Effective retention of nanocrystalline microstructure and superior mechanical properties at high temperature (∼ 0.75 Tm) via doping of Boron into AlCoCrCuFeNi high entropy alloy
Document Type
Article
Publication Title
Materials Characterization
Publication Date
1-2025
Abstract/ Summary
Superfine microstructure, especially the nanocrystalline type, impart an excellent combination of mechanical properties in any engineering material in general. High entropy alloys (HEAs) are characterised by their simple and stable microstructure often forming a single phase or a mixture of two. Therefore, a HEA, with nanocrystalline microstructure stabilized at elevated temperature, can outstandingly serve for high temperature engineering applications. The present work demonstrates the synthesis of boron-doped nanocrystalline AlCoCrCuFeNiB1 (AlCoCrCuFeNi HEA with 1 at. % B) HEA comprised of FCC/BCC phases by mechanical alloying. Thermal stability of microstructure was examined by annealing it at temperatures up to 1173 K (∼0.75 Tm). Structural characterization carried out by X-ray diffraction has revealed that the FCC phase is stable, and its volume fraction increases with the annealing temperature. Transmission electron microscopy confirms that the newly developed alloy retains nanoscale microstructure at remarkably high temperature, nearly up to 0.75Tm. Evaluation of mechanical properties through microhardness measurement has exhibited 35 % higher hardness (8.95 ± 0.7 GPa) than the base composition (6.65 ± 0.65 GPa). Furthermore, the hardness of the doped sample has been found as ∼86 % of that in milled condition. Detailed calculations have shown considerable reduction in grain growth factor and enhancement in activation energy for grain growth due to doping of B in the AlCoCrCuFeNi HEA, which have played a crucial role in retention of the nanocrystalline structure. The Molecular dynamics simulation study indicates the segregation of B in the grain boundary areas of the doped HEA. About 80 % hardness of the annealed alloy is contributed by the Hall-Petch strengthening.