Publication details

Influence of chemical composition on structure and mechanical properties of W-B-C coating deposited in industrial sputtering system

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Year of publication 2018
Type Conference abstract
MU Faculty or unit

Faculty of Science

Description Nowadays used hard protective coatings generally exhibit high hardness and high stiffness; however, these positive features are often accompanied by negative brittle deformation behaviour. The current trend in surface engineering is to sacrifice some of the hardness in favour of enhanced ductility and fracture toughness. Recently, there has been an increased interest in crystalline boron and carbon based nanolaminates with X2BC stoichiometry which are inherently nanolayered within the unit cell. According to the ab-initio models, these materials should exhibit an unusual combination of high stiffness and moderate ductility. A systematic theoretical study revealed that the nanolaminates with X = W should exhibit the best mechanical properties making them the best candidates for experimental synthesis. These W-B-C coatings were sputter deposited onto substrates performing a planetary motion around a patented central rotating cylindrical target composed from B4C, W and graphite segments in an industrial scale deposition system of company SHM. The deposition was performed at the temperature of 450 °C and bias of -100 V. Fine tuning of the chemical composition of the deposited samples was found to be crucial to grow the crystalline phase. Only the samples with the composition very close to the W2BC stoichiometry showed a narrow peak in the X-ray diffractogram at the 2theta angle of ~ 41° proving enhanced crystallinity. The samples deviating from the W2BC stoichiometry by only a few percent typically exhibited only a very broad peak centred at ~ 39° which was attributed to a short range ordered or a nearly amorphous structure. The SEM cross-section view revealed presence of a fine layered structure which was attributed to the planetary motion of the samples being repetitively directed towards and away from the target. The coatings were hard and of high fracture resistance, it was hard to form a crack in these coatings. The multilayer structure was probably beneficial for the fracture resistance as very often, the crack surface in the coating showed an irregular step-like character indicating deflection of the crack during the crack propagation.
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