Impact of NiB Coating on the Efficiency, Scuffing, and Wear of Gear Contacts

Report No. ARL-CR-713
Authors: Ahmet Kahraman
Date/Pages: May 2013; 92 pages
Abstract: The influence of various surface treatments on lubricated rolling-sliding contacts is investigated. The surfaces considered are ground, chemically polished, and highly polished, with root-mean-square roughness amplitudes of about 0.4, 0.1, and 0.02 µm, respectively. A chemically applied, low-friction nickel boron (NiB) surface coating is also investigated. These surface treatments are applied to two base materials: AISI 5120 alloy steel, representative of automotive gear steels, and AISI 9310 steel, representing the most common aerospace gear steel. A two-disk test methodology was developed using two types of oils: 80W90 as a typical ground vehicle oil and DOD-PRF-85734 as a typical aerospace gear oil. Traction (friction coefficient), wear, and scuffing experiments were performed to evaluate the performance of these surface treatments. Results of these two-disk experiments show that a reduction in surface roughness results in significant reductions in friction and wear while enhancing scuffing performance of contacts even under starved lubrication conditions. In addition, spur gear tests were performed with the same surface treatments and showed a reduction in mechanical power loss with smoother surfaces. Results of both the two-disk and spur gear experiments show that the NiB coating lacks the durability required for gear applications.
Distribution: Approved for public release
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Last Update / Reviewed: May 1, 2013