Mechanical properties of hard and moderately ductile X2BC coatings
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| Year of publication | 2019 |
| Type | Conference abstract |
| MU Faculty or unit | |
| Citation | |
| Description | The main effort in the field of protective coatings manufacturing has been focused on the increase of the coatings fracture resistance without decrease of its high hardness. One way to independently control toughness and hardness is to prepare structures with intrinsic ductility which consist of alternating stiff and soft layers. It was recently shown that ductile ceramic materials with intrinsically layered structures are possible with the X2BC structure, where X= Mo, Ta or W. These materials possess unusual chemical, physical and mechanical properties that combine the best attributes of metals and ceramics. In this work we discuss the impact of deposition conditions on mechanical properties and thermal stability of X2BC (Mo, Ta, W) coatings. The coatings were deposited using mid-frequency pulsed magnetron sputtering of three targets (B4C, C and metallic) for controlling the stoichiometry. The hardness and elastic modulus were measured by nanoindentation and the fracture resistance was estimated by comparison of the cracking around the residual high load indentation imprints. The microstructure was evaluated by X-ray diffraction and transmission electron microscopy. The atomic composition was determined by Rutherford backscattering spectroscopy. It was shown that the presence of heating during the deposition plays the crucial role in the crystallinity of resulting coatings whereas the bias voltage affects mainly the atomic composition. Mo-B-C, W-B-C as well as Ta-B-C coatings showed hardness around 27 GPa and effective elastic modulus close to 480 GPa while their fracture resistance remained high, so it was impossible to produce cracks with indentation even under severe conditions. |
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