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

• Published in: Materials & design 2023-10, Vol.234, p.112298, Article 112298
• Main Authors: Ryou, KenHee, Ji Im, Hye, Park, Jiwon, Choi, Pyuck-Pa
• Format: Article
• Language: English
• Subjects: Additive manufacturing; Hot cracking; Ni-based superalloy; Phase-field modeling
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2023.112298

[Display omitted] •The addition of 2.5 wt% of Hf suppressed the hot cracking in direct-laser-deposited non-weldable Ni-based superalloy.•The Hf induced the increased γ-γ' eutectic and the η phase resulting in rapid solidification not to accumulate the strain to be torn.•The Hf promoted much more activated side-branching of dendrites, enabling resistance to hot cracking through interconnection.•Phase-field modeling confirmed the side-branching and discontinuous liquid pockets by Hf, in contrast to the thin liquid films of Hf-free alloy.•The quantitative calculation of thermal strain and cracking susceptibility demonstrated a decreased value as a result of the Hf addition. 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.