添加元素 Nb 對於 CoCrFeMnNi 高熵合金薄膜微結構及機械性質之影響

Effects of Nb addition on microstructures and mechanical properties of Nbx-CoCrFeMnNi high entropy alloy films

梁雨萱(Yu-Hsuan Liang)

指導教授 ： 薛承輝

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202003184

摘要

本實驗利用磁控濺鍍系統，透過調整 Nb 靶材上的功率，固定 CoCrFeMnNi 靶材的功率以及其他的參數，共濺鍍製備出 Nbx-CoCrFeMnNi (0 - 7.2 at.% Nb) 高熵合金薄膜，從中探討不同 Nb 的添加比例對其薄膜的機械性質與微結構所造成的影響。從 XRD 的結果顯示，在無添加 Nb 的薄膜裡為單一 FCC 結構。隨著薄膜裡 Nb 含量的增加，主峰的強度明顯變弱以及高角度的峰消失。TEM 的結果顯示，在 0.6 at.% Nb 的薄膜裡有許多的奈米雙晶生成，奈米雙晶隨著 Nb 含量的增加而減少。在 1.8 at.% Nb 的薄膜裡開始有非晶的產生。在 1.8 及 4.1 at.% Nb 的薄膜裡，可以觀察到奈米晶嵌入在非晶中。最後到 7.2 at.% Nb 的薄膜才轉為全部非晶結構。由奈米壓痕測試結果得出薄膜的硬度和彈性模數，顯示出添加Nb後，硬度從 6.5 GPa 升至 8.1 GPa ，彈性模數從182.3 GPa降至162.2 GPa。由In-situ奈米壓痕試驗機對奈米柱壓縮的測試結果得出屈服強度、極限抗壓強度隨著 Nb 含量變多而增加。屈服強度從 1.08 GPa 升至 2.70 GPa ，極限抗壓強度從 2.56 GPa 升至 5.76 GPa 。薄膜強度的提升犧牲了部分的延展性，壓縮延性從 >29.4% 降至 15.8% 。在 Nb 含量大於 1.8 at.% 的奈米柱裡，壓縮後可以觀察到剪切帶，其對應的應力-應變圖顯示鋸齒流變，對應到非晶相的產生。

關鍵字

高熵合金薄膜 ； 磁控濺鍍 ； 機械性質 ； 微結構 ； 添加鈮

並列摘要

In the present work, Nbx-CoCrFeMnNi high entropy alloy films (HEAFs, 0 to 7.2 at.% Nb) were fabricated by RF magnetron co-sputtering of CoCrFeMnNi alloy and Nb targets. The influence of Nb addition on the microstructures and mechanical properties of HEAFs were systematically investigated. For Nb-free film (0 at.% Nb), the FCC peaks were identified in the XRD pattern. The addition of Nb resulted in the broadening of diffraction peaks, the decrease of peak intensity and the vanishment of high-angle peaks. TEM images indicated that profusion of nanotwins were formed at low Nb concentrations, and a transition from a single phase FCC solid solution to an amorphous phase was observed with the increasing Nb concentration. The films were strengthened with the increase of Nb concentration. Specifically, the hardness characterized by nanoindentation increased from 6.5 to 8.1 GPa. The compressive yield strength and fracture strength measured from micropillar compression test were improved from 1.08 GPs and 2.56 GPa to 2.70 GPa and 5.76 GPa, respectively, whereas the fracture strain decreased from >29.4% (no fracture) to 15.8%. Additionally, shear banding was observed in the presence of amorphous phase.

並列關鍵字

High entropy alloy films ； Sputtering ； Mechanical properties ； Microstructure ； Nb addition

參考文獻

[1] J.W. Yeh, S.K. Chen, S.J. Lin, J.Y. Gan, T.S. Chin, T.T. Shun, C.H. Tsau, S.Y. Chang, Nanostructured high-entropy alloys with multiple principal elements: Novel alloy design concepts and outcomes, Adv. Eng. Mater. 6(5) (2004) 299–303.

[2] B. Cantor, I.T.H. Chang, P. Knight, A.J.B. Vincent, Microstructural development in equiatomic multicomponent alloys, Mater. Sci. Eng. A 375 (2004) 213–218.

[3] Z.F. Lei, X.J. Liu, Y. Wu, H. Wang, S.H. Jiang, S.D. Wang, X.D. Hui, Y.D. Wu, B. Gault, P. Kontis, D. Raabe, L. Gu, Q.H. Zhang, H.W. Chen, H.T. Wang, J.B. Liu, K. An, Q.S. Zeng, T.G. Nieh, Z.P. Lu, Enhanced strength and ductility in a high-entropy alloy via ordered oxygen complexes, Nature 563(7732) (2018) 546–550.

[4] Z.M. Li, K.G. Pradeep, Y. Deng, D. Raabe, C.C. Tasan, Metastable high-entropy dual-phase alloys overcome the strength-ductility trade-off, Nature 534(7606) (2016) 227–230.

[5] O.N. Senkov, G.B. Wilks, D.B. Miracle, C.P. Chuang, P.K. Liaw, Refractory high-entropy alloys, Intermetallics 18(9) (2010) 1758–1765.