Grain-boundary segregation and superior mechanical properties in a multicomponent L12 Ni46.5Co24Fe8Al12.5Ti9 superlattice alloy

Ni3Al superlattice alloys with the L1(2) structure have garnered much attention due to their attractive high-temperature mechanical properties; however, their grain-boundary brittleness and low ductility in the ambient temperature range have greatly restricted their widespread application. In this study, we developed an L12 structure multicomponent Ni46.5Co24Fe8Al12.5Ti9 (at. %) superlattice alloy that notably suppressed the room-temperature intergranular brittleness and exhibited a large tensile elongation of 17.1% +/- 5.2% together with a high ultimate tensile strength of 1,080.2 +/- 57.4 MPa. Multiple microstructural examinations reveal an L1(2) equiaxed-grain microstructure, with the presence of a minor B-2 phase. Moreover, the co-segregation of Fe and Co atoms, and the associated reduction or elimination of the L1(2) chemical order at the grain-boundary regions were characterized, which were proved to be the root cause of the suppression of intergranular brittleness and the high tensile ductility. Further theoretical calculations show that alloying of Fe and Co to binary Ni3Al reduced the ordering energy, which promoted intergranular segregation and associated disordering. This observation demonstrated that the elimination or reduction of interfacial chemical order is an effective ductilizing method for superlattice alloys.