Micro-structural characterization of laser interference irradiated Ni/Al multi-films

Biological solutions to enhance strength and stability often use lateral and hierarchical composite structures from nano- to micro-scale. The effect does not consist of a large chemical variety but it is realized by structural composites (namely phase changes and orientations). A new developed bio-mimetic laser interference structuring technique uses this biological approach to optimize mechanical properties of surfaces and thin films. In past, laser interference irradiated Ni/Al multi-films showed periodical properties in the range of interference period. The hardness and modulus could be varied periodically and the texture and stress situation could be significantly changed. In this work, the micro-structural evolution of irradiated Ni/Al multi-films is analyzed by transmission electron microscopy (TEM) measurements to justify the properties change. The grain size can be obtained to be laterally oscillating between 5 and 10 nm and up to 100 nm and the layer interface to be semicoherent. Up to a certain depth, intermetallic compounds are found in the layer interface.