Microstructural evolution and hot cracking prevention in direct-laser-deposited Ni-based superalloy through Hf addition

Abstract

Additive manufacturing (AM) is an emerging new paradigm in the production of industrial parts since it allows the fabrication of near-net shape products directly from designs, which is impossible with conventional manufacturing techniques. However, hot cracking phenomena in AM are a critical issue with non-weldable alloys, rendering manufactured parts unusable. There are solutions to this problem, such as alloying Hf with non-weldable Ni-based superalloys to improve cracking resistibility. Although this solution was proposed a few decades ago, the mechanisms of how Hf could prevent hot cracking in Ni-based superalloys have not been clarified in detail, until now. In this study, we revealed the Hf-driven microstructural changes in direct-laser-deposited Ni-based superalloys using various characterization techniques and phase-field simulations. Moreover, the calculated thermal strain and cracking susceptibility decreased with the Hf addition. The results demonstrated that Hf induced specific solidifying processes and resulting microstructural changes that are advantageous to the prevention of hot cracking.