Effect of substrate orientation on crystal growth in selective electron beam melting of nickel-based superalloy

Abstract

Selective electron beam melting (SEBM) has proven to be a possible method for fabricating single-crystal structures owing to its high preheating temperature and directional temperature gradient, which can promote the directional growth of columnar grains. Researchers have conducted experiments to obtain a CMSX-4 single-crystal structure; however, when a polycrystalline substrate was adopted, a 9–15 mm competitive growth stage could not be avoided. There are still two key questions that need to be addressed: 1) Whether the use of a single-crystal substrate can avoid the competitive growth stage and a single-crystal structure grown directly from the substrate, and 2) the effect of single-crystal substrate orientation (001, 001, or 111) on grain growth behavior.Polycrystalline substrates and single-crystal substrates with different crystallographic orientations were used in this study. It was found that the (001) substrate promoted single-crystal structure growth in the SEBM process. When SEBM was carried out with (011) and (111) substrates, because of the complicated temperature field and crystallographic orientation in the first few layers, stray grains were found and epitaxial growth was difficult to maintain. These findings provide an important foundation for the direct fabrication of single-crystal blades.