Research Information System
Journal of Materials Engineering and Performance, 2026 (SCI-Expanded, Scopus)
This study investigates the incorporation of recycled GG25 gray cast iron machining waste as a sustainable and cost-efficient partial substitute for conventional steel fibers in composite friction materials engineered for aircraft clutch systems. Five composite formulations were manufactured using powder metallurgy by systematically varying the ratios of steel fibers and GG25 particulates (<500 µm) from 0 to 20 wt.%, while maintaining constant total metallic reinforcement (20 wt.%), binder, filler, and modifier content. Density, hardness, and tribological performance were characterized via mass-volume evaluation, Shore D hardness testing, and ball-on-disk wear experiments simulating operational sliding distances of aircraft landing. Microstructural and phase analyses were conducted using optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD). The lamellar graphite morphology of GG25 promoted more stable friction behavior through solid lubrication, whereas steel fibers primarily increased hardness, wear resistance, and mechanical integrity. Among the tested formulations, the hybrid sample containing equal proportions of steel fiber and GG25 waste (St10Ct10) demonstrated the most balanced performance, exhibiting the lowest wear volume (0.238 mm3), moderate hardness (79.3 Shore D), and the smallest friction deviation (standard deviation 0.093) across the five compositions. This combination yielded a wear rate of 1.19x10−5 mm3/N.m exceeding both the steel-only (St20) and GG25-only (Ct20) formulations. These findings establish that recycled GG25 machining scrap can optimally replace 50% of steel fiber reinforcement without detriment to key functional properties, enabling circular material reuse, reduced production cost, and enhanced sustainability in the design of aviation-grade friction components. The equal-ratio hybrid formulation emerges as the most promising candidate for further development.