The Problem with Titanium

On September 30th, 2017, an Airbus A380 cruising high over the North Atlantic suffered one of the most dramatic engine failures in recent aviation history. Air France flight 66 was flying from Paris to Los Angeles when a loud bang shook the cabin. One of the four engines had torn itself apart. The entire front fan

assembly had separated in flight, shredding the nacelle and scattering debris into the sky. The crew diverted to Goose Bay, in Canada, and landed safely. But the engine was destroyed. The failure was traced to the engine's fan hub, the massive rotating component that carries the fan blades. It was forged from a titanium alloy, Ti-64.

Nothing unusual there. This is the kind of high-performance application where titanium alloys excel. But when investigators finally pinpointed the failure mechanism, it wasn't overstress, poor design, or conventional fatigue. It was something far more subtle, a hidden weakness of the material that only appears under specific conditions. And it forced the industry to reconsider how

it uses titanium. To understand why, we need to look at what's happening inside titanium alloys, all the way down at the atomic scale. If you zoom all the way into a block of pure titanium, you'll find that, like all metals, its atoms pack together in a very regular, grid-like lattice. The underlying unit of this structure is a

repeating hexagonal cell called the hexagonal close-packed structure, HCP. This is how titanium is structured on the atomic scale at room temperature. Heat it up, though, and at 882° C, the atoms suddenly become more stable in a different configuration and undergo a phase transformation, rearranging from hexagonal close-packed to a body-centered cubic structure where the