Control of microstructure and mechanical anisotropy of biomedical superelastic titanium alloys through introducing high density lattice defects.

本研究旨在阐明无镍生物医学形状记忆合金，特别是TiNbAl合金，通过热机械处理，通过严重变形引入高能、高密度的晶格缺陷，其微观结构、缺陷与力学性能之间的关系。为了提高其超弹性能，材料强化以提高滑移变形的临界应力是有效的，这是通过冷轧到99%的压下率和快速凝固的严重变形来尝试的。首先，研究了马氏体相变温度较低的Ti-26Nb-3A1合金织构的形成和超弹性变形。研究发现，形变织构的发展与真应变密切相关，当真应变大于3时，织构迅速长大。固溶处理后，虽然晶粒尺寸在500μm左右粗大，但在…后，晶粒变得细小随着轧制方向的增加，更多的针状形状被拉长。然后，研究了不同冷轧变形量对再结晶织构的影响。结果表明，再结晶织构的发展强烈依赖于压下率，并形成了不同的织构。冷轧变形量小于90%时形成{001}_β&lt；110&β织构，进一步增加冷轧变形量，形成的织构转变为{112}_β&lt；110&gt；_β织构。与{112}_β&lt；110&gt；_β织构相比，{001}_β&lt；110&gt；_β织构的超弹性各向异性较小，因此，{001}_β&lt；110&β织构更适合于实际应用。其次，研究了α“型和α”+β型TiNbAl合金织构的形成。结果表明，β合金的形变织构和再结晶织构分别为{112}_β&lt；110&gt；_β和{111}_β&lt；110&gt；_α“+β。此外，α“合金的形变织构和再结晶织构分别为{223}_&lt；α”&gt；_&lt；302&gt；_&lt；α“和α”&gt；&lt；311&gt；_&lt；α“&gt；α”。因此，织构形成的类型以及超弹性强烈地依赖于TiNbAl合金中稳定相的类型。冷轧线材也得到了类似的结果。最后，对Ti-24Nb-3Al合金进行了快速凝固，但在快速凝固过程中没有形成织构，也没有形成细小的晶粒。结果表明，通过适当的形变和适当的形变处理可以控制钛合金的织构和超弹性能。较少

The purpose of this research is to clarify the relationships among microstructures, defects and mechanical properties of Ni-free biomedical shape memory alloys, especially TiNbAl alloys, through thermo-mechanical treatments to introduce high-energy and high-density lattice defects by severe deformations. In order to enhance their superelastic properties, material strengthening to increase critical stress for slip deformation is effective and this was tried by severe deformations of cold rolling up to 99% in reduction thickness and rapid solidification. Firstly, the formation of texture and superelastic deformation were investigated using Ti-26Nb-3A1 alloy with relatively low martensitic transformation temperatures. It was found that the development of deformation texture is strongly related to true strain and that the texture is rapidly grown after when the true strain becomes over 3. Although the grain size after the solution treatment is coarse around 500μm, the grains become fine an … More d needle-like shape elongated with the rolling direction. Then, the development of recrystallization texture was investigated with various cold rolling reductions. It was found that the development of recrystallization texture is strongly dependent on reduction rate, and that different textures are developed. {001}_β<110>_β type texture is formed when cold rolling reduction is lower than 90%, and further increasing cold rolling reduction, the texture formed is changed to {112}_β<110>_β type. {001}_β<110>_β type exhibits less anisotropy in superelasticity than {112}_β<110>_β, resulting that {001}_β<110>_β type texture is more useful for practical applications. Secondly, the texture formation of α" and α"+β type TiNbA1 alloys was investigated. It was found that deformation and recrystallization textures are {112}_β<110>_β type and {111}_β<110>_β for the α"+β alloy, respectively. Besides, deformation and recrystallization textures of α" alloy are {223}_<α"><302>_<α"> type and {011}_<α"><311>_<α"> for the α" alloy, respectively. Therefore, the type of texture formation as well as superelasticity strongly depends on the type of stable phase in the TiNbAl alloys. Similar results were obtained for the cold rolled wires. Finally, the rapid solidification was done for Ti-24Nb-3A1 but neither texture nor fine grains were formed even though the high energy process of the rapid solidification. It is conclude that texture and superelastic properties of the titanium alloys can be controlled through a proper thermomechanical treatment combined with severe deformation. Less