"添加合金元素(Al, Ti)對於CoCrFeMnNi 高熵合金薄膜微結構 及機械性質之影響"

Abstract

本實驗以Co、Cr、Fe、Mn 及Ni 金屬元素依等比例熔煉成CoCrFeMnNi 高熵合金靶材，利用磁控濺鍍系統分別與Al 及Ti 靶材在Ar 電漿氣氛下製備CoCrFeMnNiAlx (x = 0, 0.07, 0.3, 0.6, 1.0, 1.3, x 為莫耳比) 及 CoCrFeMnNiTix (x = 0, 0.2, 0.4, 0.6, 0.8, x 為莫耳比) 高熵合金薄膜，探討添加Al 及Ti 之合金元素對CoCrFeMnNi 高熵合金薄膜相轉變、微結構及機械性質等影響。根據XRD 及TEM之選區繞射圖(SAED) 結果顯示，當x 為0.6 時，CoCrFeMnNiAlx 高熵合金薄膜之晶體結構從FCC 相轉變成FCC + BCC 雙相結構，隨著鋁含量增加至x = 1.0 時，晶體結構最終相轉變成BCC 相。此趨勢使得CoCrFeMnNiAlx 高熵合金薄膜之硬度隨著鋁含量的增加而有所提升，例如：未添加Al 合金元素時(x = 0)，硬度值為5.71GPa，當相轉變成單一BCC 結構時(x = 1.3)，硬度值提升至8.74 GPa。然而對CoCrFeMnNiTix 高熵合金薄膜而言，當x 為0 及0.2 時，薄膜呈現柱狀晶結構，且觀察到大量的奈米雙晶。根據選區繞射圖結果可知，在此兩種Ti 含量下(x = 0, 0.2)，薄膜之晶體結構為單一FCC 相。隨著鈦含量增加至x = 0.4 時，此薄膜之基底為非晶結構，且有不同結構形成於非晶基底中，例如：奈米晶粒及奈米雙晶，最終當鈦含量增加至x = 0.8 時，此薄膜呈現出非晶結構。因此由此可知，隨著鈦含量的增加，薄膜之晶體結構從FCC 相轉變成非晶結構，同時由奈米壓痕測試結果可得到，硬度值隨著鈦含量的增加從6.62 GPa (x = 0) 提升至8.99 GPa (x = 1.3)。

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.