Achieving Strengthening And Toughening Of High Entropy Alloy Reinforced Aluminum Matrix Composites By Constructing Heterogeneous Interface

Compared to traditional ceramic particle reinforcement,high-entropy alloy(HEA)has emerged as a promising metal material reinforcement due to its exceptional strength,high plasticity,and superior wettability with aluminum(Al)alloys.The inclusion of multi-component HEA particles in Al matrix can result in the formation of either a mechanical bonding interface or a multi-component intermetallic compound interface.However,this can limit the potential for strengthening and toughening effects of the HEA.Therefore,the optimization of Al matrix composites can be achieved through the design of the interface between HEA and Al matrices.In this study,Al0.5CoCrFeNi single-phase BCC structure HEA particles were subjected to heat treatment in nitrogen and argon atmospheres to produce nitrogen and argon-modified reinforced phase powders(NHEA and AHEA).After that,we analyzed the phase change structures.Then added the modified reinforcement powders to the 2024Al matrix and then prepared NHEA/Al and AHEA/Al composites through spark plasma sintering(SPS).On the other hand,HEA was subjected to oxidation and heat treatment at various temperatures to produce the oxidized reinforced phase(OHEA),which was used to investigate the phase transition behavior of OHEA and prepare OHEA/Al composites.We delved into the interface structure,mechanical properties,corrosion performance,and the corresponding mechanisms for strengthening and toughening of the composite materials.The key findings of this paper are summarized as follows:(1)This study investigates the microstructure evolution and performance improvement mechanism of Al matrix composites reinforced with high-entropy alloy(HEA)after heat treatment in an inert atmosphere.Two types of HEA powders,NHEA and AHEA,were prepared by heat-treating HEA at 700℃ for 1 hour in nitrogen and argon,respectively.Upon heat treatment,the BCC diffraction peak of the HEA decreased,while the FCC phase precipitated at the grain boundary.Additionally,nanopits are formed on the surface of NHEA,while both nanopits and nanoparticles are present on the surface of AHEA.The prepared interface layers of HEA/Al,NHEA/Al,and AHEA/Al exhibit similar characteristics,all having diffusion layers of approximately 1 μm.The interface between HEA/Al and AHEA/Al diffusion layers primarily forms the Al9Co2 phase,while the thickness of the nitride(MxNy)at the interface of the NHEA/Al diffusion layer increases.Taking HEA/Al composites as an example,the stress is primarily distributed within the Al matrix.As the material undergoes stretching,the crack typically originates from the diffusion layer and gradually propagates into the Al matrix,ultimately leading to the fracture of the composite material.Fine grain strengthening,thermal mismatch strengthening and geometric dislocation strengthening play the main roles.The tensile strength(σuts),yield strength(σy)and elongation(εf)of HEA/Al are 284.9 MPa,170.8 MPa and 16.44%,respectively.The σy,σuts and εf of NHEA/Al are 165.4 MPa,293.3 MPa and 15.1%,respectively,and the σy,σuts andεf of AHEA/Al are 151.6 MPa,284.1 MPa and 11.6%.(2)Microstructure and performance enhancement mechanism of Al matrix composites reinforced by HEA by oxidation heat treatment.HEA powder was oxidized at 500-900℃ for 1 h to obtain BCCFCC dual-phase structure OHEA powders.According to SEM and XPS analysis,the nanoparticles formed on the surface of OHEA are multi-element metal oxide mixtures.The OHEA/Al composites was prepared by the same SPS process,and the σy,σuts,and εf are 323.81 MPa,198.72 MPa,and 18.16%,respectively,which were 35.31%,57.34%,and 63.33%higher than that of the 2024 Al matrix,showing excellent toughness.Among them,the reaction between OHEA and Al matrix is accelerated,and OHEA reacts almost completely to form a transition interface of about 20～30 μm.Oxidative heat treatment affects the redistribution of HEA solutes,resulting in the transition interface being the FCC structural phase(soft phase)evolved from the FCC phase reaction in OHEA during thermal processing and the monoclinic structural phase(hard phase)evolved from the BCC phase,and the two interweave together,they build a multiphase and multiscale hybrid interface.During the stretching process,cracks are preferentially initiated in the hard phase region due to severe stress concentration,and the soft phase region can retard crack growth.The synergistic effect of hard phase and soft phase realizes the strengthening and toughening of composite materials.