Laser powder bed fusion of oxide dispersion-strengthened IN718 alloys: A complementary study on microstructure and mechanical properties

Abstract

<p>In this study, two new grades of oxide dispersion strengthened (ODS) Inconel 718 (IN718) alloys were designed by the thermochemical CALPHAD method and produced by laser powder bed fusion (LPBF) technique. Alloys designated as IN718-YF and IN718-YFH, that consist Y 2 O 3 -FeO and Y 2 O 3 -FeO -Hf, respectively, were fabricated with &gt;99.9 % densification using optimized process parameters. CALPHAD calculations were highly consistent with experimental findings, highlighting the formation of Al -containing Y -Ti -O and Y -Hf -O nano -oxides in both alloy types. Texture analyzes revealed no significant texture development in as -built (AB) or heat -treated (HT) alloys. Heat treatment was applied at 1050 degree celsius for 1 h to enhance nano -oxide density. The nano -oxide number density remained similar in IN718-YF while it decreased in IN718-YFH alloy as a result of carbide formation after the heat treatment. Besides, formation of secondary gamma ' particles was observed in the IN718-YFH/HT alloy. Even though the yield strengths of IN718-YF and IN718-YFH alloys in both AB and HT conditions were similar, the ductility of IN718-YFH was -50 % less in almost all conditions compared to the ductility of IN718-YF. This has been shown to be as a result of irregular shaped micron -sized Y-Hf-O oxides, martensite formation in AB condition, increased amount of carbides and existence of secondary gamma ' particles in HT condition in IN718-YFH. High density of stacking faults (SF) forming at the interface of the nano -oxides have been detected in IN718-YF alloys. Besides dislocation/nanoparticle interactions, SFs which are responsible for the delocalization of the deformation improve the ductility of IN718-YF alloys. Overall, high temperature mechanical tests exhibit that both alloys have higher strength with improved ductility compared to the standard IN718 alloys, indicating the contribution of the nano -oxides.</p>