Crack nucleation and elastic / plastic deformation of TiAl alloys investigated by in-situ loaded atomic force microscopy

The crack propagation mechanisms of gamma-titanium aluminides with fully lamellar microstructure have been studied using in-situ deformation in the Atomic Force Microscope (AFM). AFM demonstrated the unique capability to detect elastic as well as plastic deformation during in-situ tests from topography changes on the surface. It was found that the crack nucleation, which can occur at gamma/gamma and alpha 2/y interfaces as well as inside the gamma-phase, is always preceded by strong local elastic deformation. No cracking inside the alpha 2-phase was observed. The elastic and plastic deformation was confined inside the gamma-phase and especially pronounced near interfaces which can be explained by the differences of the elastic and plastic deformation behavior of the gamma-and alpha 2-phase.