On the origin of multilayered structure of W B C coatings prepared by non reactive magnetron sputtering from a single segmented target
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| Year of publication | 2019 |
| Type | Conference abstract |
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| Description | Machining tools are routinely coated with thin films to enhance their performance and durability. Nowadays used hard protective coatings exhibit high hardness and high stiffness; however‚ these positive features are often accompanied by negative brittle deformation behaviour‚ which facilitates formation and spreading of cracks. This leads to a premature degradation of the coated tool. A solution would be to prepare coatings simultaneously exhibiting high hardness together with enhanced ductility. Recently‚ there has been an increased interest in crystalline metal-boron-carbon based coatings [1] with X2BC stoichiometry which is inherently nanolaminated within the unit cell. According to the ab-initio models [1]‚ 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 [1] making them the best candidates for experimental synthesis. Thus W-B-C coatings were sputter deposited in non-reactive atmosphere onto substrates performing a planetary motion around a central rotating cylindrical target composed from boron-carbide‚ tungsten and graphite segments in an industrial scaled deposition system of company SHM‚ Sumperk‚ Czech Republic. The coatings were deposited at the temperature of 450 °C and bias of -100 V by direct current magnetron sputtering. The SEM and TEM cross-section view revealed the presence of multilayered structure. The pattern of the multilayered structure was dependent on the type of planetary rotation around the central target. According to EDX and GDOES‚ the multilayered structure consisted of tungsten-rich layers alternating with boron- and carbon-rich layers. The whole structure consisted of thin layers with the thickness not exceeding 15 nm. The number of the multilayers was correlated with the number of the revolutions the sample performed during the deposition process. The multilayered structure was attributed to different transport pathways of heavy (W) and light (C and B) atoms sputtered from the target and scattered by working gas. 3D DSMC model was developed to explain the transport of sputtered atoms. The model is using the experiment geometry and initial velocities of sputtered particles calculated by TRIM. Results obtained with this model are in good agreement with experiment. [1]H. Bolvardi‚ J. Emmerlich‚ M. to Baben‚ J‚ von Appen‚ R. Dronskowski‚ J.M. Schneider‚ Systematic study on the electronic structure and mechanical properties of X BC (X = Mo‚ Ti‚ V‚ Zr‚ Nb‚ Hf‚ Ta and W)‚ J. Phys.-Condens. Mat. 25 (2013) 045501. |
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