High Temperature Aircraft Turbine Engine Bearing and Lubrication System Development

Abstract

Results are reported for a project sponsored by the United States Air Force Wright Laboratories entitled “High Temperature Bearing / Lubricant System Development.” The major emphasis of this project was the evaluation of bearing materials with improved corrosion resistance, high hot hardness, and high fracture toughness, intended to meet the requirements of the Integrated High Performance Turbine Engine Technologies (IHPTET) Phase II engine. The project included material property studies on candidate bearing materials and lubricants which formed the selection basis for subscale and full-scale bearing rig verification tests. The carburizing stainless steel alloy Pyrowear 675 demonstrated significant fatigue life, fracture toughness, and corrosion resistance improvements relative to the M50 NiL baseline bearing material. The new Skylube II (MCS-2482) lubricant provided significant thermal degradation improvements with respect to the Skylube 600 (PWA-524, MIL-L-87100) lubricant. Two 130 mm bore Pyrowear 675 hybrid ball bearings with silicon nitride balls were run successfully for 231 hours with Skylube II lubricant at temperatures consistent with IHPTET II requirements.

Phosphate Esters, Thiophosphate Esters and Metal Thiophosphates as Lubricant Additives

“…Advances in the performance of modern aircraft engines have required more advanced bearing materials [77]. In general, these materials have resulted in changes in the surface chemistry from primarily iron oxide to a mixture of carbides.…”

Rolling Contact Fatigue Evaluation of Advanced Bearing Steels with and Without the Oil Anti-Wear Additive Tricresyl Phosphate

“…The lower carbon percentage replaced by nitrogen leads to improve corrosion resistance and fine uniformly distributed carbides. Pyrowear 675 [10] and CSS 422 [11] are case carburized stainless steels. They have very good fracture toughness and offer improved corrosion resistance over M50 but are not as corrosion resistant as Cronidur 30.…”

Interaction of anti‐wear additiveTCPwith advanced bearing steels

“…Some of the key bearing performance attributes needed to meet these emerging engine needs include materials with good core fracture toughness for high‐speed/high‐load operation, excellent hot‐hardness for surface wear and fatigue resistance, and good corrosion resistance for operation in hostile environmental conditions among other desirable properties. Towards this end, a number of advanced steels have been developed and extensively characterised with the potential of meeting these requirements including Pyrowear 675 (P675), Cronidur 30, CSS‐42L and nitrided M50NiL 1–8 . The high hardness and strength of these materials is mostly attributed to a combination of grain size and alloying elements such as Cr, W, Mo, V and Co, all of which are known to form carbides during the heat treatment (carburisation) process.…”