Abstract
In this experiment we prepared mechanically alloying high-entropy alloy powders based on CoCrFeNiV (5E) by sequentially adding Al (6E), AlTi (7E) and AlTiCu (8E). XRD results showed that 5E to 8E alloy powders all were solid-solution-homogenized after 4-h ball milling where 5E was FCC, and 6E to 8E were BCC, while 6E to 8E were amorphized after 60-h ball milling. SEM mapping showed that the solid-solutionization sequence of composed elements was Al →Cu →Ni →Co →Fe →Ti, Cr, V. It showed that the sequence was closely related to the melting points of involved elements in the alloys. DTA and DSC analyses showed 60-h amorphized 6E to 8E alloys precipitated BCC phase at 370, 402 and 359 oC, respectively, and solutionized for σ-CoCrNi phase at 1045, 1080, and 1067 oC, respectively, while the FCC solid-solutionized 5E alloy had no phase transformation during heating to high temperature. The derived Young’s modulus difference (□E) from hardness Hv values of 5E to 8E alloys vs. mixing enthalpies (□Hm) and vs. mixing free energy (□Gm) showed linear dependence as □E = -5.89 □Hm, and □E = -4.58 □Gm, respectively. Finally, it showed that radii, at which the main peak and other lower peaks of the K-edge Fourier transform values for any of the containing elements in alloys occurred, decreased or peak merged, as the number of elements in alloys increased. Among them, radii for the main peak is principally decreased and compressed, while other lower peaks are principally merged to new broadened lower peaks. For 6-h ball milling 5E mechanically alloy powders EXAFS ( Extended X-ray Absorption Fine Structure ) data showed that the FCC structure was constructed principally by the structure of elemental Ni and Co, while the BCC structure of 6E and 7E alloy powders ball-milled for 6-h were principally composed of that of elemental Cr and Fe as we compared the K-edge Fourier transform EXAFS data of 6-h mechanically alloying state to that of elemental state.