Phase Decomposition of a Single‐Phase AlTiVNb High‐Entropy Alloy after Severe Plastic Deformation and Annealing

An equiatomic AlTiVNb high‐entropy alloy is deformed by high pressure torsion inducing a nanocrystalline microstructure. The samples then are subjected to isochronal heat treatments between 300 °C and 1000 °C. The hardness increase from ≈7.4 GPa for the as‐ processed state to 10.4 GPa for an annealing temperature of 700 °C, while for higher temperatures the hardness starts to decrease. Furthermore, the reduced modulus increases after annealing treatments as well. It will be shown that the unusual annealing response can be related to the formation of intermetallic phases creating a multi‐phase nanocomposite material during annealing. The results give new insights into the thermodynamic stability of this alloy, which are also relevant for coarser‐grained microstructures. An AlTiVNb high‐entropy alloy is subjected to high‐pressure torsion leading to a pronounced grain refinement. The nanocrystalline samples are subjected to various heat treatments, which results in a significant increase in hardness and reduced modulus. Subsequently, investigations by electron microscopy, synchrotron x‐ray diffraction, and nanoindentation are performed in order to determine the origin of this annealing response.