Additive manufacturing of oxide dispersion-strengthened CoCrNi medium-entropy alloy by in situ oxide synthesis

Abstract

The additive manufacturing of oxide dispersion-strengthened (ODS) alloys has been challenging due to difficulties in forming nanosized dispersoids and achieving a uniform distribution of dispersoids. To overcome these challenges, this study proposes a novel ODS feedstock preparation strategy using the surface modification and reinforcement transplant (SMART) process and an in situ dispersoid synthesis strategy that could be applied during direct energy deposition (DED). The feedstock of ODS CoCrNi was prepared with Co-Y alloy powder and NiO or TiO2 as the Y and O suppliers, respectively. To evaluate the in situ dispersoid synthesis effect, a counterpart was prepared by adding Y2O3 using an ex situ dispersoid addition approach. The addition of TiO2 to induce the supply of O and Ti led to an in situ synthesis of ODS CoCrNi with a 63.5 % reduction in dispersoid size compared to the pristine CoCrNi resulting in the strengthening of the CoCrNi MEA matrix. This study suggests that ODS alloys with an optimal microstructure can be fabricated using the DED process through in situ dispersoid synthesis aided by Ti and O suppliers.