Fatigue Behavior Of CoCrFeNi-particle-reinforced 6061Al Matrix Composites Fabricated By Cold Spray-friction Stir Processing Composite Additive Manufacturing

Particle reinforced metal matrix composites prepared by traditional high energy beam additive manufacturing technology have poor fatigue properties.To solve the above problem,this study adopts a new additive manufacturing technology—cold spray-friction stir processing composite additive manufacturing（CFAM）.Innovatively,high-entropy alloy particles are used to replace traditional ceramic particles as reinforcing phases to improve the interfacial bonding ability with metal matrix.In addition,the microstructure evolution of CoCrFeNi_p/6061Al during the additive manufacturing process and the fatigue behavior of the composites were systematically studied.Based on the microstructure characteristics of CoCrFeNi_p/6061Al composites,the influence of CFAM technology on the fatigue properties of composites is analyzed.At the same time,the strengthening mechanism of CoCrFeNi particles in high cycle fatigue and fatigue crack propagation was revealedDuring the cold spraying process,the deposited particles undergo heterogeneous deformation,and adiabatic shear occurs at the particle boundary,which induces continuous dynamic recrystallization and significantly refines the grains.In the CS sample,the micropores and weak connections of deposited particles result in low tensile strength,elongation and fatigue properties.During the friction stir processing,CoCrFeNi particles are significantly broken by the stirring tool,and Al grains are significantly refined by particle-induced recrystalli-zation nucleation.At the same time,the intermetallic compounds produced by the interfacial reaction are dispersed into the Al matrix.The severe plastic deformation promotes the homogenization and densification of the microstructure,which makes the CFAM sample have excellent tensile strength,elongation and fatigue properties.The tensile strength of CFAM composites with 0 vol%,6 vol%,12 vol%and 18vol%CoCrFeNi is 217 MPa,262 MPa,293 MPa and 331 MPa,respectively.The tensile fracture mechanism is dimple fracture.The broken CoCrFeNi particles and the intermetallic compound particles produced by the interfacial reaction can improve the fatigue performance by preventing the yield of the Al matrix.The fatigue strength of CFAM composites with 0 vol%,6 vol%,12 vol%and 18 vol%CoCrFeNi at 10⁶cycles is 175 MPa,190 MPa,205 MPa and 215 MPa,respectively.The main fatigue crack initiation mechanism of CFAM composites is local yield on the surface of the sample and crack initiation induced by surface defects.The results of fatigue crack growth experiments show that the crack growth rate thresholds of 12 vol.%CoCrFeNi composites prepared by CS and CFAM processes are are 2.11 MPa·m^1/2 and 4.14 MPa·m^1/2,respectively.For CS composites,due to the low bonding strength between particles,cracks propagate along the weak bonding interface between particles,which results in fast crack growth rate.For CFAM composites,due to the high bonding strength between CoCrFeNi particles and Al matrix,cracks mainly propagate in Al matrix or Al matrix near the interface of CoCrFeNi particles.In the process of crack propagation,CoCrFeNi particles with high fracture toughness can effectively hinder crack propagation and reduce crack propagation rate.However,the increase of CoCrFeNi volume fraction reduces the passivation ability of plastic deformation on crack tip.