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|Title:||Grain size effect on self-mated CVD diamond dry tribosystems|
|Author(s):||Abreu, C. S.|
Oliveira, F. J.
Fernandes, A. J. S.
Silva, R. F.
Gomes, J. R.
|Citation:||"Wear". ISSN 0043-1648. 259:1 (2005) 771-778.|
|Abstract(s):||Chemical vapour deposited (CVD) diamond coatings are important for tribological applications due to their unique combination of properties. Previous work demonstrated that silicon nitride (Si3N4) excels as a substrate for diamond coatings due to its low thermal expansion coefficient mismatch relative to diamond films resulting in a significant adhesion improvement. In this study, dense Si3N4 substrates were fabricated by pressureless sintering and diamond coated by microwave plasma chemical vapour deposition (MPCVD). The deposition time varied between 1 and 10 hours in order to investigate the effect of the diamond grain size and film thickness on the tribological behaviour of self-mated CVD diamond coatings on Si3N4. Reciprocating dry sliding ball-on-flat wear tests were performed in air up to 16 hours, at room temperature, with normal applied load ranging from 10 N to 105 N. The stroke and frequency of the sliding motion were kept constant with values of 6 mm and 1 Hz, respectively. Several characterisation techniques (SEM, AFM, micro-Raman) were used to identify the prevailing surface damage mechanisms. After a very short running-in regime, with high friction coefficients, a steady-state regime is reached, characterized by extremely low friction values (f~0.03). A mild wear mode was achieved for the longer runs, with wear coefficient values around 10-8 mm3N-1m-1. The larger grain sized and thicker coatings present smaller compressive residual stresses (below 1 GPa) due to a better in-depth accommodation of the contact pressure. This delays film delamination to much higher applied loads (105 N) than the thinner, small grain sized coatings, grown for 1 hour that fail in sliding under 35 N of normal load.|
|Appears in Collections:||CIICS - Artigos em revistas de circulação internacional com arbitragem científica|