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Structure parameters of martensite in Ti alloys modified by presence of oxygen atoms
Šalata, Kristián ; Preisler, Dalibor (advisor) ; Lukáč, František (referee)
Structure parameters of martensite in Ti alloys modified by presence of oxygen atoms This study discusses the influence of beta-stabilizing elements and oxygen on the martensitic structure in metastable β titanium alloys. The introduction describes the crystallographic nature of the metastable martensitic phase and its relation to the bcc and hcp phases. Additionally, the study presents the results of a measurement of transmission X-ray diffraction, by which we determined two components involved in the formation of the martensitic phase - shear and shuffle. The analysis of the first component, shear, was carried out quantitatively using lattice parameters. The second component, shuffle, was analyzed by determining the crystal structure of the martensitic phase and all atomic positions. Finally, the study also demonstrates a HRTEM measurement with subsequent image processing to confirm or disprove the presence of O' phase nanodomains.
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Beta-Ti alloys for medical applications
Preisler, Dalibor ; Stráský, Josef (advisor) ; Karlík, Miroslav (referee) ; Caram jr., Rubens (referee)
1 Title: Beta-Ti alloys for medical applications Author: Dalibor Preisler Department / Institute: Department of Physics of Materials Supervisor of the doctoral thesis: doc. PhDr. RNDr. Josef Stráský, Ph.D., Department of Physics of Materials Abstract: Interstitial strengthening by a high amount of oxygen can be used in metastable beta-Ti alloys, for achieving very high strength without compromising ductility. The content of oxygen however influences the phase stability and consequently increases the Young's modulus. Several alloys with various content of beta-stabilizing elements were prepared by common metallurgical route. On top of that, dozens of compositions were prepared by a high-throughput powder metallurgy method and thoroughly studied. Lattice softening due to proximity to a martensitic transformation was utilized to minimize the Young's modulus. Effect of omega phase was thoroughly studied; it was found that the embrittlement by the athermal omega phase is most probably connected with the high oxygen content and its room-temperature diffusion into omega particles. Fundamental difference between elastic behaviour of alloys containing a significant fraction of omega and those with only a limited amount of omega was demonstrated. Regarding the plastic deformation mechanisms, it was found that...
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Metastable beta titanium alloys for biomedical use
Preisler, Dalibor ; Stráský, Josef (advisor) ; Janeček, Miloš (referee)
In this work the effect of die-forging and annealing on the mechanical properties and microstructure of biocompatible metastable alloy Ti-35.3Nb-7.3Zr -5.7Ta-0.7O (wt. %) was studied. Light and scanning electron microscopy, microhardness tests and tensile tests were used to study all prepared conditions. As-cast and as-annealed conditions showed chemical inhomogeneities exhibited as dendritic structure, grains with size of hundreds of micrometers and numerous pores having size of units of micrometers. Precipitation of alpha phase particles was negligible in as-annelaed conditions and only grain boundary alpha paticles formed. Die-forged condition showed grain sizes in the wide range of hundreds of micrometers down to micrometers. Both as-annealed and die-forged conditions showed increased microhardness compared to as-cast condition, but there were no significant differences between different annealing conditions. Yield stress of 870 MPa was found for as-cast condition while as-forged condition exhibited even higher yield stress of 1120 MPa. In both conditions, good room-temperature ductility was demonstrated. Due to its high strength, this alloy is perspective for manufacturing of joint implants.
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Low-modulus titanium alloys for biomedical use
Šalata, Kristián ; Preisler, Dalibor (advisor) ; Janeček, Miloš (referee)
Titanium alloys belong to a group of perspective biomaterials used for production of joint endoprotheses. In order to develop a biocompatible material with better mechanical properties, twelve alloys with 0.7 wt% of oxygen and different contents of Nb, Ta, Zr, Fe were fabricated. Microstructure and phase composition were studied by means of scanning electron microscopy, mechanical properties were determined by microhardness measurements and tensile testing. As follows from the microstructure analysis, only single alloy with composition Ti-20Nb-7Zr-0,7O (wt%) contained also the martensitic phase apart from the metastable phase. In case of other alloys we observed only phase. We found out that the microhardness of alloys gradually decreases with increasing content of -stabilizing elements until the solid solution is saturated. The high value of microhardness in case of alloys with low content of -stabilizing elements is thus considered as indirect proof of the presence of the brittle phase . Tensile tests showed that none of the alloys with increased hardness has undergone strain hardening. The interstitial oxygen atoms led to yield strengths of more than 1000 MPa for all investigated alloys. In some cases, the ultimate tensile strength was more than 1200 MPa. The most promising alloy for the...
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Oxygen-strengthened biomedical beta titanium alloys
Preisler, Dalibor ; Stráský, Josef (advisor)
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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Oxygen-strengthened biomedical beta titanium alloys
Preisler, Dalibor ; Stráský, Josef (advisor)
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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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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Metastable beta titanium alloys for biomedical use
Preisler, Dalibor ; Stráský, Josef (advisor) ; Janeček, Miloš (referee)
In this work the effect of die-forging and annealing on the mechanical properties and microstructure of biocompatible metastable alloy Ti-35.3Nb-7.3Zr -5.7Ta-0.7O (wt. %) was studied. Light and scanning electron microscopy, microhardness tests and tensile tests were used to study all prepared conditions. As-cast and as-annealed conditions showed chemical inhomogeneities exhibited as dendritic structure, grains with size of hundreds of micrometers and numerous pores having size of units of micrometers. Precipitation of alpha phase particles was negligible in as-annelaed conditions and only grain boundary alpha paticles formed. Die-forged condition showed grain sizes in the wide range of hundreds of micrometers down to micrometers. Both as-annealed and die-forged conditions showed increased microhardness compared to as-cast condition, but there were no significant differences between different annealing conditions. Yield stress of 870 MPa was found for as-cast condition while as-forged condition exhibited even higher yield stress of 1120 MPa. In both conditions, good room-temperature ductility was demonstrated. Due to its high strength, this alloy is perspective for manufacturing of joint implants.
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