Yttrium for the selective laser melting of Ti-45Al-8Nb intermetallic: Powder surface structure, laser absorptivity, and printability

Abstract

High Nb-TiAl alloys are important materials to realize critical, light-weight parts of high-temperature applications. It has been challenging, however, to realize their laser-based additive manufacturing (AM) due to the materials’ high crack sensitivity. To mitigate the cracking problem particularly relating to oxygen, this study is designed to investigate the impact of introduced rare earth element (Y) on the microstructure, surface chemistry, and laser absorptivity of gas-atomized Ti-45Al-8Nb powder, and consequently on the printability of the alloy regarding its selective laser melting (SLM). It is observed that the Y addition significantly improves the SLM printability of the alloy and realizes samples that are free of macrocracks. The change in the surface structure of the powder is regarded as a critical factor contributing to improved printability. The corresponding chemical state and layer thickness of the oxide film covering the powder are determined by X-ray photoelectron spectroscopy (XPS) depth profile and transmission electron microscopy (TEM). It is further found that the surface structure of the powder leads to a higher laser absorption. As suggested by the study, modification of powder chemistry and powder surface structure by rare earth elements can be an effective means to improve the SLM formability of crack-sensitive materials.