Fracture and fatigue crack-growth behavior of single crystal NiAl

The plane strain fracture toughness for pre-cracked, single crystal NiAl + 0.25%Fe was determined to be -6.5 MPa√m for the {110}t Ol crack orientation. The fatigue crack-growth behavior for this orientation was also studied. Fractography indicates the possibility of fatigue crack propagation on planes other than the preferred cleavage plane. Fatigue on these alternate planes also resulted in increased plastic deformation on the fracture surface. Finally, the transient crack-growth response following compressive overloads have been shown to be effective in reinitiating fatigue crack-growth. This effect may be due to a reduction in shielding from roughness induced crack closure.