Nitrogen-doped TiAl alloys Part I Microstructure control

Effects of nitrogen addition on the microstructure control of two-phase TiAl intermetallic compounds were investigated. 1.0 at.% nitrogen addition leads 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 precipitates 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 alloy. 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 temperature elongation and increased room temperature yield strength by two times in the fully lamellar microstructure.