「第一屆國際高熵合金材料會議」開幕典禮致詞 (中英文)

「第一屆國際高熵合金材料會議」開幕典禮致詞

我很榮幸能有機會在「第一屆國際高熵合金材料會議」開幕典禮說幾句話。身為清華大學的資深成員，我首先要歡迎大家來參加盛會。「高熵合金材料」這名詞，在不久以前，即使是對材料科學學者而言都很陌生，如今我們得以在此地舉辦有眾多國內外知名學者參與的國際會議，見證了一個學術新地景的誕生。事實上，高熵合金材料領域在近年漸趨興盛，這可由今年五月知名的自然期刊以一篇名為「金屬混合學-將金屬混合產生強度高、韌性佳與延展性優的合金﹔材料科學交創造下世代具有優良特性的混合金屬」以兩頁篇幅做專題報導，可見其發展的盛況。

清華大學是此新領域的誕生地之一，也因此以主辦「第一屆國際高熵合金材料會議」為莫大光榮。本人亦有幸親身見證新奇「高熵合金材料」觀念的發展。大約在二十年前，我在清華大學材料系很受人敬重的同事葉均蔚教授開始有「高熵合金」的想法，當時並不能為得到材料學界廣為接受。由於大家了解葉教授是個很有創意的科學家，因此不至於立刻拒斥其想法，但由於此新奇觀念與傳統冶金學認知有很大的差異，因此也有困難得到嚴肅對待。主要原因包括﹕第一、在合金的強化機制中，如固溶強化、析出強化等，一般了解如加入太多其他合金元素，材料通常會變脆而失效﹔第二、以材料研究不可或缺的工具「相圖」而言，科學家對三元以上「相圖」瞭解很少，因此在研究上常遭遇很大的障礙﹔第三、材料多元相與各式缺陷交互作用的鑑定極為困難，不易建立結構與性質的相互關係，因而對材料的了解受到相當大的限制﹔第四、合金元素中，除基本金屬，如鐵、鋁、銅等較便宜，有許多相當昂貴，如果大量使用，將會讓成本大幅增加，恐不符成本效益。這些考量都有其相當根據與道理，也是一般學者對發展多元素材料的疑慮，我們很高興看到，即使遭遇多重困難，目前「高熵合金」已演化成一個充滿前景的領域，如今科學家們已成功製作許多具有特殊優良性質的「高熵合金」，整個領域有相當大的進展，而可期待在未來會有令人興奮的新發現。

另一方面，新領域未來也面對很大的挑戰﹕首先是包括多種元素的複雜系統可能提供過多的可能性與選擇，材料科學理論計算變得極為緊要。遺憾的是，在這方面，有足夠經驗與訓練解決問題的學者與學生嚴重不足﹔其次，過去學者們研究重點集中於結構特性，而對於功能特性，如電子與磁性特性，較為忽略﹔最後是希望能夠讓目前限於實驗室產品的狀況，能由改善成本效益，擴大規模，打入市場，促進產業進步，創造經濟價值。很明顯的，未來需要更多努力，才能充分發揮潛力。

最後，我要再次表達我的歡迎之意並向各位對此領域的卓越貢獻致敬。希望大家享受你在清華大學開會的時光並帶回許多新觀念回家，未來能讓領域更上層樓，同時我也要祝大家在此困難領域的研究上好運。

Opening Remark at the First International Conference on High Entropy Materials

I am very pleased to have the opportunity to say a few words at this important occasion. As a senior member of the University, let me also welcome you to take part in the First International Conference on High Entropy Materials. Until very recently, not many materials scientists, not to say general public, have heard the words of high entropy materials. The fact that we are now holding the First International Conference on the topics with many prominent scientists around the world travelling from afar and reporting new discovery and exchanging of the new ideas testifies to the birth of a new landscape in materials science. Indeed, the field had ben flourishing in the past few years, highlighted by a special report on the subject with the title: Metal mixology - Mixed-up metals make for stronger, tougher, stretchier alloys: Materials scientists are creating next-generation mixtures with remarkable properties“ in the prestigious journal Nature in May this year.

As one of the birthplaces of the new field, NTHU is proud to host the Conf. I myself was privileged to witness the development of the novel idea with the firsthand experience. About 20 years ago, when my respected colleague, Prof. Jiun-Wei Yeh, started to toy with the idea of mixing a number of metallic elements in equal amount together, there were very few believers. As Prof. Yeh was known to be rather creative and innovative, he could not be dismissed outright. Nevertheless, it was difficult to take the idea seriously since it is rather outlandish form traditional metallurgy mindsets. First of all, among the hardening mechanisms for alloys, such as solution hardening and precipitation hardening, it was not too prudent to add large amount of alloying elements so that the materials would become brittle and useless. Secondly, we had very little knowledges of phase diagrams, considered to be indispensable tool for materials research, beyond ternary phase diagrams. Thirdly, the characterizations of multiple phases together with interactions of crystalline defects are daunting tasks. Therefore, to establish structure-property relationships is more likely to be elusive. Fourthly, it may not make much economic sense since many of the alloying elements are relatively expensive, compared to the basic metals, such as Fe, Al and Cu. However, despite these legitimate concerns, we are glad to see that high entropy alloying evolves into a promising field. Today, many high entropy alloys with remarkable properties have been produced. Much progress has been made and exciting new discoveries are expected.

On the other hand, many challenges apparently lie ahead for the field. To start with, for complex systems involving many elements with perhaps too many possibilities and choices, computational materials science is apparently in urgent need. It is to our regret that in our community few scientists and students nowadays have been trained and in possession of the sufficient skills to tackle the enormous tasks efficiently. Secondly, the field has placed emphasis on improving structural properties with much less work devoted to developing alloys with specific functional properties, such as electronic and magnetics properties. The other challenge is to show commercial value so that it can move from the laboratory to the market place, which in turn, to advance the industry and impact the economy. Apparently, much more work has to be done to realize the full potential of the field.

With that, I wish to welcome all of you again and congratulate you on the extraordinary achievements in the past. It is my hope that you will enjoy the stay and bring back many fresh ideas back home and work to the further advance of the field. Last, but not the least, I wish you a great deal of luck in your work in this difficult field.