Microstructural evolution and high-temperature oxidation behavior of oxide dispersion strengthened Inconel 625 superalloy fabricated by directed energy deposition

In the present study, wire arc -directed energy deposition (DED) technology was developed to fabricate the Oxide dispersion strengthened (ODS) Ni-based superalloy employing an Inconel 625 flux -cored wire including nanoLa 2 O 3 oxides. The microstructural evolution, mechanical properties and high -temperature oxidation behavior were systematically investigated. The results indicate that the melting and decomposition of La 2 O 3 are thought to take place within the melt pool, followed by rapidly combining with Ti to re -precipitate as La 2 Ti 2 O 7 oxides during DED. These oxides can serve as a highly effective nucleation site according to edge -to -edge matching calculation, resulting in the columnar-to-equiaxed transition and the refinement of grains. However, it is found that plenty of La elements are absorbed by the molten flux in the filler wire, resulting in the formation of slag and the loss of La. Consequently, the strength increases slightly due to the combined effects of precipitation strengthening and grain boundary strengthening. Furthermore, The ODS Inconel 625 sample can achieve a higher oxidation resistance after high -temperature oxidation at 900 degrees C for 150 h. The fine microstructure promotes the rapid formation of dense Cr 2 O 3 oxide scales. On the other hand, the precipitation of La -rich oxides retards the outward transport of cation such as Ni, Fe and Nb, leading to the formation of a protective delta -Ni 3 Nb layer beneath the Cr 2 O 3 layer to prevent the oxidation of matrix.