Abstract:
The demand for metal matrix composites (MMCs) is increasing dramatically as more applications require higher performance lighter weight materials. Powder Metallurgy (PM) is an ideal method of fabrication for MMCs because of the ability to produce near net shapes and little material waste associated with the process.
Due to the increased strength associated with the part after fabrication, machinability of the part can be difficult. This research examines the best type of reinforcement fiber to be used with aluminum matrixes via PM routes, and the effect that these fibers have on green strength of the part.
The results show that alumina fibers should be used in the form of either continuous or discontinues fibers to produce the highest mechanical properties, whereas silicon carbide should be in the form or particulates and whiskers.
Introduction:
Powder blending and consolidation, a solid state method of fabrication, consistently produces superior mechanical properties distributed evenly throughout the material [2]. The increase in strength observed after the sintering process decreases the machinability of the material creating new challenges. Each MMC fabrication process varies in nature, resulting in unequal costs and properties associated with the final components.
Although the fabrication method plays a role in the mechanical properties of the MMCs, the materials chosen for the matrix and reinforcement fibers play an equally important role. Numerous metals including aluminum, titanium, magnesium, and copper have been used as matrix materials in MMCs .
Aluminum is the most widely used matrix material in structural components as it provides relatively high strength and toughness, while still remaining lightweight. In an effort to increase the strength of the aluminum matrix while still maintaining the low density and moderate ductility of the aluminum, reinforcement fibers of either alumina or silicon carbide are distributed throughout the matrix.
When selecting materials for a MMC, it is critical that the materials selected for the matrix and reinforcement fibers are not only evaluated on their individual properties, but also on their reactivity with each other during the forming process.
Often times the interactions between matrix and fiber materials impose restrictions on the type of constituents that can be combined [3]. In an attempt to reduce the reactivity of the constituents, a barrier coating is often applied to the reinforcement. This barrier surrounds the reinforcement fibers preventing any contact between the unstable constituents during the high temperature forming process.
It is also critical to evaluate the temperature that MMCs will be subjected to in service in an effort to prevent any potentially dangerous reaction between unstable constituents.
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