| The upgrading of nuclear power plants puts forward higher requirements on the radiation resistance of metal materials.Compared with traditional nuclear power materials,high-entropy alloys have excellent the radiation resistance due to its unique slow diffusion effect.However,the mechanical properties of the existing radiation-resistant high-entropy alloys are too poor to meet the requirements of high pressure and high temperature water in nuclear power plants,it is necessary to improve their strength and toughness to meet the needs of newer generation nuclear power plants.For the low strengths and plasticities,the mechanical properties of Fe-Mn-(Ni,Co)-Cr series high-entropy alloys with good radiation resistance are improved by means of microalloying and hot working and the deformation mechanism are also investigated,which provide a experimental basis for the preparation of high-entropy alloys with high strength and high radiation-resistance.FeMnNiCr and FeMnCoCr series high-entropy alloys are prepared in a non-consumable vacuum arc melting furnace following solution treatment at 1200? and hot rolling treatment at 1100?,and then the microstructure,mechanical properties and fracture mechanism are studied by XRD,SEM,EDS,EBSD,Vickers hardness instrument and electronic universal testing machine.The main research results obtained are as follows:After adding a trace of Zr element,the content and size of Cr-rich BCC phase in FeMnNiCrZr0.02 alloy decrease and a small quantity of Ni11Zr9 compounds with BCC structure are precipitated in the matrix.The yield strength,tensile strength and percentage elongation after fracture of the alloy is 279.3MPa,686.2MPa and 27.3%respectively,which has the best comprehensive mechanical properties among FeMnNiCrZrx alloys.After adding a small amount of C element,the Cr-rich BCC phase in FeMnNiCrCx alloys basically disappears and FeMnNiCrCo0.1 alloy has the best comprehensive mechanical properties among FeMnNiCrCx alloys with the yield strength of 352.9MPa,tensile strength of 666.7MPa and elongation after fracture of 32.5%.With increase of the content of Zr or C elements,intermetallic compounds are precipitated in FeMnNiCrZrx and FeMnNiCrCx alloys and their tensile fracture mechanism change from ductile fracture to brittle fracture.After adding 2at.%C element,the microstructures of as-cast(Fe80-xMnxCo10Cr10)98C2 alloys consist of a single FCC phase.After further adding lat.%Mo element,uniformly distributed dot-like ? phases are precipitated on FCC matrix to lead to the increase of the hardness,strength and elongation after fracture.After solution treatment at 1200?,? phases disappear in FCC matrix of(Fe80-xMnxCo10Cr10)97C2Mo1 alloys,and for the fine-grain strengthening effect,the hardness of(Fe50Mn30Co10Cr10)97C2Mo1 alloy is slightly higher than that of as-cast alloys.After hot rolling treatment at 1100?,(Fe80-xMnxCo10Cr10)9 7C2Mo1 alloys are still of a single FCC phase and the strength and plasticity are significantly higher than that of as-cast alloys.With the decrease of Mn content,the hardness and strength of as cast,as solution treated and as hot rolled alloys gradually increase,the elongation after fracture first increases and then decreases and the tensile fracture mechanism all belongs to the microvoid aggregation ductile fracture.As hot rolled(Fe50Mn30Co10Cr10)97C2Mo1 and(Fe45Mn35Co10Cr10)97C2Mo1 alloys have excellent comprehensive mechanical properties with the tensile strengths of 792.5 and 760.3 MPa,the elongations after fracture of 86.3 and 88.6%,and the strength plastic products of 68.4 and 67.4GPa-%.The deformation mechanisms of as hot rolled(Fe80-xMnxCo10Cr10)97C2Mo1(x=30,35,40)alloys are mainly the TWIP(twin-induced plasticity)effect.the deformation mechanism of as hot rolled(Fe55Mn25Co10Cr10)97C2Mo1 is dominated by the TWIP and TRIP(transformation-induced plasticity)effects. |
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