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

Abstract

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 α (Ti-based solid solution) phase field followed by cooling at four constant rates ranging from 5 to 50 °C/min. The increase in carbon content leads to an increase in both start and finish α phase decomposition temperatures. During continuous cooling, the carbon atoms segregate along α2(Ti3Al)/γ(TiAl) lamellar interfaces and hinder lateral growth of γ 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 α2-α2 interlamellar spacing λ is proposed. Vickers microhardness HVm increases with increasing both the carbon content and cooling rate. The Vickers microhardness depends on interlamellar spacing λ according to the Hall-Petch relationship.