Al的添加與氮化作用對於NbTiVZr高熵合金薄膜之顯微結構差異與機械性質探討

Abstract

本實驗透過磁控濺鍍系統，製備一系列(NbTiVZr)100-xAlx (x=0, 3.5, 7.3, 12.4, 12.9)高熵合金薄膜與(NbTiVZrN)100-xAlx (x=0, 0.7, 2.3, 3.6, 4.0)高熵合金氮化薄膜，並且以雙靶材共鍍的方式，鍍在單晶矽(100)上，透過調控施加在鋁靶材上不同的功率，並且固定其他參數，去探討Al的添加量對NbTiVZr高熵合金薄膜與氮化薄膜之微結構差異與機械性質的探討。在高熵合金薄膜結果方面，從X光繞射儀與穿透式電子顯微鏡的結果中可看出，所有薄膜皆為非晶結構，從選區繞射圖型可以看到明顯的非晶環，在掃描式電子顯微鏡下則可以發現所有試片皆為葉脈狀結構，而這結構也是在非晶相中最常出現的結構之一。 高熵合金氮化薄膜的討論中，在X光繞射儀與穿透式電子顯微鏡的結果中發現在未添加鋁的薄膜中，主要是由氮化鈦 (TiN) 主導，並且在電子顯微鏡的橫截面圖形出現雙層結構，上層為柱狀晶結構而下層則是非晶的結構，而非晶結構也在後續高解析電子顯微鏡被驗證為奈米晶散落在非晶母相中。隨著鋁的添加後，由於鋁與鈦的混和焓 (mixing enthalpy) 很負因而形成三鈦化鋁 (Ti3Al)，導致氮轉而與鈮與鋯結合，分別形成氮化鈮 (NbN) 與氮化鋯 (ZrN)，這兩種氮化物主導了添加鋁氮化薄膜的結構與其優異的機械性質。這也在後續的X射線光電子能譜儀 (XPS)結果中被驗證。機械性質方面，本實驗量測硬度、破裂韌性與摩擦係數。結果顯示，隨著鋁含量添加至x=3.6 時，硬度與破裂韌性分別達到最大值，其原因可歸因於固溶強化與主導之氮化物的轉變。在奈米刮痕方面，隨著鋁的添加，所得摩擦係數從0.082降到0.065，因此可知鋁的添加強化高熵合金氮化薄膜的磨耗性質。

In this study, the effects of Al addition on the phase evolution, morphology and mechanical properties of (NbTiVZr)100-xAlx (x = 0, 3.5, 7.3, 12.4, 12.9) high entropy alloy films (HEAFs) and (NbTiVZrN)100-xAlx (x=0, 0.7, 2.3, 3.6, 4.0) high entropy alloy nitride films (HEANFs) were systematically investigated. For the (NbTiVZr)100-xAlx HEAFs, all the films exhibited amorphous structure and the hardness increased slightly. For the nitride films, the XRD patterns revealed FCC structure and the preferred orientation transferred from TiN(200) to (Nb, Zr)N(111) as the Al content increased. The results of the corresponding selected-area electron diffraction patterns of TEM images agreed well with the XRD results. Cross-sectional SEM and TEM observations exhibited ultra-fine columnar structure with a few inclusions and voids. XPS was conducted in order to further investigate the bonding between the constituent elements, and the replacement of the dominant compounds was confirmed. The nanoindentation test were performed to acquire the mechanical properties of the films. The hardness, reduced modulus and fracture toughness of nitride film increased with the increasing Al concentration and reached the maximum values of 28.1 GPa, 253 GPa and 2.08 MPa×m0.5, respectively, for x = 3.6. The significant improvement could be ascribed to solid solution strengthening, inverse Hall-Petch effect and the replacement of dominant nitride compounds. As the Al content increased to x = 4.0, the coefficient of friction decreased from 0.082 to 0.065. The relationship between the microstructure and mechanical properties was studied for the (NbTiVZrN)100-xAlx HEANFs in this work.