Diffusion phenomena in shape memory NiTi alloys subjected to severe plastic deformation

金属间化合物Ni-Ti形状记忆合金由于其上级的形状记忆效应、超弹性、力学性能、耐腐蚀性和生物相容性等优点而成为目前形状记忆合金中最受欢迎的一类。然而，仍然知之甚少的扩散系数的组件。在这种材料中，Ti在本体中和沿着短路扩散路径（位错和晶界）的扩散根本没有研究，尽管它可能决定例如高温蠕变速率。扩散现象在纳米结构的NiTi合金中尤其重要，其提供关于生物物理性质和技术性能的显著优势。目前的项目的目的是首先研究体和晶界扩散的Ti和Ni的化学计量和富Ni的NiTi合金在B2相领域。将在延长的温度间隔内测量关于两种组分的流动性的可靠数据。这是第一次直接获得关于假设最慢组分Ti的扩散速率的直接数据。剧烈的塑性变形将产生纳米和超细晶材料。短路扩散将仔细研究作为晶粒尺寸，弹性和超弹性变形和热处理的函数。研究结果可用于预测超细晶NiTi合金在机械和热载荷下的蠕变速率和疲劳寿命性能，以及改善其塑性。

Among commercial shape memory alloys the intermetallic Ni-Ti alloys are the most exploited ones because of their superior shape memory effect and superelasiticity, mechanical properties, corrosion resistance and biocompatibility. However, still little is known about the diffusivities of the components. Diffusion of Ti in bulk and along short-circuit diffusion paths (dislocations and grain boundaries) in this material is not investigated at all, although it probably determines e.g. the hightemperature creep rates. The diffusion phenomena are especially important in nanostructured NiTi alloys, which offer significant advantages concerning biophysical properties and technical performance. The current project aims first to study bulk and grain boundary diffusion of Ti and Ni in the stoichiometric and Ni-rich NiTi alloys in the B2 phase field. Reliable data on mobility of both components will be measured in an extended temperature interval. For the first time the direct data about the diffusion rate of the hypothetically slowest component, Ti, will directly be obtained. Nanostructured and ultrafine-grained material will be produced by severe plastic deformation. Shortcircuit diffusion will carefully be investigated as a function of grain size, elastic and superelastic deformation and thermal treatment. The results could be used for the prediction of e.g. creep rates and fatigue life performance under mechanical and thermal load and for the ductility improvement of ultrafme grained NiTi alloys.