Studying On Preparation Of AlCoCrNiFe High-entropy Alloy By Hot Oscillating Pressure And Performance Optimization

High entropy alloy（HEA）was one of the three major breakthroughs in alloying theory in recent years.Because of its unique alloy design concept and simple phase structure,HEA has good performance in strength,hardness,corrosion resistance.At present,the main preparation methods of HEA were solidification,additive manufacturing and powder metallurgy.Among them,the solidification and additive manufacturing has low utilization rate,high cost,which was easily cause element segregation and reduce the properties of the alloy.The traditional powder metallurgy method has some shortcomings such as low density of samples and high sintering energy consumption.Recently,the emergence of hot oscillating pressing（HOP）was expected to improve the properties of HEA and reducing energy consumption.Based on this,AlCoCrNiFe HEA was sintered by HOP.The effects of sintering temperature,holding time and oscillating pressure（the median value of pressure,the amplitude of pressure）on the microstructure and properties of AlCoCrNiFe HEA were systematically studied.The main content of this paper are as follows:（1）The sintering temperature has an important effect on the microstructure,density,hardness and corrosion resistance in 3.5wt.%Na Cl solution of AlCoCrNiFe HEA.At different sintering temperatures,the AlCoCrNiFe HEA was a dual-phase coupled eutectic structure of FCC and BCC phase.With the increasing of sintering temperature,the original powder boundary profile of AlCoCrNiFe HEA was gradually disappeared,the microstructure uniformity was improved,and the density increased gradually.When the sintering temperature was 1100℃,the density of samples sintered by HOP could reach99.23%,and the hardness was 488.8HV₁,while the corrosion current density and corrosion rate in 3.5wt.%Na Cl solution were only 1.5μA/cm²and 0.01mm/year,which were better than those of samples sintered by HP at the same sintering temperature and similar materials reported in the literature.（2）The holding time has an important effect on the microstructure,density,hardness and corrosion resistance in 3.5wt.%Na Cl solution of AlCoCrNiFe HEA.With the extension of holding time,the density,hardness and corrosion resistance of AlCoCrNiFe HEA sintered by HOP were improved.Under the same holding time,HOP can effectively promote the disappearance of the original powder boundary profile,improving the microstructure uniformity and reducing the internal pores,so that the density,hardness and corrosion resistance of samples sintered by HOP were better than those of samples sintered by HP.When the holding time was 1.5h,the density and hardness of AlCoCrNiFe HEA sintered by HOP could reach 99.18%and 479HV₁,while the corrosion current density and corrosion rate were only 6.5μA/cm² and 0.055mm/year.（3）The oscillating pressure（the median value of pressure,the amplitude of pressure）has an important effect on the microstructure,density,hardness and corrosion resistance in 3.5wt.%Na Cl solution of AlCoCrNiFe HEA.In the same control group,the density,hardness and corrosion resistance in 3.5wt.%Na Cl solution of the samples sintered by HOP were better than those sintered by HP.With the increasing of oscillating pressure（the median value of pressure,the amplitude of pressure）,the boundary of the original powder of AlCoCrNiFe HEA melted,the densification rate and the density of the samples increased,the hardness and the corrosion resistance of the sample increased as well.With the increasing of oscillating pressure,when the median value of oscillating pressure was60MPa,the density and hardness of AlCoCrNiFe HEA sintered by HOP were 95.91%and443HV₁,respectively.The corrosion current density and corrosion rate of samples sintered by HOP in 3.5wt.%Na Cl solution were 14.9μA/cm² and 0.104mm/year,respectively.When the amplitude of pressure was±10MPa,the density and hardness of AlCoCrNiFe HEA sintered by HOP could reach 99.11%and 481HV₁,while the minimum corrosion current density in 3.5wt.%Na Cl solution was 9.1μA/cm² and 0.076mm/year.