• PDF / 1,000,701 Bytes
• 11 Pages / 593.972 x 792 pts Page_size
• 101 Downloads / 200 Views

DOWNLOAD

REPORT

---

THE development of metal matrix composites (MMC) has attracted attention over the last few decades for the purpose of improving fatigue, strength, and creep behavior at elevated temperatures. Most engineering metals and their alloys, such as Al, Ti, and Ni, have been used as base materials, while the inclusions considered were fibers and particles. Metal matrix nanocomposites are a newer addition to the list of studied materials. These are usually mixtures of ceramic nanoparticles into a metal or metallic alloy base. As in polymer-based nanocomposites, the hope is that dramatically enhanced properties can be obtained JOSE´ J. GRA´CIO, Professor, GABRIELA VINCZE, Assistant Professor, and CLAUDIA BUCHHEIM, Ph.D. Student, are with the Department of Mechanical Engineering, TEMA, University of Aveiro, 3810-193, Portugal. Contact e-mail: [email protected] CATALIN R. PICU, Professor, and NITHIN MATHEW, Ph.D. Student, are with the Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180. THOMAS SCHUBERT, Dr.-Ing., is with Fraunhofer-Institut fu¨r Fertigungstechnik und Angewandte Materialforschung (IFAM) Dresden, Institutste il Pulvermetallurgie und Verbundwerkstoffe, Winterbergstraße 28, 01277 Dresden, Germany. AUGUSTO LOPES, Assistant Professor, is with the Department of Ceramic and Glass, CICECO, University of Aveiro, 3810-193, Portugal. Manuscript submitted December 29, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS A

with very small volume fractions of additives. The particles are supposed to act as obstacles to dislocation motion and to effectively pin grain boundaries, conferring therefore microstructural stability to the composite. The fillers have very good thermal stability as their melting point is usually much higher than that of the matrix. The matrix may have regular grains of microns of larger dimensions, or nanograins. In the second case, the large number of grain boundaries contributes to strengthening. At present, there are two ways to produce metal matrix nanocomposites. The melt technology requires that nanoparticles are dispersed in the melt of the matrix metal. This procedure is similar to the fabrication of polymer nanocomposites and faces similar challenges, the most important being the poor wettability of the particles by the melt.[1,2] This limits the concentration of fillers that can be properly dispersed to approximately 4 pct.[3] In addition, due to the high temperature of the melt, chemical reactions take place at the interface between the fillers and the matrix, which in some cases leads to the formation of a brittle interphase the presence of which reduces the material performance. The most promising fabrication technology is powder metallurgy based.[4–6] This method requires mixing the two materials in the powder form, mechanical alloying by ball milling followed by pressing, sintering, and/or hot pressing (e.g., extrusion). This method allows

avoiding issues with miscibility and generally leads to sharp, mechanically strong interfaces between na