Demchenkov S. Effect of structural-phase state on the properties of Al-Ni and Fe-Ni foils of different functional purposes.

This work considers the effect of the size of the characteristic microstructure elements on properties of functional materials (FM) with unstable and stable initial structure on the example of multilayer Al-Ni and invar Fe-Ni foils, respectively. It is shown that for both types of the foils fabricated by electron beam physical vapor deposition (EBPVD) there is a range of sizes of the foils microstructural elements within of which the higher level of their structural-sensitive properties is achieved for providing their more effective practical applications. It was established that the Al/Ni multilayers with a period from 200 nm to 500 nm in the process of fabrication and aging exhibit an optimal combination of high values of the heat formation intensity (not less than 1,2 kW/cm2) and the stability of the values of the reaction parameters (at the level higher than 85 % of the initial state). It was found that foils of Fe-(35...36 wt.%)Ni alloys having the structure of the γ-phase and the size of the microstructure elements in the range of 50...150 nm show an optimum combination of high strength (up to 4,5 GPa) and invar properties similar to those of industrial Fe-Ni invar alloys (coefficient of thermal expansion is not higher than 1,5...2·10-6 °С-1 in the temperature range of 0...100 °C). The reduction of the size of the characteristic elements below a certain level for both the Al-Ni and Fe-Ni foils leads to structural-phase transformations during the manufacturing process which are accompanied by the formation of additional phases: the metastable monoclinic phase of Al9Ni2 and anomalous nickel-enriched solid solution α-(FeNi) in the foils of Al-Ni and Fe-Ni systems, respectively. Formation of additional metastable phases in the process of EB-PVD of foils with nanoscaled microstructure is found to be a major factor in reducing the reactivity of Al-Ni multilayer foils and the loss of invar effect of Fe-Ni foils. The results obtained were used as a scientific base for the development of technology for the production of: (i) composite Sn/(Al/Ni)/Sn foils for the reaction soldering that combine high intensity of heat formation and stability of the parameters of the self-propagating high-temperature synthesis (SHS) reactions after long-term storage; (ii) thin bimetal foils (Fe-Ni-Co)/Cu having high strength and heat-sensitivity for the use as elements of miniature thermostat design.