Fantin, A.; Cakir, C. T.; Kasatikov, S.; Schumacher, G.; Manzoni, A. M.: Effects of heat treatment on microstructure, hardness and local structure in a compositionally complex alloy. Materials Chemistry and Physics 276 (2022), p. 125432/1-6
10.1016/j.matchemphys.2021.125432
Abstract:
Unlike conventional alloys, high entropy alloys are characterized by one or more solid solution phase(s) without a clearly defined solvent, all element contribute to the matrix in a way that is still not entirely understood. In addition, it is not known to what extent classic thermodynamic rules can be applied to these multi-element alloys, especially concerning the question about what factor incites the matrix to undergo a phase transformation. This work tackles directly some of these aspects on a chosen alloy, Al8Cr17Co17Cu8Fe17Ni33 (at.%), which presents a high temperature single-phase gamma state and a two-phase state with gamma' precipitates, above and below 900 °C, respectively. A combined investigation via microstructural observations, hardness testing, X-ray absorption and photoelectron spectroscopy was carried out above the gamma' formation temperature. Hardness values are independent of the annealing temperatures, microstructural analysis shows no phase formation and X-ray absorption spectroscopy does not reveal observable changes in neither local atomic nor electronic structure, indicating that approaching gamma' formation temperature is not influenced by atomic or electronic rearrangements. Interestingly, short-range chemical order remains quantitatively compatible at any annealing temperature in the single-phase gamma state, and the observed preferred pairs Al–Cu and Al–Ni in the gamma state match with the gamma’ precipitates composition below 900 °C.