Preparation,Microstructure And Properties Of CoCrFeMnNi High-Entropy/Aluminide Laminated Composites

In this paper,CoCrFeMnNi high-entropy alloy foil with high fracture toughness prepared by selective laser melting（SLM）was selected as the ductile layer.Based on CoCrFeMnNi/Al multiple interdiffusion system,CoCrFeMnNi high-entropy/aluminide laminated（HAL）composite was prepared by vacuum hot pressing sintering.The multilayer and composite intermetallic compound phase structure obtained by multiple diffusion system to improve the integrity can provide a new research idea for the strength and toughening of metal-intermetallic compound laminated composites.The microstructure was characterized by scanning electron microscopy（SEM）,energy dispersive spectroscopy（EDS）and electron back scattering diffraction（EBSD）.The physical and mechanical properties were characterized by densitometry,microhardness measurement,three-point bending,fracture toughness and dynamic compression.The atomic diffusion law,growth kinetics and second phase precipitation mechanism of multicomponent interdiffusion HAL composite at 655℃were investigated.On the basis of semi-solid reaction HAL composite,the internal toughening by annealing at 1000℃was conducted to study the diffusion form of atoms and the growth mechanism of ductile aluminide at high temperature.Finally,based on the quasi-static and dynamic mechanical properties tests,the effects of ductile aluminide of B2structure on the mechanical properties were analyzed.The main conclusions of the study are as follows:1.HAL composite at semi-solid temperature:（1）The diffusion reaction phase of HAL composite at semi-solid temperature is a four-layer aluminide structure layer based on Al₁₃（Cr,Mn,Fe,Co,Ni）₄phase,and the diffusion reaction phase is mainly based on the crystal structure of Fe-Al compound.（2）In CoCrFeMnNi-based HAL composites,the formation of chalalides in six-element diffusion system is related to the diffusion behavior of different elements.The diffusion behavior of Cr and Mn is similar,that of Co and Ni is similar,and that of Fe is similar to the intermediate type.（3）The growth model of aluminum layer of CoCrFeMnNi-based HAL composite is"grain boundary and bulk diffusion",and the growth rate is slow.The reaction process can be shortened by adjusting the thickness of Al foil or reducing the number of HEA elements,so as to improve the overall performance.（4）Due to the"hysteretic diffusion"effect of HEA,the hardness of Al₁₃（Cr,Mn,Fe,Co,Ni）₄phase based aluminum layer is lower,which is beneficial to reduce the sudden change of hardness between HEA layer and aluminum layer,and reduce the stress concentration at the interface.（5）The bending strength and fracture toughness of HAL composites can reach 750 MPa and 25MPa·m^1/2,respectively.The main energy dissipation modes of HAL composites are the deformation of ductile layer and the fracture of hard brittle layer.The dynamic impact failure modes of HAL composites are mainly plastic deformation and 45°adiabatic shear band.Its impact strength and energy consumption are up to 1800 MPa and 2260 J/mm³.2.HAL composite material after high temperature annealing:（1）Under high temperature annealing,the four-layer aluminide structure layer based on Al₁₃（Cr,Mn,Fe,Co,Ni）₄phase changes into tripartite crystal structure Al₈（Cr,Mn,Fe,Co,Ni）₅phase and then gradually changes into B2 cubic crystal structure Al（Cr,Mn,Fe,Co,Ni）phase.（2）Under high temperature annealing,Ni,Co and Fe in multicomponent diffused atoms have higher diffusion rate and diffusion amount in the aluminum layer,and the transition of aluminum mainly depends on the diffusion behavior of Ni,Co and Fe.（4）Under high temperature annealing,Al（Cr,Mn,Fe,Co,Ni）is mainly controlled by bulk diffusion and interfacial diffusion,and the growth rate of Al（Cr,Mn,Fe,Co,Ni）is much higher than that of Al₁₃（Cr,Mn,Fe,Co,Ni）₄.（4）The hardness indentation tip of the high hardness B2-Al（Cr,Mn,Fe,Co,Ni）phase obtained by annealing at high temperature has no crack,which belongs to the ductile aluminide of multi-slip system,which helps to alleviate the deformation resistance of the hard brittle layer and reduce the probability of delamination failure in the plastic deformation process of the material.（5）The bending strength and fracture toughness of HAL composites after annealing at high temperature can reach 1000 MPa and 32.5 MPa·m^1/2,respectively.The B2 structure at the interface of HEA and aluminide has a higher common degree,which makes the loading force transfer between layers better and improves the force required for interlayer failure.The dynamic impact failure forms are mainly plastic deformation and layered fracture.The maximum impact strength and energy consumption are 2317 MPa and4750 J/mm³.