The microstructures and mechanical properties of niobium-modified Ni-25Al-27·5Fe intermetallics

The Ni-25Al-27·5Fe alloy was selected from the Ni-25Al-xFe alloy system (x is from 20-40 at%) and macroalloyed with niobium to further improve the mechanical properties. The results reveal that three phases, fcc (γ); ordered fcc (γ′); and ordered bcc (β′) phases, exist in these alloys. The alloys show dendritic microstructures, and the interdendritic regions get thinner and fewer after adding niobium. After annealing at 1000°C for 4h a large amount of fcc-structured particles (γ-Fe) was precipitated within the matrix of β′-phased dendrite. This γ-Fe contained higher iron-and niobium-concentration when compared to the β′ phase. In addition, increasing the niobium content to 1 at% results in increasing all the room-temperature tensile properties. However, the tensile properties will decrease sharply with the addition of niobium beyond 1 at%. This phenomenon could be caused by decreasing the interdendritic regions after adding niobium of more than 1 at%. Moreover, the temperature effect on the tensile properties is very significant. Both the yield strength and ultimate tensile strength decrease with increasing temperature, and the elongation increases sharply when the temperature is beyond 600°C.