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Investigation of Functional Properties of Thin NiTi Filaments for Applications in Smart Structures and Hybrid Textiles
Pilch, Jan ; Dlouhý, Antonín (referee) ; Heczko,, Oleg (referee) ; Pokluda, Jaroslav (advisor)
PhD thesis focuses the field of textile application of modern functional materials, namely metallic shape memory alloys with unique thermomechanical properties deriving from martensitic transformation in solid state. Particularly, it deals with the development of a nonconventional thermomechanical treatment of thin NiTi filaments via Joule heating by electric current and related basic research involving thermomechanical testing and modeling of functional properties of the filaments, investigation of martensitic transformations and deformation processes in NiTi and investigation of the fast recovery and recrystallization processes in metals heated by short pulses of controlled electric power. The method was developed and called FTMT-EC. In contrast to conventional heat treatment of metallic filaments in environmental furnaces, this method allows for precise control of the raise of the filament temperature and filament stress during the fast heating (rate ~50 000 °C/s). As a consequence, it is possible to precisely control the progress of the fast recovery and recrystallization processes in heat treated filaments. In this way it is possible to prepare filaments with desired nanostructured microstructure and related functional properties. A prototype equipment for application of the method for heat treatment of continuous SMA filaments during respooling in textile processing was designed and built. Comparing to the conventional heat treatment of SMA filaments in tubular environmental furnaces, this approach is faster, saves energy and allows for preparation of filaments with special functional properties. International patent application was filed on the method. It is currently utilized in the research and development of smart textiles for medical applications.
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Self Adjustable Discharge Valve
Kuruc, Marek ; Maňas, Pavel (referee) ; Technologies,, Jan Jedlička, Emerson Climate (advisor)
This dissertation deals with design of self adjustable discharge valve used in Emerson reciprocating compressors. This work contains research of current state of knowledge, technical analysis of the valve and calculations of basis parameters. Constructional proposal is then presented. Part of the dissertation is manufacturing of prototype and its test. Finally, conclusions for further development are made.
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DSC evaluation of homogenity of Ni-Ti alloys ingots
Kuběnová, Monika ; Zemčík, Ladislav (referee) ; Dlouhý, Antonín (advisor)
Alloy NiTi with nearequiatomic composition of nickel and titan belongs to a group of metal materials with a shape memory effect (Shape memory alloys). NiTi alloys are a guite attractive materials not only as practical shape memory alloys with hight strenght and ductility but also as those exhibiting unique physical properties. The production of these matrerials is complying with chemical composition. Final charakteristics of alloy are influenced by these bounderies and also by mechanical-heat treatment. This work deal with DSC evaluation of homogenity of ingot structure of NiTi alloy containing 50,8 at.% Ni. The alloy was melted in Y2O3 cricible. In the end the results of DSC method are compared to the microstructure of alloy obtained by SEM and TEM methods.
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Memory Materials
Josiek, Robert ; Šesták, Petr (referee) ; Molliková, Eva (advisor)
Currently, shape memory materials are very popular, especially intermetallic compounds NiTi. This alloy is very stable and corrosion resistant, but its production is very difficult because of the high reactivity of titanium. Shape memory effect in this material is dependent on many parameters, such as chemical composition or heat treatment. This bachelor’s thesis explains one-way and two-way memory effect. Another one phenomenon associated with the martensitic transformation, superelasticity, is mentioned, too. The applications of these materials are described in separate chapter of this bachelor’s thesis.
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The pseudoelasticity and the shape memory effect in CoNiAl alloys
Kopeček, Jaromír ; Jarošová, Markéta ; Jurek, Karel ; Heczko, Oleg
The cobalt alloys (close to the CoNiAl stoichiometry) are the less known shape memory alloys. Such behavior is consequence of the martensitic transformation. The pseudoelasticity is caused by the stress-induced martensitic transformation above the equilibrium martensite start temperature from high temperature cubic phase (austenite) to lower symmetry phase(martensite). In CoNiAl the pseudoelastic behavior can be obtained by the high temperature annealing. In presented work the effect of the annealing temperature on both pseudoelastic behavior and microstructure was investigated.
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Heat treatment conditions and their influence on precipitation of Ni4Ti3 phase in Ni-rich NiTi shape memory alloys
Dlouhý, Antonín ; Bojda, Ondřej ; Fiala, J.
The present work deals with a quantitative analysis of Ni4Ti3 precipitates after solution annealing (850°C/30min) and ageing (450°C/1hod) in air or inert argon atmosphere. The attention is given not only to the size of precipitates in the vicinity of grain boundaries and in the grain volume and to the corresponding Ni4Ti3 volume fractions, but also to subsequent martensitic transformations B2-(R)-B19’. Quantitative analysis of transmission electron microscopy micrographs is based on the automatic image processing by means of the Adaptive Contrast Control programme. Martensitic transformations were documented using differential scanning calorimetry. Results indicate a homogeneous precipitation of Ni4Ti3 with the heterogeneous distribution of crystallographic particle variants. A possible influence of the heat treatment environment on Ni4Ti3 precipitation and martensitic transformations is discussed in this work.
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Quantitative image analysis of precipitates in Ni-rich NiTi shape memory alloys
Bojda, Ondřej ; Dlouhý, Antonín ; Fiala, J.
A microstructure of a Ti-50.7at%Ni shape memory alloy resulting from solution annealing and subsequent aging at 500°C/3.6ks/8MPa is quantitatively analysed. The TEM study is assisted by Adaptive Contrast Control (ACC) routines embedded in a recent image processing system. The assessment focuses on the number density, size and distribution of crystallographic variants of Ni4Ti3 precipitates. It was found that the distribution of crystallographic particle variants in the microstructure is inhomogeneous. The influence of the heterogeneous Ni4Ti3 precipitation on the characteristics of the martensitic transformation B2®B19´ is briefly discussed.
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