镍钛基形状记忆合金大塑性变形非晶相形成机理及纳米晶化机制的多尺度研究

Nanocrystalline Nickel-Titanium-based shape memory alloy (NiTi SMA) is widely used in the biomedical engineering field since it possesses comprehensive mechanical properties, superior superelasticity,high corrosion resistance and perfect biocompatibility. In the present study, as a novel severe plastic deformation(SPD)technique, canning compression provides a new approach to causing the amporphization of NiTi SMA. In addition, the nanocrystalline NiTi SMA can be obtained by means of crystallization of amophous phase in the case of the appropriate heat treatment.By combining canning compression process experiment, heat treatment crystallization experiment, microscopic structure analysis experiment, crystal plasticity finite element method and cellular automaton simulation, from the macroscale, mesoscale, microscale and atomic scale perspective, it shall be able to lay the scientific and theoretical foundations for manufacturing nanocrystalline NiTi SMA with high properties to explore stress-induced martensite phase transformation, deformation twinning and dislocation-slip plastic deformation of austenitic NiTi SMA under canning compression, investigate martensite reorientation,detwinning and dislocation-slip plastic deformation of martensitic NiTi SMA under canning compression, establish the critical dislocation density model for occurrence of amorphous phase in the case of plastic deformation of NiTi SMA under canning compression and reveal the amorphization mechanism of NiTi SMA in the case of plastic deformation based on canning compression and nanocrystallization mechanism of the amorphous NiTi alloy.

纳米晶镍钛基形状记忆合金因为具有优良的综合力学性能、超弹性、耐蚀性和生物相容性，广泛应用于生物医学工程领域。本项目提出了一种新型包套压缩大塑性变形技术，可以实现镍钛基形状记忆合金的非晶化，对非晶镍钛基合金进行合适的热处理晶化，可以制备纳米晶镍钛基形状记忆合金。将包套压缩实验、热处理晶化实验、微观结构分析实验、晶体塑性有限元和元胞自动机相结合，通过宏观尺度、介观尺度、微观尺度和原子尺度的多尺度研究手段，探索奥氏体相镍钛基形状记忆合金在包套压缩下的应力诱发马氏体相变、变形孪晶及位错滑移塑性变形机制；研究马氏体相镍钛基形状记忆合金在包套压缩下的马氏体再取向、去孪生及位错滑移塑性变形机理；建立镍钛基形状记忆合金包套压缩塑性变形非晶相形成时的临界位错密度模型；揭示镍钛基形状记忆合金包套压缩塑性变形非晶相形成机理及非晶镍钛基合金的纳米晶化机制，为制备高性能的纳米晶镍钛基形状记忆合金提供科学的理论基础。

采用室温下为B2奥氏体相的Ni50.9Ti49.1 (原子百分数)形状记忆合金，在室温至800 ℃的范围内进行了局部包套压缩实验，研究了该合金多塑性变形机制。Ni50.9Ti49.1合金基于不同温度的多塑性变形机制涉及位错滑移、变形孪生、晶界滑动、晶粒转动、位错攀移和晶界迁移。基于统计存储位错密度和几何必要位错密度，揭示了Ni50.9Ti49.1合金包套压缩大塑性变形非晶化的基本机制，提出了存在Ni50.9Ti49.1合金局部包套压缩大塑性变形非晶化的临界位错密度，同时提出了Ni50.9Ti49.1合金存在局部包套压缩大塑性变形非晶化和晶化动态平衡的临界温度。对室温下为B2奥氏体状相的Ni47Ti50Fe3（原子百分数）形状记忆合金进行了包套压缩大塑性变形研究。在包套压缩大塑性变形条件下，Ni47Ti50Fe3合金几乎完全纳米晶化，并且存在局部非晶相，其包套压缩大塑性变形纳米晶化和非晶化的机制涉及位错滑移、应力诱发马氏体和变形孪生。对遭受包套压缩大塑性变形的Ni47Ti50Fe3合金分别在300℃、450℃和600℃进行热处理晶化两个小时。在300℃条件下，可以观察到完全的纳米晶相。在450℃条件下，可以观察到纳米晶相和粗晶相共存。在600℃条件下，几乎获得完全的粗晶相。对室温下为B19'马氏体状态的Ni50Ti50（原子百分数）合金进行了局部包套压缩大塑性变形研究，可以发现其发生了严重的纳米晶化和非晶化，其纳米晶化和非晶化机制更为复杂，涉及马氏体的再取向、变形孪生、去孪生和位错滑移。对遭受包套压缩大塑性变形的Ni50Ti50合金分别在300℃、450℃和600℃进行热处理晶化两个小时。在300℃条件下, Ni50Ti50合金中纳米晶相占主导,存在局部非晶区。在450℃条件下,几乎获得完全的纳米晶。在600℃条件下,晶粒尺寸明显增大，但仍然含有少量纳米晶相。纳米晶相显著提高了镍钛形状记忆合金的屈服强度。镍钛形状记忆合金包套压缩大塑性变形非晶化抑制了Ni4Ti3相和R相的形成。基于位错滑移晶体塑性本构模型实现了Ni50.9Ti49.1合金在400℃时的包套压缩有限元模拟。设计了新型NiTiNb、NiTiFeNb和NiTiFeTa形状记忆合金，并对其微观结构、相变和力学性能进行了表征。构建了Ni50.9Ti49.1合金热加工图，获得了该合金高温塑性变形稳定流动工艺参数。