Unveiling atomistic mechanisms governing additive manufacturing processability and mechanical behavior of a refractory complex concentrated alloy

Abstract

Extending the concept of complex concentrated alloys (CCAs) to the refractory alloys (solidus temperature over 2000 °C) space potentially facilitates the design of lightweight structural alloys with service temperatures that exceed those of Ni and Co-based alloys. However, the room and elevated temperature tensile properties of the current refractory-CCAs (R-CCAs) are inferior to those of the Ni/Co-based alloys. Furthermore, the manufacturing scalability of R-CCAs remains challenging, in that cracks are prevalent in all R-CCAs when processed using near-net shape manufacturing processes, such as fusion-based additive manufacturing (F-BAM). Still, mechanisms governing the poor F-BAM processability of R-CCAs remain unexplored. To this end, this work unveils the atomistic mechanisms underlying F-BAM process-induced cracking in a NbTiTaMoHfZrC R-CCA. The implications of light elements’ presence for intrinsic ductility and grain boundary cohesion, and subsequently for F-BAM processability and mechanical behavior, are revealed. Leveraging the insights, we accomplish what is, to the best of the knowledge, the first instance of crack-free F-BAM processing of any R-CCA. Additionally, the R-CCA exhibits over 20% tensile ductility and ≈160 MPa tensile yield strength at 1200 °C. In addition to facilitating the design of lightweight R-CCAs, findings enable scalable manufacturing of these ultra-high temperature alloys for structural applications.