鉬元素之添加對於鈷鉻鐵錳鎳高熵合金薄膜微結構與機械性質之探討

Microstructure and mechanical properties of (CoCrFeMnNi)100-xMox high entropy alloy films

黃子軒(Tzu-Hsuan Huang)

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/NTU202002772

摘要

本實驗透過磁控濺鍍的手法製備了一系列的(CoCrFeMnNi)100-xMox (x=0, 0.5, 0.99, 2.29, 4.88, 7.71, 9.06, 12.15, 14.62) 高熵合金薄膜，藉以探討添加鉬元素 (Mo) 對於薄膜微結構與機械性質之影響。利用X光繞射儀 (XRD) 以及穿透式電子顯微鏡 (TEM) 檢測發現，薄膜的晶體結構隨著鉬元素的添加，逐漸由單一的面心立方 (FCC) 結構轉變成非晶相。奈米壓痕實驗結果發現，在加入微量鉬元素時，硬度從6.27 GPa (x=0) 下降至4.62 GPa (x=0.5)，但在持續添加鉬元素含量後，硬度值隨之提升，當x=4.88時，硬度值提高至8.13 GPa 並且硬度的變化開始趨於穩定。此現象的原因可源自於雙晶尺寸大小，奈米雙晶的尺寸(twin spacing)會影響材料的變形機制，進而產生強化或弱化的效果。前者觀察到的奈米雙晶尺寸約為2.8 nm， 硬度的下降現象可歸咎於退孿晶誘發軟化 (detwinning-induced softening)，後者觀察到的奈米雙晶尺寸則大於2.8 nm，硬度值的持續上升則可歸因於固溶強化與奈米雙晶之產生。薄膜的摩擦係數以及抗磨耗係數則是使用定力模式的刮痕試驗量測。實驗結果發現添加鉬的高熵合金薄膜不僅能提升硬度，同時改善抗磨耗率以及降低摩擦係數。薄膜的降伏強度與破裂韌性由in-situ奈米壓痕機進行微米柱壓縮實驗量測。當薄膜中的鉬含量增加，壓縮降伏強度由1.69 GPa 提升至3.62 GPa，然而壓縮延性從大於25%降至16.4%。其中以鉬含量4.88 at.% 的試片擁有最佳的破壞強度，同時仍保有一定程度的壓縮延性。

關鍵字

高熵合金薄膜 ； 磁控濺鍍 ； 奈米雙晶 ； 機械性質 ； 奈米刮痕

並列摘要

A series of (CoCrFeMnNi)100-xMox (x = 0, 0.5, 0.99, 2.29, 4.88, 7.71, 9.06, 12.15, 14.62) high entropy alloy films (HEAFs) was prepared by magnetron co-sputtering to systematically study the alloying effects of Mo on the microstructure and mechanical properties. The microstructures of the films were investigated using X-ray diffractometer and transmission electron microscopy, the films transformed from a single face-centered cubic (FCC) phase to an amorphous structure with the increasing Mo content. Nanoindentation revealed an initial decrease in hardness from 6.27 GPa at x = 0 to 4.62 GPa at x = 0.5, and then the hardness increased with the increasing Mo content and stabilized at 8.13 GPa at x = 4.88. The key factor determining the transition between strengthening or softening materials was the size of twin spacing, which resulted in the transition of deformation mechanisms. While the initial decrease in hardness could be attributed to the detwinning-induced softening effect with twin spacing about 2.8 nm, the subsequent increase could be attributed to solid solution strengthening and formation of nanotwins with twin spacing larger than 2.8 nm. Scratch tests were carried out under a constant loading mode to measure the coefficient of friction (COF) and wear resistance. The current HEAFs exhibited a high hardness, good wear resistance and low COF, making it possible for the design of anti-wear applications. The yield strength and fracture strain were studied using micropillar compression tests. The compressive yield strength increased from 1.69 GPa to 3.62 GPa; however, the fracture strain decreased from >25% to 16.4% as the Mo content increased. The 4.88 at.% Mo-doped film revealed the best fracture strength with little reduction in ductility.

並列關鍵字

High entropy alloy films ； Magnetron sputtering ； Nanotwins ； Mechanical properties ； Nanoscratch

參考文獻

References

[1] W. Steurer, Single-Phase High-Entropy Alloys – A Critical Update, Mater. Charact. 162 (2020) 110179.

[2] 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.

[3] B. Cantor, I.T.H. Chang, P. Knight, A.J.B. Vincent, Microstructural Development in Equiatomic Multicomponent Alloys, Mater. Sci. Eng., A 375−377 (2004) 213−218.

[4] 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.