The effect of chromium additions on the mechanical properties of Ni-25Al-27.5Fe-based intermetallic compounds

To further improve room temperature ductility of alloys based on Ni-25Al-27.5Fe, alloys containing additional chromium were prepared by arc-melting and drop-casting into ingots. The mechanical properties of those alloys were characterized by means of hardness testing and tensile testing. The microstructural evolution of these alloys was examined by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results reveal that two phases, γ′ and β′ phases, exist in these casting alloys. The dendritic β′ phase mixed with the interdendritic of the β′ and γ′ phases in as-cast alloys. After annealing at 1000 °C for 4 h, the ordered γ′ phase transformed to a disordered γ phase, and a large number of γ phase particles were precipitated from the β′ phase. These precipitates have almost the same chemical composition and lattice constant as the interdendritic γ phase. The γ phase contained higher iron and chromium concentrations when compared with the β′ phase. The chemical compositions of the β′ phases in both dendrite and interdendrite appear to be almost the same. Increasing chromium content in this alloy system results in increasing the hardness and elongation, but decreasing the yield strength; for example an alloy with 1 at.% chromium had 1230 MPa of ultimate strength, 484 MPa of yield strength and 11.3% of elongation.