In this paper, the characteristics of self-propagating exothermic reactions of an Al/Ni multilayer powder materials fabricated by a cold-rolling and powdering procedure are reported as initial findings of the first trial on a heat source for various applications with the energy-saving feature. Experimental results showed that, following the reaction of the developed Al/Ni multilayer powder materials in air atmosphere, the maximum temperature increased from approximately 1450 °C to over 1768 °C with increasing number of passes from 20 to 40 in cold-rolling. Furthermore, observations by scanning electron microscopy and crystallographic identification by X-ray diffraction measurements showed that the multilayer structure of powdered Al/Ni after 40 passes of cold-rolling was deformed, became thinner with below sub-micrometer thickness, and almost completely reacted to NiAl intermetallic compounds. It is possible that optimizing cold-rolling conditions enables us to control exothermic heat, which will be useful for heat sources.

The use of Al/Ni multilayer powders as a new heat source has been expected for metal joining technique owing to their instantaneous reaction and enormous amount of exothermic heat. In this study, the effects of the amount of Al/Ni multilayer powders on the electrical and mechanical properties of the joining part of Al strip specimens were examined. These electrical and mechanical properties were estimated by electric resistivity measurement using the four-terminal method and shear test, respectively. Experimental results show that Al specimens are successful joined under a limited condition and exhibit low electrical resistance and sufficiently high strength to maintain the joined state. However, overheating increases the amount of Al/Ni multilayer powder in the joined part, which causes considerable damage such as voids and dissolved loss. It is found that optimization of the amount of Al/Ni multilayer powder enables us to realize reliable joining of Al foils in electronics fields in the future.

In this study, the exothermic temperature performance of various Al/Ni multilayer powders with particle sizes ranging from under 75 to over 850 µm, which generate enormous heat during self-propagating exothermic reactions, was determined using a high-speed sampling pyrometer. The Al/Ni multilayer powders were prepared by a cold-rolling and pulverizing method. The multilayer constitution of the Al/Ni multilayer powders was examined by observing the cross-section of the powders using scanning electron microscopy; the results indicate that the powders had similar lamellar structures regardless of the particle size. Exothermic reactions were carried out to measure the temperature changes during the experiment using a pyrometer. We found that the maximum temperature and the duration of the exothermic reaction increased with an increase in the particle size caused by the heat dissipation of the surface area of the Al/Ni multilayer powder. This indicates that the thermal characteristics of the exothermic reaction of the Al/Ni multilayer powder can be controlled by adjusting the particle size of the Al/Ni multilayer powder. Finally, we concluded that this controllability of the exothermic phenomenon can be applied as a local heating source in a wide range of fields.

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