Anisotropic elastic-stiffness coefficients of an amorphous Ni–P film

Abstract

This study presents a complete set of effective elastic-stiffness coefficients of a Ni 80 P 20 amorphous-alloy thin film deposited on an aluminum-alloy substrate by electroless plating. The film thickness was 12 m. The electromagnetic-acoustic-resonance method detected resonance frequencies of the triple-layered specimens ͑film/substrate/film͒, which enabled us to determine all five independent elastic-stiffness coefficients of the film using known substrate elastic properties. The resulting coefficients were those of a transverse isotropic material. There was strong anisotropy between the in-plane and normal directions; the in-plane Young's modulus is larger than the normal Young's modulus by 34%, for example. The anisotropic coefficients can be interpreted by considering a micromechanics model for local incomplete cohesion ͑thin ellipsoidal voids͒ aligned parallel to the film surface.

Metals and Alloys

“…The anisotropic coefficients can be interpreted by considering a micromechanics model for local incomplete cohesion (thin ellipsoidal voids) aligned parallel to the film surface. Takashima and Higo (2004) measured Young's modulus of electroless-deposited Ni-P amorphous alloy thin film by microtensile testing and obtained Young's modulus of 115 GPa; this value is comparable to that obtained by Ogi et al (2002) for the in-plane direction. Takashima et al (2001) also measured fracture toughness values of Ni-P amorphous alloy thin film and obtained similar anisotropic crack growth resistance between in-plane and out-of-plane directions.…”

“…For practical applications of these materials, the evaluation of mechanical properties in the thinfilm form is required. Ogi et al (2002) measured elastic properties of a Ni-P amorphous alloy thin film prepared by electroless plating on an Al-Mg alloy substrate and obtained a complete set of effective elastic stiffness coefficients by EMAR method. The resulting coefficients were those of a transverse isotropic material.…”

Observation of higher stiffness in nanopolycrystal diamond than monocrystal diamond

“…Considering lattice anharmonicity, such a softening is attributed to the larger free volume at the grain boundaries 7 . Also, the macroscopic stiffness decreases considerably when the material contains noncohesive intergrain bonds, because displacement increases when a softer region is stressed 8,9 . Thus, low stiffness in nanopolycrystals is well established.…”

Imaging defects in a plate with complex geometries

“…Resonant spectroscopy in the ultrasonic range has also been studied. 8 Ogi et al 9 successfully measured the elastic-stiffness coefficients of thin films using non-contact resonant ultrasonic spectroscopy with electromagnetic acoustic transducers. However, resonant spectroscopy generally evaluates characteristics of a whole vibration region and cannot be used for defect location and imaging.…”