Structural investigation of the stability in temperature of some high entropy alloys as a function of their electronic structure

International audienceHigh Entropy Alloys (HEA) can be classified in three domains according to their e/a and r values, with e/a, the number of itinerant valence electrons and r the average radius for a 12 nearest atoms neighborhood. The phase composition, thermal stability and possible phase transformations of a series of HEA alloys, CoCrzFeNi-XY (with X and Y = Al, Cu, Pd, Ru, Ti and z=0 or 1), selected according to their e/a ratio were investigated in cast conditions (T0), after 3 hours homogenization at 1100°C (T1) and after 3 hours annealing at 700°C (T3). It is observed that for the alloys from domain I which contains fcc structures, the microstructure transforms from multi-to almost single-phase under homogenization (T1). In domain III alloys contains cubic (bcc and/or B2) structures very small multi-structural changes are observed. Alloys in domain II have mixed structure, i.e. several different structures in the diffraction pattern, which changes during heat treatments