FRACTURE-TOUGHNESS OF GAMMA-BASE TITANIUM ALUMINIDES

Effects of microstructures, alloying additions, and processing routes on the room- and elevated-temperature fracture toughnesses of gamma-ba se titanium aluminides were investigated. Microstructure was found to have a strong influence on the fracture toughness both at room and ele vated temperatures. Lamellar microstructure materials exhibited high f racture toughness compared with duplex microstructure materials, which in turn possessed high fracture toughness compared with the equiaxed microstructure materials. Alloying additions affected the fracture tou ghness at elevated temperatures significantly. The addition of chromiu m improved the low-temperature fracture toughness (below 800 degrees C ), while the addition of niobium increased the fracture toughness abov e 800 degrees C. Grain size refining, as a result of isothermal forgin g after casting and heat treatment, had less influence on the fracture toughness.