Theoretical modeling of toughening mechanisms in the CrMnFeCoNi high-entropy alloy at room temperature

While multiple plastic deformation mechanisms at room temperature in the CrMnFeCoNi high entropy alloy (HEA) have been revealed experimentally, the qualitative and/or quantitative effects of the microstructural evolution on crack growth are studied rarely. In this work, the effects of crack bridging, crack-tip dislocation emission, and crack deflection on crack growth are modeled and analyzed. The results show that crack bridging via plastically deformed nanobridges has a significant inhibiting effect on crack growth, and the fracture toughness increases with an increase of the bridging-zone length. The crack growth resistance is also influenced by the structural transformation of the near-crack-tip dislocation pileup, which is sensitive to the grain boundary (GB) misorientation angle Delta theta. The pileup dislocations can penetrate across the GB at a small GB misorientation angle (at Delta theta <= theta(c), where theta(c) = 33.8 degrees similar to 35.5 degrees), while at large GB misorientation angles (at Delta theta > theta(c)), the dislocation pileup initiates nanocrack generation at the GB. Crack deflection has little effect on stress field near the crack tip but has a great shielding effect on the driving force for crack growth. The driving force is decreased by similar to 60% when the crack deflection angle reaches 70 degrees. This paper provides a comprehensive understanding of toughening mechanisms and suggests some strategies of microstructure design to improve the toughness of the HEA.