Nanoquasicrystalline Al-Fe-Cr-Nb alloys produced by powder metallurgy

Abstract

Nano-quasicrystalline Al-Fe-Cr based alloys produced by rapid solidification processes exhibit high strength at elevated temperatures. Nevertheless, the quasicrystalline particles in these systems become unstable at high temperature limiting the industrial applications. In early works, it was observed that the use of Nb or Ta increases the stability of the Al-Fe-Cr quasicrystalline phase delaying the microstructural transformation to higher temperatures. Thus, these nano-quasicrystalline Al-based alloys have become promising new high strength material to be used at elevated temperatures in the automotive and aeronautical industries. In previous works, nano-quasicrystalline Al-Fe-Cr-Nb based alloys were obtained by rapid solidification using the melt-spinning technique. In order to obtain bulk alloys for industrial applications other fabrication routes such as powder production by gas atomization followed by compaction and extrusion are required. In the present work, the production of Al-Fe-Cr-Nb based alloys by powder atomization at laboratory scale was investigated. The powders obtained were sieved in different ranges of sizes and the microstructures were characterised by means of X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive of X-ray analysis. Mechanical properties have been measured by compression tests at room temperature and at 250C. It was observed that a very high temperature is required to produce these alloys by gas atomization; the icosahedral quasicrystalline phase can be retained after the atomization in powder sizes typically under 75um, and also after the extrusion at 375C. The extruded bars were able to retain a very high strength at elevated temperature, around 60% of the yield stress at room temperature, in contrast with the 10-30% typically obtained for many commercial Al alloys.