| High entropy alloys（HEAs）are becoming a research hotspot because of their high strength,high hardness,good resistance to corrosion and so forth.However,the majority of present HEAs are mostly based on transition metals with high density.Though these alloys exhibit desirable mechanical and anticorrosion properties,their relatively high density limits their application in industries that requires lightweight materials.In this study,the lightweight elements Al,Ti,V,Zr,and anti-corrosion element Nb are selected to fabricate Al2NbTixV2Zry high-entropy alloys by vaccum hot pressing.The effects of milling process,sintering process and alloy compositions on the microstructure,mechanical properties,corrosion and high temperature oxidation resistance of the alloys are investigated systematically.The main innovative conclusions are as follows:（1）A non-equiatomic Al2NbTi3V2Zr high entropy alloy with density（5.05-5.23g/cm3）slightly higher than Ti64 alloy was fabricated by combination of theoretical analysis and experiment.Raising sintering temperature resulted in the matrix phase transformed to body-centered cubic phase from simple cubic in low energy milling alloys（LE）.Meanwhile,the secondary phases（Zr,Al）-based intermetallic decreased gradually and the Ti-rich HCP phase disappeared.However,a new secondary phase（Ti,Zr,Al）-based intermetallic（β-phase）precipitated from the matrix.High energy milling（HE）not only fined and activated the powders but also stabilized and fined the microstructure of the sintered Al2NbTi3V2Zr high entropy alloy.The grain of the BCC matrix was fined while intermetallics ofαandβdispersed in granular form in the BCC matrix.（2）High energy milling improved the mechanical property of the Al2NbTi3V2Zr high entropy alloy greatly.The HE alloy sintered at 1250°C exhibited the highest hardness,compressive strength,elongation and specific strength,which were 781HV,2623MPa,20.9%and 503N·m/kg respectively.Not only was the specific strength of this alloy higher than that of all the LE and Ti64 alloys,which increased by 90%compared to Ti64,but also the comprehensive mechanical property was improved.The relations between the hardness/compressive strength and sintering temperature for alloy were closely correlated with the content of Zr in matrix,matrix phase transformation（i.e.,simple cubic phase into BCC）,grain size and precipitation of the secondary phases.（3）The microstructures and mechanical property of the alloy were further improved by optimizing the contents of Ti and Zr element in the alloy.Al2NbTi3V2Zr0.4 alloy exhibited the simplest microstructure among Al2NbTixV2Zry.Its specific strength and comprehensive mechanical property was closer to that of Ti64 alloy,but more excellent than most current HEAs.（4）The mechanism of the milling process and contents of Ti and Zr element on the corrosion property of the Al2NbTixV2Zry alloy was investigated.The main corrosion mechanism for LE alloys in 10 wt.%HNO3 was the localized corrosion,which was mainly related to the content of the secondary precipitations.HE alloys exhibited general corrosion,which was mostly correlated with finer matrix,facilitating the formation of the passive film.The anti-corrosion property of the HE alloy was superior to that of the LE,Ti64 and most current HEAs.The corrosion rate per year of HE bulk sintered at 1250°C was just 3.9×10-3mm/yr,which was lower by three orders of magnitude than that of the Ti64 alloy.（5）The mechanism of the milling process and contents of Ti and Zr element on the corrosion property of the Al2NbTixV2Zry alloy was also assessed.Results showed that the secondary Zr-richαphase can be easily oxidized and facilitated of the formation of discontinuous oxide scale at high temperature,which was attributed to the largest mixing enthalpy between Zr and O elements.Hence,the oxidation resistance was depended on the content ofαphase in the alloy.Although the oxidation property of the sintered alloy was close to that of the current high entropy alloy,it was inferior to Ti64 alloy. |
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