Insight of novel CoCrFeMnNi–Al2O3p high entropy alloy matrix composites by mechanical alloying and spark plasma sintering

In the present work, novel nano-Al2O3p reinforced heterogeneous CoCrFeMnNi matrix composites with 0-7.5 wt% Al2O3p were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS) method. The microstructure evolution and properties, i.e., density, hardness and room temperature compression were systematically studied. The results show that different degrees of heterogeneous matrix organization occurred in the composites. The CoCrFeMnNi-2.5wt%Al2O3p composite consists of CG region and UFG region of uniformly distributed nano-Al2O3p. And the addition of nano-Al2O3p can effectively refine the matrix grains. Compared to pure HEA, the grain size of CoCrFeMnNi-5.0wt%Al2O3p composite is refined by 48.5%. With the increase of nano-Al2O3 content, the hardness values of the composites increased by 23.6% to 56.7% than those of pure HEA. Among the nanocomposites, the CoCrFeMnNi-5.0wt%Al2O3p composite exhibits the best strengthening effect, while the CoCrFeMnNi-2.5wt%Al2O3p composite shows a superior strong-plastic synergistic effect with yield strength, ultimate compressive strength and fracture strain of 913 MPa, 1935 MPa and 38%, respectively. However, with the Al2O3p content further increases to 7.5 wt%, both the strength and plasticity of the composite decrease due to the serious agglomeration of nanoparticles.