Advanced Tribological Coatings for High Specific Strength Alloys, R and D 5876-MS-01
Abstract
Titanium alloys offer significant advantages over steels for aerospace applications (particularly space applications) because of their high specific strength. But they are, unfortunately, not generally suitable for tribological applications because of their low hardness and tendency to gall. In an attempt to identify and develop coatings or surface treatments for use on titanium alloy precision gears, the National Centre of Tribology has examined many different treatments. The objective of this work was to improve the tribological performance of titanium alloy by new and emerging wear-resistant surface coatings. Most of these treatments failed a preliminary screening test on a reciprocating tribometer using a maximum Hertzian contact stress of 1.76 GPa in air. Four treatments which passed this test, Beta Nitrocarburizing, Delta Nitrocarburizing, Carbonitriding, and TiN on Delta Nitrocarburized titanium, were optimized and checked for repeatability prior to being tested in nitrogen under the same conditions as the initial screening tests. Of the successful four treatments, three, Beta Nitrocarburizing, Carbonitriding, and TiN on Delta Nitrocarburized titanium, were superior in terms of both friction and wear to the untreated titanium when tested in nitrogen. The TiN on top of Delta Nitrocarburizing had the best performance in nitrogen. The Delta Nitrocarburizing treatment had a lower coefficient of friction than the untreated titanium in nitrogen, but had a similar wear rate. The target of producing and testing a surface-hardened titanium alloy gear set in vacuum was not achieved, mainly because of the difficulty of producing repeatable surface treatments. This also compromised rolling contact fatigue tests performed at the U.S. Army Materials Technology Laboratory, Watertown, USA. Nevertheless several promising wear resistant coatings (in terms of depth and surface hardness) have been produced by development of previous "conventional" thermochemical heat treatments.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 21, 1992
- Accession Number
- ADA258316
Entities
People
- M. K. Vine