Investigation On The Microstructure And Properties Of AlTiVZrB High Entropy Alloys

In this study,AlTiVZrB light high entropy alloys were prepared by using B instead of Nb in AlNbTiVZr high entropy alloys based on the previous investigation results on AlNbTiVZr series of high entropy alloys.According to the theoretical calculation,nine alloys which are closest to the high entropy alloy with simple solid solution structure are selected.Using AlTiVZr_0.2B_0.2 alloy as primary alloy,the effects of sintering temperature on the microstructure,density,mechanical properties and corrosion resistance of AlTiVZr_0.2B_0.2 alloy were investigated.On the basis of this,the influence of Al content on the microstructure,density,mechanical properties and corrosion resistance of high entropy Al_xTiVZr_0.2B_0.2 alloy（x=0.2,0.4,0.6）was investigated by using different mole fraction of Al.The following research results have been achieved:AlTiVZrB series high entropy alloys with density of 4.71-5.01g/cm³ were fabricated.The density of AlTiVZr_0.2B_0.2 high entropy alloy was decreased by 6.75 10.3% than that of AlNbTiVZr series high entropy alloy（5.05⁵.25g/cm³）.Sintering temperature didn’ change the microstructure of AlTiVZr_0.2B_0.2 high entropy alloys.All the AlTiVZr_0.2B_0.2 high entropy alloys fabricated at five sintering temperatures（i.e.,1000℃,1050℃,1100℃,1150℃ and 1200℃）were composed of matrix phase with simple cubic structure and precipitates of TiB₁₂ and Al₃Zr₂.With the increase of sintering temperature,the volume fraction of TiB₁₂ precipitates decreased while the volume fraction of Al₃Zr₂ precipitates increased.The hardness and compressive strength of AlTiVZr_0.2B_0.2 high entropy alloys first increased and then decreased with the increase of sintering temperature.The AlTiVZr_0.2B_0.2 high entropy alloy prepared at 1100 ℃ had the highest hardness（809.7Hv）and compressive strength（2080MPa）.The specific compress strength of the AlTiVZr_0.2B_0.2 alloys is obviously higher than that of TC4 titanium alloys.The reason is that there exist a lot of globular TiB₁₂ precipitat particles and Al₃Zr₂ precipitat particles in the microstructure of AlTiVZr_0.2B_0.2 high entropy alloys.When sintered at 1100℃,TiB₁₂ and Al₃Zr₂ precipitates in the microstructure AlTiVZr_0.2B_0.2 high entropy alloys had the highest dispersion degree and the most uniform distribution in matrix,and hence had the best dispersion strengthening effect to the alloys.Three kinds of Al_xTiVZr_0.2B_0.2 high entropy alloys with various Al molar fractions（x=0.2,0.4,0.6）had the same microstructure.Three kinds of alloys were composed of matrix phase with simple cubic structure,fine α phase(TiB₁₂),γ phase（V₃B₂）and a large amount of β phase（Al₂Zr₃）.With the increase of molar fraction of Al,the volume fraction of α-phase(TiB₁₂)and γ-phase（V₃B₂）decreased while β-phase（Al₂Zr₃）increased.And the XRD diffraction peak of the matrix shifted to the left.Therefore,increasing the molar fraction of Al promoted the precipitation of β phase（Al₂Zr₃）and increased the lattice distortion of the matrix.Increasing the molar fraction of Al element is beneficial to the improvement of hardness,compressive strength and specific compressive strength of Al_xTiVZr_0.2B_0.2 high entropy alloys（x=0.2,0.4,0.6）.The reason is that α phase(TiB₁₂),γ phase（V₃B₂）and β phase（Al₂Zr₃）in the microstructure of Al_xTiVZr_0.2B_0.2 high entropy alloys（x=0.2,0.4,0.6）have good dispersion strengthening and second phase strengthening effect to matrix.Furthermore,the high lattice distortion caused by high molar fraction of Al resulted in high solid solution strengthening effect of Al atoms.Among above strengthening mechanism,the strengthening of the second phase by β phase（Al₂Zr₃）and the solution strengthening by Al atoms are two main reasons for the improvement of mechanical properties of Al_xTiVZr_0.2B_0.2 high entropy alloys（x=0.2,0.4,0.6）.On the whole,Al_xTiVZr_0.2B_0.2 high entropy alloys（x=0.2,0.4,0.6,1.0）have good corrosion resistance.Among them,the AlTiVZr_0.2B_0.2 high-entropy alloy（x=1.0）prepared at 1000℃ and 1100℃ and the Al₀.6TiVZr_0.2B_0.2 high-entropy alloy（x=0.6）have the best corrosion resistance.