Release time : 2015-06-15 07:49:08
Many aerospace bearing and mechanism failures can be traced back to the intrinsic inadequacy of currently available materials. Conventional hardened bearing steels are prone to corrosion. Bearings made from corrosion resistant alloys and plastics are relatively soft and prone to wear. Hybrid ceramic ball-steel raced bearings are susceptible to denting by the much harder ceramic balls. Bearing race denting is a particularly troublesome problem for spacecraft applications where high vibrations during launch can lead to bearing damage. As a result, engineering designs often include extra safety margins or heavy and cumbersome vibration isolation systems to prevent damage. The aerospace industry could truly benefit from new materials that have high resilience and corrosion resistance.
To address these issues, the NESC is supporting an effort to assess an emerging intermetallic alloy NiTiNOL 60 (60NiTi) for use in shockproof, corrosion-immune bearings. 60NiTi is highly resistant to corrosion because it contains no iron and cannot rust. Further, it belongs to the family of super-elastic materials and exhibits the uncanny ability to withstand tremendous loads and stresses without permanent deformation (i.e. denting).
Recent experiments sought to compare the dent resistance of 60NiTi to other bearing materials by pressing ceramic (Si3N4) or hardened 60NiTi balls into flat plate specimens made from conventional bearing race materials. Depending on the specific material combination, the use of 60NiTi increased dent resistance by a factor of about 5 to 50. In addition, tests have confirmed that 60NiTis corrosion behavior exceeds that of the best corrosion resistant materials, the cobalt-based superalloys.
When hard balls are pressed into flat plates of various bearing race materials, the super-elastic 60NiTi can withstand the highest loads. This suggests it will make a very dent resistant bearing with excellent corrosion resistance.
While long-term applications include numerous satellite mechanisms and other components, the current project seeks to design, build and test 60NiTi bearings suitable for the ISS Urine Processor Distillation Assembly. This highly corrosive application currently uses relatively soft bearings made from cobalt alloys. Great care must be taken during assembly, launch and use to avoid damage and wear.