Microstructure and thermal stability of Al–Ti alloys prepared by mechanical milling and reactive sintering

Abstract

The Al–10Ti and Al–64Ti (wt-%) powders were synthesised by mechanical milling. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results show that aluminium and titanium powders are refined rapidly and mixed uniformly, and finer particles result from the increase in milling time. The average particle size reached 5 μm after 100 h of milling. The structure of a metastable Ti(Al) hexagonal close packed (hcp) supersaturated solid solution was obtained after 140 h of milling. With increasing milling time (t=300 h), an amorphous phase occurred in Al–64Ti powders. Thermodynamic results of various competitive phases in the process were calculated and compared according to the Miedema model, which revealed how these phases proceeded. The milled Al–10Ti and Al–64Ti powders were consolidated by cold pressing (15 MPa) and sintering. The longer the milling time, the more energy stored in the composite powders. Correspondingly, the activation energy of the reaction for Al–Ti intermetallics decreased. The 50 h milled powders produced Al₃Ti after heat treatment at 450°C for 5 h. In the case of 110 h milled samples, the final equilibrium phase is AlTi.