Oxygen sneaks into titanium, making it brittle

Invading atoms multiply weaknesses in the tough metal’s structure

Titanium lattice

ELBOWING IN  Oxygen atoms (black arrows) invade titanium, forcing the metal atoms out of their regular atomic structure. The blue arrows indicate where those titanium atoms would have been in the absence of oxygen.

Qian Yu

A dash of oxygen can bring superstrong titanium to its knees. And now scientists know the root of oxygen’s destructive power.

Lodged in a chunk of titanium, a single oxygen atom spurs extra defects in the metal’s atomic structure. Such flaws make titanium easy to shatter, scientists report in the Feb. 6 Science.  

Understanding how oxygen saps titanium’s strength could give scientists new clues for ways to defeat it. And being able to control oxygen’s effects could make tough metals cheaper. Pure titanium, for instance, is coveted for its light weight and strength. But it is often too expensive for making things such as ships, cars and planes.

Oxygen contamination is a big reason for titanium’s high price, says materials scientist Andrew Minor of the University of California, Berkeley. Oxygen atoms can wedge into gaps in the lattice of titanium atoms. Getting rid of invading oxygen atoms requires costly cleansings, Minor explains. Even a few lingering atoms have a big effect.

Titanium metal that carries just three oxygen atoms among 1,000 titanium atoms bumps the metal down to second-rate toughness. “That’s just a crazy amount of sensitivity,” says Minor.

The oxygen makes titanium hard, but brittle — much like glass. You wouldn’t want your car made out of glass, Minor says, or brittle metals.

Using high-powered microscopes, Minor and colleagues zoomed in on oxygen-tainted titanium, looking for structural deformities that lead to shattering. Then the researchers looked for neighboring oxygen atoms.

For years, scientists thought that little oxygen atoms would slip into the metal grid without affecting its flaws. But under the microscope, Minor and his colleagues saw something different: Oxygen atoms act as snags for atomic distortions. Instead of a single channel of contorted titanium atoms, the gnarled structure halts at an oxygen atom and splits in three.

This rift effectively multiplies flaws and boosts the metal’s brittleness, Minor explains. Computer simulations back up the observations.

“The experiments are just gorgeous,” says computational materials scientist Dallas Trinkle of the University of Illinois at Urbana-Champaign. The study offers a fundamental understanding of the metal, he says. And it also points to ways to thwart oxygen’s effects, Trinkle says, such as adding chemicals to stifle the oxygen.

Scientists could also wield oxygen’s powers intentionally, turning spongy metals crisp, Minor says.

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