Metal-Graphite Couples Synthesized by Means of Mechanical Milling
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Metal-Graphite Couples Synthesized by Means of Mechanical Milling. I. Estrada-Guel, C. Carreño-Gallardo, R. Pérez-Bustamante, J.M. Herrera-Ramírez and R. Martínez-Sánchez. Centro de Investigación en Materiales Avanzados (CIMAV), Laboratorio Nacional de Nanotecnología, Miguel de Cervantes No. 120, C.P. 31109, Chihuahua, Chih., México. ABSTRACT The aim of this work is the characterization of some graphite-metal couples prepared by mechanical milling (MM). The morphological and microstructural changes during MM of graphite processed with metallic powders of Cu, Ni and Ag (10 and 15 at. %) are studied. Milling is performed in a high-energy ball mill under an inert atmosphere during 1, 4 and 8 hours. The process is also repeated with a pure graphite sample in order to compare the role of metal type and concentration on the morphological characteristics of milled samples. The results show that increasing the concentration of metal particles accelerates the milling process as a result of faster work hardening and particle fracture. The results of X-ray diffraction analysis show that some crystallographic characteristics of the milled couples change as a function of milling time and metal addition. Also, SEM-EDS studies show an important effect of milling time on metal particle distribution in the prepared graphite couples. INTRODUCTION Industrial applications utilizing lightweight materials that reduce CO2 gas emissions and save on energy consumption are an environmentally friendly approach to design [1]. Currently lightweight alloys are used in small quantities due to their relatively low strength which limits their potential applications. To overcome the limitations, extensive research has been done on producing metal matrix composites (MMCs) [2]; these materials have the ability to blend the properties of ceramics (high strength and modulus) with the ductility and toughness of metals [3]. Besides, MMCs offer superior operating performance and resistance to wear [4]. Due its superior properties have been used in the aircraft, space, defense and automotive industries [5]. Al-alloys are some of the most widely used materials as the matrix in MMCs, in industrial applications due to their low density and cost compared with Mg or Ti [6]. On the other hand, graphite fibers have been recognized as high strength, low density materials because of their high strength to mass ratio [7]. Its excellent structural stability and mechanical performance at high temperatures are other reasons to consider graphite as a promissory material [8]. Generally, the processes used to synthesize the Al/C composites can be classified into three categories: (i) liquid phase; (ii) solid phase; and (iii) two phase (solid–liquid) routes [9]. Although the preparation of such composites by liquid routes is by far the most economical [4] there are some inherent problems related both to the apparent non-wettability of graphite by liquid Al-alloys [10] and the large density differences between C and Al. These differences result in porosity formation at the i
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