High-Entropy Alloys in Cryogenic Turbopump Bearings: Wear, Fatigue, Friction, and Rotor dynamic Stability

High-Entropy Alloys (HEAs) have emerged as next-generation bearing materials for cryogenic turbopumps used in high-performance liquid rocket engines. These turbopumps operate under extreme thermomechanical and tribological conditions, including rotational speeds exceeding 50,000–120,000 rpm, cryogenic temperatures as low as 20 K for liquid hydrogen (LH₂), high Hertzian contact stresses, severe lubrication starvation, pressure oscillations, cavitation, and intense vibrational and rotordynamic loads. Conventional bearing materials—such as M50 steel, 440C stainless steel, Cobalt-based alloys, ceramics, and advanced coated steels—struggle to survive such environments due to rolling contact fatigue (RCF), hydrogen embrittlement, cryogenic brittleness, thermal shock sensitivity, and rapid wear. HEAs, due to their multi-principal element architecture, exhibit exceptional cryogenic strengthening, low-temperaturetoughness, improved resistance to adhesive and abrasive wear, high resistance to hydrogen-induced damage, and stable microstructures under extreme thermal cycling. This research paper presents a comprehensive analysis of HEAs for turbopump bearings, examining their thermodynamic foundations, deformation mechanisms, wear behaviour, cryogenic fatigue performance, hydrogen embrittlement resistance, rotordynamic stability effects, and long-term failure modes. The investigation demonstrates that HEAs significantly outperform conventional bearing alloys under extreme cryogenic, mechanical, and dynamic loading, positioning them as a transformative material platform for reusable liquid rocket engines such as SpaceX Raptor, Blue Origin BE-4,ArianeGroup Prometheus, and NASA RS-25 upgrades.