AlxCoCrCuFeNi高熵合金相圖之模擬研究

傳統合金主要以單一元素為主，且主元素顯少超過三個，所以我們都在傳統合金的觀念下配製合金、開發製程、研究微結構性質以及開發應用，因此無形中也就限制了合金發展的自由度及空間，但近年來一種新興合金—高熵合金打破這觀念，發展出無主要元素的多元合金，為金屬材料開創一個新領域。當合金成分個數增加時，相的種類並未如一般預期的複雜及難以分析，反而是趨於單純化。而且不同於傳統合金在X-ray繞射圖上呈一寬廣峰，反而僅呈現完全散射的背景強度，BCC 相則雖為結晶相，但也因多種元素之固溶，散射效應很大，以致結晶繞射強度大幅下降。為了使高熵合金能做更廣泛的應用，相圖的建立有其必要性，因此利用商用軟體Thermo-Calc.自建多元合金系統資料庫，藉由改變Al含量，繪製出AlxCoCrCuFeNi六元高熵合金相圖。以真空電弧爐熔煉所設計的合金，取樣做金相、電子顯微鏡分析、X-ray分析及熱分析進行印證工作。金相觀察的結果發現該系統合金呈現樹枝晶與樹枝間晶結構，並透過EDS分析後發現樹枝間主要是富Cu的偏析結構。另外隨著Al的增加（x＝1），樹枝部分會轉變成網狀的節點分解結構。 Al含量在0.8份以下僅為單純的FCC相；Al含量在0.8及1.0份間為FCC相與BCC相共存；Al含量超過1.0份開始出現節點分解（spinodal decomposition）；當Al含量超過2.8份，FCC相幾乎不存在，只有葉脈狀的節點分解結構。利用這些不變點（invariant point）作為研究的對象，做進一步的熱分析，確認其相變溫度點，與所模擬之相圖相變點是否符合。

關鍵字

高熵合金；相圖模擬；微結構；偏析；熱分析

並列摘要

In tradition, the development of an alloy system is almost based on a principal element as the matrix, such as iron-, copper-, and aluminum based alloys, limiting the number of applicable alloy systems. Traditional metallurgical theory suggests that multiple elements in an alloy system may lead to the formation of many compounds with complex microstructure and poor mechanical properties. Recently this paradigm has been broken by high entropy alloy, which has excellent material properties such as high temperature thermal stability, corrosion resistance, high strength, hardness, high oxidation resistance, will be a new potential material for development. In particular, not only were all XRD peak intensities of alloys with multiprincipal elements markedly lower than the corresponding ones of conventional alloys under the same XRD measurement conditions, and these XRD peaks were slightly broadened and superposed on a broad peak. In order to make more extensive applications of high entropy alloy, it is necessary to establish the phase diagrams of these alloys. We use commercial software, Thermal-Calc., and set up database for this system, select an appropriate thermodynamic module for the calculation of phase diagrams. By changing the contents of Al, the phase diagrams of AlxCoCrCuFeNi will be plotted. Experimentally, the designed alloy is synthesized by an arc-melting. These samples were examined with optical microscope, scanning electron microscope analysis, X-ray analysis, and thermal analysis to verify the result of the phase calculation. Dendrite and inter-dendrite structures were observed in these systems of alloys. By energy dispersive spectrometry analysis, Cu enriched inter-dendrite structure was obtained. With more addition of aluminum (x=1), the dendrite subsequently transformed into net-like structure due to the spinodal decomposition. With little aluminum addition, the alloys were composed of a simple fcc solid-solution structure. As the aluminum content reached x= 0.8, a bcc structure appeared and constructed with mixed fcc and bcc eutectic phases. Spinodal decomposition occurred further on when the aluminum contents were higher than x= 1.0. A single ordered bcc structure was obtained for aluminum contents larger than x= 2.8. Utilizing these invariant points as the object, and making further thermal analysis to confirm the phase transition temperature agreed with the phase diagram we simulated.

並列關鍵字

High-entropy alloy ； Phase diagram simulation ； Microstructure ； Segregation ； Thermal analysis ； Thermo-Calc

參考文獻

[11] 陳皇仁；“Al0.5CoCrFeNi2高熵合金之相變化研究”，國立台灣科技大學材料科技研究所碩士論文，2005

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[2] 吳正德；“高熵合金相圖模擬之研究”，國立台灣大學材料科學工程研究所碩士論文，2005

[7] L. Kaufman and H. Bernstein；“Computer Calculation of Phase Diagrams”，Academic Press，New York，1970

[9] U.S. Hsu, U.D. Hung, J.W. Yeh, S.K. Chen, Y.S. Huang, and C.C. Yang；“Alloying behavior of iron, gold and silver in AlCoCrCuNi - based equimolar high-entropy alloys”，Materials Science and Engineering A，2007，pp. 403-408

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AlxCoCrCuFeNi高熵合金相圖之模擬研究

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