FRACTURE-TOUGHNESS OF MONOLITHIC NICKEL ALUMINIDE INTERMETALLICS

The fracture toughness of several nickel aluminide intermetallics have been determined in accordance with standard testing techniques. The intermetallics tested, Ni3Al (24 at.% Al), Ni3Al + 0.2 at.% B and NiAl (45 at.% Al), were produced by conventional vacuum hot-pressing techniques while processing conditions were varied to produce systematic changes in grain size. The toughnesses obtained and details of the fracture behavior were distinctly different for the materials studied. Ni3Al exhibited an initiation toughness of 20 MPa m1/2, while the boron-doped material had a toughness exceeding 30 MPa m1/2. NiAl, on the contrary, demonstrated toughness values of about 5 MPa m1/2. These differences are discussed in the light of deformation and fracture mechanisms operating at the crack tip in the cases described. In situ fracture monitoring and post-failure analyses are utilized in support of the discussion.