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

本研究的目的是阐明无镍生物医用形状记忆合金，特别是TiNbAl合金，通过热机械处理引入高能和高密度的晶格缺陷，通过剧烈变形的微观结构，缺陷和力学性能之间的关系。为了提高它们的超弹性性能，材料强化以增加滑移变形的临界应力是有效的，并且这通过在减薄厚度和快速凝固中高达99%的冷轧的剧烈变形来尝试。首先，研究了马氏体相变温度较低的Ti-26 Nb-3A 1合金的织构形成和超弹性变形。结果表明，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。虽然固溶处理后的晶粒尺寸在500μm左右较粗，但晶粒变得细小， ...更多信息 d针状形状随着轧制方向伸长。然后，再结晶织构的发展与不同的冷轧变形量进行了研究。研究发现，再结晶织构的发展强烈依赖于压下率，不同的织构发展。{001}当<110>冷轧压下量小于90%时，形成了_β _β型织构，进一步增加冷轧压下量，形成的织构转变为{112}_β<110>_β型织构。{001}_β<110>_β型织构比{112}_β _β型织构具有更小的超弹性各向异性<110>，因此{001}_β<110>_β型织构更有实用价值。其次，研究了α”和α"+β型TiNbA_1合金织构的形成。发现α"+β合金的变形和再结晶织构分别为{112}_β<110>_β型和{111}_β<110>_β型。此外，α”合金的形变织构和再结晶织构分别为{223}_&lt;α"&gt;<302>_&lt;α"&gt;和{011}_&lt;α"&gt;<311>_&lt;α"&gt;。因此，织构形成的类型以及超弹性强烈地依赖于TiNbAl合金中的稳定相的类型。对于冷乳线材获得了类似的结果。最后，对Ti-24 Nb-3A 1进行了快速凝固，但即使在快速凝固的高能过程中也没有形成织构或细晶。结果表明，通过适当的形变热处理和剧烈的变形，可以控制钛合金的织构和超弹性性能。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