Increase of Readiness Level of a Powder Metallurgy Steel for Aerospace Applications

Abstract

The trends in the aerospace market of reducing fuel consumption and polluting emissions create the need to reduce the weight of mechanical components: for example, a reduction in bearing ring weight means that the ring steel must withstand greater loads. To significantly increase load-carrying ability, powder metallurgy (PM) steels have been considered in recent years as a consistent solution. At the last ASTM congresses, ASP2055, a PM steel presenting an interesting hardness-toughness compromise, was presented. In 2016, the potential of this steel for aerospace applications was demonstrated by a thorough analysis of the inclusion cleanliness and matrix mechanical properties regarding the subsurface performance. In 2019, the reliability of the process and properties regarding performance were discussed. This paper presents the readiness level increase in terms of both manufacturing and application performance. Since 2016, extensive work has been done at NTN Europe to qualify and quantify the performance of ASP2055 in rings for all-metal and hybrid aerospace bearings. The subsurface rolling contact fatigue (RCF) performance was already qualified in terms of inclusion cleanliness and matrix intrinsic mechanical properties. Additional tests were carried out under high load to confirm the high reliability of PM steelmaking. Rolling bearings of small size were manufactured to test the performance of ASP2055 in representative conditions and to test ASP2055 for other bearing functions (surface RCF and core properties). More recently, real-size turbine engine bearings were manufactured for representative manufacturing and testing. The lessons learned for the technology readiness level (TRL) and manufacturing readiness level (MRL) increase are presented in this paper.