Microstructures and mechanical properties of Ni-Al-Fe-X intermetallics based on Ni-25Al-27.5Fe alloy

For improving the room-temperature ductility alloys based on Ni-25Al-27.5Fe (atomic percent) alloy by addition of the fourth element, such as chromium, niobium and zirconium, were prepared and cast into ingots. These alloys showed a dendritic microstructure and had the same phases (β′γ and γ′ phases) in the as-cast state. In spite of this, additions of the fourth element would change the morphologies of the interdendritic regions. Both the zirconium and niobium would decrease the volume fraction of the interdendritic regions. On the contrary, the element of chromium would increase the volume fraction of the interdendritic regions. The variation of the morphologies of the interdendritic regions significantly affects the mechanical properties. Additions of zirconium decrease both the elongation and ultimate tensile strength, but increase the yield strength and the hardness. Increasing the Cr-content results in increasing the elongation and ultimate tensile strength, but decreasing the yield strength. The alloy with 1 at.% niobium additions exhibits the best combination of mechanical properties, but all the tensile properties decrease sharply with increasing niobium above 1 at.%.