Microstructure Evolution and Mechanical Properties of AlCoCrFeNix High-entropy Alloys Heat-treated at High Temperature
Due to dendrite growth and element segregation during solidification,dual-phase high-entropy alloys cannot possess good comprehensive mechanical properties.Different from the design of eutectic alloy and the modification of casting process,phase transition of the metastable phase provides an optional route to regulate the microstructure and mechanical properties of the high-entropy alloy.However,phase constitution and distribution are closely related to the type and content of the alloying element,resulting in the varying effect of the solid-state phase transformation on the microstructure and mechanical properties of the multi-component high-entropy alloys.AlCoCrFeNix(1.4 ≤x≤ 1.7)high-entropy alloys were prepared by arc-melting method and the effect of high-temperature heat treatment on the microstructure and mechanical properties was investigated.As the Ni content is increased,the proportion of dendrite region(BCC/B2 spinodal structure)decreases gradually,while the proportion of interdendrite region increases with the structure evolving from FCC dendrite to FCC/B2 eutectic.Correspondingly,the yield strength and tensile strength of the alloys decrease from 1 067 Mpa(x=1.4)and 1 416 Mpa(x=1.5)to 464 Mpa and 1 191 Mpa(x=1.7),respectively,and the elongation increases from 1.7％(x=1.4)to 11.5％(x=1.7).After heat treatment at 1 100 ℃,the BCC/B2 spinodal structure transforms into FCC and B2 dual-phase structure,giving rise to the increase of plasticity and the decrease of strength.The heat-treated AlCoCrFeNi1 6 and AlCoCrFeNi1.7 high-entropy alloys present the typical network structure of the FCC phase,which contains the B2 precipitates and can prevent the reduction of the yield strength.The heat-treated AlCoCrFeNi1.7 high-entropy alloys possess the good comprehensive mechanical properties with 52.2％increment in elongation,while the decrement in yield strength and tensile strength are only 4.1％and 7.5％,respectively.
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