Study On Microstructure And Mechanical Properties Of The Al_0.5CoFeNiMn_xc_y High Entropy Alloys

The high entropy alloy has a"cocktail"effect,and the changes in the element types?no less than 5?and content?no more than 35at%?will cause a significant change in its performance.Al_0.5Co Fe Ni alloy is FCC structure,with excellent plasticity and fracture toughness.However,the strength of this alloy is relatively low,and the yield strength is about 350MPa in the as-cast state.in as-cast state.For the formation of the interstitial solid solution,C element can improve the strength of the alloy matrix and for a stable austenite phase element,Mn is beneficial to enhance of the plasticity of the alloy matrix.Therefore,the effects of Mn and C elements on the microstructure and mechanical properties of Al_0.5Co Fe Ni alloy will be studied in this paper.In this paper,the microstructure and mechanical properties of Al_0.5Co Fe Ni Mn_xC_0.1 and Al_0.5Co Fe Ni Mn_xC_0.05 high entropy alloys were analyzed and measured by means of XRD,SEM/BSE,TEM,Vikers-hardness tester and electronic universal testing machine and the effects of annealing treatment on the microstructure and mechanical properties of Al_0.5Co Fe Ni Mn_0.15C_0.1 alloy were studied.Draw the following conclusions:Al_0.5CoFeNiC_0.1 high-entropy alloy has the typical dendric structure with BCC phase in the interdendrite and FCC phase in the dendrite along with the precipitatedkphase with ordered FCC crystal structure and the addition of Mn element does not change the phase composition and microstructure morphology of the alloy.With increase of Mn content,the particle size and volume fraction ofkphase first decrease then increase,the yield strength of the alloy increases first and then decreases and the plasticity linearly increase.The strengthening of the alloy is mainly the strengthening of thekphase nanoparticles and the strengthening of the BCC phase,among them,Al_0.5Co Fe Ni Mn_0.3C_0.1 alloy has relatively excellent comprehensive mechanical propertieswith yield strengths_0.2,tensile strengths_max and elongation of 1000 MPa,1007 MPa and 25.8%,respectively.Al_0.5CoFeNiMnx C_0.05 series high-entropy alloy has the same phase structure and micromorphology as Al_0.5Co Fe Ni Mn_xC_0.1 series high-entropy alloy,but the effect of Mn element onkphase particles is different.With increase of Mn element in Al_0.5Co Fe Ni Mn_xC_0.05alloy,both the particle size and volume fraction ofkphase decrease,the effect of the second phase strengthening is reduced and the yield strength and tensile strength of the alloy increase and the plasticity decreases.Al_0.5CoFeNiMn_0.15C_0.1 alloy annealed at 750? for 6h?24h and 48h still has a dendritic structure,but a lamellar eutectic structure composed of FCC phase and BCC phase are formed in the dendrite.With increase of the annealing time,thekphase region in the dendrite gradually decreases,and the eutectic structure region gradually increases.In addition,compared with those of as-cast Al_0.5Co Fe Ni Mn_0.15C_0.1 alloy,the strength of the alloy increased and the plasticity decreased after annealing at 750?.However,with the extension of the annealing time,the strength of the alloy decreases and the plasticity is basically unchanged.