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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...
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Analysis of cutting insert performance when machining of a titanium alloy
Fasora, Jan ; Sliwková, Petra (referee) ; Píška, Miroslav (advisor)
This bachelor thesis is divided into two parts. The theoretical part deals with machinability of titanium alloys, cutting performance and wear of indexable cutting inserts (ICO) when turning. The experimental and very basic part of the work is presented with experiments in several series, where the cutting ability and wear of the selected inserts are assessed. Apart of some other measurements the results are justified with 3D measuring device and a scanning electron microscope analyses.
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Metastable alloy Ti-15Mo prepared by powder metallurgy
Veverková, Anna ; Bartha, Kristina (advisor) ; Chráska, Tomáš (referee)
This diploma thesis focused on manufacturing and characterization of Ti-15Mo metastable beta-Ti alloy prepared by cryogenic milling and spark plasma sintering. Initial powder was prepared by gas atomization and consequently deformed by cryogenic milling (milled powder). Both initial and milled powders were compacted by spark plasma sintering (SPS) at temperatures from 750 řC to 850 řC. Dependence of microstructure and mechanical properties on the parameters of preparation was studied. During cryo-milling, powder particles significantly changed shape from ball-shaped to disc-shaped. Particles were not refined by milling, but severely plastically deformed. SEM observations showed that all prepared samples contain duplex alpha + beta structure. Volume fraction of alpha phase is significantly higher in the sintered milled powder due to increased beta- transus temperature caused by contamination by oxygen and also due to easier alpha phase precipitation caused by refined microstructure. Maximum microhardness of 350 HV was achieved for both types of sintered powders. High microhardness of sintered initial powder can be attributed to formation of omega phase during cooling, while sintered milled powder is strengthened by refined microstructure and small alpha phase precipitates. Cryogenic milling prior to...
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Microstructure and mechanical properties of Ti15Mo alloy prepared by ECAP
Terynková, Anna ; Stráský, Josef (advisor) ; Šíma, Vladimír (referee)
In the bachelor thesis, mechanical properties and microstructure of Ti-15Mo alloy prepared by equal channel angular pressing were studied along with their dependence on the number of passes. Microhardness was studied by Vickers method, microstructure was studied by scanning electron microscopy and by electron back-scattered diffraction (EBSD). Finally, the elasticity modulus was measured by resonant ultra-sound spectroscopy. Mircohardness significantly increased after the first ECAP pass. After the second and the third pass it was almost constant and it again distinctly rose after the fourth pass. Grains with the size of hundreds of micrometres were observed in all samples. The volume fraction of twinned material increased with the number of passes. Deformation bands were also observed, namely in samples after two and three passes. Elastic modulus significantly increased with increasing deformation by ECAP and the evolution of elastic modulus is qualitatively similar to the evolution of microhardness. Considering that the material was processed by ECAP at 250řC, the omega phase may have formed during the processing. The increase of microhardness and elastic modulus can be explained by the increasing volume fraction of the omega phase.
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Oxygen-strengthened biomedical beta titanium alloys
Preisler, Dalibor ; Stráský, Josef (advisor) ; Kužel, Radomír (referee)
Oxygen strengthened biomedical beta titanium alloys Beta titanium alloy Ti-35Nb-6Ta-7Zr-0.7O (wt. %) exhibits a low Young's modulus and high strength thanks to interstitial strengthening effect of oxygen. These mechanical properties are promising for implant production. In this thesis, the aforementioned alloy is thoroughly studied in conditions prepared by various thermomechanical treatments, namely: material after casting, hot compression testing, die-forging, hot rolling and finally, cold-swaged and annealed condition. Mechanical properties and microstructure of prepared conditions are studied with special interest of enhancing the fatigue performance that is poor after casting due to porosity and large grains. The hot rolling was shown to improve the fatigue performance significantly, mainly through grain refinement. It is shown that by combining the effects of cold-swaging and recrystallization annealing, extensive refinement of grain structure can be achieved. Industrial aspects of implant production by the studied methods were discussed. In the second part of the thesis, the possibility of lowering the Young's modulus by reducing the beta phase stability (by reducing of Nb and Ta content), while retaining high strength caused by high interstitial oxyen content is explored. Several alloys were...
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Machining of titanium alloys
Horáček, David ; Mouralová, Kateřina (referee) ; Píška, Miroslav (advisor)
This thesis is focused on titanium and its alloys, in terms of properties and uses. The problems of machinability, cutting tools, quality of machined surfaces and machining method are discussed. Threads in titanium alloys Ti-6AI-4V were cut in the practical part. The intention was to compare torque moments and surface quality of threads by using two cutting oils.
