Lattice defects in severely deformed biomedical Ti-6Al-7Nb alloy and thermal stability of its ultra-fine grained microstructure

0502368 - ÚFP 2019 RIV NL eng J - Journal Article
Bartha, K. - Zháňal, P. - Stráský, J. - Čížek, J. - Dopita, M. - Lukáč, František - Harcuba, P. - Hájek, M. - Polyakova, V. - Semenova, I. - Janeček, M.
Lattice defects in severely deformed biomedical Ti-6Al-7Nb alloy and thermal stability of its ultra-fine grained microstructure.
Journal of Alloys and Compounds. Roč. 588, 5. 6. 2019 (2019), s. 881-890. ISSN 0925-8388. E-ISSN 1873-4669
R&D Projects: GA ČR GA17-17016S
Institutional support: RVO:61389021
Keywords : Electrical resistance * Equal channel angular pressing * Microstructure * Positron annihilation spectroscopy * Titanium alloys
OECD category: Materials engineering
Impact factor: 4.650, year: 2019
https://www.sciencedirect.com/science/article/pii/S0925838819306255?via%3Dihub

Biomedical Ti-6Al-7Nb alloy was prepared by a dedicated thermal treatment followed by equal-channel angular pressing (ECAP) and extrusion. Ultra-fine grained duplex microstructure consisting of deformed primary α-grains and fragmented α + β region was achieved. Microstructural changes during heating with the rate of 5 °C/min were studied by in-situ electrical resistance. Microstructure after deformation and also after subsequent heating was thoroughly characterized by scanning electron microscopy, X-ray diffraction, and positron annihilation spectroscopy (PAS). X-ray diffraction and positron annihilation spectroscopy proved a very high dislocation density and the presence of high concentration of vacancy clusters in deformed material. The ultra-fine grained microstructure of Ti-6Al-7Nb alloy is stable up to 440 °C, while upon heating to 550 °C and to 660 °C, the dislocation density decreases and vacancy clusters disappear. Enhanced microhardness can be achieved by ECAP followed by aging at 500 °C. Upon heating to 660 °C, the microhardness decreases due to ongoing recovery and recrystallization. Coincidence Doppler broadening (CDB), a special method of PAS, proved that dislocation cores are preferentially occupied by Al atoms that are known to cause substitutional solid solution strengthening.
Permanent Link: http://hdl.handle.net/11104/0294313