Effect of Al Content on Grain Morphology of Laser Deposited(CoCrFeNi)-Al High Entropy Alloys
Laser deposition technology is expected to be an ideal method for preparing high entropy alloys(HEAs).However,the HEAs prepared by laser deposition prefer to present the microstructure of coarse columnar grains,which limits the wide application of laser deposition in preparing HEAs.(CoCrFeNi)1-xAlx(x=0,0.10,0.15,0.20)HEAs were prepared by laser deposition.The evolution of phase and grain morphology of laser deposited(CoCrFeNi)1-xAlx HEAs were studied.The solidification behavior of the HEAs was analyzed by differential thermal analysis.The results show that with the increase of Al content,the phase of laser deposited(CoCrFeNi)1-xAlx HEAs changes from face centered cubic(FCC)single phase to FCC and body centered cubic(BCC)dual phase structure.The content of BCC phase in the HEAs with different Al contents is 3vol%(x=0.10),24vol%(x=0.15)and 52vol%(x=0.20),respectively.With the increase of Al content,the grain morphology of the laser deposited HEAs also changes from coarse columnar grains to fine elongated grains,and the grain size decreases significantly from 116 μm(x=0)to 40 μm(x=0.20).This can be owing to the decrease in nucleation undercooling(ΔTN)and the increase of growth restriction factor(Q)of(CoCrFeNi)1-xAlx caused by the increase of Al content,which can promote more significant constitutional undercooling and boost the nucleation behavior.
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