V對於CoCrFeMnNiVx高熵合金薄膜微結構與機械性質之影響

Abstract

本實驗利用磁控濺鍍系統，以單晶矽(100)為基底，控制其他參數不變，通過改變V靶材不同的射頻功率，共鍍製備了CoCrFeMnNiVx (x = 0, 0.07, 0.3, 0.7, 1.1) 高熵合金薄膜，並討論了V的加入對該薄膜成分、結構與機械性質的影響。XRD的結果表明，當x=0, 0.07時，薄膜為單一的fcc結構；x = 0.3, 0.7, 1.1時，X-Ray繞射峰變寬，通過TEM結果得知，這是因為隨著V的含量增加，薄膜的結構趨於非晶態。TEM結果也表明，當x = 0, 0.07時，薄膜中存在大量雙晶，同時APT的結果表明，這兩個參數下的V原子完全嵌入晶格中，沒有產生析出物，這種微結構使得薄膜的機械性質顯著提升。利用奈米壓痕試驗，檢測了薄膜的微硬度和楊氏模數，可發現V的加入可使薄膜的微硬度有所提升，由約6.8 GPa提高至8.7 GPa。在x = 0.07時，楊氏模數達到最大值206.4 GPa，更高含量的V會使楊氏模數下降，這是由於薄膜中非晶相的產生，導致抵抗變形能力的降低，符合TEM的結果。薄膜的屈服強度、極限抗壓強度、壓縮延性及斷裂韌性由In-situ奈米壓痕試驗機經奈米柱壓縮試驗檢測。該壓縮應力-應變曲線表明，當V的含量為x = 0.07時，屈服強度可達為3.8 GPa，極限抗壓強度可達約4.9 GPa，並保持了約13%的壓縮延性。同時，x ≥ 0.3時，在壓縮後的奈米柱上發現剪切帶，且對應的應力-應變曲線呈現鋸齒流變，這些現象均表明非晶態的產生。觀察壓縮後的奈米柱的TEM結果得知，薄膜中產生的奈米雙晶在壓縮過程中有效緩衝了塑性形變，使薄膜的機械性質有大幅提升。

In the present work, CoCrFeMnNiVx (x = 0, 0.07, 0.3, 0.7, 1.1) high entropy alloy films were fabricated by magnetron co-sputtering. For low contents of V, typical face-centered cubic (fcc) peaks were identified in X-ray diffraction patterns. With the increasing V content, the diffraction peaks became broadening and the formation of amorphous phase was promoted. TEM observations showed abundant nanotwins in films with low V contents and the transition from fcc to amorphous structure with the increasing V content. The 3D APT reconstruction results revealed no precipitate in the as-deposited films (x = 0, 0.07). Mechanical properties of the films were studied using nanoindentation and micro-pillar compression tests. The films exhibited high hardness ranging from 6.8 to 8.7 GPa. The serrated flow associated with shear banding showed in the stress-strain curves for films with x ≥ 0.3. When x = 0.07, excellent yield strength of ~3.8 GPa and ultimate compressive strength of ~4.9 GPa were achieved with little sacrifice in ductility. The presence of nanotwins contributed to the strain hardening effect.