Friction coefficient, microstructure and thermal stability of amorphous a-C coatings

Correlation between the microstructure, friction properties and ratio of sp(2)/sp(3) carbon bonds in amorphous a-C coatings on AISI M2 steel was studied in this work. The coatings were formed using pulsed cathodic-arc vacuum deposition (CAVD), with negative bias voltage of 0.2-20 kV applied to the sample. The dose of assisting ion fluence was 3 X 10(15)-10(17) ions cm(-2). The best friction properties were found for amorphous a-C coatings formed with a negative bias voltage of 5-20 kV and ion assistance dose of 10(17) ions ?m(-2). Raman spectra with a diffused asymmetric maximum at 1545 ?m(-1) and I-D/I-G ratio in the range 2.3-2.7 are characteristic for these coatings. Deterioration of the friction properties of a-C coatings occurs with an increase in annealing temperature from 300 to 600 degreesC. This is accompanied by a transformation of the amorphous carbon into submicron graphite crystallites. (C) 2002 Elsevier Science B.V. All rights reserved.