Innovators at NASA's Glenn Research Center have developed a new method for making small-diameter, high-grade ball bearings that are less than 0.25” in diameter thanks to the development of a new alloy made of 57.6% Nickel (Ni), 39.2% Titanium (Ti), and 3.2% Hafnium (Hf). The use of non-corrosive NiTi alloy instead of steel is an inexpensive way to increase the load capability and reduce the weight of a ball bearing.
To address this challenge, Glenn innovators have created a new, more advanced alloy consisting of NiTi and Hf that can produce high-quality ball bearings of any size, but most notably less than 0.25” in diameter. The bearings are corrosion-resistant, shockproof, and have been rated at a grade 10 or higher on the Annular Bearing Engineering Committee (ABEC) scale (an industry-accepted tolerance standard for bearings).
The production of standard NiTi alloy ball bearings that are smaller than 0.375” in diameter has proven challenging for multiple reasons — the primary reason 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.
The powder metallurgy process by which these ball bearings are manufactured combines many new techniques with several existing ones. 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.