Study of thermal and structural characteristics of mechanically milled nanostructured Al-Cu-Fe quasicrystals

Abstract

Single phase nanostructured Al-Cu-Fe quascrystalline powders, with various grain sizes, were synthesized by low intensity mechanical milling of spray deposited icosahedral quasicrystals. Structural evolution as a function of temperature was studied in-situ using high energy synchrotron X-ray diffraction. Coefficient of thermal expansion was calculated using the change in d-spacing. The diffraction results revealed a change in the lattice parameter, grain size and quasi-lattice strain with increasing temperature. During heating, onset of appreciable grain growth in different nanostructured quascrystalline powders was observed at a certain critical temperature, which was closely related with the milling time. Quasicrystalline powders milled for 1 and 80 h exhibited appreciable grain coarsening at 923 and 573 K, respectively. For all the samples, the activation energy for grain growth (E-gg) was similar to 30-35 kJ/mol. In addition, the beta Al(Cu,Fe) phase with B2-type structure evolved during heating of powder samples milled for 10 h. Onset temperature for beta phase formation showed an inverse relationship with the milling time.