Structure and properties of rapidly solidified Al-Cr-Fe-Ti-Si powder alloys

In the present paper, microstructure, phase composition and elevated temperature behaviour of two rapidly solidified (RS) AlCr6Fe2Ti(0-1.5)Si1 (in wt.%) powder alloys are described. Rapidly solidified powders were composed of α(Al) solid solution matrix and finely dispersed intermetallic phases of spherical or irregular shapes. XRD and TEM investigations revealed the presence of quasi-crystalline icosahedral Al84.6Cr15.4, Al82Fe18, Al95Fe4Cr, Al74Cr20Si6 and crystalline Al, Al13Cr2, Al13Fe4, Al3FeSi phases. The fraction of quasi-crystalline phases in the form of spheroids was reduced as the powder particle size increased. The presence of titanium significantly increases the fraction of icosahedral phases. DTA measurement revealed an exothermic reaction at 450-500 °C in the fine powder fraction (size 25-45 μm) of the AlCr6Fe2Ti1.5Si1 alloy. This fraction also exhibited a hardening after annealing at 350 °C/50 h. The hardening, as well as the exothermic effect were due to a decomposition of the icosahedral phases described by the reaction Al95Fe4Cr(Ti, Si) + Al84.6Cr15.4(Ti, Si) + Al74Cr20Si6(Fe, Ti) → Al13Cr2 + Al3FeSi + TiSi.