Fly ash based sintered materials are identified as potential brake pad materials for wind turbines. However, fly ash based friction materials fabricated through conventional techniques results in more porosity and undesirable tribological properties. This study attempts to develop liquid phase sintering technology for fly ash using Cu as a liquid phase sintering agent. The study presents a comprehensive analysis of the evolution of microstructure, microhardness, and tribological performance of the specimens sintered in Argon and Air environment.
Copper-based functionally gradient composite material is developed using powder metallurgy processing technique, as a potential wind turbine brake pad material. The developed composite has a gradient composition of Cu, CeO 2 , Al 2 O 3 , Fe, and C g to enable joint strength at the interface (brake calliper) and wear resistance at the contact surface (brake disc). The article presents a comprehensive analysis on the microstructure, microhardness, and tribological performance of the developed composite. The wear mechanism is deduced through surface morphology, elemental composition, and phase composition analysis using field emission scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffractometer, and X-ray photoelectron spectroscope. A maximum hardness of 198.2 HV was obtained at the contact surface. Experimental values from tribology tests show that a decreasing trend was obtained with a wear rate of 2.013 × 10 −7 g N-m −1 and a friction coefficient was 0.215.
The tribological and thermal properties enable iron based sintered materials with hard phase ceramic reinforcements as promising friction material for heavy-duty wind turbines. In wind turbines, the braking system consists of aerodynamic and mechanical braking systems. During application of mechanical brakes, the friction materials are pressed against the rotating low-speed shaft. The desired braking efficiency is achieved by utilizing a number of friction materials, which in turn are joined in a steel backing plate. Though this arrangement increases the braking efficiency, the hard phase ceramic reinforcement particles reduces the bonding strength between the friction material and steel backing plate. The joint failure leads to catastrophic failure of wind turbine. Therefore, the need of the hour is to develop friction materials with functional gradients that have high wear resistance (contact area) and high bond strength (interface). In this study, an attempt is made to fabricate and characterize a friction material with gradient profile of composition along the cross section to provide functional gradient property. The functional gradient friction material is synthesized by gradient deposition of Fe, Cu, Cg, SiC and fly ash powders which is then compacted and sintered. The prepared functional gradient friction material was characterized in terms of microstructure and microhardness. The tribological performance (wear rate and coefficient of friction) of the developed functionally gradient friction material was investigated at various loads using pin-on disc apparatus. The results show that as the load increases, the wear rate decreases and at the same time the COF tends to increase at higher loads. The predominant wear mechanism was deduced from the morphology of the worn surface.
Fe/Cu-based sintered friction materials are proven potential materials for
heavy-duty applications. The current research explores the influence of rare
earth oxide (Nd2O3) and graphite on the tribological characteristics of
Fe/Cu-based friction materials. The constituents present in the friction
material are Fe, Cu, Cg (1%, 3%, 5%, 7%), BaSO4, and Nd2O3 (5%). Optical
microscopy and elemental mapping studies reveal the homogeneous distribution
of elements in the matrix. Sintered density of the specimens showed a
maximum of 70% of the theoretical density measured by Archimedes' principle.
XRD analysis shows no new phase formation in all the sintered specimens. A
peak microhardness result of 96 HV is obtained in specimen NG-01. The
pin-on-disc tribotests are performed at an axial load of 50 N at a sliding
velocity of 5.5 m/s. Specimen NG-03 with 3% graphite exhibited an optimum
wear rate with a friction coefficient of 0.45. The surface morphology and
elemental composition of the worn specimens are investigated. The
morphological features inferred that the wear mechanism is predominantly
mixed abrasive and adhesive.
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