| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 107 === The phase evolution, microstructures and mechanical properties of CoCrFeMnNiAlx (x = 0, 0.07, 0.3, 0.6, 1.0, 1.3 in molar ratio, denoted as Alx hereafter)and CoCrFeMnNiTix (x = 0, 0.2, 0.4, 0.6, 0.8 in molar ratio, denoted as Tix hereafter) high entropy alloy films (HEAFs) were studied in this work. HEAFs were successfully deposited by RF co-sputtering. For CoCrFeMnNiAlx HEAFs, the XRD results indicated the phase transformation from FCC to BCC with the increasing Al content. Also, the corresponding selected area electron diffraction (SAED) patterns proved the phase transition from FCC to duplex phases (FCC + BCC) in Al0.6 and to BCC phase in Al1.0. The hardness value increased from 5.71 GPa in Al0 to 8.74 GPa in Al1.3. The structural transitions from FCC to BCC lead to the hardness enhancement with the increasing Al content. For CoCrFeMnNiTix HEAFs, the Ti0 and Ti0.2 films exhibited the columnar structure and the abundant nanotwins were observed in both films. The corresponding SAED patterns confirmed that the crystalline structure of both films was identified to be a single FCC phase. In Ti0.4, the matrix exhibited an amorphous structure. The
nanocrystalline grains and nanotwins embedded in the amorphous matrix. With further addition of Ti, the Ti0.8 film transformed to an amorphous structure. As a result, there was a phase transition from a single FCC structure to an amorphous structure with the increasing Ti content. Nanoindentation tests showed that the hardness of the films increased from 6.62 GPa in Ti0 to 8.99 GPa in Ti0.8.
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