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Transmission Electron Microscopy Study on Microstructrue of β Type Ti-Alloys

Author: XingHui
Tutor: SunJian
School: Shanghai Jiaotong University
Course: Materials Science
Keywords: metastableβTi-alloy plastic deformation mechanism elastic modulus High-resolution Transmission Electron Microscopy Electron Energy Loss Spectrum
CLC: TG146.23
Type: PhD thesis
Year: 2009
Downloads: 291
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Abstract


In this dissertation, the microstructure of TNTZO （Ti-23Nb-0.7Ta-2Zr-1.2O at. %） alloy and Ti-Mo alloy was investigated by Transmission Electron Microscopy （TEM）. Then integrated with calculation, the mechanism of plastic deformation in TNTZO alloy was theoretically analyzed. Additionally a new method to measure modulus of materials by means of Electron Energy Loss Spectrum （EELS） was discussed with Ti-Mo alloy as sample. Specific study mainly included two parts as follows:Ⅰ. Study on the microstructure and mechanism of plastic deformation in TNTZO alloyThe elastic property and structure of dislocation in Gum Metal are investigated by anisotropic elastic theory and high-resolution transmission electron microscopy （HRTEM）. The results show that the elastic energy coefficients for the 1/2<111> perfect dislocations nearly equal to zero as the shear modulus along <111>{110}, {112}, {123} when the valence electron number e/a reaches 4.2, which implies a low intrinsic critical resolved shear stress for dislocation glide. HRTEM observations further revealed 70.53°dislocations in Gum Metal after severe cold working. The substantial plastic deformation is considered to originate from the conventional dislocation mechanism, rather than from the dislocation-free mechanism in Gum Metals.{112}<111> mechanical twinning and stress-induced omega transition were further observed by high-resolution transmission electron microscope in TNTZO after deformation. The orientation relationships between theωphase andβparent matrix are and , and the habit plane of for the stress-inducedωtransition is different from that of often observed for the thermalωtransition. Both mechanical twinning andωtransition arise from the shear along <111>{112}. A dislocation mechanism for mechanical twinning and stress-inducedωtransition was discussed additionally.Ⅱ. Study on the phase composition、microstructure and measurement of elastic modulus in Ti-Mo alloyThe phase composition and microstructure of Ti-Mo alloy （with Mo content about 69% respectively） after solution treatment was firstly investigated: The lattice constants ofα" phase varied linearly with Mo content; orientation relationships betweenα" andβparent matrix are [100]β// [100]α" and ;α" type twinning exits inα" phase; orientation relationships between nonthemalωphase andβparent matrix are , and .Sequentially a new method to measure micro modulus was discussed. The modulus of differentα" and in Ti-8%Mo alloy was measured and a change law about modulus ofβphase with Mo content in three alloys （Ti-820%Mo）was expected to obtain. The results show the elastic modulus ofα" phase is higher than that ofβphase by 19% in same alloy and modulus ofβphase of different alloys increased with higher Mo content. Finally Ti L2,3 edge intensity ofβphase in Ti-820%Mo alloy was measured using EELS. The results show the ionization peak intensity of Ti L2,3 decreased gradually due to hybrid between d-orbits of Ti and surrounding Mo atoms.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallic materials > Non - ferrous metals and their alloys > Light non-ferrous metals and their alloys > Titanium
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