%0 Journal Article
%T Columnar-to-Equiaxed Transition in Metal-Matrix Composites Reinforced with Silicon Carbide Particles
%A Alicia E. Ares
%A Carlos E. Schvezov
%J Journal of Metallurgy
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/628495
%X The present work is focused on the study of the effect of directional heat extraction on the silicon-carbide (SiC) distribution in zinc-aluminum matrix composites (MMCs) and on the columnar-to-equiaxed (CET) position in directionally solidified samples. To this end, a ZA-27 alloy matrix was reinforced with ceramic particles of SiC and vertically directionally solidified. The cooling rates, temperature gradients, and interphase velocities were then measured, and their influence on the solidification microstructure of the MMCs was analyzed. The recalescence detected and measured during the equiaxed transition was of the order of 3.5¡ãC to 1.1¡ãC. The values of the temperature gradients reached a minimum during the CET and were even negative in most cases (between £¿3.89£¿K and 0.06£¿K). The interphase velocities varied between 0.07£¿mm/s and 0.44£¿mm/s at the transition. Also, the presence of ceramic particles in ZA-27 alloys affected the thermodynamic local conditions and the kinetics of nucleation, producing a finer microstructure. 1. Introduction A metal-matrix composite (MMC) is composite material with at least two constituent parts, with one being a metal. The other material may be a different metal or another material, such as a ceramic or organic compound. The matrix is the monolithic material into which the reinforcement is embedded and is completely continuous. The reinforcement does not always serve a purely structural task but is also used to change physical properties such as wear resistance, friction coefficient, or thermal conductivity. The reinforcement can be either continuous or discontinuous [1]. The aspect ratio of the reinforcement is an important quantity, because the degree of load transfer from the matrix to the reinforcement is directly proportional to the reinforcement aspect ratio. Particle or short fiber reinforced metals have a much lower aspect ratio, so they exhibit lower strengths than their continuous fiber counterparts, although the properties of these composites are much more isotropic [1, 2]. Metal-matrix composites can be processed by several techniques. Some of these important techniques are liquid-state processes (casting or liquid infiltration, squeeze casting, or pressure infiltration), solid-state processes (diffusion bonding, deformation processing, powder processing, sinter-forging, and deposition techniques), in situ processes, and spray-forming of particulate MMCs [2]. Metal-matrix particulate composites such as SiC particle-reinforced aluminum can offer a 50¨C100% increase in Young¡¯s modulus over that of unreinforced
%U http://www.hindawi.com/journals/jm/2013/628495/