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Fe-Mn-Si-Cr-Ni-N合金马氏体相变特征及其形状记忆效应

The Character of Martencitic Transformation and Shape Memory Effect in Fe-Mn-Si-Cr-Ni-N Alloy

【作者】 丁坤英

【导师】 林晓娉;

【作者基本信息】 河北工业大学 , 材料加工工程, 2006, 硕士

【摘要】 本文利用X射线衍射仪(X-ray)、透射电镜(TEM)、扫描电镜(SEM)、原子力显微镜(AFM)、万能拉伸试验机等试验设备研究了Fe-25.27Mn-5.54Si-6.89Cr-5.06Ni-0.16N合金的马氏体相变类型、相组成、形态、宏观点阵变形特征及形状记忆效应,揭示了形状记忆性能与合金微观组织、宏观点阵变形特征之间的联系,探讨了影响合金形状记忆效应的形态学及晶体学因素。 研究结果表明,马氏体类型、形态及含量随预变形量的增加而变化。预变形1%时,诱发γ→ε马氏体相变,薄片占马氏体呈平行态分布,其含量为20.0%;预变形4%时,ε马氏体呈矛头状或菱形自协作组态生长,含量为50.4%;预变形6%时,ε马氏体出现交叉生长模式并诱发非热弹性α′马氏体,此时ε马氏体含量为43.8%,α′马氏体含量为18.9%;预变形9%时,ε马氏体含量下降为22.0%,α′马氏体含量增加到54.3%。 试验合金的形状回复率随预变形量的增加呈下降趋势。预变形量为1%、4%、6%、9%时,试验合金的形状回复率分别为56.3%、50.2%、42.5%、35.7%。热循环训练工艺可以改善试验合金的记忆性能,经1%、4%、6%、9%预变形、训练2次后,合金的形状回复率分别为63.5%、59.3%、57.2%、43.2%。ε马氏体的交叉及非热弹性α′马氏体的生成是试验合金形状记忆效应下降的主要原因,适当次数的训练可以使ε马氏体重新形核并排列,减少交叉几率,提高了ε马氏体的逆转变率。 利用原子力显微镜研究了应力诱发马氏体相变及逆相变过程中的宏观点阵变形特征。结果表明,应力诱发马氏体相变表面浮凸为单倾“N”型,呈平行态和交叉态两种形态分布。平行态表面浮凸的高度、分布密度随变形量增加而增加,在逆相变过程中呈现良好的热恢复性能;密集排列的平行态表面浮凸引起程度较大的晶格畸变,预变形量大于6%时,诱发非稳态8H结构的“次浮凸”,在拉应力作用下“次浮凸”可向2H结构的稳态浮凸转变。预变形量大于6%时,诱发高度、宽度较小的交叉态表面浮凸。交叉态表面浮凸热恢复性能很差,减小了马氏体相变点阵变形的可逆性,使ε→γ逆相变受阻。 应力诱发ε马氏体的形态和相变过程中的点阵变形特征影响着合金的形状回复率。当预变形量较小时,应力诱发的ε马氏体及相变点阵变形形成的表面浮凸都呈平行态分布,逆相变过程中已改变的晶体排列方式可按原路径返回,此时合金可获得较高的形状回复率;当预变形量较大时,ε马氏体呈交叉态生长且诱发非热弹性的α′马氏体,表面浮凸也出现交叉分布形态,晶格点阵排列发生紊乱,相变可逆性下降,形状回复率受到影响。

【Abstract】 Martensite morphology, macroscopic lattice deformation and shape memory effect(SME) in Fe-25.27Mn-5.54Si-6.89Cr-5.06Ni-0.16N alloy were studied by tensile testing machine ,X-ray, Scanning Electron Microscope(SEM) , Transmission Electron Microscope(TEM), Atomic Force Microscope(AFM) and so on. The relationship between SME and microscopic structure was revealed. The factors on SEM about morphology and crystallography were also investigated.The results show that morphology and content of martensite changed with pre-strain. γ→ s martensitic transformation occurred after 1% pre-strain and e martensite with 20.0% volume were distributed in parallel pattern. The pattern changed to rhombus self-accommodate after 4% pre-strain and the volume became to 50.4%. While, the pattern changed to intersection and α’ martensite appeared after 6% pre-strain, then, the volume of α’ martensite was 18.9% and e martensite was 43.8%. When the pre-strain increased to 9%, the volume of ε martensite was 22.0% and more intersecting e martensite appeared, then, the volume of α’ martensite increased to 54.3%.The results of shape memory effect show that the recovery ratio descended with pre-strain. The recovery ratio was 56.3%,50.2%,42.5%,35.7%, respectively, with 1%,4%,6%,9% pre-strain. While, SME could improve by thermomechanical training method. The recovery ratio was 63.5%,59.3%,57.2%,43.2%, respectively, after 2 circle training. The reasons for recovery ratio descent were £ martensite intersection and α’ martensite appearance,ε martensite could rearrange after appropriate training method so that the recovery ratio was improved.The macroscopic lattice deformation was analyzed by AFM. The results show that surface relief morphology had relations with pre-strain. The stress-induced surface relief is "N"-shaped including parallel and intersecting arrangement. The height of parallel surface relief increased with pre-strain. Then, the width of parallel surface relief decent after 6% pre-strain. The intersecting surface relief appeared after 6% pre-strain. While, the height, width, angle was feebler than parallel surface relief, respectively. The inverse deformation ratio was very low after 873 ×120s h1eating. The test alloy could get better shape recovery ratio when the surface reliefwas parallel arrangement. While,the recovery ratio descended when the surface relief was intersection, which inhibited reverse transformation.The SME was infected with martensite morphology and macroscopic lattice deformation. The higher shape recovery ratio could be obtained when martensite morphology and surface relief parallel arranged. While,the higher shape recovery ratio could be obtained when martensite morphology and surface relief intersecting arranged. Then, the lattice arrangement would be confused and the shape recovery ratio would decrease.

  • 【分类号】TG139.6
  • 【被引频次】2
  • 【下载频次】276
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