Thermal-spray (TS) technology was applied on NixCo0.6Fe0.2CrySizAlTi0.2 high-entropy alloys in this research. The results indicate that the hardness of high-entropy alloys undergoing a TS+ heat treatment (1100 degrees/10 h) is significantly increased to a near as casted state (1045 Hv) and provides excellent coarsening resistance performance resulting from the Cr3Si and several unidentified phases. This NixCo0.6Fe0.2CrySizAlTi0.2 alloy system does precipitate during casting, which is quite different compared to many applied alloys. The typical TEM images of the as casted NixCo0.6Fe0.2CrySizAlTi0.2 alloys with addition/removal of Mn, Si, and Ni element are also compared in this study. The results showed a significant amount of nano size particles (ranging from 5 to 10 nm), atoms segregation, twining structure and subgrain structure were distributed in the matrix. However, after the TS+ 1100 degrees C/10 h treatment, the main features found in the TEM are large amounts of nano size precipitates and dislocations. The mechanism of the dislocation formation and correlation of the hardness of the TS layer associated with the heat treatment are discussed. Crown Copyright (C) 2010 Published by Elsevier EN. All rights reserved.