Tensile strength of Ni/Cu/(001)Ni triple layer films

Tensile properties of Ni/Cu/(001)Ni triple layer films and single crystal films of (00l)Cu and (00l)Ni were studied. The specimen films having the thickness of 50 to 500 nm were prepared by the epitaxial evaporations on (001)NaCl substrates. The stress-strain curves of tensile tests in the direction of [100] of Ni/Cu/(001)Ni triple layer films were almost linear until fracture and showed extremely small plastic deformation. The yield stresses of these specimens were 600 to 700 MPa independently of the layer thicknesses, which were 2.5 to 5 times higher than those of Ni or Cu single crystal films, and were also higher than the values given by the mixture rule for Ni and Cu single crystal films. The increase of yield stress was evaluated from the repulsive force acting on the mobile dislocations originating from the stress fields of misfit dislocation arrays at the Ni-Cu interface. Formerly Graduate Student, Faculty of Engineering, Osaka University