Abstract: Abstracts: Shroud dry friction dampers, as critical components for vibration suppression in aero-engine turbine blades, have interface contact characteristics that directly affect the service life and reliability of the structure. Aiming at the fretting wear failure problem at the damper/blade interface under extreme working conditions, this study used an SRV-V multifunctional tribometer to establish a cylinder/plane line contact model, systematically investigating the fretting tribological behavior of K417 high-temperature alloy under simulated working conditions (750 ℃) with different normal loads (84, 334, 522 N). The results showed that normal load dominated the evolution of fretting operation regimes by regulating contact stress distribution: at low load (84 N), the contact stress was small, the interface operated in a full-slip state, and The friction-displacement (F_t-D) curves exhibited a parallelogram shape, with high-frequency fluctuations in friction coefficient (peak value 0.745) due to the dynamic equilibrium of third-body debris; at medium load (334 N), the contact stress gradient induced a transition from full-slip to mixed regime with central sticking and edge slipping—repeated deformation of surface asperities and failure of semi-dense third-body films synergistically exacerbate wear, leading to a peak wear volume of 0.016 mm³; at high load (522 N), debris was rapidly compacted into a gradient third-body layer composed of an outer oxide film and an inner metallic transfer layer, which isolated direct metal contact through interlayer shear, reducing the friction coefficient to 0.401 (a 46.17% decrease) and the wear rate by 82.12% compared with 84 N. Energy dissipation analysis revealed that the third-body layer at high load reduced substrate damage via a "shear energy dissipation-stress buffering" mechanism, forming a "high-load, low-damage" effect. This study revealed the evolution law of normal load driving third-body from "dynamic oxide film" to "gradient shear layer" in high-temperature environments, providing a design basis for "load-third-body matching" to prevent fretting wear of nickel-based alloys under high-temperature conditions.