Effect of Dynamic Pre-Compression on Micro-Scale Indentation Hardness of CoCrFeNiMn High-Entropy Alloy

High-entropy alloys have excellent mechanical properties, such as high hardness, high strength, high resistivity, excellent wear resistance, excellent magnetic properties, and high-temperature mechanical and oxidation resistance. This also makes high-entropy alloys have a very broad application prospects. In the application of high-entropy alloys, there will be pre-existing plastic strains in the alloys. However, the mechanical properties of plastic deformed high-entropy alloys (such as the hardness under micro-scale compression) were less studied. In the micro-indentation test, it is necessary to eliminate the influence of the scale effect by adopting the corresponding micro-indentation test theory. Dynamic pre-compressions of CoCrFeNiMn high-entropy alloy at room temperature and high temperature (600, 800, 1000 ℃) were performed with split Hopkinson pressure bar in this paper, so that the alloy has different pre-compression plastic strains, and Nix-Gao which describes the scale effect is adopted. The hardness of dynamic pre-compression specimens with different plastic deformations was characterized at the micro-scale with the micro-scale indentation theory model. The results show that different plastic deformations under macro-precompression have a significant effect on the micro-scale indentation hardness of the alloy. Compared with axial compression, the hardness that eliminates the scale effect is greater than that of sample under radial compression. This research method establishes the relationship between the macroscopic plastic deformation and the micro-scale indentation hardness, and also provides a new idea for the realization of the micro-scale indentation test to determine the research method of the internal plastic deformation of materials.