Structural aspects of rapidly solidified Al-Cr-Fe-Ni alloy

Abstract

An aluminium alloy for potential high temperature application containing substantial additions of chromium, iron, and nickel has been examined. Structural changes during consolidation, phase identification, and structural stability of the extrudate have been assessed. The rapidly solidified powders are non-spherical and contain a considerable proportion of particles in the size range 30–60 μm. The microstructure of the powder particles exhibits fine, individual spherulites surrounded by an aluminium matrix containing fine precipitates. X-ray analysis shows that the powder contains α Al, Al₁₃Cr₂, and an unknown phase or phases, the spherulites being a mixture of all these phases. The powder is readily cold compacted and a linear relationship between compaction pressure and density is shown. Clearly defined powder particles are retained in the billet section during the extrusion sequence and a break-up of oxide envelopes occurs, but no oxide presence is found in the extrudates. The multiphase spherulites transform to individual precipitates of Al₁₃Cr₂ and Al₁₃Fe₄ and a fine subgrain structure is formed. The extrudates are structurally stable at temperatures up to 450°C.