NiTi Alloy Ball Bearings

For the very first time, NASA Glenn has successfully produced large quantities of high-grade ball bearings that are less than 0.25" in diameter thanks to the development of a new alloy made of 57.6% Ni, 39.2% Ti and 3.2% Hf. Smaller, shockproof balls improve load capability in conventional steel races, aircraft control surface joints, actuator gearboxes, and more. The production of standard NiTi alloy ball bearings that are smaller than 0.375" in diameter has proven challenging for multiple reasons, the primary being that small parts made from NiTi alloys cool excessively before they can be quenched (an important step in attaining high hardness). NiTi-Hf alloy, on the other hand, does not require such high-rate quenching to achieve high hardness. Consequently, the production of small, extremely durable NiTi ball bearings is now a reality. The powder metallurgy process by which these high-quality NiTi-Hf ball bearings are manufactured combines many new techniques with several existing ones. First, a high-purity NiTi-Hf powder is created through an atomization process and transformed into long, cylindrical rods through hot isostatic pressing. The rods are then cut into cylinders and machined into spheres somewhat larger than the desired finished ball size. Finally, the spheres are hardened through heat treatment and polished until the desired finished size diameter and surface finish (typically 1 micro-inch root mean square roughness) is achieved. The result is a non-corrosive, very hard, highly elastic yet remarkably strong ball bearing with unbridled potential.