The ribbons strengthen the metal by making it hard for dislocations to form and, once they form, to move. The search for a champion metal-metal composite is guided by both scientific and practical criteria. But the bottom line is that the scientists must beat the best structural alloys now in use. For the aircraft industry, which values lightness, that means beating aluminum alloys. The other light elements are either very expensive or reactive.
Scandium costs about ten times more than gold.
The team is having the best luck with magnesium and aluminum. The magnesium composite is interesting because of its surprising high-temperature performance. In general, heat coarsens the microstructure of metal-metal composites, decreasing their strength. The two scientists have combined magnesium with titanium, niobium and iron. These composites deformed well, and their strength increased, but they were no better than the best commercial alloys.