Nitrogen-doped TiAl alloys - Part I - Microstructure control

Effects of nitrogen addition on the microstructure control of two-phase TiA l intermetallic compounds were investigated. 1.0 at.% nitrogen addition lea ds to remarkable grain refinement in the fully lamellar microstructure but had little effect on the duplex microstructure. Only Ti3AlN precipitate was formed in 0.3 at.% nitrogen-doped alloy and both Ti2AlN and Ti3AlN precipi tates were formed in 1.0 at.% nitrogen-doped alloy. Since the formation of the gamma phase is retarded by nitrogen addition, long-term heat treatment is needed for the duplex microstructure in the 1.0 at.% nitrogen-doped allo y. Though 0.3 at.% nitrogen-doped alloy had much lower elongation than the mother alloy, 1.0 at.% nitrogen addition had little effect on room temperat ure elongation and increased room temperature yield strength by two times i n the fully lamellar microstructure. (C) 2000 Kluwer Academic Publishers.