Influence of cooling rate on microstructure and mechanical properties of a Ti-48Al alloy

The microstructure of a Ti-48Al alloy cooled after a solution treatment in the alpha-field is influenced by the cooling rate. In order to characterize the lamellar structure and to know the values of alpha(2)-volume fraction, width of alpha(2)-lamellae, and interlamellar spacing, we developed a method of measurement based on an observation of laths in the scanning electron microscope. The study revealed the heterogeneous distribution of the lamellar structure in a commercial purity Ti-48Al alloy cooled from the alpha-field at a rate of 35 degrees C/min. The evolution of alpha(2)-volume fraction with the cooling rate showed that the microhardness is determined by the quantity of alpha(2)-phase. The values of yield stress also increased and were all the less scattered as the structure became more perfectly lamellar. Yield stress and interlamellar spacing are linked by a Hall-Fetch relation. (C) 1999 Elsevier Science Ltd. All rights reserved.