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

金属间镍钛合金具有优异的形状记忆效果和超弹性、力学性能、耐腐蚀性和生物相容性，是目前应用最为广泛的形状记忆合金。然而，对于这些成分的扩散系数仍然知之甚少。Ti在该材料中的整体扩散和沿短路扩散路径（位错和晶界）的扩散根本没有被研究，尽管它可能决定了例如高温蠕变速率。扩散现象在纳米镍钛合金中尤为重要，在生物物理性能和技术性能方面具有显著的优势。目前的项目首先是研究Ti和Ni在化学计量和富Ni NiTi合金中B2相场的体扩散和晶界扩散。将在延长的温度区间内测量两种组分的迁移率的可靠数据。第一次直接得到了假设中最慢组分Ti的扩散速率数据。剧烈的塑性变形将产生纳米结构和超细晶材料。将仔细研究短路扩散作为晶粒尺寸、弹性和超弹性变形以及热处理的函数。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，以及提高其塑性。

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.