@article {3803, title = {Stable a-CSi:H films with a wide range of modulus of elasticity and low internal stress}, journal = {Surface and Coatings Technology}, volume = {459}, year = {2023}, pages = {129147}, abstract = {

Amorphous hydrogenated silicon carbide (a-CSi:H) thin films were deposited by plasma-enhanced chemical vapor deposition using tetravinylsilane as organosilicon precursor. The mechanical properties of the thin films, namely the modulus of elasticity, hardness, and elastic recovery parameter, were determined by nanoindentation, as well as the internal stresses by scanning electron microscopy and optical profilometry. It was found that the modulus of elasticity increased from 10 to 137\ GPa with increasing power (2{\textendash}150\ W) delivered to plasma, while the hardness increased from 1.5 to 14.5\ GPa. This improvement in mechanical properties with increasing energy delivered to the plasma is related to greater fragmentation of the precursor which led to an increase in the crosslinking of the material network. The compressive internal stresses in the films reached low values of -0.04 to -0.2\ GPa with increasing power (2{\textendash}75\ W) and an acceptable -0.5\ GPa for 150\ W. The elastic recovery parameter decreased with increasing power from 0.86 to 0.64, i.e., the thin films behaved more plasticity with increasing power. The modulus of elasticity and hardness were investigated in terms of the aging of the films for a period of 6\ years when samples were stored under ambient conditions. No significant changes in these properties were observed. However, minor changes were observed in the indentation curves obtained for the 2\ W and even less for the 10\ W samples. Small changes were then also observed for the elastic recovery parameter, whose value for these samples partially decreased which may be related to postdeposition oxidation. No changes in internal stress values over time were observed. The wide range of mechanical properties of stable a-CSi:H films with low internal stress increases their application potential and their wide use as materials with tailored properties from polymer-like to tough material.

}, keywords = {AIF, MF}, issn = {0257-8972}, doi = {https://doi.org/10.1016/j.surfcoat.2022.129147}, url = {https://www.sciencedirect.com/science/article/pii/S0257897222010684}, author = {Tomas Plichta and Vaclav Sulc and Miloslav Ohlidal and Vladimir Cech} } @article {3628, title = {Experimental analysis of microhardness changes of subsurface areas affected by WEDM}, journal = {Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering}, volume = {236}, year = {2022}, pages = {1979-1991}, abstract = {

The influence of the surface area by the impact of high temperatures after wire electric discharge machining (WEDM) is a known fact. However, the affected parameters also include a change in microhardness. In order to further investigate this statement, 5 different ferrous and non-ferrous materials were selected, from which three samples were always made with different settings of machine parameters (gap voltage, pulse on and off time, wire feed and discharge current). This examined not only the effect of the machining itself on the material but also whether the change in the microhardness of the material is affected by the setting of the machine parameters. In order to measure the microhardness of the subsurface layer, a metallographic preparation was made from each sample, which enabled accurate measurements always in the same area. Subsequent evaluation revealed that the microhardness may not be affected at all and everything depends only on the type of material being machined. The changes in microhardness affected by setting machine parameters are negligible.

}, keywords = {AIF, MF}, doi = {10.1177/09544089221078383}, url = {https://doi.org/10.1177/09544089221078383}, author = {Katerina Mouralova and Stefan Michna and Radim Zahradnicek and Josef Bednar and Tomas Plichta and Jiri Fries} } @article {3630, title = {Surface topography affects the nanoindentation data}, journal = {Thin Solid Films}, volume = {745}, year = {2022}, pages = {139105}, abstract = {

The near-surface mechanical properties of thin films as well as bulk materials are amongst the key parameters important for their application, and instrumented nanoindentation is a standard technique for determining these mechanical properties. However, it is known that the surface topography of the characterized materials may affect the nanoindentation data when a sharp indenter for small penetration depths (displacements) is used. A thin film of hydrogenated amorphous silicon carbide with a thickness of 1.0\ μm was deposited on a silicon wafer by plasma-enhanced chemical vapour deposition. The cyclic nanoindentation was used to construct a depth profile of mechanical properties for the flat surface (0.5\ nm roughness) of the thin film, which made it possible to determine its modulus of elasticity of 83\ GPa and hardness of 8.6\ GPa unaffected by the silicon substrate. Grains with a spherical cap geometry with a typical radius of 0.5\ {\textmu}m and a\ height of 60\ nm are distributed along the flat surface of the film. The grains have the same mechanical properties as the deposited film. Depth profiles of mechanical properties were determined for different types of contact between the Berkovich indenter with a radius of 50\ nm and the selected grain (grain top, grain foot, two or three grains); i.e. for these measurements the following applied - the radius of the tip curvature was less than grain radii (RBerkovich \< Rgrain). Residual imprints after nanoindentation measurements were carefully observed by atomic force microscopy and scanning electron microscopy. The near-surface mechanical properties were significantly affected by the surface topography, and the determined modulus of elasticity and hardness were crucially under- or overestimated in the range of 50\% to 100\% compared to the real values. The nature of these deviations was discussed. The solution is to use cyclic nanoindentation performed on the flat surfaces or on the top of grains, followed by extrapolation of the depth profiles to the zero-contact depth (film surface).

}, keywords = {AIF, MF}, issn = {0040-6090}, doi = {https://doi.org/10.1016/j.tsf.2022.139105}, url = {https://www.sciencedirect.com/science/article/pii/S0040609022000268}, author = {Tomas Plichta and Radim Zahradnicek and Vladimir Cech} }