Key Engineering Materials Vol. 662

Abstract: The goal of the paper is to model and evaluate the total load capacity of the reinforced concrete beams. A non-linear analysis and finite element method were used for that purpose. The model consists of 3D finite elements. The constitutive model of concrete for the non-linear analysis is based on a fracture-plastic theory. The input parameters are the data obtained in previous tests which included both standard tests and additional tests of the testing bodies. There is no shear reinforcement in the beams. The non-linear calculations were carried out for several variants. The study takes into considerations the influence of concrete properties as well as the size of the finite elements.

Abstract: NiTi shape memory alloy thin film sputter-deposited on a large scale silicon wafer was characterized by means of instrumented (depth-sensing) indentation technique. Thickness of deposited thin film was measured by calotest device. Microstructure of thin film was observed using differential interference (Nomarski) contrast. It was shown that the local mechanical properties are different in areas containing different phases (austenite and martensite) according to different deposition conditions (kinetic energy of deposited atoms when impacting the substrate surface).

Abstract: In this work we have studied local mechanical properties of CoCrFeSiB ribbons prepared by planar flow casting (PFC). Recently improved PFC technology enabled us to use two melts simultaneously and to prepare a bilayered Co₆₉Fe₂Cr₇Si₈B₁₄/Co₅₉Fe₁₂Cr₇Si₈B₁₄ ribbon with a good homogeneity of the layers and well defined interface. Single-layered ribbons of the two compositions above were prepared as well. The microstructure and the composition profiles were studied by means of analytical electron microscopy. Nanoindentation tests were carried out on the cross sections of the bilayered ribbon as well as of single-layered ribbons. The in-situ SPM imaging was used in order to achieve nanometer precision positioning of the indents and to get information about the surface topography before and after the tests.

Abstract: Amorphous silicon carbonitride (a-SiC_xN_y) thin films were deposited using reactive magnetron sputtering of SiC target in the mixture of Ar and N gasses. The films with nitrogen content from 0 - 40 at.% were sputtered at various N₂/Ar flow ratios in the range of 0 - 0.48. The as deposited films were additionally annealed in argon at 700 °C and vacuum at 900 °C. Analysis of mechanical properties was performed using the regular nanoindentation and short duration nanoindentation creep test (600 s).Hardness of the a-SiC_xN_y films increases with the decrease of nitrogen content from approx. 19 GPa (a-Si₃₀C₃₀N₄₀) to 22 GPa (a-SiC). Annealing of the films in inert atmosphere or vacuum leads to the increase of both the hardness and the elastic modulus. This increase is more pronounced for the SiC film than for the SiCN films. The nanoindentation creep test (600 s) showed that the rate of the steady-state creep growths with the increase of nitrogen content.

Abstract: Several series of W-C based coatings were deposited by HiPIMS and HiTUS deposition technologies with different deposition parameters (power, frequency and pulse length in HiPIMS and pressure, acetylene content and RF bias in HiTUS). To investigate their effect on the hardness and tribological properties. The hardness of HiTUS coatings was up to 36 GPa and CoFs of these coatings were around 0.5, whereas the HiPIMS coatings exhibited lower hardness (18 – 20 GPa) but also lower CoFs (0.18 - 0.2).

Abstract: The FIB/SEM investigations of the microstructure changes in the hard brittle W-C based coating deposited on softer steel substrate after nanoindentation tests revealed that a set of approximately equidistant circular cracks forms in the coating in a sink-in zone around the indent and single cracks appear under the indenter tip. Finite element modeling (FEM) indicated development and concentration of the highest principal tensile stresses in the sink-in zone and in the zone below the indenter, which are considered to be the reason for the experimentally observed cracking. The distance from the indenter tip to the first circular crack combined with the calibration curve obtained from the FEM of the location of tensile stress maxima in sink-in zone can be used as a simple method for the determination of the strength of the studied coatings.

Abstract: The effects of residual stresses in thin W-C based coatings were investigated with the aim to find their influence on nanohardness and indentation modulus. Ten samples of W-C based coatings were deposited on microslide glass substrates using DC magnetron sputtering at the identical deposition parameters. Their thickness was in the range from 500 to 600 nm. The residual stresses in the coatings varied from 1.5 GPa up to 4.4 GPa. Increase of residual stress caused linear increase of H_IT from 16 to 19.5 GPa. This increase was only the result of the compressive stresses. E_IT of the studied coatings was not sensitive to residual stresses and corresponded to 185 GPa ± 15 GPa.

Abstract: The HVOF (high velocity oxygen fuel) thermal spraying technology is widely used for creation of coatings notable for their resistance against various kinds of loading. Depending on the sprayed material, the coatings suitable for high temperature applications can be sprayed as well. The coatings, based on CrC or Co/Ni alloys, offer the advantageous combination of high temperature oxidation resistance and the wear resistance. In the paper, the attention is paid to the evaluation of the influence of the high temperature on the coatings microstructure and mechanical properties, namely hardness. The stability of the hardness values in respect to the time of the high temperature exposure is presented and related to the phase composition changes.

Abstract: Coating properties determine its behavior in operation. The simulation of future operational conditions is therefore the best quality test. The evaluation during operation is usually not possible to perform, and the coatings are therefore frequently characterized by their physical or mechanical properties. This text deals with the high temperature corrosion of HVOF sprayed Stellite 6 coating and with changes of its local mechanical properties before and after the corrosion testing. High temperature corrosion is defined as a corrosion in the presence of molten salts. In this case, the mixture of salts in composition of 59% Na₂(SO)₄ with 34.5% KCl and 6.5% NaCl was used. Two exposure temperatures 525 °C and 575 °C were selected and the tests for both temperatures were performed in the time interval of 168h in the autoclave. The coating with salt mixture layer was analyzed using scanning electron microscopy and nanoindentation. The high temperature resistance of Stellite 6 coating was evaluated according to the changes in the coating surface and by the occurrence of individual phases formed on the coating surface during the test. Generally, it can be said that the Stellite 6 alloys deposited by HVOF technology show selective oxidation under the salt film. This fact was also proved in this study. Furthermore, the nanoindentation measurements of Stellite 6 coating were performed before and after the corrosion testing. These measurements were used to evaluate the change of local mechanical coating properties.

Abstract: The scratch test is a well-established instrumental method for assessment of the cohesive-adhesive parameters of thin films and coatings. Its evaluation is classically performed using the microscopic analysis of residual scratch and the indenter depth-change record. However, these analysis methods can be insufficient for detection of the very first film-to-substrate adhesion failures. To overcome this difficulty, an independent method of detection of acoustic emission signals can be employed. The detection system of acoustic emission, developed in our laboratory, utilizes a special holder and continuous recording during the whole scratch test. The piezoelectric sensor with 2 MHz sampling rate and sophisticated software allow a thorough post-process analysis of recorded acoustic emission signal. Failure events can be observed on microsecond scale and their frequency spectra can be evaluated.The demonstration of the acoustic emission probe detection capability is performed on the model layers. Comparison of the acoustic emission record to residual scratch image and indenter depth-change record shows a detection sensitivity of the method. Analysis of failure mode dynamics at the appropriate time scale is outlined.