Research On Architecture Tailoring And Properties Of Al-Si Matrix Composites Hybrid Reinforced By CrNiCuAlFe High Entropy Alloy And SiC Particles

Al matrix composites are widely used in aerospace,automotive,and national defense fields because of high specific strength and good wear resistance.However,the wettability between the reinforcements such as traditional ceramic particles and Al matrix is poor,resulting in formation of the relatively weak bonding interface,which is not conducive to improve performance of the composites.High entropy alloys(HEA)are ideal reinforcements for the preparation of Al matrix composites due to high strength and good thermal stability among with natural metal properties that can effectively improve the interfacial wettability of the HEA/metal matrix.However,the performance difference between HEA and Al generally makes it difficult to coordinate deformation,the characteristic structure and intrinsic properties of HEA reinforced particles are difficult to control and so on,which limit the performance improvement of HEA reinforced composites to a certain extent.In this paper,Al-20Si matrix hierarchical composites were prepared based on the coupling of"tailoring HEA structure" and "building architecture".The composite reinforcements of SiC nanoparticles embedded in HEA particles(SiC@HEA)was obtained by shift speed ball milling,and hierarchical(HS,hierarchical structure)composites were prepared by spark plasma sintering(SPS).By adjusting the SPS sintering,cryogenic treatment process and the spatial distribution of HEA and SiC,the SiC@HEA composite reinforcements,SiC@HEA/Al interface,mechanical properties,corrosion resistance and strengthening and toughening mechanism were analyzed.The main research contents are as follows:(1)The SiC@HEA composite reinforcements was prepared by shift speed ball milling,Ar gas heat treatment(HT,heat treatment;temperature 1000℃,holding time 30 min and 60 min respectively),mixed with Al-20Si powder ball milling,SPS sintering(holding temperature 420℃,holding time 9 min)to prepare HS SiC@HEA/Al-20Si,HT30 SiC@HEA and HT60 SiC@HEA hierarchical composites.During the heat treatment,the decrease of surface energy acts as the driving force,triggering the migration of uniformly dispersed SiC nanoparticles on the HEA surface to form agglomerates.At the same time,hard and brittle intermetallic compounds such as AlCu,Al13Cr2 and Cr3Ni2 are formed at the interface of composites,which seriously weakens the mechanical properties of the composites.However,the presence of intermetallic compounds lead to significant increase in hardness of composites after heat treatment.As a comparison,the UTS(214.83 MPa),YS(119.55 MPa)and εf(4.47%)of the HS SiC@HEA/Al-20Si composite are higher than the UTS(181.33 MPa),YS(117.57 MPa)and εf(3.34%)of the HT30 SiC@HEA composite increased by 18.47%,1.68%and 33.83%,respectively.(2)The non-heat-treated SiC@HEA particle-reinforced composites in(1)were deep cryogenically treated(DCT)for different times.When the SPS sintering process is holding temperature 420℃ and holding time 1 min,the corresponding composites(DCT 60 h,DCT 96 h and DCT 120 h)achieve simultaneous improvement in mechanical properties and corrosion resistance.Compared with composite without DCT,the UTS(207.03 MPa)of the DCT 96h composite increased by 21.11%,but the YS decreased.It suggests that UTS can be enhanced by sacrificing plasticity,where strength enhancement is mainly attributed to increase in residual stresses inside composite.The DCT 120h composite has the lowest Icorr(5.31 × 10-6 A/cm2)and relatively positive Ecorr(-1.02 V),indicating that long-term DCT is beneficial to improve corrosion resistance of composite.The improved corrosion resistance can be attributed to the enrichment of Ni and Si elements in the interface layer.It is conducive to form Ni(OH)2 and NiOOH composite film in corrosive medium since Ni element can participate in anode passivation.(3)In order to maximize strengthening and toughening efficiency of the hierarchical structure,SiC@HEA/Al-20Si composites were prepared by adjusting the SPS sintering(holding temperature 480℃ and holding time 5 min)process.Compared with the homogeneously dispersed SiC+HEA/Al composite,the SiC@HEA/Al composite has the best mechanical properties with UTS and εf reaching 250.62 MPa and 9.03%respectively,achieving synergistic improvement in strength and plasticity.The SiC@HEA reacts with the Al matrix to form the double interface layer.The inner layer(～200 nm)near the HEA is composed of Ni2Si,FeNi,Ni3Si2 and FeSi phases,while the outer layer(～300 nm)adjacent to Al matrix is rich in NisSi2,Ni2Si and FeNi,which is beneficial to enhance the load transfer and crack passivation effect.At the same time,the constructed fine-grained "SiC@HEA hard phase region(NPR)"and "Al matrix soft phase region(NPF)" are alternately arranged in space to form the hierarchical structure,which is conducive to the coordination of strengthening and plastic deformation.The NPR region exerts strengthening effect by increasing the dislocation density and grain refinement,while theα-Al grains in the NPF region can promote plastic deformation.