|
|
Influence of thermal processing to microstructure of various steels
Kocman, Lukáš ; Havlík, Petr (referee) ; Štěpánek, Roman (advisor)
This bachelor thesis deals with the heat treatment of steel, especially measuring the influence of individual heat treatment technologies on changes in the microstructure of steels. The theoretical part of the work presents alloys of iron and carbon, furthermore describes their phase transformations in the solid state, particularly the transformation diagrams of steels. In another part of theoretical part, the basic heat treatment technologies and their influence on the mechanical properties and microstructure of steels are described. The experimental part deals with the preparation of metallographic samples and presents results of examining the microstructure and measuring the hardness of individual samples. At the end of the work the synthesis of the theoretical part and results of the experimental part is used for the partial and overall evaluation of the influence of heat treatment on the microstructure of steels.
|
|
|
Ab initio calculation of doping in Ni2MnGa alloy
Janovec, Jozef ; Černý, Miroslav (referee) ; Zelený, Martin (advisor)
Cieľom tejto práce je teoretické štúdium systému Ni-Mn-Ga, vykazujúceho efekt magnetickej tvarovej pamäti. Pri výpočtoch bola použitá metóda Exaktných Mufiin-Tin Orbitálov v kombinácii s aproximáciou koherentného potenciálu vrámci Korringa-Kohn-Rostoker formalizmu. Totálna energia bola spočítaná pomocou metódy úplnej nábojovej hustoty. Skúmaný bol vplyv dopovania zinkom alebo kadmiom na totálne energie pozdĺž tetragonálnej deformačnej dráhy a následne na teplotu martenzitickej premeny TM a Curieho teplotu TC. Taktiež boli skúmané nestechiometrické zliatiny prebytkom Mn na úkor Ga. Výsledky predikujú nárast TM po všetkých pozorovaných substitúciách v podmriežke Ga a pokles TM po substitúciách v podmriežke Mn. Curieho teplotu znižujú všetky študované substitúcie s výnimkou zmeny magnetického usporiadania v martensite nestechiometrickej zliatiny.
|
|
|
Phase transformation in magnesium MgZnAl-based alloys
Kodetová, Veronika ; Vlach, Martin (advisor) ; Mathis, Kristián (referee)
In the present work, there was analyzed thermal evolution of the phase transformation in the MgZnAl and MgZnAlCa alloys with different concentration of the Zn and Ca. The grains were occupied by the phase with quasicrystaline icosaedral structure in the as-cast alloys and after isochronal annealing up to 240 řC. The thermal measurements revealed two exothermic effects in the MgZnAl alloy and three exothermic effects in the MgZnAlCa alloy during linear heat treatment in the temperature range of 100 - 250 řC. In agreement to the thermal response, two and three stages of electrical resistivity decrease were observed in the same temperature range. The lower thermal changes, absolute resistivity changes and microhardness were observed in the alloy with Ca-addition and lower concentration of Zn.
|
|
|
Phase transformations in modern titanium alloys
Šmilauerová, Jana ; Janeček, Miloš (advisor) ; Kalvoda, Ladislav (referee) ; Strunz, Pavel (referee)
This study deals with phase transformations in metastable β titanium alloys, focusing on the investigation of evolution of nanoparticles of thermodynamically metastable ω phase. For the purpose of this research, single crystals of two metastable β titanium alloys - LCB (Ti-6.8Mo-4.5Fe-1.5Al) and Ti-15Mo (in wt. %) - were grown in an optical floating zone furnace. It was established by differential scanning calorimetry that the phase transformations occurring in the material did not change significantly as a result of the single crystal growth process. Using single crystal X-ray diffraction, the shape and the size of ω particles were determined in a series of aged samples. The lattice parameters of ω particles and the β matrix, as well as the misfit between the two structures were calculated. The β phase was found to be locally deformed in compression around ω particles. Small-angle X-ray scattering (SAXS) experiments revealed a spatial ordering of ω particles in the β matrix in a disordered cubic array with the basis vectors along 100 β directions. The SAXS data also allowed the evaluation of the mean ω particle sizes and distances and confirmed that the ω particle growth obeys the t1/3 law following from the Lifshitz-Slyozov-Wagner theory. In situ SAXS performed during isothermal ageing at selected...
|
|
|
Effect of molybdenum content on phase transformations in binary Ti-Mo alloys
Valešová, Veronika ; Stráský, Josef (advisor) ; Janeček, Miloš (referee)
Title: Effect of molybdenum content on phase transformations in binary Ti-Mo alloys Author: Veronika Valešová Department: Department of Physics of Materials Supervisor: PhDr. RNDr. Josef Stráský, Ph.D., Department of Physics of Mate- rials Abstract: β titanium alloys are highly appreciated group of structural materials. They provide an extraordinary combination of strength, toughness and fatigue resistance. These alloys are used predominantly in aerospace sector, chemical industry and medical engineering. We have studied three binary titanium alloys: Ti-12Mo, Ti-15Mo and Ti-18Mo (wt %). Apart from low temperature hexagonal close packed α phase and high temperature base centered cubic β phase, a metastable ω phase can be also found in this type of alloys. The ω phase is created in a diffusionless process by shifting the planes in the β phase and affects both mechanical properties and the α phase precipitation. We have examined the phase transformations occurring in the studied alloys using both in-situ and ex-situ methods. Resistometry, dilatometry and differential scanning calorimetry were used as the indirect in-situ methods. For the ex-situ methods, scanning electron microscopy and microhardness measurement were used. Complex characterization of β metastable titanium alloys showed the formation of the...
