Performance Evaluation of “Duplex Hardened” Bearings for Advanced Turbine Engine Applications

Abstract

Reliability is one of the most important competitive factors in aeroengines. Engine manufacturers have to provide guarantees for maintenance cost and dispatch reliability. Failures of mainshaft and gearbox bearings can represent a major debit to overall engine reliability. Duplex hardening (conventional hardening followed by special nitriding) has the potential to provide the bearing performance improvements necessary to yield increased engine reliability and reduced cost of ownership. The bearing rig tests performed demonstrate superior performance of duplex hardened M50 and M50NiL bearings over conventional M50 and M50NiL bearings under various operating conditions. Rig tests evaluating a wide range of operating conditions, such as high load, low or boundary lubrication, heavily contaminated lubrication, and oil off were performed. Additional tests were completed to evaluate the spall propagation behavior of duplex hardened bearings in comparison to conventional steel bearings. The results showed that the main benefits of using duplex hardened bearings arise in low or boundary lubrication conditions and contaminated lubrication conditions. The spall propagation tests showed that spall propagation rates are slower for duplex hardened M50 and M50NiL bearing components, hence allowing more time until catastrophic bearing failure in an aeroengine and other applications.

Duplex Hardening of Steels for Aeroengine Bearings

“…To mimic the worst-case scenario during bearing operation, the testing conditions reported in the literature include boundary lubrication conditions, 3,6,20,24,29) and sometimes the introduction of artificial indentations in the rolling contact zone. 6,40) Duplex hardening of M50 balls performed by Beer 33) also shows favourable test results.…”

“…Streit and colleagues 40) conducted delicate experiments where spall propagation on M50NiL bearing raceways and its duplexhardened variant was investigated. Figure 13 shows the spall area measured at an intermediate stage of laboratory bearing testing.…”

Dry tribological properties of M50 bearing steel under different temperatures

“…Aero-engine is the 'hear' of the airplane, and bearing is the critical safety component and core foundation department unit. Because of the harsh environment of aero-engines operation, the bearing material should have high reliability, high contact fatigue life and excellent dimensional stability [1][2][3]. M50 bearing steel is a high speed steel with high contents of Cr and Mo, and it was developed in 1950s and used widely as the bearing material of aeroengine [4][5][6][7].…”

A Novel Decarburizing-Nitriding Treatment of Carburized/through-Hardened Bearing Steel towards Enhanced Nitriding Kinetics and Microstructure Refinement

“…Rhoads M50 to HV 1000~1250 and prolonged the rolling contact fatigue life by 8~10 times with duplex hardening [4]. Streit et al reported that duplex-hardened M50 bearings had lower spall propagation rates over conventional counterparts in low or boundary lubrication conditions and contaminated lubrication conditions due to the high surface hardness [5]. For steels with reduced carbon content, duplex hardening can be achieved for surface by nitriding the pre-carburized case [6].…”