Mechanical properties of nanocrystalline Ti–Al–X alloys

Nanocrystalline alloys have been produced by means of mechanical milling and spark plasma sintering. Two types of materials have been obtained, TiAl–X and Al3Ti–X alloys, X represents Cr, Mn or Fe. Sintered TiAl–X alloys have a two-phase microstructure consisting of the γ-TiAl phase and the α2 phase, this last one with a globular morphology. Their average grain size varies between 100 and 150 nm. The Al3Ti–X alloys are constituted by a single phase with an L12 structure and an average grain size of about 30 nm. Compression tests are used to evaluate the mechanical properties of these materials at temperatures ranging from 298 to 773 K. Very high flow stresses are found for the TiAl–X alloys, with maximum values of approximately 3 GPa. Surface traces develop during deformation at room temperature of these materials. Microscopic observation reveals dislocation activity in the larger grains. The nanocrystalline Al3Ti–X alloys show no ductility at room temperature and a rather high fracture strength of about 2.5 GPa. Deformation of heat-treated Al3Ti–X alloys (larger grain sizes) produces plastic deformation with dislocation activity and lower flow stresses (∼1 GPa).