Fracture behavior of micro-sized specimens with fatigue pre-crack prepared from a Ni-P amorphous alloy thin film

Fracture toughness tests have been performed for an electroless deposited Ni-P amorphous alloy thin film with different crack growth directions, which are perpendicular and parallel to the deposition growth direction. Cantilever beam type specimens with dimensions of 10 by 10 by 50 μm³ were prepared from a Ni-P amorphous thin film, and notches with different direction were introduced by focused ion beam machining. Fatigue pre-cracks were introduced ahead of the notches. Both introduction of fatigue pre-cracks and fracture tests were performed using a newly developed mechanical testing machine for micro-sized specimens. Fracture behavior is different between the two types of specimens. K_IC values were not obtained as the criteria of plane strain requirements were not satisfied for this size of the specimen, so that the provisional fracture toughness K_Q values were obtained. The K_Q value of the specimen with crack propagation direction being parallel to the deposition growth direction was 7.3 MPa m^1/2, while that with crack propagation direction being perpendicular to the deposition growth direction was 4.2 MPa m^1/2. These results suggest that the electroless deposited amorphous alloy thin film has anisotropic mechanical properties.