WEB Stress and deformation effects on the phase formation in reactive Ni/Al multilayersWednesday (23.09.2020) 09:45 - 10:00 F: Functional Materials, Surfaces, and Devices 1 Part of:
Reactive multilayer systems consisting of thin alternating layers of Ni/Al in the nanometer scale are characterized by a large negative heat of mixing. Therefore, the energy can be released in a very quick self-propagating high-temperature synthesis [1,2]. Although this multilayer system is one of the best studied, there is a lack of understanding the effects of mechanical stress. It is known from previous investigations that mechanical stresses – either internal or external – have an influence on phase transformation and phase equilibrium . This can be caused by effects on the diffusion coefficient  as well as on the diffusion driving force. Especially in thin films and multilayers, respectively, the interrelation between stress and diffusion is important owing to the close proximity of the surfaces and interfaces .
For the above-mentioned multilayer system, various investigations have been carried out regarding the influence of mechanical stresses, both internally and externally. The investigated samples were varied in period and total layer thickness. Furthermore, various substrate materials were tested. Tensile loading was applied to the samples and correlated to the reaction velocity measured by a high-speed camera. Furthermore, the temperature profile during the reaction was measured with a high-speed pyrometer. With regard to the internal stress, different initial states are given by varying the substrates, bilayer- and total thickness as well as deposition parameters.