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Development of high strength and high ductility nanostructured TWIP steel.

机译：开发高强度，高延展性的纳米结构TWIP钢。

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摘要

Strength and ductility are two exclusive mechanical properties of structural materials. One challenge for material research is to develop bulk nanostructured metals with simultaneous high strength and good ductility. To meet this objective, steels with twinning induced plasticity (TWIP) effect are selected for surface mechanical attrition treatment (SMAT) in this study. Tensile tests reveal extremely high yield strength and simultaneously sufficient ductility in these SMATed TWIP steel samples. With the duration increase of SMAT, both yield strength and tensile strength firstly monotonically increase to a maximum value of 2.25GPa with 18% total elongation. However, further increase of SMAT duration results in decreases of both strength and elongation.;The excellent ductility of coarse-grained TWIP steels is attributed to the instantaneous generation of deformation twins in tension. Based on this, an interesting hierarchically tertiary twinning system is revealed by TEM/HRTEM in SMATed samples, composed of multi-scale twins respectively produced by annealing treatment, SMAT and tensile deformation. On one hand, boundaries of hierarchical twins with different orientations form three-dimensional networks that restrict each other and act as strong barriers to dislocation motion, leading to ultrahigh strength. On the other hand, stress concentration is relieved due to deformation transfer caused by twinning from grain to grain, resulting in large plasticity. Therefore, the hierarchical twinning structure is regarded as the most effective element that induces both extraordinary ultrahigh strength and good elongation in SMATed TWIP. The stable austenite also contributes to the preservation of good ductility. Martensite is only observed in SMATed TWIP by longest SMAT duration.;Another route of fabricating nanostructured TWIP is performed by combining SMAT and thermomechanical treatment. The interval heat treatment between double SMAT benefits the total elongation to over 50%, with 980 MPa yield strength. Nanograins are observed at 60μm depth, different from their usual emergence on top surface. Martensitic phase transformation is discovered.;Most nanostructured SMATed TWIP samples demonstrate typical ductile fractures with large quantities of dimples in different sizes, following the same trend of gradient grains. Long SMAT duration produces slight brittle crack with tearing ribs. Microvoids coalescence with manganese carbides leads to final rupture.
机译：强度和延展性是结构材料的两个专有机械性能。材料研究的挑战之一是开发同时具有高强度和良好延展性的块状纳米结构金属。为了达到这个目的，本研究中选择具有孪生诱导塑性（TWIP）效果的钢进行表面机械磨损处理（SMAT）。拉伸试验表明，这些SMATed TWIP钢样品具有极高的屈服强度和足够的延展性。随着SMAT持续时间的增加，屈服强度和抗拉强度首先单调增加至最大值2.25GPa，总伸长率为18％。但是，SMAT持续时间的进一步增加会导致强度和伸长率的降低。；粗粒TWIP钢的出色延展性归因于张力瞬间产生变形孪晶。在此基础上，通过TEM / HRTEM在SMATed样品中揭示了一种有趣的分层三级孪生系统，该系统由退火处理，SMAT和拉伸变形分别产生的多尺度孪晶组成。一方面，具有不同方向的分层双胞胎的边界形成了相互制约的三维网络，并成为位错运动的强大障碍，从而导致了超高强度。另一方面，由于晶粒间的孪晶引起的形变转移减轻了应力集中，从而导致较大的可塑性。因此，分层孪生结构被认为是在SMATed TWIP中引起非凡的超高强度和良好的伸长率的最有效元素。稳定的奥氏体也有助于保持良好的延展性。马氏体仅在SMATed TWIP中观察到最长的SMAT持续时间。;通过将SMAT与热机械处理相结合，可以完成另一种制造纳米结构TWIP的方法。两次SMAT之间的间隔热处理可使总伸长率超过50％，屈服强度为980 MPa。在60μm的深度观察到纳米颗粒，这与它们通常在顶表面上出现的情况不同。发现了马氏体相变；大多数纳米结构的SMATed TWIP样品显示出典型的延性断裂，并具有相同大小的梯度晶粒，且具有不同尺寸的大量凹坑。 SMAT持续时间长，会产生轻微的脆性裂纹，肋骨撕裂。微孔与碳化锰的结合导致最终破裂。

著录项

  • 作者

    Kou, Hong Ning.;

  • 作者单位

    Hong Kong Polytechnic University (Hong Kong).;

  • 授予单位 Hong Kong Polytechnic University (Hong Kong).;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2011
  • 页码 182 p.
  • 总页数 182
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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