(A) study on the hot cracking mechanism and printability improving strategy for the direct energy deposited Ni-based 738 alloy

Abstract

Additive manufacturing (AM) recently got the spotlight since AM can produce complex-shaped parts for every single need by overcoming the existing limitation of traditional machining techniques. Therefore, the application of AM to the Ni-based superalloy which is used for gas turbines in the power plant and jet engines for aircraft is gathering much interest these days. However, the thermal stress resulting from AM technique-driven thermal mismatch act as a limitation of application. In addition, Ni-based superalloy with superior mechanical properties usually shows poor weldability and hot cracking occurs frequently when that alloy was used by AM. Therefore, in this dissertation, the hot cracking mechanism of Ni-based superalloy in AM was investigated and the alloy design for hot cracking prevention was conducted. The clarification of the novel hot cracking mechanism which was not reported yet was tried by proceeding with the microstructural characterization to apply AM to the Ni-based superalloy. Besides, Hf was added to prevent the hot cracking and the hot cracking prevention mechanism was also investigated using advanced characterization techniques.