Magnetically-Triggered Joining Using Nanocrystalline Fe-Al Powders

Funded by the National Science Foundation

Joining materials, particularly dissimilar materials, effectively and inexpensively while not degrading their properties is of great practical value. The research objective of this award is to evaluate a proposed new method for joining. The method involves using an alternating magnetic field (AMF) to generate hysteresis losses in two-phase nanocrystalline powders in which one of the phases is ferromagnetic and the other is aluminum. When the powders are subjected to an AMF of appropriate strength and frequency, the ferromagnetic phase heats up, triggering an exothermic reaction between the phases. The heat output from this magnetically-triggered reaction can be used to either melt the powders to form a joint directly, heat a joining layer of solder or braze, or melt the surfaces of the materials to be joined. The metal aluminide resulting from the reaction will solidify into a new non-ferromagnetic crystal structure, which cannot be subsequently heated by an AMF. The research effort will be to produce powders, characterize them both microstructurally and magnetically, and examine joining different materials under an applied AMF. The method is generic and could, in principle, be applied to many materials and used for many applications.

(a)	(b)
(c)	(d)
Cross-section microstructure (a) (b) and micro-area EDS patterns (c) (d) of the as-heated Fe-Al powders performed in alternating magnetic field.

Temperature vs Time curves of Fe-40Al specimen performed in 160 Oe alternating magnetic field at different frequencies	Temperature vs Time curves of Fe-40Al specimen performed in alternating magnetic field at a frequency of 400 kHz with different magnetic induction intensity

Images and graphs provided by Hong Wu