07 - Systems, Subsystems and Equipment
LIGHTWEIGHT BIMETALLIC GEARS FOR AEROSPACE TRANSMISSIONS ENABLED BY OPEN-AIR DIFFUSION BONDING
Z.C. Xu¹, E. Tang¹, N. Teyssier¹, M.F. Humphreys¹, J. Jiang¹; ¹Imperial College London, United Kingdom
Aerospace transmission programmes are increasingly constrained by rotating mass and inertia as torque density rises and efficiency/NVH requirements tighten. Full substitution away from steel is often impractical because the tooth surface still needs steel-class hardness, wear resistance, and established heat-treat routes. The opportunity is therefore “right material in the right place”: retain steel where contact mechanics demand it, and replace steel where it mainly penalises inertia.rnrnThis work presents a bimetallic gear architecture that separates functions. A steel tooth/rim provides the tribological and fatigue-critical surface, while the core is replaced with a lightweight metal to reduce mass and polar moment of inertia (inertia scales strongly with radius, so core lightweighting delivers disproportionate dynamic benefit). Two material pairings are positioned for different duty levels. Steel–aluminium is optimised for secondary gears and moderate temperatures where maximum inertia reduction is valuable. Steel–titanium is aimed at more critical gears, where higher temperature capability and stiffness margins are required while still achieving meaningful weight savings.rnrnThe key enabler is a novel low-temperature open air diffusion bonding route (invented at Imperial in 2024) that operates in air and avoids melting. Conventional joining of steel to aluminium or titanium is typically constrained by stable oxide films and/or brittle intermetallic reaction layers at high temperature, while vacuum diffusion bonding becomes slow, size-limited and costly for realistic gear geometries. Our approach uses a tailored interlayer and a controlled pressure–temperature pathway to achieve metallurgical bonding with low thermal exposure, reducing distortion risk and preserving compatibility with downstream heat treatment on the steel rim.rnrnWe report first steel–aluminium bimetallic gear prototypes. Relative to a monolithic steel baseline of the sa
DOI: 10.71945/icas2026_0991