Estimating the average size of crystallites and microstresses in mechanically alloyed
composite Al – 15 wt. % (Ni – Ln)

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I. I. Tipikina, Yu. V. Kuzmich, S. А. Kotov, S. V. Ganin

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The behavior of crystallites in a mechanically doped aluminum-based composite alloy annealed at 300 – 500 °С has been investigated. In alloying of aluminium substrate, the dope additive contained nickel, aluminum and rare-earth element intermetallides. The target alloy contained 15 wt. % dope additive. The results of XRD analysis of the composite samples are presented. The average size of the Al and Al5CeNi2 crystallites in three states, i.e. after mechanical alloying and after annealing at 300 and
500 °С has been estimated by extrapolating the dependence of converted broadening b*(2θ) on the magnitude of the scattering vector s to zero scattering vector. Variation of microstresses emerging during annealing at different temperatures has been estimated. The average microstress value e was determined from the slope angle j of the dependence of converted broadening on the magnitude of the scattering vector. The microstresses emerging in the alloy manifest themselves in the character of diffraction reflexes behavior in XRD patterns showing as varying intensity and broadening of reflexes. When investigating the annealing process of composite mechanically doped alloy, which is under stress after the high-energy impact followed by compaction, we observed a considerable stress relief in the crystals. In the examined temperature range, the microstresses were observed to almost totally disappear at about 500 °С. It was discovered that hot pressing of a composite aluminum-based alloy, doped with an experimentally tested hardener does not produce any microstresses.

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Кeywords: mechanically alloyed composites, microstress, annealing, aluminium, rare-earth metals, intermetallic compounds.