為了不同的性質需求，尤其是在機械性質與腐蝕能力的改善，合金設計一直不斷地被開發。在這些研究之中，包含了許多著重在高溫強度以及熱穩定性的耐熱高熵合金塗層。本研究著重於耐熱VNbMoTaW、VNbMoTaWAl、TiZrNbTaFe及TiZrNbTaFeN高熵合金塗層之製作。使用原子力顯微鏡(AFM)、場發射掃描電子顯微鏡(FE-SEM)、納米壓痕器、X光繞射(XRD)、穿透式電子顯微鏡(TEM)和X光電子光譜儀(XPS)，對高熵合金塗層進行分析。研究不同耐熱高熵合金塗層的機械特性、磨損和刮傷試驗，最後對高熵合金塗層進行腐蝕試驗，以揭示整體高熵合金塗層的特性和性能。
本研究考量合金之熱穩定性選用耐熱VNbMoTaWl高熵合金為基礎，並選用3種不同Al添加量的VNbMoTaWAl高熵合金，使用脈衝直流磁控共濺系統進行高熵合金塗層之製作。當Al含量達8.5 at.%以上時，BCC結構得以維持；塗層的表面粗糙度、晶粒大小以及密度，均隨Al含量的增高而減少。由於固溶強化之作用，Al的添加可使硬度增加到18.1 GPa。含Al量2.4 at.%的VNbMoTaWAl塗層在0.5 M H2SO4溶液中具最佳耐腐蝕性，而在3.5 wt.% NaCl水溶液中，最佳的耐腐蝕性則為8.5 at.%鋁含量的VNbMoTaWAl塗層。本研究同時提出了VNbMoTaWAl塗層的等效電路。此外，在乾燥空氣500 °C和750 °C的3小時高溫氧化，500 ºC氧化後，4種塗層的BCC結構均保持不變且氧化動力學遵循拋物線率。含Al的耐熱高熵合金塗層的氧化速率低於VNbMoTaW合金。然而，耐熱高熵合金塗層在750 °C的空氣高溫氧化能力變差，可觀測到質量損失。
本研究另以高功率脈衝磁體濺射(HiPIMS)採用不同氮氣流速比(RN2)進行耐熱TiZrNbTaFe和4種耐熱(TiZrNbTaFe)N高熵合金塗層的製作。隨著RN2的增加，HiPIMS峰值功率密度值也隨之增加。當RN2的添加量達32.0 N(10.0% RN2)，非晶質相轉變為細柱狀FCC結晶微觀結構。塗層的沉積速率隨著N含量的增加而降低，由於金屬氮化物的形成和各種元素的固溶強化，含32.0 N (10.0% RN2)塗層的硬度最高，為36.2 GPa。在3.5 wt.% NaCl水溶液中，32.0 N (10.0% RN2)塗層也獲得了3.08 x 106 Ω.cm2的最佳耐腐蝕性。
經由本研究性質與性能之分析，成果可應用於耐熱高熵合金塗層於合金設計與製程最佳化之規劃。除了在750 °C有較差的抗高溫氧化性之外，VNbMoTaWAl系列耐熱高熵合金塗層可應用於不同的結構應用；(TiZrNbTaFe)N系列耐熱高熵合金，則可應用於保護性硬塗層之製作。

Alloys with different properties are continuously being designed for various different applications, particularly for improved mechanical properties and corrosion properties. Several studies of refractory high-entropy alloy (HEA) coatings have been performed, with focus on high temperature strength and stable thermal properties. The present work will focus on fabricating refractory VNbMoTaW, VNbMoTaWAl, TiZrNbTaFe, and TiZrNbTaFeN HEA coatings, and mechanically characterizing the HEA coatings by applying atomic force microscopy (AFM), field-emission scanning electron microscopy (FE-SEM), nanoindenter, X-ray diffractometer (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) to study the mechanical characteristics of different refractory HEA coatings and study tribological performance using wear and scratch test, and finally perform corrosion analysis on the HEA coatings, in order to reveal the overall refractory HEA coating properties and performances.
The refractory VNbMoTaW and three refractory VNbMoTaWAl HEA coatings were grown using a pulsed direct current magnetron co-sputtering system. The refractory materials were selected due to their stable thermal properties and high temperature strength, while Al was selected due to its lightweight. The body-centered-cubic (bcc) structure was maintained after the addition of 8.5 at.% Al. The surface roughness, grain size and density of film decreased with higher Al content. The addition of Al element into VNbMoTaW coating can increase its hardness up to 18.1 GPa due to solution hardening effect. Best corrosion resistance in 0.5 M H2SO4 solution was obtained for 2.4 at.% Al contained VNbMoTaWAl coatings, whereas the best corrosion resistance in 3.5 wt.% NaCl solution was obtained for 8.5 at.% Al contained VNbMoTaWAl coatings. The equivalent circuit of the VNbMoTaWAl coating was also proposed. Further, high temperature oxidation was studied in dry air at 500 ºC and 750 ºC, respectively, with exposure time of 3 h. The bcc structure of four coatings remained after 500 ºC oxidation. The oxidation kinetics of four coatings at 500 ºC followed the parabolic rate law. The oxidation rate of the Al containing RHEAL coating were lower than those of equimolar VNbMoTaW alloy. The HEA coatings however had poor high temperature air oxidation at 750 ºC with mass loss observed.
The refractory TiZrNbTaFe and four refractory (TiZrNbTaFe)N HEA coatings were grown using high power impulse magnetron sputtering (HiPIMS) at different nitrogen gas flow rate ratios (RN2). The HiPIMS peak power density values increased with increasing RN2. The phase transformation from amorphous to face-centered-cubic (fcc) structure was obtained after the addition of 32.0 at.% N (at 10.0% RN2), and the fcc structure exhibited a fine columnar microstructure and enhanced crystallinity. The deposition rate of the coating was found to decrease with increasing N content. The 32.0 at.% N (at 10.0% RN2) contained (TiZrNbTaFe)N coating had the highest hardness of 36.2 GPa primarily due to its high residual stress and secondarily due to formation of metal-nitride phase and solid solution strengthening of various elements. In 3.5 wt.% NaCl solution, the best corrosion resistance of 3.08 x 106 Ω.cm2 was obtained for (TiZrNbTaFe)N coatings grown at RN2 of 10.0%.
The refractory HEA coating properties and performances analyzed during our study can be useful in the material design and optimization stage of product manufacturing. The refractory VNbMoTaWAl HEA coatings can be applied in various structural applications, however these have poor oxidation resistance in air at 750 ºC, while the refractory (TiZrNbTaFe)N HEA coatings can be used for protective hard coating applications.

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