S T R U C T U R E O F M A T E R I A L S

S C I E N T I F I C H I G H L I G H T S

1 2 2 H I G H L I G H T S 2 0 2 2 I

a non-transforming grain can impede the MT in a well-oriented grain, leading to an increase of its stress level. As martensite was not indexed, FEM was used to identify the activated martensite variants inside the grains and it was found that they were not always the ones with the highest Schmid factor. These results have emphasised the role of local stress induced by neighbourhood on the MT.

By coupling FEM and 3D X-ray imaging techniques, this work has made it possible to validate a micromechanical model at the grain scale. The most recent developments of such techniques will also allow the validation of the MT micromechanical model at intragranular scale in the near future (e.g., scanning 3D-XRD using a focused and narrowed beam).

PRINCIPAL PUBLICATION AND AUTHORS

Multiscale in-situ mechanical investigation of the superelastic behavior of a Cu-Al-Be polycrystalline shape memory alloy, Y. El Hachi (a), S. Berveiller (a), B. Piotrowski (a), J. Wright (b), W. Ludwig (c), B. Malard (d), Acta Mater. 235, 118107 (2022); https:/doi.org/10.1016/j.actamat.2022.118107 (a) LEM3, Arts et Métiers Institute of Technology, Université de Lorraine, CNRS, HESAM Université, Metz (France) (b) ESRF (c) MATEIS, Lyon (France) (d) CIRIMAT, Université de Toulouse, CNRS, INPT, UPS, Toulouse (France)

REFERENCES

[1] H. Horikawa et al., Metall. Trans. 19A, 915-923 (1988). [2] M. Sade et al., Mater. Sci. Eng. A. 609, 300-309 (2014). [3] P. Šittner et al., Mater. Sci. Eng. A. 378 97-104 (2004). [4] D. Rios-Jara et al., Scr. Metall. Mater. 25,6, 1351-1355 (1991).

Shining a light on the formation mechanism of biominerals with X-ray total scattering

The importance of amorphous calcium carbonate precursors in the biomineralisation process has been recognised, but a quantitative understanding of these amorphous phases is lacking. X-ray total scattering revealed the presence of multiple states of amorphous calcium carbonate and their interplay to form the prismatic layer of the pearl oyster Pinctada margaritifera.

Biomineralisation is a widely employed strategy by animals to build functional skeletons. This remarkable process fulfils the many requirements of the living organism by choosing the appropriate nanostructural arrangement [1] and crystalline polymorph for the task. A unifying feature in this process is the involvement of an amorphous calcium carbonate (ACC) phase [2] in the early stages, which can still be found as a residual phase once the mineralisation is complete [3] and the crystalline calcium carbonate phase has formed. The model organism investigated here was the pearl oyster Pinctada margaritifera (Figure 115a), where the growth zone of the shell is characterised by disc-like units forming a prismatic layer (Figure 115b) often containing residual ACCs [2,3], as shown by red regions in Figure 115c, compared with crystalline calcite (blue).

Fig. 114: Evolution of the six components of the elastic stress tensor in Grains 1 and 2 versus the macroscopic strain, as obtained by the 3D-XRD (a,b) and FEM (c,d) measurements.