High Entropy Alloys (HEA) are widely studied because their high-performance properties. A 5%Cu-35%Cr-35%Fe-20%V-5%Ti HEA has been produced by vacuum arc-melting under a low-pressure He atmosphere, melting the sample at least five times to ensure high chemical homogeneity. Isochronal vacuum thermal treatments up to 900 ºC were performed, and samples were characterized by Positron Annihilation Spectroscopy (PAS) (Doppler Broadening Spectroscopy (DBS) and Positron Lifetime Spectroscopy (PLS) techniques). Previous studies show that this alloy presents a dendritic microstructure, with a Cr-enriched dendritic region with a fine distribution of nanometer spherical Cu particles; and the interdendritic regions consist of two phases: Ti and Fe enriched phase and Cu enriched phase. Ti precipitates can be observed homogeneously distributed in the sample. The microstructure is stable with temperature, and the only noticeable change is the growth of the Cu particles in the dendritic region. A “base” 4-element alloy (5.26%Cu 36.84%Cr 36.84%Fe 21.05%V) has been used to reference the CDB measurements in order to highlight the contribution of Ti. Figure 1 shows the studied samples CDB curves referenced to the 4-element alloy for selected temperatures, and pure annealed defect-less Cu and Fe CDB curves (for comparison purposes). CDB curves show that the environment of the vacancy-type defects is mainly associated to Cu in the low and mid temperature range. In the low temperature range (25 º C – 400 ºC) its contribution is relatively low, while in the mid temperature range (500 ºC to 700 ºC) it increases significantly. In opposition, in the high temperature range (800 ºC – 900 ºC) this significantly changes revealing the main contribution of Fe to the vacancy grouping. This change is also evidenced by PLS results by an increase in the mean lifetime from 138(1) ps to 150(1) ps.
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