M. Khodaei

Mechanochemically Synthesized Metallic-Ceramic Nanocomposite; Mechanisms and Properties

Solid state chemical reaction is attributed to the chemical reaction performed at temperature which reactants are solid. In most solid state chemical reactions the reaction volume continually diminishes as the reactants become spatially separated by the products. As a result, the kinetics of solid state chemical reactions are limited by the rate at which reactant species are able to diffuse across phase boundaries and through intervening product layers. Hence, the conventional solid state technique invariably require the use of high processing temperatures to ensure that diffusion rate is maintained at a high level (Schmalzried, 1995), (Stein et al., 1993). On the other hand, high temperature process invariably leads to formation of coarse-grained products due to the occurrence of grain growth. Such coarse-grained materials are generally undesirable for manufacturing advanced engineering components due to their problems such as poor mechanical properties, poor sinterability, and etc. Consequently, there is considerable interest in alternative synthesis techniques that either reduce the required processing temperature or eliminate the need for applied heating altogether (McCormick, 1995), (McCormick & Froes, 1998). Mechanical milling has been recognized as an effective way of occurrence the solid state chemical reaction at low temperature. This process is considered as a means to mechanically induced solid state chemical reaction that occur in precursors powder mixture during collision in the grinding media (Suryanarayana, 2001). Mechanical milling could be classified as mechanical grinding, mechanical alloying (MA), and Mechanochemical synthesis (MCS) according to the precursors powder mixture as well as structural and chemical changes that occur during milling. The milling process that there is no change in chemical composition of precursors is attributed to the mechanical grinding. The mechanical alloying is refers to the formation of alloys by milling of precursor materials. Finally, in mechanochemical synthesis process the chemical composition of precursors changes as a result of mechanically induced solid state reaction. This process is also termed as reactive milling (Suryanarayana, 2001), (Takas, 2002). In this chapter book, the fundamental and mechanisms of mechanochemical process is presented and the recent developments in mechanochemically synthesized metallic-ceramic nanocomposite are overeviewed.