Quantitative study of surface relief produced by formation of lamellar microstructure in a γ-TiAl based alloy

Surface relief produced during lamellar transformation in a Ti48Al2Cr2Nb (at.%) alloy was quantitatively studied. Three-dimensional representations and quantitative data exhibit there are three kinds of surface reliefs, single-tilt, regular-terrace and irregular-strip, corresponding to narrow-width, moderate-width and large-width lamellae, respectively. Observation on fine structure reveals that kinks and ledges of the three kinds of surface reliefs are different. All the surface reliefs are related to diffusional terrace-ledge-kink growth mechanism and only single-tilt surface relief combines displacive character. The γ lamellae grow forward by nucleation of growth islands one upon the other and increase length and width by kink migration. The kink density and size control the lateral growth and further determine the lamellar width.