釹元素添加和後退火處理對於 (CoCrNi)93Al7中熵合金薄膜顯微結構與機械性質的影響

Abstract

本實驗使用磁控濺鍍系統以三靶 (CoCrNi靶、Al靶和Nd靶)共濺鍍方式製備了一系列 (CoCrNi)93−xAl7Ndx (x = 0, 0.22, 0.56, 1.05, 1.73, 2.55, 3.53) 中熵合金薄膜進行分析，旨在研究引入不同含量的稀土元素釹 (Nd) 對 (CoCrNi)93Al7中熵合金薄膜系統造成的微結構及機械性質的影響。XRD的結果表明，隨著釹元素添加量增加，晶粒變得細小，且晶體結構漸漸由FCC固溶相轉變為非晶相。由TEM分析進一步顯示了柱狀結構的細化現象，並觀察到少量的NdNi5析出物在非晶相結構中形成。透過納米壓痕和微柱壓縮測試評估薄膜的機械性能，結果表明，在釹元素的含量添加至x=0.56時，薄膜表現出最佳的硬度（10.16 GPa）和簡化模數（223.83 GPa），這歸因於固溶強化和晶粒細化機制的作用。然而，隨著釹元素含量進一步增加，由於inverse Hall-Petch effect和非晶相的形成，硬度和簡化模數急劇下降，分別至8.23 GPa 和166.18 GPa。微柱壓縮測試結果顯示，降伏強度和極限強度與硬度呈相同的趨勢。 研究發現，退火處理可使原子擴散和遷移，促進晶格重排和大量析出物的形成。為了進一步產生HCP及BCC相的析出物來改善 (CoCrNi)93−xAl7Ndx的機械性質，本實驗將第一部分之薄膜進行550°C 10分鐘的後退火處理。XRD和TEM 的分析結果發現在x=0時並無任何相轉變及析出產生，但隨著釹元素含量上升，不同晶體結構之析出物隨之出現，如NiAl、Ni3Al和NdNi5和富Cr相偏析。此外，經由機械性質量測，我們還發現退火後 (CoCrNi)93−xAl7Ndx中熵合金薄膜硬度、降伏強度和極限強度比起未退火前之薄膜均有明顯的提升，這類型的強化歸功於晶界鬆弛、析出強化及介面強化，使得硬度方面達到最大值11.45 GPa。

In this work, a series of (CoCrNi)93−xAl7Ndx (x = 0, 0.22, 0.56, 1.05, 1.73, 2.55, 3.53) medium entropy alloy films (MEAFs) was fabricated, aiming to study the influence on doping different contents of rare earth element neodymium (Nd) on the microstructure and mechanical properties of the (CoCrNi)93Al7 MEAFs system. The results of XRD showed that the grain size became finer and the crystal structure gradually changed from FCC solid solution to an amorphous phase with the increasing Nd content. The refinement of the columnar structure was further revealed by TEM analysis, and a small amount of NdNi5 precipitates were observed to form in the amorphous phase structure. The mechanical properties of the film were evaluated by nanoindentation and micropillar compression tests, and the results showed that the film exhibited the highest hardness (10.16 GPa) and reduced modulus (223.83 GPa) when 0.56 at.% of Nd was added. The reasons could be attributed to solid solution strengthening and grain refinement mechanisms. However, as the Nd content further increased, the hardness and reduced modulus decreased sharply to 8.23 GPa and 166.18 GPa, respectively, due to the inverse Hall-Petch effect and the presence of amorphous phase. The micropillar compression test results showed that the yield strength and ultimate strength versus Nd content had the same trend as hardness.