Self-propagation Combustion Behavior with Varying Al/Ni Ratios in Compression-Bonded Ni-sputtered Al Foil Multilayers
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INTRODUCTION
RECENT developments in mechanically bonded multilayers have stimulated interest in forming alloys and compounds through self-propagating high-temperature synthesis (SHS).[1–3] SHS has numerous applications in joining, brazing, sealing, soldering, welding, igniting, and propelling secondary reactions.[2–5] In particular, Al/Ni systems are relevant for both metallization and joining applications, including soldering and welding.[6] The Al/Ni multilayers can be preferentially combusted with a stoichiometry of Al:Ni = 1:1 during the SHS, which was determined using dynamic transmission electron microscopy (DTEM)[7,8] and in situ X-ray microdiffraction.[9] Recently, much research on Al/Ni multilayers has been conducted in order to define the Kinetics of SHS including the propagation velocity, activation energy, and maximum temperatures.[10,11] However, these studies have primarily analyzed Al/Ni multilayers using sputtered multilayers with tens to hundreds of nanometers of bilayer thickness. Only a few studies have attempted to define the Kinetics of SHS using multilayers with micrometer-scale bilayer thicknesses.[12] Early research theoretically estimated the velocity of SHS for multilayers with a few micrometers of bilayer thickness.[13] However, according to the SHS experiments using multilayers with micrometer-scale bilayer SEOUNG WOO KUK, Ph.D. Student, and JIN YU, Professor, are with the Department of Material Science and Engineering, Korea Advanced Institute Science and Technology, Yuseong-gu, Daejeon 305 701, Republic of Korea. Contact e-mail: [email protected] HO JIN RYU, Professor, is with the Department of Nuclear and Quantum Engineering, Korea Advanced Institute Science and Technology. Manuscript submitted April 16, 2014. Article published online August 14, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
thickness, self-propagation using mechanically bonded Al/Ni multilayers is unstable.[14,15] Recently, Stover et al.[14] attempted to identify the self-propagation velocities during the SHS of cold-rolled multilayers. However, the cold-rolled multilayers exhibited an unstably reacted propagation with transverse direction propagation; the narrow reaction band propagation progressed in parallel to the global reaction front.[14–16] Furthermore, the velocity of the unstable propagation has been difficult to define due to the instability of the combustion in cold-rolled multilayers. Moreover, it is not easy to measure the bilayer thickness from mechanically bonded Al/Ni multilayers due to the irregular and discontinuous bilayers that cause severe local chemistry variations. Therefore, cold-rolled multilayers appear to be inappropriate for describing the self-propagation velocities as a function of the Ni/Al ratio or bilayer thickness. Meanwhile, the interpretation of the local reaction velocity in various Ni/Al ratios is necessary for the use of localized heat sources for joining and the use of igniters for initiating secondary reactions with mechanically bonded multilayers.[17] In the previous study, comp
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