The concept of an ideal SKF aero-engine bearing steel was developed in order to translate the VHBR aero-engine application conditions into the metallurgical requirements for the steel rings for the hybrid bearings.
For the VIM-VAR route, a new patented novel composition (ARCTIC15 steel) have been designed and produced using an industrial 16-ton VIM/VAR melt. The development of a low pressure carburizing heat-treatment for the ARCTIC15 has been conducted with university and supplier partnerships to reach the economic and technical targets. The complete metallurgical and physical characterization of the ARCTIC15 has then been performed.
For the PM steel technology evaluation, the AMS6560 has been selected based on first elementary rolling contact tests as the best solution for through hardened high temperature PM steel. Regarding to the case-hardened PM steel, it has been decided to base the approach on the same composition than the novel ARCTIC15 alloy, applying to the VIM-VAR melt ingot an atomization, then a HIPed process. The result (PM-HIPed ARCTIC30 steel) has been also metallurgically characterized to confirm a good microstructure integrity.
The validation of the steel developments, couple with the introduction of ceramic rolling elements (=advanced hybrid bearing) has been performed by a multi-scale back-to-back demonstration of +15% (for conventional route steel) up to +30% (for powder metallurgical steel) in loading capacities compared to current aero-engine steel solutions (i.e. M50NiL rings + M50 balls). These increases of performance have been demonstrated in nominal running conditions but also in degraded running conditions (poor lubrication, polluted oil, high temperature, etc...).
On a general overview on the results from elementary to full-scale tests, the new bearing technologies (ARCTIC15 steel, PM AMS6560 and ceramic rolling elements) have over-performed the baseline bearings, even if running at higher loads.
Additional tasks have been run to convert the testing results into design rules and manufacturing parameters usable by the bearing design office and the manufacturing teams.
Coupling the results of a semi-analytical contact model and some experimental characterization of the studied steels, an evaluation of the rolling contact fatigue endurance limits has been made for aerospace application temperatures. The estimation seems aligned with the legacy design rules for the M50NiL. These endurance limits are clearly increased for the ARCTIC15 and for the AMS6560 reaching the initial project targets
After 6.5 years of development activities, the ARCTIC project has achieved its objectives.
