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Abstract:
Tungsten diboride alloyed with transition metals provides an opportunity to obtain exceptional mechanical, physical, and chemical properties. We report a strategy for designing and synthesizing of superhard and low-compressible ceramic thin films with increased toughness and lowered residual stresses (σ < −0.9 GPa) deposited with high-power impulse magnetron sputtering (HiPIMS) from one target. The addition of 7–12 % titanium promotes additional strengthening mechanisms of the layers in one material, leading to the improvement of wear resistance compared to an alloyed WB2-z yet at even higher hardness 43.8 ± 2.1 GPa and nanoindentation toughness 4.9 ± 0.2 MPa√m. The compression of the micropillar shows that titanium addition changed the type of nanoindentation from cracking along the slip plane to bulging on the top of the pillar and next the crack initiation along column boundaries. The highest adhesion of the layers is obtained for addition of 7 % titanium and in all cases the wear has abrasive character. The controlled use of 200 μs pulses during synthesis with HiPIMS allows for an increase in the deposition rate and maintaining exceptional mechanical properties of the layers even at a substrate temperature of 300 °C.

Keywords:
Ternary transition metal diboride thin films, Mechanical properties, HiPIMS magnetron sputtering, Wear resistance and adhesion

Abstract:
In recent years, the search for improved materials for green energy, aerospace and automotive has been the focus of interest of scientists and industry. As an example transition metal borides such us ZrB2, TiB2, WB2 can be mentioned with their extraordinary thermal, mechanical properties and oxidation resistance even above 500˚C. Also in the form of thin films they are competitive with commercially used nitrides. The last studies have been show that disadvantages like low fracture toughness can be improved by alloying them with other transition metals TM= Ti, Cr, Zr, Mo, Ta, Hf etc. or the choosing of suitable deposition method. In this work the doping of tungsten diboride with titanium is presented. Also, two different method of deposition like High-Power Impulse Magnetron Sputtering (HiPIMS) and hybrid PLD-MS, which give possibility to produce a plasma with the higher energy than conventional DC magnetron sputtering are studied. Such solution allows to obtain coatings which are very hard and fracture resistant simultaneously. Deposited by HIPIMS coatings are smooth and possess lower hardness (40 GPa) than films deposited with PLD-MS method (51±8 GPa). However produced by hybrid method films are rougher and are characterized by higher Young modulus (520 GPa vs. 354 GPa) what cause that they are characterized by lower fracture resistance. Additionally, HIPIMS crystalline films can be obtained in 300˚C (520˚C for PLD-MS) what increase possibility of their future application. I should be noted that tungsten borides have very high potential for its implementation as a wear protecting coatings on tools and also in nuclear energy solutions

Keywords:
magnetron sputtering, transition metal borides, protective coatings