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Mathematical analysis and computer simulations of deformation of nonlinear elastic bodies in the small strain range
Kulvait, Vojtěch ; Málek, Josef (advisor)
Title: Mathematical analysis and computer simulations of deformation of nonlinear elastic bodies in the small strain range. Author: Vojtěch Kulvait Department: Mathematical Institute of Charles University Supervisor: prof. RNDr. Josef Málek, CSc., Dsc. Abstract: Implicit constitutive theory provides a suitable theoretical framework for elastic materials that exhibit a nonlinear relationship between strain and stress in the range of small strains. We study a class of power-law models, where the nonlinear dependence of strain on the deviatoric part of the stress tensor and its trace are mutually separated. We show that these power-law models are capable to describe the response of a wide variety of beta phase titanium alloys in the small strain range and that these models fit available experimental data exceedingly well. We also develop a mathematical theory regarding the well-posedness of boundary value problems for the considered class of power-law solids. In particular, we prove the existence of weak solutions for power law exponents in the range (1, ∞). Finally, we perform computer simulations for these problems in the anti-plane stress setting focusing on the V-notch type geometry. We study the dependence of solutions on the values of power law exponents and on the V-notch opening angle. We achieve...
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Mathematical analysis and computer simulations of deformation of nonlinear elastic bodies in the small strain range.
Kulvait, Vojtěch ; Málek, Josef (advisor) ; Kovtunenko, Victor A. (referee) ; Kružík, Martin (referee)
Title: Mathematical analysis and computer simulations of deformation of nonlinear elastic bodies in the small strain range. Author: Vojtěch Kulvait Department: Mathematical Institute of Charles University Supervisor: prof. RNDr. Josef Málek, CSc., Dsc. Abstract: Implicit constitutive theory provides a suitable theoretical framework for elastic materials that exhibit a nonlinear relationship between strain and stress in the range of small strains. We study a class of power-law models, where the nonlinear dependence of strain on the deviatoric part of the stress tensor and its trace are mutually separated. We show that these power-law models are capable to describe the response of a wide variety of beta phase titanium alloys in the small strain range and that these models fit available experimental data exceedingly well. We also develop a mathematical theory regarding the well-posedness of boundary value problems for the considered class of power-law solids. In particular, we prove the existence of weak solutions for power law exponents in the range (1, ∞). Finally, we perform computer simulations for these problems in the anti-plane stress setting focusing on the V-notch type geometry. We study the dependence of solutions on the values of power law exponents and on the V-notch opening angle. We achieve...
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Microstructure and mechanical properties of ultra-fine grained titanium alloys
Václavová, Kristína ; Stráský, Josef (advisor)
Title: Microstructure and mechanical properties of ultra-fine grained titanium alloys Author: Bc. Kristína Václavová Department / Institute: Department of Physics of Materials Supervisor of the master thesis: PhDr. RNDr. Josef Stráský, Ph.D. Abstract: Metastable β-Ti alloys Ti-15Mo and Ti-6.8Mo-4.5Fe-1.5Al (TIMETAL LCB) were subjected to severe plastic deformation by high pressure torsion. Microhardness of Ti-15Mo and TIMETAL LCB alloys increases with increasing inserted deformation, i.e. with increasing number of HPT rotations and also with increasing distance from the centre of the sample. The highest microhardness after HPT exceeds significantly the microhardness of two-phase α + β heat-treated material. Increasingly deformed microstructure was also demonstrated by scanning electron microscopy and by electron back-scattered diffraction (EBSD). Significant twinning was observed in both studied alloys. Mechanism of multiple twinning contributes notably to the fragmentation of grains and thus to the refinement of the microstructure. Defect structure in Ti-15Mo alloy was studied by positron annihilation spectroscopy. It was proved that dislocations are the only detectable defects in the material by positron annihilation spectroscopy and that dislocation density increases with the number of HPT revolution and...
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Structure and properties of welded joint TiAl6V4 / 6061 made by electron beam technology
Král, Michael ; Jan, Vít (referee) ; Foret, Rudolf (advisor)
Titanium and aluminium alloys are among the most used construct materials due to their physical and mechanical properties except steels. The joining of these alloys can improve properties of whole construction but it is still difficult task. Especially welding of titanium and aluminium alloys is difficult cause formation of undesirable intermetalic phases in the weld. This thesis focuses on influences of electron beam welding parameters especially focusing and deflection of beam and preheating of base material to quality of heterogeneous join of titanium alloy Ti6Al4V and aluminium alloy EN AW-6061 – T651. There is described preparation of welded joins and brazed joins in the thesis, which are evaluated by light microscopy, scanning electron microscopy and EDS analysis of chemical composition. There was evaluated presence and chemical composition of formated intermetalic phases in the welded joins and quality and defects in the brazed joins.
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