Research On The Effect Of Nitrogen On Microstructure And Mechanical Properties Of Dual Phase High Entropy Alloy Fe₅₀Mn₃₀Co₁₀Cr₁₀

High entropy alloys are a new class of alloys that have been developed in recent years.Due to their excellent comprehensive performance,high entropy alloys have a broad application prospects.Fe50Mn30Co10Cr10 is a dual phase high entropy alloys with TRIP effect,which possesses better strength-ductility combination than most traditional alloys and high entropy alloys,so it is promising to be a new engineering material.However,the yield strength of Fe50Mn30Co10Cr10 high entropy alloy can't meet the requirements of engineer application,which needs further improvement.Therefore,interstitial atom N is considered to introduce into the Fe50Mn30Co10Cr10 high-entropy alloy to improve mechanical properties.In this study,the influences of nitrogen on the microstructures and mechanical properties of as-cast and solid solution Fe50Mn30Co10Cr10dual phase high entropy alloy was investigated.The effect of nitrogen on the microstructures of Fe50Mn30Co10Cr10dual phase high entropy alloy was investigated by means of optical microscope(OM),scanning electron microscope(SEM),X-ray diffraction(XRD)and electron backscatter diffraction(EBSD).The effect of nitrogen on the mechanical properties of Fe50Mn30Co10Cr10 dual phase high entropy alloy was investigated by using universal material testing machine and impact testing machine.The microstructures of high-entropy alloys with different strains were observed to analyze the effect of nitrogen on deformation mechanism of Fe50Mn30Co10Cr10dual phase high entropy alloy.The main conclusions are as follows:Inclusions types of 1.15N high entropy alloy were consistent with those of 0N high entropy alloy,which were composite inclusions composed of oxides and sulfides.And no nitride inclusion could be observed.The addition of nitrogen refined the grain size of as-cast high entropy alloy.At the same time,nitrogen inhibited the thermally induced martensitic transformation of Fe50Mn30Co10Cr10 high entropy alloy during cooling,and converted the high entropy alloy from dual phase structure to single phase fcc-structure.Nitrogen acted as a solid solution strengthener in as-cast high entropy alloy.In addition,the addition of nitrogen inhibited the deformation induce martensitic transformation during tensile deformation,so the deformation of the as-cast high entropy alloy is mainly controlled by dislocation sliping and deformation twinning.The combination of various strengthening and toughening mechanisms resulted in the higher yield strength and elongation of as-cast 1.15N high entropy alloy at room temperature,but the tensile strength is slightly lower.The room temperature impact results of as-cast high entropy alloy showed that the impact toughness of the 1.15N high entropy alloy was better than that of the 0N high entropy alloy.After solution treatment,the high-entropy alloys were composed of only FCC phase.The addition of nitrogen significantly refined the grain size.Moreover,there was no nitride precipitation in 1.15N high entropy alloy,so the nitrogen element was fully dissolved in the matrix,the 1.15N high entropy alloy benefited profoundly from interstitial solid solution strengthening and fine grain strengthening.In addition,the addition of nitrogen inhibited the deformation-induce martensitic transformation during tensile deformation,so the deformation of the solid solution high entropy alloy was mainly controlled by dislocation sliping and deformation twinning.The combination of various strengthening and toughening mechanisms resulted in the higher yield strength,tensile strength and elongation of solid solution 1.15N high entropy alloy at room temperature.In addition,the impact results showed that the addition of nitrogen increased the impact toughness of the solid solution high entropy alloy at room temperature.However,nitrogen inhibited deformation-induced martensitic transformation during impact at liquid nitrogen temperature,resulting in a significant reduction in the impact toughness of the alloy.