Fázové transformace v moderních slitinách titanu

Šmilauerová, Jana

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...

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