Effects of grain size and precipitated phases on mechanical properties in TiAl gradient materials

Effects of grain size and precipitated phases on creep properties, fracture toughness and crack propagation behavior are investigated in Ti-44Al-6Nb-1Cr-2V/Ti-44Al and Ti-44Al-6Nb-1Cr-2V-BY/Ti-44Al-6Nb-1Cr-2V gradient materials. Creep tests were performed at 850 °C/200 MPa and fracture toughness tests were performed at room temperature. Results show that the prepared gradient materials have continuing and subtle variation in composition. In Ti-44Al-6Nb-1Cr-2V/Ti-44Al, the content of γ + B2 precipitated phases increases with the increase of pulling length. The creep life decreases with the increase of the content of precipitated phases and the precipitated phases promote the crack and cavity nucleation. In Ti-44Al-6Nb-1Cr-2V-BY/Ti-44Al-6Nb-1Cr-2V, the grain size decreases with the increase of pulling length. The creep life decreases with the decrease of grain size and the fine lamellar colony provides an increasing opportunity for cavity nucleation at colony boundary. After fracture toughness tests, the crack tends to propagate along the precipitated phases and lamellar interface. The KIQ values decrease with the increase of the content of precipitated phases and they decrease with the decrease of grain size.