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Streszczenie:
This work compares experimentally measue properties of W-Al-B thin films with mechanical properties, density, and thermal conductivity values calculated using DFT methods. Theoretical modelling was conducted to simulate two WB2 stable structures alloyed with varying amounts of aluminium: α-WB2 (P6/mmm) and ω-WB2 (P63/mmc), as well as α-AlB2 (P6/mmm). Using the HiPIMS-DC magnetron sputtering technique, films with α-WB2 structure and varying aluminium contents were deposited at 400 °C. When layers are composed with x = 1.4% aluminium (where x = at%Al / (at%Al + at%W)), their microstructure changes from amorphous to crystalline columnar. A back transformation to an amorphous microstructure occurs when the amount of aluminium exceeds x = 7.3%. An original method was used for the film density studies, which combined mass measurements and microscopic observation. These measurements were then used to determine the layers' thermal conductivity using the thermoreflectance method. The measured conductivity of the deposited ceramic films range from 3 to 6 W/(mK). Moreover, the obtained films are very hard, e.g. H = 36.1 ± 1.7 GPa for x = 1.4% Al, but exhibit a much lower Young's modulus than the theoretical values. The relatively high H/E⁎ ratio > 0.1 for films with low aluminium content indicates anmore elastic character. Ab-initio calculations showed that, based on the criteria of Cauchy pressure (C12-C44) and Pugh's ratio (B/G), the α-WB2 structure may have a ductile nature in contrast to the other structures. However, the deposited films are rather brittle in nature, resulting from an excess of boron. The fracture toughness measurements show higher KIC values for low aluminium content. They are 3.8 MPa√m for WB2, 2.8 MPa√m for x = 1.4%, and 3 MPa√m for x = 7.3% aluminium

Słowa kluczowe:
thin films, high-power impulse magnetron sputtering, density, thermal conductivity, fracture toughness, stiffness tensor

Streszczenie:
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.

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

Streszczenie:
In this work, a facile, wet chemical synthesis was utilized to achieve a series of lithium manganese oxide (LiMn2O4, (LMO) with 1–5%wt. graphene oxide (GO) composites. The average crystallite sizes estimated by the Rietveld method of LMO/GO nanocomposites were in the range of 18–27 nm. The electrochemical performance was studied using CR2013 coin-type cell batteries prepared from pristine LMO material and LMO modified with 5%wt. GO. Synthesized materials were tested as positive electrodes for Li-ion batteries in the voltage range between 3.0 and 4.3 V at room temperature. The specific discharge capacity after 100 cycles for LMO and LMO/5%wt. GO were 84 and 83 mAh g^−1, respectively. The LMO material modified with 5%wt. of graphene oxide flakes retained more than 91% of its initial specific capacity, as compared with the 86% of pristine LMO material.

Słowa kluczowe:
lithium manganese oxide, LiMn2O4, graphene oxide, cathode material, lithium ion battery