Despite what parents may tell their children, watching television is not always a waste of time. For Douglas Hofmann, it led to a graduate project helping to produce a new class of metal alloys that are more resistant than other types to fracture under stress.

In 2003, Hofmann saw William Johnson, a professor of materials science at the California Institute of Technology (Caltech) in Pasadena, on a televised history programme. Johnson talked about his invention of bulk metallic glasses — an unusual group of metal alloys. Typically, these are about twice the strength of similar metals as a result of their amorphous microstructure; traditional metal alloys consist of crystalline matrices of atoms.

Intrigued by the topic, Hofmann, who had been searching for a materials engineering programme, enrolled as a graduate student at Caltech, with Johnson as his adviser. There, he learned that metallic glasses do have a weakness: when overloaded, they fracture without warning. Unlike their crystalline counterparts, metallic glasses don't show any signs of breaking under stress — a property known as ductility. “Ductility is important for structural things, such as bridges,” says Hofmann. “You want to see signs that they will buckle or break.”

On the basis of previous research by several groups, Hofmann and his colleagues knew that to make metallic glass ductile they would need to add 'dendrites' — branched crystalline particles that form in a liquid. Through a series of metal 'bending' experiments, they discovered that, to make the metallic glass less brittle, the crystalline particles had to be softer than the metallic glass — like adding bits of rubber to plastic — and of a fairly large size. “Once we figured these two things out, actually making the composite was the next step,” says Hofmann.

This took the researchers into uncharted territory. “We had no idea how to make the particles sufficiently large for ductility,” says Hofmann. But, as it turned out, their first attempt was successful. “I took a shot in the dark and it worked,” Hofmann says.

He admits that fortune smiled on their efforts. He decided to use an induction coil — an instrument that heats over a lower range of temperatures and provides better temperature control than other instruments typically used to melt metals in alloy production.

In a subsequent analysis of the technique, Hofmann learned that when the metal–glass composites are heated in the temperature range above the melting point of glass and below that of the dendrites, two phases form. The metallic glass becomes a liquid with little crystalline particles floating in it. When this 'slush' is cooled, the crystalline particles grow larger. “It was a lucky choice,” says Hofmann, “but now that we look at the thermodynamics, it seems so obvious” (see page 1085).

The technique, which Hofmann has dubbed “slushy processing”, resulted in a final glassy composite with large coarsened dendrites, providing the microstructure needed for ductility.

Now that the researchers understand the process needed to impart ductility to metallic glass, they want to refine it further. Eventually, Hofmann would like to create bulk metallic glass composites that are both lighter and cheaper — made using iron, for example, rather than titanium or zirconium. And, if he succeeds, perhaps he'll find himself on television.