Fe–Cr–Ni–Zr alloys with bi-modal grain size distribution: Synthesis, mechanical properties and oxidation resistance

This is an investigation of the hypothesis that a bimodal grain size distribution (50% nanocrystalline and 50% microcrystalline) may confer considerable oxidation resistance to an Fe–Cr based alloys at much lower Cr contents as compared to a microcrystalline Fe–Cr alloy yet achieve considerably superior mechanical properties as compared to an entirely nanocrystalline alloy of same composition. Cylindrical pellets of Fe–Cr–Ni–Zr alloys, with varying Cr and Zr content, were produced using mechanical alloying-hot compaction route. New synthesis routes for bimodal, nanocrystalline and microcrystalline Fe–Cr–Ni–Zr alloys have been proposed in this study. Mechanical properties of these alloys have been compared using hardness and shear punch tests. Oxidation resistance of these alloys was compared by subjecting them to oxidation in air at 550 °C for up to 150 h. It is suggested that for bimodal alloys, the nanocrystalline component helped in significantly improving the high temperature oxidation resistance whereas the microcrystalline component imparted considerable ductility, thereby, providing a combination of the two attractive properties.