材料科学与工程学科的“四要素”

------兼顾说明组织、结构的认识

邓安华认为，组织、结构是两个不同的概念。陈明彪提到了在英语著述中，组织、结构的表述使用了同一个词：structure (结构)；并且分别从组成材料的原子结构( structure 或architecture)、原子排列结构、晶粒及晶界结构组成相及其结构进行表述。这显然不够简明，而且不如中文著作中使用“结构”(指原子结构或原子的组合结构) 和“组织”(指材料组织状态) 这两个不等同的概念更方便和合乎逻辑。

这里，两位特别关注了“组织、结构”的专业人士认为组织、结构是不同的；但是，一个认为是“不同的概念”，一个认为是在使用过程中“更方便和合乎逻辑”。这两个认识虽然都认可了“组织”、“结构”的中文提法，但是，却是本质上的不同，而不是“细节上有所差异”。

我个人倾向于陈明彪的认识，只是需要明确的是：组织、结构在这里是一回事；之所以在不同的地方使用“组织”或者“结构”，确实是与观察的对象的尺度范围有关。当跨越原子级别后，更多的采用“结构”的说法。

对于这一概念的认识，我个人的来源是源于工作中的一位同事兼导师。他曾经问过我一个问题：我们平时总说的“金相组织”到底是什么？电镜观察的事物是不是“金相组织”？最初，我有些懵，感觉有些不好回答。我的导师最后说明：从本质上讲，所观察到的都可以称之为“组织”；仅仅因为技术手段不同，分辨能力、表述形式上有所差异。

在《Introduction to Structures in Metals》（Metallography and Microstructures, Vol 9, ASM Handbook, ASM International, 2004, p. 23–28）中对于structure (结构)的表述，也体现了这一内涵。英语著述中的structure (结构)，涵盖了整个实际、可能的从宏观、到现有技术手段可以达到的最微小的尺度范围内的。

不过，从对于“组织、结构”认识的差异看，有必要认真分析一下。最有效的方式，应当是从学科内涵着手，那么，学科四要素（四面体）就是一个最直接、立即想到的。有意思的是，四要素的四面体也有很多细节上的差异。

我们以“Materials_science_tetrahedron”在google图片中检索，可以看到最常见的两种样式，实际上是一样的。参看http://www.newworldencyclopedia.org/entry/Materials_science　，在示意图下的文字是：The Materials Science Tetrahedron shows the four main areas in which materials are studied. It often includes Characterization at the center.

http://svr225.stepx.com:3388/materials-science/file/30059.jpg http://commons.wikimedia.org/wiki/File:Materials_science_tetrahedron;structure,_processing,_performance,_and_proprerties.ES.svg

Materials_science_tetrahedron;structure,_processing,_performance,_and_proprerties.JPG

在这一地址：http://dmseg5.case.edu/classes/emse201/overheads/MatTetra.pdf ，有一个文档，较为详细地说明了材料四面体每个要素的意义。其中，常见的processing，变成了SYNTHESIS；参见下面的左图。在SYNTHESIS中提到了Raw materials（Purity、Natural vs. synthetic）；Chemical composition -- bond type & strength（Metallic、Ionic、Covalent）；Processing（Batching、Reactions、Mechanical & thermal treatments、Fabrication）。所有这些项目，最后：All of these have an effect on COST。

同时，比较了performance和proprerties的概念；

左                                                                           右

      孙常全说：在他的“材料科学四面体“理论讲述的是以下四因子间的关系：材料结构，材料特征，材料性能，制作流程。参见上面的右图。其文章的摘要：The concept of materials science tetrahedron (MST) concisely depicts the inter-dependent relationship among the structure, properties, performance, and processing of a drug. Similar to its role in traditional materials science, MST encompasses the development in the emerging field of pharmaceutical materials science and forms a scientific foundation to the design and development of new drug products. Examples are given to demonstrate the applicability of MST to both pharmaceutical research and product development. It is proposed that a systematic implementation of MST can expedite the transformation of pharmaceutical product development from an art to a science. By following the principle of MST, integration of research among different laboratories can be attained. The pharmaceutical science community as a whole can conduct more efficient, collaborative, and coherent research.

