A Study on the Microstructure Development in Laser-Cladded Tantalum Layers

In this study, the microstructure development of a laser-cladded tantalum (Ta) layer formed on an iron (Fe) substrate was mainly analyzed. The results showed that typical dendritic crystalline structures were formed in the Ta layer. Fe was detected in the Ta layer, indicating that the upward diffusion of Fe from the substrate occurred. By applying thermodynamic and kinetic calculations, the microstructure development observed in the experiment can be well understood. In the fully molten zones, typical eutectic structure was formed containing BCC-Ta dendrite and MU-TaFe inter-dendrite. While in the partially molten zone away from the laser heating, spherical Ta particle morphology was kept without dendritic structure. To achieve purer Ta layers or coatings by minimizing the effect of the upward diffusion of substrate elements, a high-melting-point tungsten substrate was used in both laser cladding and plasma spraying processes.