Microstructure And Mechanical Properties Of Thermally Stable And Low-activation V-based Multi Principal Alloys

With the development of new nuclear fusion reactor design,it is urgent to develop the first wall lining structural material.Vanadium-based alloys have gradually become a research hotspot due to their low activation characteristics,high melting point and excellent radiation resistance.However,their relatively low strength and the-lack of mechanical properties data at high temperatures limits the engineering application of vanadium alloys.The stable single-phase structure and low activation properties under high temperature and strong radiation conditions determine the service safety of the material.The innovative goal this project is to design V-based high entropy alloy by using low-activation elements,prepare master alloy by vacuum argon arc smelting,adjust and stabilize the structure of the alloy by regulating the composition of each element and doping of trace elements La,Ta,W and Y,optimize the mechanical properties of the alloy,and prepare low-activation V-based multi-principal high entropy alloy with a single-phase BCC structure,a high thermal stability and strong radiation resistance.The V-Fe-Cr-Mn and V-Fe-Cr-Mn+X_x multi-component alloys prepared in this dissertation have a single-phase BCC structure.V₅₀Fe₁₅Cr₁₅Mn₂₀ alloy was obtained by screening V-Fe-Cr-Mn solid solution alloys with a single-phase BCC structure.Solution strengthening results in excellent mechanical properties of the alloy.Yield strength and compressive strength of the alloy under room-temperature compression test are 1189 MPa and 1591 MPa,respectively,the fracture strain is 27%.The alloy phase structure remains stable at 1000?whereas Fe Mn_xC/O precipitates appear after annealing at 1200?after1h.These precipitates can strengthen the alloy matrix.The properties of alloy after 10 h annealing at 1000?recover to some extent,and the yield strength and compressive strength are 901 MPa and 1689 MPa,respectively.The compressive yield strength of V₅₀Fe₁₅Cr₁₅Mn₂₀ alloy at 800?is as high as 795 MPa,which is much higher than that of the same kind of radiation-resistant material.The low-activation V-based alloys were designed.It was found by thermal stability test that the mechanical properties of the material could be significantly improved with the increase of alloying element type.In addition,the stability of the single-phase BCC structure during long-term high-temperature annealing can be maintained.The experiment proves that the V₅₀Fe₁₅Cr₁₅Mn₂₀ alloy has the best phase structure stability.High density dislocation loops were produced in alloy after irradiation at 400?with 6 Me V Au³⁺and1E16 ions/cm² dosage.The average nano-indentation hardness in the range of 300-600 nm ion implantation depth showed that the pure V material hardened obviously.The hardening also occurred in the direction of ion implantation depth of V-based multicomponent alloy.However,the increase of element type could protect the inner layer matrix and reduce the depth of hardening layer.The overall hardening of V₅₀Fe₁₅Cr₁₅Mn₂₀alloy was not obvious and its radiation resistance should be relatively good.The phase structure of the five-component alloy basically remains stable after doping alloying elements.V₅₀Fe₁₅Cr₁₅Mn₂₀ alloy doped by La and Y elements purify the alloy melt to form impurity compounds which are dispersed in the matrix.Some of them form an alloy solid solution with the main elements,which can improve the plasticity of the alloy.Doping W and Ta elements can further enhance the strength of V₅₀Fe₁₅Cr₁₅Mn₂₀alloy.Yield strength,compressive strength and fracture strain of V₅₀Fe₁₅Cr₁₅Mn₂₀+La_2.0alloy are 1065 MPa,1590 MPa and 33%,respectively.Yield strength,compressive strength and fracture strain of V₅₀Fe₁₅Cr₁₅Mn₂₀+W_2.0 alloy are 1241 MPa,1684 MPa and30%,respectively.High temperature compression test shows that doping La_2.0 and Y_0.5will increase the plasticity of the alloy.However,the high temperature yield strength gradually decreases.The high-temperature properties of the alloy are significantly improved by doping W_2.0,Ta_1.0,and the high-temperature strength remains stable at800?.The V₅₀Fe₁₅Cr₁₅Mn₂₀+W_2.0 alloy is with the best high-temperature compression yield strength 1064 MPa at 600?,857 MPa at 800?and 173 MPa at 1000?.The high-temperature properties and thermal stability of the alloy are better than that of the irradiation-resistant structural materials and traditional V-based materials.