Micro-structural refinement and tribological enhancement of inconel X-750 superalloy through surface mechanical attrition treatment

Abstract

Inconel X-750 is a nickel–chromium super alloy used in aerospace and nuclear components, where surface wear governs service life. Surface Mechanical Attrition Treatment (SMAT) is a simple, rapid, low-cost, and eco-friendly method that produces a gradient nano-crystalline surface layer at room temperature without coatings, lasers, chemicals, or heat and is suitable for curved and irregular surfaces. In the present work, SMAT was applied to stress-relieved and age-hardened Inconel X-750 samples to enhance the tribological performance. The surface topography, microstructure, friction, and wear behaviour were characterised across a range of applied normal loads. Scanning Electron Microscope (SEM) analysis revealed three concurrent wear features, namely abrasive grooves, a mechanically mixed layer (MML), and adhesive pull-out, all intensifying with load. Electron Back Scatter Diffraction (EBSD) showed that the surface grains were refined from \(\sim\)70 µm to \(\sim\)39 µm, which raised the near-surface hardness by 12.5 \(\%\), from 6.24 to 7.02 GPa, and is the main reason for the improved tribological response. Despite increased surface roughness, the wear volume reduced by 27–47 %, the normalised wear mass loss dropped from 3.80 to 2.30 µg/N, and the coefficient of friction decreased by up to 25 %. The wear data were further interpreted through analytical formulation and these findings establish SMAT as an effective and scalable way to improve the tribological performance of Inconel X-750 in sliding-contact applications.