing under physiological loads until full integration and healing are reached. Despite extensive efforts and first encouraging results, current biomaterials for tissue regeneration tend to suffer common limitations: insufficient tissue-material interaction and an inherent lack of strength and toughness associated with porosity. The challenge persists to synthesize materials that mimic both structure and mechanical performance of the natural tissue and permit strong tissue-implant interfaces to be formed. In the case of bone substitute materials, for example, the goal is to engineer high-performance composites with effective properties that, similar to natural mineralized tissue, exceed by orders of magnitude the properties of its constituents. It is still difficult with current technology to emulate in synthetic biomaterials multi-level hierarchical composite structures that are thought to be the origin of the observed mechanical property amplification in biological materials. Freeze casting permits to manufacture such complex, hybrid materials through excellent control of structural and mechanical properties. As a processing technique for the manufacture of biomaterials, freeze casting therefore has great promise.

Biomaterials by freeze casting

Most models that describe the interaction of an insoluble particle with an advancing solid-liquid interface are based on the assumption of steady state. However, as demonstrated by experimental work, the process does not reach steady state until the particle is pushed for a while by the interface. In this work, a dynamic mathematical model was developed. The dynamic model demonstrates that this interaction is essentially non-steady state and that steady state eventually occurs only when solidification is conducted at sub-critical velocities. The model was tested for three systems: aluminum-zirconia particles, succinonitrilepolystyrene particles, and biphenyl-glass particles. The calculated values for critical velocity of the pushing/engulfment transition were in same range with the experimental ones.

An analytical model for the interaction between an insoluble particle and an advancing solid/liquid interface

The behaviour of titanium diboride particles in molten aluminium was investigated by conducting casting experiments at different cooling rates and particle addition levels, starting with a master alloy containing in situ formed TiB2 particles. The particle pushing/engulfment phenomena and particle clustering effects were studied for two matrix alloy systems, commercial purity (CP) aluminium and an Al-4% Mg (A514) alloy. The critical velocity, which is the solidification velocity below which the particles are pushed and above which they are engulfed, was calculated. The results were validated against the predictions of the models available in the literature. The assumptions, limitations and comparative success of the different models were discussed. The critical velocity observed in CP-Al ranged between 4 and 8 μm/s at low particulate concentration ( The hypothesis that particle clustering could result in erroneous critical velocity predictions was explored and it was concluded that particle clustering must be included for accurate prediction of particle pushing in these alloys.

Effect of clustering on particle pushing and solidification behaviour in TiB2 reinforced aluminium PMMCs

Directional solidification results were obtained in order to investigate particle behavior at the solid-liquid interface in Al-2 pct Mg (cellular interface) and Al-6.1 pct Ni (eutectic interface) alloys. It is found that particles can be entrapped in the solid if adequate solidification rates and temperature gradients are used. Model results showed critical velocity values slightly higher than those obtained experimentally.

Behavior of ceramic particles at the solid- liquid metal interface in metal matrix composites

Aluminum-6.1 wt. pct. nickel-silicon carbide composites containing varying volume fractions and particle sizes of SiC were directionally solidified at different translation rates and temperature gradients, under variable gravity levels. High-gravity, high-volume fractions of particles or high effective viscosity of liquid favored the engulfment of particles by the melt interface. Solidification under low gravity seemed to deflocculate the SiC particle agglomerates, while opposite results were obtained when solidifying under high gravity. Intercellular spacings were higher under low gravity solidfication.

A. Moitra

Papers

Behavior of ceramic particles at the solid- liquid metal interface in metal matrix composites

Directional solidification of Al-Ni/SiC composites during parabolic trajectories

Fatigue Crack Growth Behavior of Nitrogen-Alloyed Low-Carbon Austenitic Stainless Steel at Room Temperature