Speaker
Description
Introducing metastable austenite in steels can be essential for obtaining improved mechanical properties such as ductility, toughness and fatigue resistance [1]. The austenite to martensite transformation leads to increased plastic deformation by means of the transformation induced plasticity (TRIP) effect. The prediction of the deformation induced by the martensitic transformation process is essential to assess TRIP and guide the design of better-performing alloys.
Here, we combine High-Resolution Digital Image Correlation (HR-DIC) to obtain fine-accuracy in-plane deformation fields with a new, predictive theory of martensite crystallography [2] to determine the full 3D transformation strain in situ (“shape deformation”) in a model Fe-20.2Ni-5.4Mn (wt%) alloy. Neutron diffraction and TEM are used to determine the austenite and martensite alloy lattice parameters. The crystallographic orientation of both austenite and martensite are measured by Electron backscatter diffraction and they serve as input for the crystallographic theory of martensite, along with the alloy lattice parameters. Tensile tests are then performed until martensite forms, and HR-DIC yields the 3 in-plane strain measurements.
The crystallographic theory predicts within experimental accuracy 2 of the 3 in-plane measurements [3]. The third measurement is captured by including the contribution of crystallographic slip, which is observed experimentally. This work validates the crystallographic theory proposed in [2]. Furthermore, combined experimental-theoretical analysis reveals for the first time the full, 3D transformation strain in-situ, associated with the austenite-martensite transformation in Fe-Ni-Mn.
It is shown that a larger transformation strain correlates with increased ductility. The theory, which is general for the face-centered-cubic to body-centered-cubic transformation, can then be used to predict new, tougher alloys.
References
[1] M. Koyama et al. (2017) Science 355, 1055-1057.
[2] F. Maresca, W.A. Curtin (2017) Acta Materialia 134, 302-323.
[3] F. Maresca, E. Polatidis, M. Šmíd, H. van Swygenhoven, W.A. Curtin (2020) Acta Materialia 200, 246-255.
| Speaker Country | Netherlands |
|---|