A study on spherical particles in Al65Cu20Fe15 alloy prepared by arc melting

Al-Cu-Fe alloys are important due to reports that stable icosahedral quasicrystalline phase with composition in the vicinity of Al65Cu20Fe15 can be prepared. However, it has been widely reported that the as-prepared alloy, very often by arc-melting, is porous, consisting of particles with different morphologies. Among these, one type of particles of a spherical shape is considered as pure cubic beta phase in previous reports. In this research, this spherical particle was studied using a Scanning Electron Microscope, Energy Dispersive X-ray Spectroscopy, Transmission Electron Microscope, and Electron Diffraction. It was found that the particles are not single phase, consisting of icosahedral quasicrystalline grains embedded inside single crystal matrix of tau phase. Additionally, there are places where the tau phase appears to have out-most layer enriched in Cu. The surface of the particles is faceted and the facets can be classified to three types according to their detailed structures. A close examination and analysis led to the conclusion that these three types are parallel to the atomic planes of {1 1 0}, {1 1 1}, and {1 0 0}, respectively. A model for the spherical particle formation is suggested and the reasons for the formation of facets are discussed. This report is valuable in clarifying some discrepancies in previous reports, and in understanding the phase development in an Al-Cu-Fe alloy system.