Metallic glasses are a revolutionary class of alloys that have the outstanding mechanical properties of metals, but which may also easily formed into complex shapes, much like polymers. One limitation, however, is the difficulty in joining individual metallic glass components into larger assemblies. Traditional welding techniques cannot be easily applied to metallic glasses, because the heat applied tends to crystallize the alloys, degrading their mechanical properties.
A promising approach to joining metallic glasses is to use reactive multilayer foils, which are a new class of nano-engineered materials consisting of hundreds of alternating nanoscale layers of elements which have a strong tendency to react with each other. An extremely rapid chemical reaction can be generated in such a foil with a small spark, generating temperatures of 1500 C or more in a few thousandths of a second. This makes it possible to use a reactive multilayer as a local heat source for joining metallic glasses. Because the heating is highly localized at the interface and readily dissipated, reactive multilayers are ideally suited to joining heat-sensitive materials, including metallic glasses. By combining experimental and computational tools, the design of the foils will be optimized to produce high strength, high toughness joints. A second goal is to develop an entirely new class of multilayers that themselves form amorphous metallic phases (similar to metallic glasses) as a result of the chemical reaction. Because amorphous alloys soften at low temperatures, have excellent wetting characteristics, and are strong and tough, these foils should be outstanding for bonding a wide variety of engineering materials.
In this GOALI program, researchers from Johns Hopkins University and Howmet Research Corporation will work together to develop reactive multilayers tailored to joining of metallic glasses. As part of this interaction, graduate students will spend several months each year on site at Howmet. In addition to the industry-academia interaction, the PIs will continue to add to their strong record of undergraduate participation in research, including female and minority students.
