Design,Microstructure And Mechanical Properties Of W-Mo-V Base High-Density High-Entropy Alloys

High-entropy alloys（HEAs）usually contain 4-5 or more principal elements,and the atomic percentage of each element is more than5%.This concept shows great potential for designing novel materials with extraordinary properties.In this paper,advanced high-density W-Mo-V base HEAs with excellent mechanical properties were developed by following the concept of HEAs.The relationships among alloying compositions,microstructures and mechanical properties were systematically studied.First,a W₃₅Ta₃₅Mo₁₀Nb₁₀V₁₀（at%）HEA was designed and fabricated by mechanical alloying（MA）and spark plasma sintering（SPS）.Microstructure evolution and mechanical properties of the HEA samples with different SPS temperatures and times were investigated.With the increase of ball-milling time during MA,the alloying effect in the W₃₅Ta₃₅Mo₁₀Nb₁₀V₁₀ mixed powders becomes more significant.Upon sintering from 1600℃to 1800℃,a supersaturated body-centered-cubic（BCC）matrix with Ta₂VO₆ precipitates are obtained.The alloy has the best combination of properties when sintered at 1700℃for 10 min,and the average density,microhardness and ultimate compressive strength are14.65 g·cm^-3,6.50 GPa and 2519 MPa,respectively,showing the characteristics of high hardness and high strength.The strengthening mechanisms of the high-density non-equiatomic HEA include substitutional solid solution strengthening by the five principal elements,interstitial solid solution strengthening by impurity elements such as O and C in BCC matrix,grain boundary strengthening with fine grains,and precipitation strengthening by Ta₂VO₆ precipitates.Further,the concept of multiphase design was introduced,and two multiphase high-density HEAs,i.e.,W₅₀Mo₁₀V₅(Fe₆₄Ni₃₆)₃₅（at%）and W₅₅Mo₁₅V₅(Fe₆₄Ni₃₆)₂₅（at%）,were developed.The phase evolution during MA-SPS processes,microstructural characteristics,mechanical properties and deformation mechanisms of the multiphase bulk alloys were systematically investigated.The powders of the two alloys exhibited a dual-phase structure with coexistence of BCC and face-centered-cubic（FCC）phases after 15 h MA process.The W₅₀Mo₁₀V₅(Fe₆₄Ni₃₆)₃₅ alloy samples sintered in the temperature range from 1150℃to 1350℃for 10min,and the W₅₅Mo₁₅V₅(Fe₆₄Ni₃₆)₂₅ alloy samples sintered at 1250℃for5 to 10 min were all characterized by a multiphase structure composed of BCC matrix,FCC1,FCC2 and V-rich phases.The bulk W₅₀Mo₁₀V₅(Fe₆₄Ni₃₆)₃₅ alloy sintered at 1250℃for 10 min exhibited the best combination of properties,i.e.,an average mass density of 14.94 g·cm^-3,a yield strength of 1255 MPa,an ultimate compressive strength of 2639MPa and a fracture strain of 32%at room temperature.The enhanced mechanical properties of the multiphase high-density HEAs can be mainly attributed to the multiphase toughening,substitutional solid solution strengthening and grain boundary strengthening effects.Herein,BCC and BCC-FCC multiphase W-Mo-V base HEAs have been developed by compositional design and microstructural tuning,realizing the combination of high density and superior mechanical properties.In particular,the design strategy of BCC-FCC multiphase composite alloys can provide an important reference for the future development of high-density HEAs.