Theoretical and experimental investigations of electron beam surface remelting and alloying

A central problem in the numerical treatment of melting and resolidificatio n, as well as alloying processes at metal surfaces, is the coupling of the physical phenomena. Among these phenomena, Marangoni convection, conjugated heat transfer, species transport and free-surface deformation occur simult aneously. The involved transport mechanisms take place at different time sc ales, which enables the decoupling of the governing equations in the soluti on process. This decoupling procedure has been proven to be capable of comp utation of metal-surface remelting and alloying processes. In this article, scaling analysis is presented to determine both the time scales and charac teristic velocities. Using this information, two-dimensional transient calc ulations of velocities, temperatures, and species concentration in both liq uid and solid phases have been carried out. These theoretical results have been compared with experiments utilizing the high-speed scan deflection tec hnique in electron-beam (EB) surface remelting and alloying of a Ck45 speci men (AISI 1045) with chromium. It was shown that the shape of the resolidif ied surface is determined by the fluctuation of the vapor pressure. This fl uctuation is due to temperature oscillations induced by the transient behav ior of the electron beam.