Revealing mechanisms underlying powder reusability of Ti-48Al-2Cr-2Nb intermetallic in electron beam powder bed fusion process

Abstract

Metal powder bed fusion additive manufacturing (PBF-AM) has been widely adopted in the aerospace and orthopedic industries. As the feedstock, the condition of metal powders affects the quality of the PBF-AM part and contributes significantly to the overall cost. However, it is not feasible to adopt virgin powder for every single build. Therefore, reusing the powder feedstock in subsequent builds becomes an economical method to reduce manufacturing costs. However, there is no standard for reusing powder, whose quality may change with increasing reuses and in turn deteriorate the PBF-AM part's quality. Herein, we evaluate the reusability of Ti-48Al-2Cr-2Nb intermetallic powder in electron beam powder bed fusion (EB-PBF) process up to 15 times (∼300 h in total cumulative build time). The powder characteristics, chemical compositions, microstructure, and mechanical properties of the EB-PBF parts are evaluated to understand the mechanisms of powder quality changes. We found that Ti-48Al-2Cr-2Nb powder can be reused up to 15 times without compromising the resultant microstructure and mechanical properties. However, contaminations are unavoidable and their formation mechanisms are revealed here. These findings provide an in-depth understanding of the process-powder-microstructure relationship in additively manufactured Ti-48Al-2Cr-2Nb intermetallic and can be applied to other alloys with volatile elements (such as Al, Mg, Zn, Pb, Mn). Further, these mechanisms underlying powder reusability are universal for all materials involved in the EB-PBF process.