Christopher DellaCorte, a tribology and rotating machinery expert at NASA, was trying to use nickel-titanium alloys to make spherical bearings because traditional ball bearings are prone to rusting and pitting in extreme environments, especially when flying in aerospace. But nickel-titanium alloys are different from traditional bearing steels. Nickel-titanium alloys are made of a combination of nickel and titanium, usually combined with other metals. The most common alloy is Nitinol 55, a well-known shape memory alloy (SMA). SMAs are highly elastic materials that can be twisted and bent but still return to their original shape.
Ball bearings made from nickel-titanium shape memory alloy won’t rust or corrode
DellaCorte was initially skeptical about testing any Nitinol material as a ball bearing. The dimensionally unstable material would be hard to produce good bearings, which need to be precise and not change over time. It’s critical for precision aerospace and commercial flight instruments to maintain dimensional stability, and Nitinol wasn’t sure it could meet that requirement. It also had to be nonmagnetic, very hard and able to withstand heavy friction—all of which would impair flight capabilities. The version of the alloy used in the test, called Nitinol 60, was very stable and could be hardened through careful heat treatment. DellaCorte and a team of technical experts from NASA Glenn Research Center and Abbott Ball decided to test it.
The result was a high-quality Nitinol bearing ball that works similarly to superhard rubber. One commercial application for the new ball bearing is for wing components, because the metal is not affected by the corrosive de-icing agents used to treat aircraft at low temperatures. The team is currently conducting further tests on the bearing.