Scale dependent plastic deformation of nanomultilayers with competitive effects of interphase boundary and grain boundary

Multilayered Ni/Al thin films with different wavelengths (λ) on Si substrate were mechanically characterized using Continuous Stiffness Method (CSM) of nanoindentation, along with the microstructural investigation with X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). The results revealed that the hardness at a certain indentation depth dramatically increases with the decreasing wavelength. Moreover, there exists a critical wavelength which induces a scale dependent mechanical response to different loading depths and structural factors. For λ > 30 nm, the number of depth-dependent hardness tends to increase with the enhancement of loading depth. However, the highest depth hardness shows the lowest value for λ < 30 nm. By studying both the hardness variation and the characteristic microstructural sizes it can be assessed that there are the competitive effects of interphase boundaries and grain boundaries on deformation resistance of nanomultilayered materials.