在常见的应变速率范围内, 多数金属材料的冷加工变形主要是通过位错增殖、形变孪晶或马氏体相变等机制实现, 这些变形机制无法有效地细化晶粒,通常只有采用剧烈塑性变形方法制备无缺陷的金属纳米材料. 最近在研究β型Ti-Nb-Zr-Sn钛合金形变过程时,发现塑性失稳导致局域化非均匀塑性变形对晶粒细化具有显著作用；利用该变形机理, 采用常规冷轧方法即可以轧制出厚度为1.5 mm 板材, 其晶粒尺寸小于50 nm.本文主要论述该合金冷加工组织细化过程和时效强化机理, 并讨论非均匀塑性变形方式的可能原因.
To obtain fully dense nano-structured metallic materials, severe plastic deformation technique usually has to be used because normal deformation mechanisms, such as dislocation interaction, deformation twins and/or martensitic transformation, are ineffective in grain refinement. Recently we found localized unstable plastic deformation in a $\beta$ type Ti-Nb-Zr-Sn titanium alloy that is very effective in grain refinement.By taking advantage of this deformation mechanism, grain size less than 50 nm can be easily achieved in conventionally cold-rolled sheet with thickness of 1.5 mm. In this paper we examine the conditions under which such an unusual deformation mechanism can be realised and report further strengthening of the nano-structured alloy by aging treatment. The origin of this deformation mechanism will be discussed.
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