Composition Design And Microstructure Research Of Nial Based Eutectic High-entropy Alloy

NiAl alloy has the advantages of low density(5.9g/cm3),high melting point(1638?),high thermal conductivity(76W/m.K)and excellent oxidation resistance.It is expected to become a new generation of ideal structural materials,but its low strength and brittleness at room temperature limit its application.At present,most of the methods to improve its strength and brittleness are to alloy NiAl alloys to form NiAl-based eutectic alloys,such as NiAl-34Cr,NiAl-9Mo,NiAl-28Cr-6Mo,NiAl-39V,NiAl-1.5W and other alloys,but it is difficult to obtain high strength and plasticity at the same time.Recently,it has been noticed that eutectic high-entropy alloys can combine the respective advantages of the matrix phase and high-entropy phase to obtain good performance.Therefore,the concept of eutectic high-entropy alloys is considered to be applied to NiAl,that is,to add multiple elements to NiAl at the same time.A number of NiAl-based eutectic high-entropy alloys are designed in order to obtain excellent performance.Using the design ideas of eutectic high-entropy alloys for reference,the elements of Mo,Cr,V and Fe are introduced into NiAl alloys to form eutectic high-entropy alloys based on NiAl.Combined with JMatPro software to simulate the solidification path and trial and error method to find the eutectic composition points of the alloy,the NiAl-MoCrV series,NiAl-MoCrFe series and NiAl-MoCrVFe series eutectic high-entropy alloys were designed respectively.Among them,the NiAl-MoCrV series high-entropy alloy adjusts the element content in the alloy.With the increase of the Mo,Cr,and V element content in the alloy,the alloy structure evolution process is:NiAl primary phase+eutectic phas?eutectic phase?MoCrV Primary phase+eutectic phase.The eutectic composition point of the system is NiAl-Mo8.7Cr8.7V8.7,and its structure is composed of NiAl phase and MoCrV phase.The yield strength of NiAl-Cr8.7Mo8.7V8.7 eutectic high-entropy alloy is 1557.49MPa.The value is 10.27%.In contrast,hypereutectic NiAl-Mo10Cr10V10 alloy has higher strength(1708.52MPa)and strain value(20.93%).In the NiAl-MoCrFe system,with the increase of Mo,Cr,Fe element content,the alloy structure evolution process is:NiAl primary phase+eutectic phase?eutectic phase?MoCrFe primary phase+eutectic phase.The eutectic composition point of the alloy system is NiAl-Mo14.5Cr14.5Fe14.5.Due to the higher hardness of the MoCrFe phase,the hypereutectic NiAl-Mo16Cr16Fe16 alloy has a larger volume fraction of MoCrFe,so the alloy has the highest strength and hardness.The compression fracture mode of the alloy is cleavage brittle fracture mode.In the NiAl-MoCrVFe system,by adjusting the content of Mo,Cr,V,and Fe elements,the eutectic composition point of the high-entropy alloy of the system is NiAl-Mo10Cr10V10Fe10.The eutectic high-entropy alloy is composed of NiAl phase and MoCrVFe phase.The research results show that in hypereutectic NiAl-Mo11Cr11V11Fe11,due to the large amount of MoCrVFe primary phases,the MoCrVFe phase has high hardness,which results in high yield strength of the corresponding alloy.NiAl-(MoCrVFe)44 has the best compressive performance,with a yield strength of 2190.23MPa,a compressive strength of 3542.46MPa,and a strain value of 19.43%.