|
|
Microstructure of non-equiblirium Al-Mn based solid solutions
Poková, Michaela
Heat exchangers in automotive industry are often manufactured from aluminum-based alloy AW 3003. In recent time, the aim to reduce the weight of the cars leads to thickening of the foils, which are used for manufacturing of the heat exchangers. In order to fulfill all requirements on mechanical properties of the exchanger, new materials and thermo-mechanical treatments have to be found. Modified alloy AW 3003 with addition of zirconium seems to be perspective. Zirconium forms metastable precipitates Al3Zr, which pin moving grain boundaries and shift recrystallization to higher temperatures. The most effective heat treatment, which leads to precipitation of these particles, seems to be a two-step annealing at temperatures 250 řC and 450 řC with slow heating rate. The precipitates formed were of diameter 10 nm.
|
|
|
Investigation of Functional Properties of Thin NiTi Filaments for Applications in Smart Structures and Hybrid Textiles
Pilch, Jan ; 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.
|
|
|
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.
|
|
|
Optimizing of Polymer Surface Treatment for Microscopic Examination
Horská, Pavlína ; Poláček, Petr (referee) ; Bálková, Radka (advisor)
Supramolecular structure of eight commercial types of iPP, its blends with poly(L-lactide) (PP-PLLA) and copolymers with ethylene-propylene rubber (PP-EPR) together with four types of polyethylene (LDPE, HDPE) was uncovered and observed in this work. The spherulitic structure of iPP and PE homopolymers and PP copolymers was uncovered by etching of six different solutions of mineral acids with KMnO4 and by dissolution in four selected solvents. The latter was found to be ineffective. The structure of PP-PLLA blends was uncovered only after recrystallization (the change of structure by annealing and cooling rate). The uncovered crystalline structure was observed directly by confocal laser scanning microscope (CLSM) and SEM. Crystallinity together with a size distribution of crystallites was determined by DSC. It was proved that spherulitic supramolecular structure was easy to uncover by chemical etching only for molded samples and for fracture surfaces of injected samples. The efficiency of etchants varied but, generally, the samples with high degree of crystallinity were etched earlier. The etchants containing nitric acid and high content of sulphuric acid uncovered fine details of shperulites with respect to mixtures containing orthophosporic acid. It was also observed that not only the etchant (especially with nitric acid) itself but also its vapors were effective. The structure was revealed later but the appearance was plastic (3D) and the structure was very fine. The supramolecular structure of PP-PLLA blends differed with amount of each component. The ethylene-rubber phase came forth with increasing time of etching while PP spherulites disappeared in PP-EPR samples. CLSM was shown to be very good tool for observing supramolecular structure of studied samples with respect to SEM, which was proved to be entirely unsuitable for polyolefines. DSC is recommended to be performe before uncovering supramolecular structure for basic information about proportion of amorphous/crystalline phase and size of crystallites.
|
|
|
Heat processing principle of operation thermal resistance annealing.
Špičková, Petra ; Humár, Anton (referee) ; Kalivoda, Milan (advisor)
The project assigned for the bachelors study program B 2307 analyses the theory of heat processing in general and furthermore resistance annealing with the focus on the technology developed by the company Heatmasters. Examples of processing methods used at other technology providers are presented, inclu-ding documentation and datasheets. Resistance annealing is based on the heat transfer from a resistive wire, which heats up by electrical current. The thermal energy is then transferred to the target material through heat radiation or con-ductance. The resistance heat processing is used both for welding and for an-nealing. Nowadays is the documentation and recording of the heat processing of significant importance. Possibilities exist that allow recording of temperature during the entire cycle of the heat processing and subsequently providing the result evidence in a form of a certificate.
|
guest ::
