Research On Microstructure And Properties Of High Entropy Alloy Reinforced Copper Matrix Composites Prepared By SPS Method

Particle reinforced metal matrix composites are a kind of metal matrix composites with wide application range and good application prospects because of their low cost and high performance.Copper-based composite materials not only maintain the excellent thermal conductivity and electrical conductivity of the matrix,but also have good comprehensive mechanical properties,and are currently widely used in electronics,automobiles,aerospace,machinery and other fields.However,the wettability between the traditional ceramic reinforcing particles and the copper matrix is poor,and the thermal expansion coefficient between the two is quite different,and defects are easily formed at the interface,which affects the performance of the composite material.As a potential new alloy,high-entropy alloys exhibit excellent properties that traditional alloys do not have due to their unique"four core effects".At the same time,it is a potential reinforcement of metal matrix composites because of its good wettability with the metal matrix and a similar thermal expansion coefficient compared with the metal matrix.If it can be used as a reinforcement for copper matrix composites,it is expected to overcome the defects caused by the infection of ceramic particles.In this paper,AlCoCrFeNi_2.1/Cu composites and CoCrFeNiTi/Cu composites were prepared by spark plasma sintering technology,and the effects of sintering temperature and reinforcing phase content on the microstructure and mechanical properties of the composites were investigated.The specific conclusions are as follows:（1）AlCoCrFeNi_2.1 high-entropy alloy is uniformly distributed in the matrix,and the combination with the copper matrix is good.With the increase of sintering temperature,the bonding mode between the copper matrix and the high-entropy alloy particles gradually changes from mechanical bonding to diffusion combined,an"interlocking region"is formed at the interface between the high-entropy alloy and the copper matrix,which is mainly related to the diffusion of Cu elements into the high-entropy alloy along with the BCC phase in the high-entropy alloy and the diffusion of Al and Ni elements into the matrix.the"interlocked region"consists mainly of Cu-rich and Co Cr Fe-rich phases.（2）In the preparation process of 10wt.%AlCoCrFeNi_2.1/Cu composites,the optimum sintering temperature is 800℃,the heating rate is 50℃/min,the sintering pressure is 40MPa,and the heat preservation is 10 min,the Brinell hardness of the composites reaches 60.4 HBW,the yield strength is 130.9MPa,the density is 98.4%,and the electrical conductivity is67.4%IACS.The density of the composite material increases first and then decreases with the increase of the sintering temperature.The AlCoCrFeNi_2.1 high-entropy alloy has a certain degree of decrease in the hardness of the reinforced phase due to the diffusion of Al and Ni elements in the BCC phase.The diffusion of elements in the alloy into the copper matrix reduces the electrical conductivity of the composite.（3）With the increase of reinforcing phase content,the phase structure of AlCoCrFeNi_2.1/Cu composites gradually appeared the diffraction peak of high-entropy alloy FCC phase,the density and electrical conductivity of composites decreased with the increase of reinforcing phase content,the hardness and the yield strength increase with the increase of the reinforcing phase content.When the mass fraction of HEA is 25wt.%,the hardness of the composite is 78.3HBW,and the yield strength is 201.3MPa,which is about 87%and 137%higher than that of pure copper,respectively.（4）With the increase of sintering temperature,Fe₂Ti type and Ni_2.67Ti_1.33 type intermetallic compounds gradually appeared in CoCrFeNiTi/Cu composites,and the structure of high-entropy alloy reinforced phase gradually changed from fine dendritic structure with the increase of sintering temperature as a three-phase structure,slight diffusion occurred between the high-entropy alloy and the matrix,and no diffusion layer or interlocking structure was formed.（5）The density and hardness of CoCrFeNiTi/Cu composites increased with the increase of sintering temperature.At 750°C,the density and Brinell hardness of the composite material are 97.77%and 74.9HBW,respectively.When the sintering temperature was 950°C,the density and Brinell hardness of the composite material increased to 98.85%and 82.5HBW,respectively;In addition,the Vickers hardness of the matrix and the reinforcing phase also increased.When the sintering temperature increased from 750°C to 950°C,the hardness of the high-entropy alloy increased from 704HV to 969HV,but its plasticity decreased significantly,and cracks appeared at the indentation tip.The electrical conductivity of the composite decreases with the increase of the sintering temperature,which is caused by the accelerated diffusion of elements between the high-entropy alloy and the matrix.At 950°C,the compressive yield strength of the composite is 204.7 MPa,which is higher than that of pure copper about 140%.Compared with pure copper,the wear resistance of composites is improved obviously,and the wear mechanism of composites is gradually changed from adhesion wear and fatigue wear of pure copper to abrasive wear and adhesion wear.