Effect of Surface Topography on Room Temperature Tensile Ductility of TiAl

Abstract

Room temperature tensile ductility of extruded Ti-47Al-1.5Nb-1Cr-1Mn-0.5B (at.%) with different surface topographies was investigated. Tensile specimens were subjected to grinding with sandpaper of different grits and electrolytic polishing to achieve different surface topographies. Surface morphology/topography and tensile ductility of different surface preparations were compared. Results show that for ground samples, when the mean amplitude deviation (Ra) exceeds 0.1 mu m, initiation of tensile failure transits from the sample interior to surface, and tensile fracture strain decreases linearly with increasing Ra. Electrolytic polishing improves the surface topography of TiAl not only by reducing Ra, but also by modifying the amplitude shape and distribution of the surface, and it therefore increases ductility. The present work suggests that surface amplitude deviation (Ra), skewness (Rsk) and kurtosis (Rku) are appropriate parameters to evaluate the surface topography of intermetallic materials with limited ductility such as TiAl.