COMBINING SCRATCH, WEAR, FRICTION AND NANOINDENTATION TESTS IN THE ASSESSMENT OF TRIBO-MECHANICAL PROPERTIES OF DLC AND DLC-Si FILMS

This work addresses the evaluation of the tribo-mechanical performance of DLC and DLC-Si films deposited onto AISI 4340 steel by the use of a combination of tribological and mechanical tests. Polished AISI 4340 steel substrates were submitted to a plasma nitriding process prior to the deposition of DLC and DLC-Si thin films in a PECVD system using N(2), CH(4) and CH(4)+5%v. SiH(4) plasmas. Scratch test results showed higher critical load values for the DLC-Si films (8.7 N) when compared with DLC (5.3 N), indicating better adhesion to the substrate when Si is present in the DLC structure. Nanoindentation tests showed typical hardness values for DLC films (16-21 GPa) and lower hardness values for the DLC-Si films (13-15 GPa). Average friction coefficient was 0.13 for DLC films and 0.05 for the DLC-Si films, both much lower than the values found for the uncoated AISI 4340 steel (0.71), as expected. Wear rates obtained for DLC films (0.1 x 10(-6) mm(3)/Nm) were lower than the ones found for DLC-Si films (0.47 x 10(-6) mm(3)/Nm). Obtained data from scratch, wear, friction and nanoindentation tests are set together as a valuable tool for the study of thin films.