Ignition properties of multilayer nanoscale reactive foils and the properties of metal-ceramic joints made with the same.

摘要

A novel method for joining metals and ceramics using an Al-(Ni-7V) reactive multilayer foil as a heat source was studied. The components in the joint are first pre-wet or pre-metallized with a solder or braze before the reactive foil is placed between them and reacted, melting the solder or braze. On cooling, a solid joint is formed. It was shown using a SiC-Ti joint system that for a given joint system, there is are critical values for the foil's heat of reaction and total heat below which the braze in the joint will not melt, with foil heat of reaction having more of an impact than total heat. Experimental results from Al-Al and Al2O3-Al2O3 joint systems showed that the interface between the solder and the joint component can play a critical role in determining joint strength. Experimental results and numerical predictions using Al-Al2O3 and Al-glass joint systems showed that the elastic strain energy (ESE) and residual stress in a metal-ceramic reactive foil have two sources: The bending, caused by the uneven thermal profile across each joint component created by the reacting foil, that the joint components undergo while the solder or braze is molten and which is locked in when the solder or braze solidifies, and uneven average thermal contraction between the two components. The distribution of elastic strain energy and stress in a reactive foil joint is determined by the thermal diffusivities and coefficients of thermal expansion of the two joint components.; The ignition requirements of reactive foils were investigated using two experimental methods, an electric pulse and mechanical stab detonation, and a numerical simulation of the electric pulse ignition method. Experimental results and numerical predictions showed that increasing foil bilayer or increasing intermixed layer thickness will make a foil more difficult to ignite. An estimated energy density of 1GJ/m3 was found experimentally to be an upper limit of the minimum energy density required for ignition of a 1:1 molar ratio Al-(Ni-7V) reactive foil with 50nm bilayers and a 2.25nm intermixed layer thickness. An autoignition temperature of approximately 419K was found using both experimental results and numerical predictions, both of which accounted for heat spreading during an ignition attempt.