近年來隨著原油價格持續上漲，導致航空業者運輸成本不斷增加。而為了降低油耗成本，可以從兩種面向發展，第一種為降低機體重量，如:使用輕量化材料、減去多餘的座椅，提供站票；另外一種則是提升引擎工作效率，而本研究主要投入在提升引擎效率方面。根據卡諾循環得知，提高引擎工作溫度可以提升效率，而目前航太業者主要使用的引擎材料為可耐高溫的超合金，其中主要的成分為Ni或是Co。除了基底元素之外，超合金內還會添加許多難冶金屬，如:Re、Mo、Nb、W等等。在開發次世代超合金材料時，以往人們皆是使用直接配料、加工、分析，透過大量的試錯經驗來抓取合適的成分範圍。但此種方式會消耗大量的貴重金屬，成本太高，過於浪費材料與時間。而本研究打算以CALPHAD熱力學方法直接從相圖觀點、吉布斯自由能根本處進行研究。有了完善的相圖與熱力學模型可以有效地預測不同成分及溫度下之各種相變態，藉機開發所需要的微結構與合金成分以降低成本與提升研發速度。目前已有許多與Ni、Co相關的熱力學模型被報導出來，但除了與基底成分有關的熱力學模型外，也要有各添加元素間的熱學模型參數才能夠有效地描述各成分元素間的交互作用。
而本研究主要探討常見的參雜元素Mo-Nb-Re三元系統中各熱力學交互作用參數，其中Mo-Nb、Nb-Re、Mo-Re分別有Xiong等人、Liu等人與Yang等人提出各自的熱力學模型，但Liu等人與Yang等人對σ相的模型描述皆不相同。Liu等人將σ相設計為(Re)10(Nb)4(Nb,Re)16，而Yang等人則將σ相設計為(Re)10(Mo,Re)4(Mo,Re)16。由於模型的差異導致無法直接合併，因此本研究使用較為廣泛的σ相模型(Re)10(Nb,Re)4(Nb,Re)16，重新優化Nb-Re二元系統。此外本研究亦會使用第一原理方法(ab-initio calculation)計算介金屬化合物之終點化合物(end-member)在0 K之生成能，與使用特殊準隨機結構(special quasirandom structure)計算bcc與hcp固溶相之非溫度項交互作用參數。
使用第一原理輔助熱力學計算(ab-initio aided CALPHAD)來建構Mo-Nb-Re熱力學模型將會使得此模型更具備物理意義，而降低過多的數學描述。本研究已成功重新優化Mo-Nb、Nb-Re、Mo-Re二元子系統，並優化出Mo-Nb-Re三元系統熱力模型參數。本研究所建構的Mo-Nb-Re三元熱力學模型，相信在未來對次世代超合金的合金設計會具有相當大的幫助。

Conventionally, Ni-based superalloys have been employed as the high-temperature materials for engines that directly determine their efficiency. Rare-earth elements, such as Mo, Nb, Re, etc, are usually alloyed in next-generation superalloys to increase their melting temperatures as well as to enhance their high-temperature mechanical properties.
In this works, we employed ab initio-aided CALPHAD modeling for developing the thermodynamic description for the Mo-Nb-Re ternary system. With the computation-assisted materials design, only a few experimental verifications are needed, so progress for new materials developments can be significantly accelerated and the cost can also be reduced. In the Mo-Nb-Re ternary system, there are three solution phases, the liquid, body-centered-cubic (BCC), and hexagonal-close-pack (HCP) phases, and two compounds with noticeable homogeneity ranges, the σ and χ phases. The thermodynamic models of constituent systems, namely the Mo-Nb, Mo-Re, and Nb-Re binary systems, have recently been proposed by Xiong et al., Yang et al., and Liu et al., respectively. However, the compound energy formalism models for the σ phase are different, i.e. (Re)10(Mo,Re)4(Mo,Re)16 in the Mo-Re binary
system and (Re)10(Nb)4(Nb,Re)16 in the Nb-Re binary system, and cannot be integrated in the Mo-Nb-Re ternary system. Therefore, we firstly re-optimized the Nb-Re system with a more general sublattice model, (Re)10(Mo,Nb,Re)4(Mo,Nb,Re)16, for the σ phase. In addition, we used special quasi-random (SQS) models to reassess the BCC and HCP phases. Finally, we constructed the tentative thermodynamic parameters of the Mo-Nb-Re ternary system.

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