Variations in the alpha(2)/gamma lamellar microstructure in Ti48Al alloys as a function of cooling rate and oxygen content

The alpha(2)/gamma lamellar microstructure in Ti-Al alloys is currently con sidered as promising and a study of microstructure as a function of cooling rate is presented. Appropriate microstructural parameters, such as alpha(2 ) volume fraction, average width of the alpha(2) plates, average spacing be tween them and grain size, have been measured by scanning electron microsco py and image analysis procedures. These measurements have then been systema tically correlated with the cooling rate and the oxygen content of both com mercial purity, oxygen doped and ultra high purity synthetic alloys. This h as enabled clear trends between different cooling rates, microstructural pa rameters, hardness and yield stress to be established. The alpha(2) volume fraction is seen to be a dominant feature. The yield stress follows a Hall- Fetch type relation with the interlamellar spacing as the determining lengt h scale. Finally, the stability of the lamellar microstructure will be brie fly discussed.