Mechanical properties modification and design of high entropy alloys studied based on Molecular dynamics simulations

As a new type of structural material, high entropy alloys have unique microstructures and excellent comprehensive properties such as high strength and toughness, friction and wear resistance, corrosion resistance, radiation resistance, and high temperature resistance. They have promising application potential in the fields of transportation, aviation, and aerospace, and have attracted the attention of more and more researchers. However, a single metal alloy will have performance limitations for various service processes. The modification of high entropy alloy composites is expected to overcome the bottleneck of the inverse strength-toughness relationship of conventional alloys. At the same time, high entropy alloy composites effectively improve the radiation resistance of materials. The existing experimental conditions are difficult to meet the research needs of the microscopic deformation mechanism and mechanical properties of high entropy alloy materials. Therefore, the research on the mechanical properties of high entropy alloys is still in the development stage, and people have insufficient knowledge of the microscopic mechanism of high entropy alloys. In response to the above problems, this paper studies the performance optimization and microscopic mechanism of the AlCoCrFeNi high entropy alloy system based on the molecular dynamics simulations, and carries out the following researches.
Firstly, the deformation behaviour and irradiation resistance of high entropy laminates are studied using FeCoCrNiAl1.7 MG and FeCoCrNiAl0.5 HEA nanolaminate model, revealing the effect of interfaces on deformation mechanisms and irradiation response. The combination of glass and crystal nanolayers biases plastic deformation towards the region near the glass-crystal interface at lower strains, thereby reducing the activation barrier for the onset of dislocation nucleation and propagation. As the applied strain increases, dislocations are absorbed into the amorphous sheet by slippage at the glass-crystal interface, triggering the activation of uniformly distributed shear transition zones (STZs) in the amorphous sheet. Competing deformation mechanisms suppress the formation of local shear bands and increase the resistance to dislocation motion, thereby promoting the enhanced ductility and strength retention of MG-HEA nanolaminates. The combination of HEA and MG and the complex deformation behaviour overcome the typical strength-ductility trade-off. HEA and MG share the atomic displacement and structural damage from the high energy primary knock-on atom. The interface acts as defect sinks, accelerating the annihilation of interstitials at the interface. This results in the accumulation of residual vacancies in the crystallisation zone after the first cascade and the segregation distribution and imbalance between vacancies and interstitials in the HEA plate. The accumulation and aggregation of vacancies accelerates the formation of stacking faults and complex dislocation networks in the HEA plate. The interface also acts as a crystallisation seed, accelerating the crystallisation of the MG plate during irradiation. The redistribution of free volume generated in the collision cascade zone mitigates the structural damage in the MG plate, thereby maintaining the structural stability of the laminate in the overlap cascade.
Then, the crack-healing mechanisms and structural responses for FeCoCrNiAl0.5 HEA and FeCoCrNiAl1.7 MG are investigated. irradiation induces localized melting and rapid quenching processes in the collision cascade core. For HEA, the irradiation-induced interstitial defects in the cascade core diffuse into the crack area, leading to crack healing during the subsequent recrystallization process. In addition, the corresponding vacancies accumulate and form large-sized vacancy clusters, resulting in stacking faults and complex dislocation networks distributed around the healed crack area. As the number of irradiation times increases, the defect recombination rate increases and the phase stability is further improved. For HEMG, enhanced atomic diffusion accelerates the redistribution of free volume, allowing the crack area to heal. Defects in the HEMG structure generate more free volume during irradiation, leading to recovery of structural integrity and rejuvenation. Therefore, irradiation-controlled repair of cracks can effectively recover the structural integrity, thereby extending the service life of high entropy materials in advanced nuclear structural applications.