Study On Microstructure And Properties Of CoCrFeMnNi/6061Al Composites Prepared By SPS

Particle reinforced composites are an important branch of metal matrix composites.Aluminum-based composite materials have various advantages such as high specific strength and specific stiffness,good thermal stability,good thermal conductivity,wear resistance and corrosion resistance.Therefore,they are widely used in advanced technologies such as aerospace,optical instruments and electronic packaging.However,ceramic particles are mainly used as particle reinforcement phases.The biggest problem of ceramic particles as reinforcement is the poor wettability of the particles and the matrix and the low interface bonding strength.However,metal-based particles and matrix do not have these problems,so high-entropy alloy particles are introduced as reinforcements for aluminum-based composites.High-entropy alloys are new alloys developed in recent years with high tensile strength,high hardness and good thermal stability.In order to study the properties of high-entropy alloy particle reinforced aluminum matrix composites,CoCrFeMnNi/6061Al composites were prepared by SPS method.The microstructure of the composite was characterized by scanning microscope,the phase of the composite was analyzed by X-ray diffractometer,and the density of the composite was determined by electronic analytical balance.After that,the hardness test,tensile test and friction and wear test were carried out to study the macroscopic mechanical properties of the composites.Finally,nano-indentation test was carried out to study the micro-nano mechanical properties of the single particles on the composite.The spherical CoCrFeMnNi particles with high entropy of 75 micron and spherical 6061 aluminium alloy powder with 13 micron were mixed uniformly by high energy ball milling.The ball-to-batch ratio is 8:1,the rotation speed is1200 r/min,and the ball milling time is 4 h.The ball mill tank used is a stainless steel ball mill tank with argon gas protection.The uniformly mixed powder was placed in an SPS sintering furnace,sintered at 580°C and kept hot for 5 min.Finally,the CoCrFeMnNi/6061Al composite material without obvious holes,cracks or other defects was obtained,and the reinforced particles were evenly distributed in the matrix.The sintered composite materials formed an interfacial reaction layer with a thickness of about 20 microns between the matrix and the reinforced particles,and the interfacial shape was petal-shaped.The interface layer can be divided into two parts:interface layer I and interface layer II.From the XRD diffraction pattern,it is found that the BCC solid solution phase is newly formed in the composite material,and no intermetallic compound is formed.Therefore,it is presumed that a new Al_x?CoCrFeMnNi?_100-x?x is at%?high-entropy alloy was formed at the interface due to the gradient distribution of Al element.Both the theoretical density and actual density of the composite increase with the increase of the reinforcement particle content,but the relative density decreases.The relative density of the composites is good,the highest is 99.3%,the lowest is 97.7%.The macroscopic hardness increases with the increase of reinforcement.When the reinforcement content is 10%,the Brinell hardness value reaches 73 HB.The composite interface layer II has the highest microhardness value of 691 HV_0.1.The tensile test of the composite with the reinforcement content of 0.5⁷wt%shows that the ultimate tensile strength of the composite increases first and then decreases,and the elongation decreases.When the content of the reinforcement is 1wt%,the composite has good comprehensive mechanical properties.The ultimate tensile strength is 280.04MPa,which is about 83%higher than the matrix and the elongation is 11.3%.The fracture morphology obtained by tensile test is mainly that the reinforcement particles are pulled out of the matrix,and the cracks usually deflect and propagate in the interface layer during fracture.The friction and wear tests were carried out on the composites with the reinforcement content of10⁴0wt%,and the wear resistance increased with the increase of the reinforcement content.When the reinforcement content is 40wt%,the specific wear rate reaches 6.65?10^-7 mm³/N?m.When reinforcement content is 10wt%and 20wt%,the wear mechanism of composites is mainly adhesion wear,delamination wear and abrasive wear.The micro-nano mechanical properties of individual particles on the composite were studied,and it was found that the elastic modulus and hardness of the interface layer were greater than that of the reinforced particles and matrix,indicating that the interface layer had better micro-nano mechanical properties than the reinforced particles and matrix.Therefore,the interface layer plays an important role in the improvement of the macroscopic mechanical properties of the composite material.The study of the micromechanical properties of the material can effectively guide the design of the composite material to obtain the desired macroscopic mechanical properties.