Influence of 2.8% zirconium addition on the microstructure of rapidly solidified Al-8Fe-4Ni alloy

Microstructure and hardness of atomised powders of Al-7.7Fe-4Ni and Al-8.2Fe-4.3Ni-2.8Zr (wt.%) alloys were investigated as a function of powder particle size. For both alloys, decreasing the powder particle size changes the primary phase upon solidification from Al3Fe to τ-phase and then to α-Al. The sub-25 μm powder particles present an optically featureless (Zone A) and a dendritic (Zone B) structure. The zone A structure is characterised by much higher hardness values than the zone B structure. The only phases present in the sub-45 μm size fraction powders are α-Al and τ, with the amount of τ decreasing with decreasing particle size. This τ-phase can accommodate a significant amount of Zr. For higher size fractions, metastable L12-Al3Zr forms at different locations within the interdendritic areas depending on the primary phase upon solidification.