Research And Preparation Of Strength And Toughening Of CoCrFeNiMo Series High-entropy Alloys

High entropy alloy（HEA）is a multi-component alloy,which has become a potential candidate material for core components such as aerospace engines and tank protective armor because of its excellent comprehensive mechanical properties.Compared with traditional alloys,lattice distortion caused by multi-component special design will significantly increase the strength of HEA,however,it will bring about a decrease in its plasticity.Co Cr Fe Ni Mo series HEAs are expected to become the next generation of hot-end components due to their high strength and plasticity,high-temperature strength and corrosion resistance,which have been widely studied and concerned.A large number of studies have shown that their strength and toughness can be improved by microalloying and various deformation heat treatment processes.For example,the tensile strength and plasticity of(Co₄₀Cr₂₅Fe₁₆Ni₁₆Mo₃)_99.5C_0.5HEA reach825MPa and 75%respectively.In order to further improve its strength and toughness,the rolling heat treatment process of(Co₄₀Cr₂₅Fe₁₆Ni₁₆Mo₃)_99.5C_0.5is regulated in this paper.The effects of solution,rolling,annealing and hot rolling on the structure and properties of(Co₄₀Cr₂₅Fe₁₆Ni₁₆Mo₃)_99.5C_0.5HEA were studied.The stacking fault energy,stacking fault energy and stacking fault energy were studied by X-ray diffraction（XRD）,scanning electron microscope（SEM）,transmission electron microscope（TEM）and electron backscattering diffraction（EBSD）.The main conclusions are as follows:The HEA(Co₄₀Cr₂₅Fe₁₆Ni₁₆Mo₃)_99.5C_0.5can keep the FCC single-phase structure when it is warm rolled.When the HEA(Co₄₀Cr₂₅Fe₁₆Ni₁₆Mo₃)_99.5C_0.5is warm rolled,it can be seen that the nano-scale ultra-fine microstructure will be formed,and this ultra-fine microstructure will be rolled together by distribution.With the warm rolling temperature,The distribution is gradually uniform.When the HEA(Co₄₀Cr₂₅Fe₁₆Ni₁₆Mo₃)_99.5C_0.5is warm rolled at 500℃,the properties of the HEA reach the best,and the yield strength,tensile strength and elongation are1501MPa,1858MPa and 9.5%respectively.The deformation mechanism is mainly phase transformation-induced plastic deformation mechanism,supplemented by twin-induced plasticity.The low-temperature annealed(Co₄₀Cr₂₅Fe₁₆Ni₁₆Mo₃)_99.5C_0.5HEA is a single-phase FCC structure,and the rearrangement of dislocations in its sheet will form some regions with low dislocation density.With the increase of annealing temperature,dislocations are gradually entangled to form cellular structures,and the density of most other dislocations is greatly reduced,which forms a pinning effect on grain boundary movement.When the temperature continues to rise,dislocations soften,and the cellular structure entangled by dislocations is released,and the pinning effect is greatly reduced.The yield strength and tensile strength of the high entropy alloy first increase and then decrease with the increase of annealing temperature.When the annealing temperature is 500℃,the yield strength and tensile strength of the alloy increase to 2046MPa and 2244MPa at the same time,showing excellent ultra-high strength.With the further increase of the temperature,the recrystallization areas gradually increase until the alloy is annealed at 750℃for 10min,and with the generation of M₂₃C₆carbide precipitation phase,when the alloy is annealed at 750℃for 10 min,The yield strength,tensile strength and elongation reached a high level,which were 927MPa,1211MPa and 42.1%in turn.At this time,it reached the best mechanical properties and showed excellent strength and toughness.The(Co₄₀Cr₂₅Fe₁₆Ni₁₆Mo₃)_99.5C_0.5HEA was annealed at 800℃for 10min.The microstructure of the alloy was composed of fine recrystallized grains and deformed grains that were not completely recovered.The yield strength of the alloy was 1052MPa,while the elongation was still 35%.The non-uniform structure made the HEA show excellent mechanical properties.With the increase of annealing temperature,the average size of each HEA increased continuously.When the annealing temperature continues to rise to 1100℃,the microstructure of the HEA consists of uniform equiaxed grains and annealing twins.After annealing at 1200℃for 10min,90.3%super plasticity of the HEA appears.