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PRINCIPAL PUBLICATION AND AUTHORS

A New Healing Strategy for Metals: Programmed Damage and Repair, M. Arseenko (a), F. Hannard (a), L. Ding (a,b,c), L. Zhao (a,d), E. Maire (e), J. Villanova (f), H. Idrissi (a,b), A. Simar (a), Acta Mater. 238, 118241 (2022); https:/doi.org/10.1016/j.actamat.2022.118241 (a) Institute of Mechanics, Materials and Civil Engineering, UCLouvain, Louvain-la-Neuve (Belgium) (b) Electron Microscopy for Materials Science, University of Antwerp (Belgium) (c) Key Laboratory for Light-weight Materials, Nanjing Tech University (China) (d) Department of Mechanics, School of Aerospace Engineering, Huazhong University of Science and Technology, Wuhan (China) (e) Mateis, INSA Lyon, Université de Lyon, UMR CNRS 5510 (France) (f) ESRF

REFERENCES

[1] N. van Dijk, S. van der Zwaag, Adv. Mater. Interfaces. 5, 1-13 (2018). [2] S. Hautakangas et al., Scr. Mater. 58, 719-722 (2008). [3] T.L. Burnett, P.J. Withers, Nat. Mater. 18, 1041-1049 (2019).

Understanding the complexity of cavity/void growth during deformation at high temperature

When metals deform under a high temperature and constant load, the phenomenon is called creep. During creep deformation, damage nucleates and grows in the form of voids that are called creep cavities [1]. In this work, the growth of such cavities in the Mg alloy AZ31 was studied by real-time 3D imaging, using in-situ X-ray nano-tomography.

AZ31 is a light magnesium alloy, suitable for light structures for automotive applications. However, room- temperature metal-forming for Mg alloys is not easy, hence, hot and warm metal-forming are commonly

employed to process and shape such alloys. In fact, at high temperature, under specific conditions, AZ31 is known to show super plastic deformation [2]. Superplasticity is broadly described as the ability of a material to sustain a large uniform tensile strain (higher than at least 200%) without local necking prior to failure in certain intervals of temperature and strain rate [3].

In this work, the growth of creep cavities in AZ31 alloy during superplastic deformation was studied using the novel technique of in-situ X-ray nano-tomography at beamline ID16B. The sample was deformed under a combination of high temperature and constant load (673 K and 3.2 MPa, resulting in a strain rate of about 6.6 × 10 −5 s −1), while simultaneously carrying out 3D nano-imaging in order to monitor the evolution of the

Fig. 75: Healing evolution with time at 400°C. a) 3D volumes and corresponding Minimum Intensity Projections (MinIP) in the initial state and after 2 hours; (voids in black, intermetallic particles in yellow, Mg2Si particles in grey). b) Evolution of the number of healed cavities with healing time for different size classes.

moderate temperature, triggers diffusion and starts void filling (by analogy with densification during sintering), and the high density of defects generated by FSP and further loading additionally facilitates the matrix material flux.

To evaluate the effect of healing efficiency on mechanical properties, the work of fracture (Wf) was analysed with tensile tests. The total work of fracture was improved by 40% in comparison to a sample fractured without a healing cycle.