Effect of carbon addition and cooling rate on lamellar structure of peritectic TiAl-based alloy

The effect of carbon addition and cooling rate on the lamellar structure of peritectic Ti-46.5Al-5Nb-0.2B-0.2C (at.%) alloy was studied. The studied alloys with a carbon content of 0.2, 0.5, 0.7 and 1.0 at.% were prepared by vacuum induction melting in graphite crucibles. The as-cast samples were subjected to solution annealing in a single alpha (Ti-based solid solution) phase field followed by cooling at four constant rates ranging from 5 to 50 degrees C/ min. The increase in carbon content leads to an increase in both start and finish alpha phase decomposition temperatures. During continuous cooling, the carbon atoms segregate along alpha(2)(Ti3Al)/gamma(TiAl) lamellar interfaces and hinder lateral growth of gamma lamellae. The interlamellar spacing decreases with increasing carbon content and increasing cooling rate. A relationship describing the complex influence of carbon content and cooling rate on alpha 2-alpha 2 interlamellar spacing lambda is proposed. Vickers microhardness HVm increases with increasing both the carbon content and cooling rate. The Vickers microhardness depends on interlamellar spacing lambda according to the HallPetch relationship.