Ductility Enhancement from Interface Dislocation Sources in a Directionally Solidified β (γ + γ′) Ni-Fe-Al Composite Alloy.

A directionally solidified β + (γ + γ′) Ni-Fe-AI in-situ composite alloy of composition Ni50Fe30Al20 (at.%) has been used to investigate the effect of a plastically soft second phase on the mechanical behavior of a B2 ordered intermetallic alloy. This material exhibits extensive plasticity during compressive deformation at room temperature and fails in shear with extensive γ + γ′ lamellar or rod pull-out. The material also exhibits ~10% tensile elongation to fracture at room temperature, with final fracture that includes substantial necking of the γ + γ′ lamellae or rods. Observation of slip lines and dislocation substructures discloses that the normally brittle β matrix undergoes extensive plasticity in order to deform compatibly with the more ductile γ phase. The plasticity of the β matrix is accomplished by the generation of glissile dislocations into the β matrix from the β/γ interface region and is enhanced because of a favorable β - γ orientation relationship for slip transfer. Ductility enhancement from interface-generated mobile dislocations generated from β-γ interfaces is compared to that observed in film-coated β-NiAl single crystals and FeAl polycrystals.