Tribological Characteristics of Copper-Based Functionally Gradient Material for Wind Turbines Brake Pads

Abstract

Copper matrix incorporated with solid lubricant and hard ceramic reinforcement is a proven potential material for wind turbine brake pad applications. Though brake pads as bulk composites possess high wear resistance, hard ceramic reinforcements at the contact area weaken the joint strength with the brake caliper. This may lead to cataclysmic failure of the mechanical braking. This study aims to develop a functionally gradient materials (FGM) for brake pads that shows variations in composition and properties along its cross section. The brake pad comprises Cu, Fe, hBN, SiC, and Al2O3 powder to obtain a gradient composition profile. Metallographic studies showed the homogeneous distribution of minor matrix (Fe), solid lubricant (hBN), and reinforcement (SiC, Al2O3). Phase analysis was carried out using XRD, and Vickers microhardness tests were performed. A maximum hardness of 133.3 HV was obtained at the top layer of the FGM. Pin-on-disc wear apparatus was used to evaluate the wear-rate and the coefficient of friction (COF) of the sintered specimen at varied loads. Specimens exhibited a low wear-rate of 2.36 × 10−7 g/N m with 0.48 as the COF value at a maximum loading condition (70 N). Surface characterization (morphology, chemical composition, and phase composition) of worn specimens was performed using FESEM, EDS, and XRD analytical techniques. The results inferred that the predominant wear mechanism was oxidative and abrasive wear mechanism at high loads.