Achieving Columnar to Equiaxed Grain Transformation in Additively Manufactured Ods-Fecral Alloy Via Inhomogeneous Composition Distribution in Melt Pool

Abstract

An oxide dispersion strengthened (ODS) FeCrAl alloy with a novel 3D network microarchitecture consisting of the lamellar martensite framework filled with equiaxed ferrite has been successfully constructed by laser additive manufacturing (LAM). It differs from the previously reported laser additive manufactured ODS-FeCrAl alloys, which produced coarse columnar grains along the deposition direction. This study achieves the columnar-to-equiaxed grain transition in LAM ODS-FeCrAl alloy. This unique microarchitecture is mainly attributed to the use of elemental powders as feedstock, which induces an inhomogeneous distribution of Fe, Cr and Al elements in the melt pool. In addition, a large number of Y-Zr-Ti-Al-O type and Y2TiO5 oxides are formed together with the complex TiO2/Y4Zr3O12 appendage, providing more effective nucleation sites for the equiaxed ferrite solidification during the rapid cooling process. The 3D network microarchitecture eliminates anisotropy in the mechanical properties.The tensile strength and the total elongation at room temperature and 873 K reach 954 MPa / 13 % and 484 MPa / 20 %, respectively, which are superior to those of previously reported LAM ODS-FeCrAl alloys prepared from pre-alloyed powders.

Keywords: ODS-FeCrAl alloy, Laser additive manufacturing, Equiaxed ferrite, Nanoparticles, Inhomogeneous elemental distribution