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During service life of Al alloys, damage occurs due to the presence of large intermetallic particles. Damage healing is a new paradigm to extend materials lifetime. In the present work, a new class of healable Al-0.5Mg2Si alloy is produced by Friction Stir Processing (FSP). In-situ tensile Scanning Electron Microscopy (SEM) tests have shown that sacrificial healable particles change damage mechanism by breaking first, while Fe-rich intermetallics are mostly remaining intact. The pre-damaged samples produced by a micro-tensile machine were further investigated by in-situ heating TEM including EDX analysis and automatic crystallographic orientation in TEM as well as atom probe tomography (APT) in order to track healing evolution of damaged particles and reveal healing mechanism. In situ X-Ray nano holotomography experiment carried out at ESRF with a pixel size of 35 nm provided additional statistical data on the healing ability of the bulk material after heating for various times at 400°C.

Optimisation of the thermoelectric properties of Fe2VAl thin films obtained by co-sputtering G. Roy, KM Karuppasamy , V. Dupont, J.F. Trelcat, A. Kashiwar, C. van der Rest, H. Idrissi, JP. Erauw, P. Guaino, P.J. Jacques The Fe2VAl Heusler compound is attracting increasing interest from the scientific community due to its excellent performance in terms of power factor [1-2] around room temperature, coupled with the high availability and non-toxicity of its constitutive elements. Thermoelectric thin films are of interest from a fundamental point of view, especially owing to the possibilities of nano-structuring, but also from an application point of view where it could facilitate the integration of thermoelectric modules for powering low power electronic devices such as autonomous sensors. Nevertheless, studies on Fe2VAl thin films are relatively scarce and some recent results still raise some questions [3-4]. In this study, Fe2VAl thin films were processed by a co-sputtering method allowing to easily control the stoichiometry of the films. After process optimisation, p- and n-type layers have been obtained with power factors of 0.8 and 1.6 10-3W/mK², respectively. In addition, we determined using advanced microstructure analysis that the increase of thermoelectric performances is related to crystal ordering during annealing. [1] Miyazaki, H. et al. "Thermoelectric properties of Heusler-type off-stoichiometric Fe2V1+ xAl1− x alloys." Materials Research Express 1.1 (2013): 015901. [2] Garmroudi, F., et al. "Boosting the thermoelectric performance of Fe 2 VAl− type Heusler compounds by band engineering." Physical Review B 103.8 (2021): 085202. [3] Hinterleitner, B., et al. "Thermoelectric performance of a metastable thin-film Heusler alloy." Nature 576.7785 (2019): 85-90. [4] Alleno, E., et al. "On the structure and electronic properties of Fe 2 V 0.8 W 0.2 Al thin films." Physical Chemistry Chemical Physics 22.39 (2020): 22549-22554.

Aluminium alloys are widely used as structural materials in transportation and aerospace. Despite the excellent combination of lightweight and strength, several properties of Al alloys, such as strength and damage tolerance, should be further enhanced to remain competitive on the market. One way of improving the strength of Al alloys is to combine them with reinforcements, thereby developing aluminium matrix composites (AMCs). AMCs present several advantages compared to classical Al alloys, such as higher strength and elevated temperature resistance. Furthermore, to improve damage tolerance of Al alloys and AMCs, friction stir processing (FSP) can be used. However, the classical approach of damage prevention is not the only solution to improve damage tolerance and meet materials sustainability requirements. Alternatively, damage management approaches like self-healing strategies can be employed to expand the lifetime of alloys. In the present study, a new healable Al alloy/composite presenting healing behaviour was produced by FSP. A new Programmed Damage and Repair healing concept was proposed. In this concept, damage appears preferentially on sacrificial particles during loading. As the selected healing heat treatment is applied, healing occurs using the matrix atoms as healing source. Healing was demonstrated by perfoming in-situ experiments using X-Ray synchrotron nano-tomography and TEM.

International audience

International audience

International audience

International audience