|
|
|
Phase transformations in ultra-fine grained titanium alloys
Bartha, Kristina ; Stráský, Josef (advisor) ; Kalvoda, Ladislav (referee) ; Vojtěch, Dalibor (referee)
Title: Phase transformations in ultra-fine grained titanium alloys Author: Kristína Bartha Department: Department of Physics of Materials Supervisor of the doctoral thesis: PhDr. RNDr. Josef Stráský, Ph.D., Department of Physics of Materials Abstract: Ti15Mo alloy in a metastable β solution treated condition was processed by high pressure torsion (HPT) and equal channel angular pressing (ECAP). The microstructure after HPT is severely deformed and ultra-fine grained, while ECAP deformation results in rather coarse-grained structure with shear bands containing high density of lattice defects. Two types of thermal treatments - isothermal annealing and linear heating - were carried out for the solution treated condition and both deformed materials. Wide spectrum of experimental techniques was employed to elucidate the differences in phase transformations, especially in α phase precipitation, occurring in deformed and non-deformed material upon thermal treatment. It was shown that the α phase precipitation is accelerated in the deformed materials due to a high density of lattice defects, which provide a dense net of preferred sites for nucleation and also fast diffusion paths necessary for accelerated growth. The enhanced precipitation of the α phase in deformed materials also affects the stability of the ω...
|
|
|
Influence of thermal processing to microstructure of various steels
Kocman, Lukáš ; Havlík, Petr (referee) ; Štěpánek, Roman (advisor)
This bachelor thesis deals with the heat treatment of steel, especially measuring the influence of individual heat treatment technologies on changes in the microstructure of steels. The theoretical part of the work presents alloys of iron and carbon, furthermore describes their phase transformations in the solid state, particularly the transformation diagrams of steels. In another part of theoretical part, the basic heat treatment technologies and their influence on the mechanical properties and microstructure of steels are described. The experimental part deals with the preparation of metallographic samples and presents results of examining the microstructure and measuring the hardness of individual samples. At the end of the work the synthesis of the theoretical part and results of the experimental part is used for the partial and overall evaluation of the influence of heat treatment on the microstructure of steels.
|
|
|
Study of Phase Transformations in Ti Alloys
Zháňal, Pavel ; Harcuba, Petr (advisor)
In this work phase transformations in metastable β Ti-15Mo alloy were stud- ied using electrical resistivity measurements. The alloy was subjected to a solu- tion treatment at a temperature higher than β-transus and quenched in water. In this condition, the microstructure of Ti-15Mo alloy consists of a metastable β-matrix and ω phase particles. During in-situ electrical resistivity measurement in a specially designed furnace, significant temperature points which indicate phase transformations in the material were detected. The dependence of elec- trical resistivity on the temperature changes during heating between increasing and decreasing according to the ongoing phase transformation. The changes were observed at temperatures 225, 356 and 560 ◦ C. A further study of these phase transformations using electrical resistivity measurements was performed on var- ious heat treated specimens. In order to control the microstructure evolution in the material, scanning and transmission electron microscopy was used. Mecha- nical properties were studied using Vickers microhardness testing. The obtained results serve to identify the type and sequence of phase transformations which take place in the Ti-15Mo alloy.
|
|
|
Phase transformation in magnesium MgZnAl-based alloys
Kodetová, Veronika ; Vlach, Martin (advisor)
In the present work, there was analyzed thermal evolution of the phase transformation in the MgZnAl and MgZnAlCa alloys with different concentration of the Zn and Ca. The grains were occupied by the phase with quasicrystaline icosaedral structure in the as-cast alloys and after isochronal annealing up to 240 řC. The thermal measurements revealed two exothermic effects in the MgZnAl alloy and three exothermic effects in the MgZnAlCa alloy during linear heat treatment in the temperature range of 100 - 250 řC. In agreement to the thermal response, two and three stages of electrical resistivity decrease were observed in the same temperature range. The lower thermal changes, absolute resistivity changes and microhardness were observed in the alloy with Ca-addition and lower concentration of Zn.
|
|
|
Phase transformations and microstructure changes in TIMET LCB alloy
Šmilauerová, Jana
In the present work, phase transformations in TIMETAL LCB titanium alloy and their influence on mechanical properties were studied. Different initial con- ditions were prepared by solution treating above β-transus immediately followed by heat treatment in α/β temperature regime. These resulted in different grain boundary α thicknesses and contiguities at a fixed α volume fraction. The sub- sequent ageing response of this material was studied by low temperature ageing at 400 ◦ C, 450 ◦ C and 500 ◦ C. Phase transformations were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and resistivity measurements. Mechanical properties were investigated using microhardness measurements and tensile tests. It has been proved that metastable ω phase is formed during annealing at 400 ◦ C and 450 ◦ C. ω particles further transform to very fine precipitates of α phase when exposed to annealing for longer time periods. These fine precipitates significantly con- tribute to increase of microhardness and achieving high value of yield stress. Keywords: Metastable beta Ti alloys, phase transformations, microstructure changes, ω phase
|
guest ::
