Mechanical, intergranular corrosion, and wear behavior of aluminum-matrix composite materials reinforced with nickel alu
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I. INTRODUCTION
MECHANICAL alloying (MA) is a powder processing method that was developed in the 1960s by The International Nickel Company (INCO),[1] but which reached its full commercial status in the 1980s.[2] Compared with other powder manufacturing methods, the entire process is carried out in the solid state at room temperature and, therefore, does not involve the melting of the constituent materials. The resulting microstructure is usually finer than that obtained in powders produced by atomization, with grain-size levels similar to those obtained using rapid solidification techniques. In its beginnings, MA was used to obtain oxidedispersion strengthened (ODS) materials and Ni-based superalloys,[3] but, presently, its applications include aluminum and copper alloys,[4] materials for thermoelectric applications,[5] and, especially, intermetallics.[6] The two methods most widely used to obtain Al-based alloys using powder metallurgy (P/M) are (1) the gas atomization (GA) technique and (2) the MA technique.[7] The GA technique[8] permits the attainment of spherical powders with a fine microstructure without segregations and with low compressibility. In the 1980s, different Al-based alloys were manufactured by GA, mainly to obtain materials with good performance at high temperatures (Al-Fe-X alloys) or alloys with high wear resistance, low thermal expansion, and high strength (Al-Si-X alloys).[9] Aluminum alloys manufactured by MA generally present better mechanical properties due to the fine dispersion of precipitates in their microstructure.[10,11] This process can lead to the “in-situ” formation of intermetallics, and the particles, which are of C.E. DA COSTA, Associate Professor, is with the Mechanical Engineering Department, Universidad do Estado de Santa Catarina, 89223100 Joinville/SC, Brazil. F. VELASCO, Associate Professor, and J.M. TORRALBA, Professor, are with the Materials Department, Universidad Carlos III de Madrid, 28911 Leganes, Spain. Contact e-mail: [email protected] Manuscript submitted September 28, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
irregular morphology, can be better compacted than gas atomized powders. Finally, the high density of dislocations, introduced in the powders by the high milling energy, of the MA process, provides many paths for the diffusion of alloying elements in the base element.[12,13,14] Once the aluminum alloy powders have been obtained they are usually processed by extrusion, which promotes the attainment of near-full density.[15] Conventional P/M processing (compacting and sintering) can also be used,[16] but the mechanical properties obtained are inferior. The development of metal-matrix composite (MMC) materials in recent years has been one of the most important innovations in the field of materials. Among them, particulated composites are widely used due to the simplicity of their manufacturing, which implies low final costs. Specifically, aluminum-matrix composites are among the most promising materials for wear-resistant and structural application
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