Effect of silicon on the kinetics and mechanisms of cyclic oxidation of titanium aluminide (Ti45Al5Nb0.5Si) developed by laser direct energy deposition

Abstract

In this study, titanium aluminides comprising of Ti45Al5Nb0.5Si (TiAl-1), Ti45Al5Nb5Si (TiAl-2) and Ti45Al5Nb10Si (TiAl-3) were developed through laser direct energy deposition (LDED) with Nd-YAG laser under optimized process parameters. The microstructure of TiAl-1 consists of α2+γ phase mixtures. Addition of 5 wt% and 10 wt% Si results in the formation of silicides in addition to γ and α2 phases. A thorough kinetics of cyclic oxidation (from 700°C to 900°C in air) demonstrates that with an increase in Si concentration the activation energy of oxidation increases from 227.99 kJ/mol (TiAl-1) to 337.55 kJ/mol (TiAl-3). The mechanism of oxidation has been established.