Complex investigation of deformation twinning in γ-TiAl by TEM and neutron diffraction

A Dislocation-Scale Characterization of the Evolution of Deformation Microstructures around Nanoindentation Imprints in a TiAl Alloy

“…At RT, twinning was observed to be the main deformation mechanism, in agreement with literature [ 2 , 7 , 8 ]. However, this runs contrary to Zambaldi et al, who prefer to suggest that ordinary dislocation glide is the main deformation mechanism at RT (without totally excluding twinning) from observations by atomic force microscopy around high-load (3000 µN) imprints [ 18 ].…”

“…One of the main weaknesses of TiAl alloys is that they are brittle at Room Temperature (RT)—i.e., below their brittle-to-ductile transition temperature, which lies between 800 and 1000 °C [ 5 ]. Despite intense research on the HT behavior of TiAl alloys, literature suffers from a lack of understanding of their RT behavior, particularly regarding the elementary deformation mechanisms and the precise role of microstructures [ 6 , 7 , 8 ].…”

“…Because of the specific structure of the γ-TiAl, it is relatively easy to know the direction for either slip of ordinary dislocations or for true twinning when the slip/twin plane is known [ 12 ]. Note also that at RT twinning and then glide of ordinary dislocations are the easiest deformation modes [ 2 , 7 , 8 ]. In this manner, Kauffmann et al suggested that increasing deformation leads to the nucleation of only a few new mechanical twins, since the dislocation movement becomes more dominant with increasing strain [ 8 ].…”

“…Among the difficulties encountered for understanding the mechanical behavior of TiAl-based alloys, most of our detailed knowledge of their deformation mechanisms has been deduced from Transmission Electron Microscopy (TEM) observations on an electron transparent lamella [ 7 , 13 ]. The investigation presented in this article focuses on the study of deformation mechanisms at the mesoscopic scale.…”

Cyclic deformation of TiAl generic microstructures at room and high temperature: Bauschinger effect & strain rate sensitivity

“…Detailed TEM and neutron diffraction investigations during cyclic tests suggest that major twins are nucleated when the strain range increase, i.e. during the first cycle of the considered strain range level [35]. This twin nucleation during the first loading part creates interfaces.…”