In this work, describes the synthesis of multi-component nanocrystalline AlCrCuFeNi high entropy alloy by mechanical alloying (MA) and the effect of process control agent (PCA), on the characteristics of AlCrCuFeNi powders during milling have been investigated by XRD, SEM and EDS. It was found that after 60 h of milling process, with increasing PCA content: (a) The milled powder has two crystalline phases FCC and BCC which with change in PCA content, percentage of BCC phase change from 42% to 76% has reached and decreased the FCC phase (b) the particle morphology has changed from spherical to plate (c) the particle size decrease and the particle size distribution has shifted from uniform to non-uniform (d) the lattice strain decreased and the crystallite size increased. In the next step, thermal properties and annealing behaviors of this alloy (with 2 wt% PCA) were investigated.The milled powder for 70 hours exhibited good phase stability until 600 ? C. by increasing the temperature up to 600 ? C, the minor sigma phase (?) is formed, at 800 ? C another FCC phase that designated as FCC 1 appears. Therefore, there are two different FCC phases, since the position of the peak and the lattice parameter the FCC 1 phase are very close to that of Cu, it can be said that because of the positive chemical enthalpies between Cu and the other elements, the Cu atom has a repulsive interaction with other elements and tends to form a Cu-Cu bond.
