On the room temperature deformation mechanisms of a TiZrHfNbTa refractory high-entropy alloy

The deformation micro-mechanisms of an as-cast equimolar refractory high-entropy alloy composed of Ti, Zr, Hf, Nb and Ta are analyzed by monotonic and relaxation compression tests coupled to transmission electron microscopy observations. The evolution of the work hardening with plastic strain displays 3 stages. After a sharp decrease until a plastic strain of approximately 3%, work hardening stabilizes at 1300±50 MPa and finally decreases again. The measured apparent activation volumes Vapp* slightly evolve with plastic strain and decrease from approximately 50b3 to 30b3. These values are coherent with a Peierls mechanism due to strong intrinsic lattice friction. In addition, the measured activation volumes correlate well with TEM observations, which give evidence that dislocation glide is controlled - in the first stages - by the movement of screw dislocations. The deformation is rapidly localized in bands in which dislocation dipoles, loops and tangles are induced at higher plastic strains.