resumo
One important issue in internal combustion engines is the performance of injection pumping systems that is related to the energy efficiency of the engines. Considering that the trend is to increase the combustion pressure, new materials of lower weight, harder, wear and corrosion resistant, and compatible with the fuel environment, are needed. In this work, ball-on-flat reciprocating tests were performed with bare and CVD diamond coated Si3N4 materials lubricated by a commercial soybean-derived biodiesel. Experiments with AISI 52100 steel were also accomplished. Two types of coatings were tested: (i) a single layer (SL) of microcrystalline diamond (MCD) and (ii) a multilayered (ML) system made of three bilayers of MCD/nanocrystalline diamond (NCD). Results show that diamond coatings give lower friction coefficient values (COF) of 0.07, as the minimum, than that of the steel tribopair, which presents a COF above 0.10, which can limit engineering applications. The SL tribopair presents a higher initial COF peak (0.35) than ML (0.15) explained by the difference in surface roughness. Regarding the wear behaviour, all the tested materials have shown similar mild wear coefficients around 10(-8) mm(3) N-1 m(-1), the same observed in dry tests with CVD diamond coatings, which constitutes a further advantage when the system is running in lubricant starved conditions. (C) 2013 Elsevier B.V. All rights reserved.
palavras-chave
SILICON-NITRIDE; COATINGS; FUEL; FRICTION; BEHAVIOR; FILMS; OPTIMIZATION; COMPONENTS; LUBRICITY; ENGINES
categoria
Engineering; Materials Science
autores
Almeida, FA; Maru, MM; Shabani, M; Oliveira, FJ; Silva, RF; Achete, CA
nossos autores
Filipe José Alves de Oliveira
Investigador Principal
Flávia Aparecida de Almeida
Bolseiro de pós-Doutoramento
Rui Ramos Ferreira e Silva
Professor associadoagradecimentos
This work was funded by FCT project MULTIDIACOAT PTDC/EME-TME/100689/2008. The authors also acknowledge Financiadora de Estudos e Projetos (Finep) for financial support. F.A. Almeida acknowledges the Portuguese FCT post-doctoral grant SFRH/BPD/34869/2007. R.F. Silva acknowledges CNPq/PROMETRO/550064/2012-5. The authors also acknowledge the Laboratory of Diffraction and Spectroscopy (Lades)-INMETRO for the Raman measurements and the Laboratory of Microscopy (Labmi) for the FEI Magellan SEM images.