Crack mitigation at interface between Inconel 718 and stainless steel 316L during directed energy deposition under N2 atmosphere
Seong Gyu Chung, Seung Hoon Lee, Du-Rim Eo, Ömer Çakmak, Eun Seong Kim, Soung Yeoul Ahn, Hyoung Seop Kim, Hwasung Yeom, Jung‐Wook Cho
Abstract
The objective of this study is to elucidate the mechanisms by which nitrogen (N 2 ) shielding gas mitigates the cracking phenomenon at the interfaces between Inconel 718 (IN718) and stainless steel 316L (316L) during directed energy deposition (DED). When these two alloys were joined under an argon (Ar) atmosphere, cracking occurred, accompanied by the formation of intermetallic compounds at the interface. In contrast, the material processed under N 2 gas exhibited approximately half the porosity and fully mitigated the cracks compared to the Ar condition. The mitigation of cracking at the IN718/316L interface in the N 2 atmosphere was attributed to the formation of complex niobium (Nb) nitride inclusions, approximately 200 nm in size, surrounding oxide inclusions. These nitrides impeded the epitaxial growth and grain growth preference. Unlike the Ar atmosphere, the N 2 atmosphere favored the formation of Nb–Mo–N nitrides over Nb–Mo Laves C14 intermetallic compounds, which act as crack initiators. • Bimetallic structure of Inconel 718 and 316L was manufactured in N2 atmosphere resulted crack mitigation and replacement of nitrides at the crack propagation site. • In situ synthesis of nitride precipitates were achieved, Nanoprecipitates including Ti and Nb in both oxide and nitride inclusion. • Laves C14 phase boundary has mitigated with additional N 2 gas element at crack propagation composition by thermodynamical calculation. • Grain size of N 2 condition was also diminished as hindrance of columnar grain growth by formation of nitride. • Printed sample produced using argon atmosphere had a yield strength(YS) of 591 MPa, ultimate tensile strength (UTS) of 884 MPa and elongation of 0.31 meanwhile in nitrogen atmosphere had shown YS of 620 MPa, UTS of 890 MPa and elongation of 0.35 at the near interface. Hardness Maxima of fully printed IN 718 region of argon condition was 249.8 HV (0.1) and nitrogen atmosphere as 303.7 HV (0.1) .