Submicron characterization of B-C:H thin films produced by RF plasma CVD

Abstract Discrepancies might arise among different laboratories when evaluating hardness values of thin coatings with conventional microhardness testers, which rely on optical examination of the indentation. These procedures can lead to significant measurement errors and misleading results if applied loads are either low, producing very small indentations that are difficult to measure, or relatively high so that penetration can be beyond coating and into the base material. This paper reports on the application of a microindentation technique to sample hardness and elastic properties of thin B-C:H films within ca. 10% of the total thickness of the coating in order to minimize the influence of the base material and to avoid optical measurement restrictions. Coatings were produced by RF plasma CVD from 5% B 2 H 6 in H 2 and CH 4 gas mixtures. Deposition parameters, mainly gas composition, RF power and total pressure were modified to obtain coatings of different C/B composition ratios and mechanical properties. Ultra-microhardness measurements were carried out dynamically under loads from 0.4 to a maximum of 25.6 mN and the indentation depth was continuously monitored as a function of applied load. Coatings with the lowest C/B% atomic ratios showed the most significant increment in hardness of about three times that of the hardened and tempered AISI M2 high speed steel base material. The coatings also presented a high elastic recovery after the indentation test, and the “hardness/(elastic modulus) 2 ” parameter indicates that the coating can provide significant protection under mild abrasive wear mechanisms. Wear tests showed an improvement in friction coefficient compared to M2 steel and TiN coating, but the wear performance of the coatings can be impaired by a lack of adhesion to the M2 steel substrate.