Effect of grain size and partial disordering on ductility of Ti3Al in the temperature range of 20-600°C

The effect of grain size and partial disordering on ductility and how stress of an intermetallic Ti3Al was studied in the temperature range of 20-600 degrees C using tension and compression testing. The ductility of the fully ordered material increased considerably when the grain size decreased from 27 to 0.1 mu m, and, at the smaller grain size, an elongation of 4.8% was achieved at room temperature. Partial disordering of the crystal lattice led to a decrease in ductility at temperatures below 500 degrees C, but had no influence on the ductility at 500 or 600 degrees C. The critical grain size at which a brittle-to-ductile transition occurred in the fully ordered material was determined for each temperature studied. This critical grain size increased as the temperature was increased. It was found that, when the mean grain size decreased and temperature increased, the fracture mode changed from a brittle transcrystalline mode to a brittle intercrystalline mode and, finally, to a ductile transgranular mode. The increased ductility was correlated with an enhanced grain boundary relaxation capability at increased temperatures and decreased gain sizes. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.