Interdiffusion of Sn and Pb in liquid Pb-Sn alloys
- PDF / 203,450 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 88 Downloads / 229 Views
RODUCTION
LIQUID diffusion in metals and alloys is not well understood, and several theories have been advanced to explain atomic transport in liquids.[1,2] Most of the theories give absolute values for diffusivities which agree reasonably well with experimental values, particularly at temperatures in the vicinity of the melting temperature. However, since experimental values for diffusion coefficients in liquid metals in the vicinity of the melting temperatures are virtually all on the order of 2 3 1029 m2/s, theoretical predictions of such values do not necessarily validate the theory. Thus, the temperature dependence of the diffusion coefficient has often MICHAEL KLASSEN, formerly Graduate Student, Department of Mechanical and Industrial Engineering, University of Manitoba, is Repair Engineer with Standard Aero, Winnipeg, MB, Canada R3H 1A1. J.R. CAHOON, Professor, is with the Engineering Materials Laboratory, Department of Mechanical and Industrial Engineering, University of Manitoba, Winnipeg, MB, Canada R3T 5V6. Manuscript submitted July 25, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
been used as an indication of the validity of particular theories, and several temperature dependencies have been proposed. Unfortunately, experimental results for liquid diffusion exhibit considerable scatter, such that temperature dependencies of the diffusion coefficients cannot be established with great confidence. Further, the sparcity of experimental results for both solvent self-diffusion and solute diffusion makes the development of a theoretical basis for liquid diffusion difficult. Therefore, an investigation was conducted to determine the interdiffusion coefficients of Sn in Pb over large concentration and temperature ranges, with the objective of obtaining reliable data that would aid in the understanding of liquid diffusion. The Pb-Sn system was chosen, because values for the solvent self-diffusion coefficient for Pb and Sn have been determined and values for the diffusion coefficients of several solutes in Pb, including Sn, have been reported. Also, molten Pb-Sn alloys can be prepared and handled with relative ease. The use of modern electron microanalytical equipment VOLUME 31A, MAY 2000—1343
allows the determination of a multitude of concentrations throughout a sample and negates the need for reliance upon a single, average concentration. Further, the variation of concentration along the length of a sample can be determined, and, thus, the concentration dependence of the diffusion coefficient for a given temperature can be established from a single experiment. II. EXPERIMENTAL The capillary-reservoir technique, adapted to obtain liquid diffusion couples for Boltzmann–Matano analysis, was selected for this study. Capillaries were made by drilling a 1.5-mm-diameter hole through 5-mm-diameter, 25-mm-long graphite rods. For the Pb-rich studies, a capillary, closed at one end, was filled with high-purity Pb (99.99 pct) by melting the Pb, contained in a large crucible, under Argon in an atmosphere-controlled fur
Data Loading...
