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Metal matrix composite alloys combine the attributes of metals and ceramic reinforcements to provide materials engineered with low density and high specific mechanical properties. Most components do not require the high performance capability of aluminum MMCs throughout their entirety. Reinforcement of only the high stress regions of a component will reduce manufacturing costs. This is referred to as selective reinforcement. Data that may be used to facilitate this approach to component design and manufacture is presented. The predicted effect of the interface between reinforced and un-reinforced regions is also discussed.

Since the advent of P/M technology as a near net shape production process, millions of mechanical components of various shapes and sizes have been produced. Although P/M continues to be one of the fast growing shaping processes, it suffers from the inability to produce intricate geometry's such as internal tapers, threads or recesses perpendicular to pressing direction. In such cases application of machining as a secondary forming operation becomes the preferred alternative. However, machining of P/M parts due to their inherent porosity is known to decrease tool life and increase tool chatter and vibration. Consequently, several attempts have been made to improve the machinability of P/M materials by either addition of machinability enhancing elements such as sulfur, calcium, tellurium, selenium, etc., or by resin impregnation of P/M parts.

This paper discusses a joint customer-supplier program intended to further develop the ability to design and apply aluminum alloy pistons selectively reinforced with ceramic fibers for heavy duty diesel engines. The approach begins with a comprehensive mechanical properties evaluation of base and reinforced material. The results demonstrated significant fatigue strength improvement due to fiber reinforcement, specially at temperatures greater than 300°C. A simplified numerical analysis is performed to predict the temperature and fatigue factor values at the combustion bowl area for conventional and reinforced aluminum piston designs for a 6.6 liter engine. It concludes that reinforced piston have a life expectation longer than conventional aluminum piston. Structural engine tests under severe conditions of specific power and peak cylinder pressure were used to confirm the results of the cyclic properties evaluation and numerical analysis.

A brief summary of many contractual efforts being sponsored by the Air Force Materials Laboratory in an effort to solve metalworking problems that exist in the areas of sheet, tubing, forging, powder metallurgy, composites, extrusion, drawing, casting, and nondestructive testing is presented. The programs are concerned with such materials as high-strength alloys, refractory metal alloys, titanium alloys, dispersion strengthened alloys, and the superalloys.