Micro-crack nucleation was observed at apparent deformation twin interactions with grain boundaries in a duplex near-gamma TiAl specimen deformed to surface tensile strain of about 1.4%. To prove that these micro-cracks were a result of twins and not dislocation slip bands, detailed characterization of the surface topography and crystallography associated with the micro-cracks was conducted and analyzed. Electron backscatter diffraction patterns were used in conjunction with selected area channeling patterns to determine the crystallography near the observed micro-cracks. Transmission electron microscopy of a selected twin, extracted using a focused ion beam, and atomic force microscopy were used to show that the observed micro-cracks could only were caused by local strain heterogeneities caused by twin interactions with grain boundaries and not by dislocation slip bands.

Crack Opening Due to Deformation Twin Shear at Grain Boundaries in Near-γ TiAl. B.A.Simkin, B.C.Ng, M.A.Crimp, T.R.Bieler: Intermetallics, 2007, 15[1], 55-60