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Nanocompression of oriented pillars from Al thin film
Kuběna, Ivo ; Kruml, Tomáš
In this paper, a new method of measurement of mechanical properties of thin films is presented. This method combines specimen preparation by focused ion beam (FIB) and compression test using nanoindentation device. Compression specimens were prepared from thin film, Al-1.5%Cu, which is commonly used in integrated circuit. Cylindrical specimens were prepared by FIB milling. The height of specimens (pillars) was about 2 mircrometers (equal to the film thickness) and their diameter was about 1.3 micrometers. The pillars are single crystalline, therefore the results depend on crystallographic orientation of pillar, which was specified by EBSD (electron backscatter diffraction). Stress-strain curves of the thin film were obtained in two representations.
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Kinetics of fatigue crack growth in Eurofer 97 steel
Kruml, Tomáš ; Hutař, Pavel ; Náhlík, Luboš ; Seitl, Stanislav ; Polák, Jaroslav
The fatigue crack growth rate in the Eurofer 97 steel was measured by two different methodologies. Small crack growth data were obtained using cylindrical specimens with a shallow notch. No artificial crack starters were used. The growth of semicircular cracks of length between 10 – 2000 m were measured in symmetrical tension-compression cycling with constant strain amplitude (R = -1). Long crack data were measured using standard CT specimen and ASTM methodology in stress control with R = 0.1. The growth of fatigue cracks with length in the range of 10 – 30 mm was determined. It is shown that the crack growth rate of both types of cracks are in a very good agreement if J-integral rep-resentation is used and reasonable assumptions of the crack closure effects are taken into account.
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Determination of mechanical properties of thin films by nanocompresion
Kuběna, Ivo ; Hutař, Pavel ; Náhlík, Luboš ; Kruml, Tomáš
Measurements of mechanical properties of objects with micrometric (or even smaller) dimensions is still not a common task. In this paper, the possibility of evaluation basic mechanical properties of a thin film by nanocompression is demonstrated. Cylindrical specimens with the axis normal to the film plane, attached by the bottom to the substrate, are prepared by the focused ion beam technique. Such pillars are deformed by a nanoindenter outfitted by a flat diamond punch. An equivalent of compression curve is obtained. It is possible to measure directly parameters as the yield stress, stress at a chosen strain level or work hardening rate. Finite elements modelling is necessary for the Young modulus evaluation. It is shown that the Young modulus can be evaluated quite precisely, even if the geometry of the pillar is not perfect.
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Optimization of preparation of microcompresion specimens from thin films films using focused ion beam
Kuběna, Ivo ; Kruml, Tomáš
In this paper new method of mechanical properties measurement of thin films is presented. This method combines preparation of specimen using focused ion beam and compressive test by nanoindenter. This paper is focused on description of the preparation microcompressive specimens. The thin film Al – 1.5 wt. % Cu was studied. The cylindrical pillars had diameter about 1.3 micrometers and their height was determined by thickness of layer (2 micrometers). The optimized reproducible process of the preparation of the microcompressive specimens was found. This process is optimized from geometry and preparation time point of view. Successfully executed compressive tests confirmed suitability specimens for microcompressive test
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Fatigue properties of Eurofer steel developed for fusion application
Kuběna, Ivo ; Kruml, Tomáš ; Hutař, Pavel ; Náhlík, Luboš ; Seitl, Stanislav ; Polák, Jaroslav
In this study fatigue properties of Eurofer 97 steel in room temperatures were measured. Fatigue parameters of the cyclic stress - strain curve and fatigue life curves (Coffin-Manson curve and derived Wöhler curve) were evaluated. Major attention was given to the measurement of kinetics of fatigue crack growth by two different methods. The initiation sites of fatigue cracks and short crack growth were observed and measured on cylindrical specimens with shallow notch. These cracks had a length from 20 micrometers to 1 mm. Kinetics of growth of long cracks with the length 15-30 mm was measured on CT specimens. It was found that results obtained by the both methods are in a good agreement if the J-integral is used. It was possible to determine the threshold values of J-integral and stress intensity factor and to calculate the Paris law parameters.
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Low cycle fatigue on Inconel 713L and Inconel 792-5A superalloys at 500 A 700 °C
Petrenec, Martin ; Obrtlík, Karel ; Polák, Jaroslav ; Hrbáček, K. ; Kruml, Tomáš
Cylindrical specimens of cast polycrystalline nickel base superalloys Inconel 713LC and 792-5A were cyclically strained under total strain control at500°C and at700°C.Structural characteristics and morphology of gama´ precipitates of both materials are documented. Dislocations structures were studied using transmission electron microscopy using technique of oriented foils in selected specimens cyclically strained up to failure. Cyclic hardening/softening curves, cyclic stress-strain curves, and fatigue life curves were obtained for both temperatures. Cyclic hardening/softening curves depend both on temperature and plastic strain amplitude. The cyclic stress-strain curves can be approximated by power law. Experimental points of fatigue life curves satisfy the Manson-Coffin and Basquin law. Stress-strain response and fatigue life characteristics are compared at both temperatures and discussed in relative to structural parameters and to dislocation structures of superalloys studied.
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Measurement of mechanical properties of thin films by nanocompression
Kuběna, Ivo ; Kruml, Tomáš ; Hutař, Pavel ; Boháč, Petr ; Stranyánek, Martin ; Čtvrtlík, Radim ; Pánek, P. ; Vystavěl, T.
Mechanical properties of thin films are not easy to be measured. This is particularly true in the case of plastic properties as the yield point, the work hardening rate or the ultimate stress. Nevertheless, such parameters are needed e.g. in the design of integrated circuits where the thermal stresses may lead to mechanical failure of the component. We applied two modern experimental facilities, the focused ion beam and the nanoindentation for exact measurement of plastic properties of a Al-1.5%Cu thin film prepared by PVD, used for electrical connection of integrated circuits. By FIB milling, cylindrical specimens were prepared. The height of the specimens was equal to the film thickness (2 m) and their diameter was about 1.3 m. These specimens were subjected to the compressive loading using the nanoindenter equipped by a flat punch. Stress-strain curves of the film were obtained rather precisely.
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Dislocation structure in the HAZ of the HSS steel after shot peening
Kruml, Tomáš ; Buirette, C. ; Degallaix, G. ; Polák, Jaroslav
The welds of a high strength C-Mn microalloyed steel with ferritic-bainitic microstructure were shot peened in order to improve the fatigue resistance. Since the weakest point was the heat affected zone (HAZ), the dislocation structure in two depth off the zone was investigated before and after shot peening. No specific dislocation arrangement was found neither in the initial state nor after shot peening and the arrangement can be characterised as random. The dislocation density was elevated in the initial state due to bainitic transformation. The shot peening resulted in appreciable increase of the dislocation density with a very strong gradient. The results were discussed in terms of the effect of surface hard layer induced by shot peening on the fatigue life of the weld and on the initiation and growth of fatigue crack in HAZ.
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