Thin film high entropy alloys (TF-HEAs) are an emerging class of equiatomic (or near equiatomic) multi-component metallic materials exhibiting an outstanding combination of mechanical properties including large yield strength and ductility (respectively >3 GPa and >20% for NbMoTaW) together with resistance high temperatures (> 800°C) and harsh environments [1,2]. However, their structural complexity (lattice distortion, microstructure and composition) together with the difficulty to fabricate and manipulate micrometer-scale specimens prevent the understating of the deformation mechanisms and mechanical properties, hindering the development of nanostructured films with improved performances and their scalability to industry applications. In this context, the MICRO-HEAs project aims to fabricate complex multicomponent TF-HEAs, investigating the relationship atomic structure–mechanical properties down to the (sub)micrometer scale. TF-HEAs will be produced by magnetron sputtering focusing on the AlxCoCrCuFeNi system reporting different atomic structures, crystalline (fcc, bcc) and amorphous varying the percentage of Al [3,4], whose mechanical properties are barely explored. In a second step, advanced TF-HEAs will be fabricated involving grain refinements, duplex phases (fcc+bcc, crystalline+amorphous) and Ti addition (in lieu of Al, TixCoCrCuFeNi), to further improve their mechanical properties and explore still unknown deformation behaviors. Cutting-edge techniques including optoacoustic spectroscopies (Brillouin light scattering and Picosecond laser ultrasonics) [5] and in-situ SEM compression/splitting tests of micropillars [6,7], will provide the entire elasto-plastic behavior and fracture toughness down to the (sub)micro-scale, uncovering the effect of the thickness/volume, composition and microstructure. Finally, the local micro-scale mechanical behavior of the CoCrCuFeNi HEA targets will be explored, with the aim to understand the change of mechanical properties for the bulk counterparts produced by different techniques and explore the scalability of the TF-HEA system. The project aims to expand the experimental capabilities available at the Laboratoire des Sciences des Procédés et des Matériaux (LSPM) with micro-pillar fabrication and advanced in-situ SEM techniques (micro-pillar compression/splitting, PI background [6,7]) so far not available, while enabling to study micro-scale plasticity/fracture and accessing to the live deformation mechanisms. Moreover, the project will be strengthened by the collaboration with Prof. Gerhard Dehm Max-Planck-Institut für Eisenforschung (MPIE, Germany) among the worldwide recognized scientist in the field of small-scale mechanics and already working on HEAs [8]. Overall, the MICRO-HEAs project is expected to generate significant breakthroughs for basic science together with clear benefits for France competiveness and industry applications in the field of high performance coatings, microelectronics, aerospace, defense and energy. References [1] D.B. Miracle, O.N. Senkov, Acta Mater. 122 (2017) 448-511. [2] Y. Zou et al., Nat. Commun. 6 (2015) 7748 [3] B. Braeckman et al., Scripta Mater. 139 (2017) 155-158. [4] M.-H. Tsai, J.-W. Yeh, Mater. Res. Lett. 2 (2014) 107-123. [5] T. Pham et al., Appl. Phys. Lett. 103 (2013) 041601 [6] J. Ast et al., Mater. Design 173 (2019) 107762. [7] M. Ghidelli et al., J. Am. Cream. Soc. 100 (2017) 5731–5738. [8] W. Lu et al., Advanced Materials 30 (2018) 1804727.