Liquid metals - diffusion and solidification

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The motion of atoms in liquid metals and alloys, known as liquid diffusion, is an important transport process that occurs in castings, welds, and all processes that involve melting and solidification. Liquid diffusion determines, in part, the distribution of alloying elements, the microstructure and macrostructure of any component that was solidified from a molten condition which in turn contribute to the strength and toughness of castings and welded components. Despite the importance of liquid diffusion, little is known concerning the atomic motions that comprise the diffusion process because of the paucity of accurate, reliable data. Until recently, convective currents have masking the atomic motion due to diffusion alone. A very few accurate results free from convective transport have been obtained from experiments performed in microgravity but the expense of and accessibility to the microgravity environment limits the amount of information that can be obtained. It has recently been shown that accurate liquid diffusion results can be obtained in unit gravity under certain conditions and it is proposed that these conditions be utilized to obtain data for a wide range of variables thus providing a data base from which a theory for liquid diffusion may be developed.