The DisMecHTRA project is motivated by the fundamental question of deformation mechanisms in refractory complex concentrated alloys (RCCA). It aims at a better understanding of their superior mechanical properties at high temperatures typically above 600°C where classical materials drastically soften. The questions raised here are then both of fundamental and technological interests for high temperature industrial applications. Up to date, deformation mechanisms, carried by dislocations, remain largely unknown and some results appear controversial. This is related to the complexity of thermally activated mechanisms in a chemically complex environment, i.e. a concentrated substitutionnal solid solution. Moreover, interstitial impurities are also suspected to strongly impact the dislocation dynamics. In this project, we will propose a combination of forefront experiments (in-situ straining TEM) at nanoscale and atomistic simulations of the dislocation interactions with interstitials, to probe elementary mechanisms in model binary and ternary RCCA in the Mo-Nb-Ti/Ta system. These investigations will be made possible thanks to a mastered material elaboration technique able to control both chemistry and microstructure, and will be complemented by macroscopic mechanical tests to assess high temperature properties.