Effects Of Plastic Deformation On The Microstructure And Property Of Al_0.3CoCrFeNi High-entropy Alloys

Al0.3CoCrFeNi high entropy alloys were synthesized using a vacuum arc melting method. Some alloys were rolled, and the other were twisted under high pressure. The effects of plastic deformation and subsequent annealing treatments on microstructure, mechanical property, corrosion resistance property of alloys were investigated by means of metallographic microscope, Scanning Electron Microscope, X-Ray Diffraction, microhardness meter and universal material testing machine. The alloys with different rolling deformation (0%,30%,60%,90%) were annealed at 200 ℃ to 1000℃ for 10h. The results showed that:The as-cast Al0.3CoCrFeNi high entropy alloy exhibited equiaxed grains with simple face-centered cubic (FCC) structure. With the increase of rolling deformation, grains were elongated along the rolling direction and finally to form fibrous tissues (90%). Accordingly, with the increase of the deformation, strength of Al0.3CoCrFeNi high entropy alloys increased, but elongation decreased.Alloys with different rolling deformation (0%,30%,60%,90%) were annealed at 200 ℃ to 1000℃ for 10h. Hardness of annealing alloys rised as the temperature rised, then decreased with the increase of temperature, and reaching maximum at 600 ℃. The second phase (Al-Ni phase) precipitated at the annealing temperature of 600 ℃. When the temperature was over 600 ℃, the number of precipitations decreased, and the size largened. Rolling deformation (30%,60%,90%) promoted annealing twins, and the temperature to form twins was more lower with the increase of deformation. Twins grew up with the rise of temperature.The corrosion current density of the Alo.3CoCrFeNi high entropy alloys with rolling deformation (30%,60%,90%) was larger in 3.5w.t% NaCl solution than that of as-cast alloys. In 3.5w.t% NaCl solution, the corrosion current density of the 900 ℃ alloy with 90% rolling deformation was lowest, suggesting best corrosion resistance property. While the corrosion current density of the 90% alloy annealed at 600 ℃ was largest, suggesting worst corrosion resistance property. In lmol/L H2SO4 solution, the corrosion current density of the alloys with rolling deformation (60%) was lowest, indicating best corrosion resistant.30% alloy was corroded most serious. Pitting corrosion occurred in all of the alloys. In 1 mol/L H2SO4 solution, the corrosion current density of the alloy with 90% rolling deformation before annealing was lowest, indicating best corrosion resistance property. The corrosion current density of the 90% alloy annealed at 600 ℃ was largest.Alo.3CoCrFeNi high entropy alloy was still FCC structure after high pressure torsion. The shear strain augmented with the increase of torsional turns and the distance from disc center. Accordingly grains were seriously refined to be more homogeneous. In the process of high pressure torsion, alloys deformed by the mechanism of dislocation combined with twins. Grains misorientation and dislocation increased with the increase of the deformation, eventually resulting into formation of nanoscale equiaxed grains. The hardness of alloy increased with increasing torsional shear, and then became stable.