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Compression of ecaped titanium micro-pillars for two principal orientations
Vokoun, David ; Maňák, Jan ; Tesař, Karel ; Habr, Stanislav
The thermomechanical processing by equal-channel angular pressing (ECAP) is used for certain metals and alloys in order to make their structure fine and to increase material strength. In the previous study done at our institute, grade 2 titanium was successfully processed using four consecutive route A passes via a 90° ECAP die with high backpressure at room temperature. Orientation dependence of compressive and tensile loading of ECAPed titanium samples was demonstrated at macro-scale. However, scarce attention has been paid so far to the mechanical behavior of ECAPed titanium samples at micro-scale. In the present study, compression experiments on titanium micro-pillars, fabricated using focused ion beam, are carried out for two main directions in respect to preceding ECAP pressing (insert and extrusion directions). The purpose of this study is to discuss the orientation dependence of mechanical response during compression of the as-ECAPed titanium micro-pillars.
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Fabrication, heat treatment and characterization of thin layer NiTi alloys
Svatuška, Michal ; Vokoun, David (advisor) ; Dlouhý, Antonín (referee) ; Novák, Pavel (referee)
NiTi alloys with nearly equiatomic chemical composition are the most studied and the most practically utilized materials from the group of the shape memory alloys (SMA). The NiTi alloy has a thermoelastic martensitic transfor- mation (MT), which its two most important properties are based on: the shape memory and the superelasticity. Thin films of NiTi alloys with thicknesses from hundreds of nm to units of µm have a wide use mainly in microelectromechanical systems (MEMS). The doctoral thesis deals with a fabrication of thin NiTi films using a deposition on silicon substrates with two techniques - the magnetron sputtering and the pulsed-laser deposition (PLD), an investigation of their mi- crostructure using x-ray diffraction, a heat treatment of amorphous NiTi films and with a verification of MT using resistometry. Furthermore, thermomechan- ical properties of a system NiTi-polyimide (NiTi-PI), namely a dependence of a curvature radius of a NiTi-PI bilayer on temperature, are studied. 1
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The Common Mechanical Factor of Shape Memory
Kafka, Vratislav ; Vokoun, David
Shape memory is observed in elastic bodies, springs, bi-metals, in many mechanical actuators, such as thermostats and others, in many biological materials, and in special "shape memory alloys". It is shown that all systems or materials have one common factor: at least one elastic or thermoelastic continuous substructure, in the case of "shape memoryalloys" this substructure is on the atomic scale.
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