FRACTURE-TOUGHNESS OF THE L1(2) COMPOUNDS AL66TI25MN9 AND AL66TI25CR9

Fracture toughness was determined for the cast, homogenized, and isothermally forged L1(2) trialuminides, Al66Ti25Mn9 and Al66Ti25Cr9, as a function of temperature using notched three-point bend specimens. Toughness increases gradually from approximately 3.5 MPa square-root m at ambient temperature to approximately 11 MPa square-root m at 973 K. Fracture modes in these notched specimens were comparable to those of unnotched specimens, exhibiting a gradual transition from transgranular cleavage at ambient temperature to mostly intergranular failure at 973 K. High strain rate tests at 973 K produced intergranular fracture in both air and in vacuum (1.3 x 10(-3) Pa), suggesting that external environment may not be responsible for grain boundary fracture in these intermetallics. Although a ductility minimum was previously noted in uniaxial tension at intermediate temperatures, this trend did not manifest itself in fracture toughness.