*C.C. Sun. Materials Science Tetrahedron – a useful tool for pharmaceutical research and development. J. Pharm. Sci. 98:1671-1687 (2009) http://onlinelibrary.wiley.com/doi/10.1002/jps.21552/pdf

有网友提问说：资深院士师昌绪也搞过类似的关系，不知道博主与之有何区别？未见其回答。

实际上，其文章中提到：The term materials science tetrahedron (MST) was first conceived to guide research and development in the field of materials science and engineering.22,23 MST describes the interplay of the four elements, structure, properties, process, and performance (Fig. 2)。也就是说，孙常全并不是“四面体”的首倡者，他的文章的题目是：《Materials Science Tetrahedron--A Useful Tool for Pharmaceutical Research and Development》。所以，是一个药物研究者的“四面体”关系的应用。研究金属材料的师昌绪，恐怕孙常全并不知道；5要素、六面体就更不会熟悉了。因此，提问者可能是个金属材料方面的相关人员，向药物研究者提出一个问题，有些不太恰当。

在地址http://www.interciencia.org/v19_04/art02/ ，有JOSE ROBERTO G. DA SILVA的《MATERIALS SCIENCE AND ENGINEERING》。其四要素的标识更充分，与地址：http://dmseg5.case.edu/classes/emse201/overheads/MatTetra.pdf地说明是一致的。文中说：The basic elements of MSE are "structure," "properties," "synthesis, preparation and processing" and "function, application and performance" according to the COSMAT Report (1974), Silva (1986 and 1989) and Silva and Padilla (1991) using the same unified approach to all materials in such a way that those elements occupy the vertices of the so-called "tetrahedron of the basic elements MSE" (see Figure 1).

Figure 1

李强、陈文哲的《美国和欧洲的材料科学与工程教育》中，对于四要素有另一种标识。参看下图。

      在《美国和欧洲的材料科学与工程教育》中提到：为力求原汁原味地介绍国外材料教育的状况, 特翻译、整理了材料科学与工程领域世界顶尖级的两所大学麻省理工学院和剑桥大学的世界著名材料科学家和教育家M.C.Flemings 教授和R.W.Cahn教授近期发表在Acta Materialia (The Millennium Special Issue,V. 48 (1) (2000) ) 和Metall. M ater. Tran s. A (V. 32 (4) (2001) ) 上关于美、欧材料科学与工程教育的文章, 期望这对于我国材料科学与工程学科的教学改革与课程体系建设有所启发和参考。

范拓源在《美国金属材料学科发展及启示》中说：美国金属材料学科趋向于把核心金属材料学科看成一个体系, 该体系的中心是结构--工艺--性能--使用效能。

    在R.W.CAHN 的《THE COMING OF MATERIALS SCIENCE》的尾声（Epilogue）中，对MSE四面体有最权威的说明。（在这里http://smse.sjtu.edu.cn/mintro/xxzn/xxzn-3.htm　，可以下载THE COMING OF MATERIALS SCIENCE）的电子版）。《尾声》部分转载如下：

The time has come to draw together the threads of what has gone before. MSE is a huge domain; again and again I have had to warn the reader that I could only scratch the surface of some theme in the space available to me, and still 1 have　covered more than 560 pages with a combination of history and depiction.

First, what is materials science? I have gone through my professional life almost without addressing this question explicitly; I have always believed that the right way to address it is by means of what philosophers call an ‘ostensive definition’, pointing to something and saying “This is it”. This inclination was my main reason for accepting, in 1965, the hard labour of creating a new Journal Of Muteriuls Science; that journal was meant to demonstrate what my novel subject actually was, and I　believe it helped to do that. This book is also an essay in ostensive definition. When I had just been appointed professor of materials science at Sussex University, I did write an article under the title ‘What is materials science? (Cahn 1965). Summarising my disquisition, I wrote: “...the materials scientist has to work at several levels of organisation, each of which is under-pinned by the next level. Here, again, he is brother under the skin of the biologist, who does just the same: starting with the cell wall, say, he goes on to study the morphology and economy of the cell as a whole.　then the isolated organ (made up of cells), then the organism as a whole.” I still hold　today that this feature is central to our subject - applied to inanimate and artificial nature by us and to animate nature by biologists - and that the concept of microstructure is the most important single defining theme of MSE. To this can be added the slightly broader modern concept of mesostruclure, a term particularly beloved of modellers and simulators of polymers.. . the level of organisation in between the atomic/molecular level and macroscopic appearance.

Merton Flemings, a very experienced profcssor of MSE at MIT, has recently discussed (Flemings 1999) the question: “What next for MSE departments?’ He faces, foursquare, the issue whether something can be both a muItidisc@line, bringing　togethcr for use many classical disciplines, and a discipline in its own right. He is sure that MSE is both of these. The path out of the dilemma “is to view the broad　engineering study of structure/property/processing/performance relations of materials, with engineering emphasis.. . as a discipline”. That is, he asserts, what mainline, independent MSE departments teach. This fourfold way is depicted in Figure 15.1(a), a little tetrahedron which was first proposed in a 1989 report. Flemings goes so far as to say that “our survival as a discipline and as independent academic departments within the university system depends on how well we succeed in　articulating this paradigm and employing it to contribute to society”. Others prefer to make this little diagram more complicated; thus Shi (1999), a veteran Chinese　materials scientist, is insistent that ‘composition’ is an equally important variable, distinct from structure, ‘processing’ should be linked with ‘synthesis’, and at the heart of the whole enterprise he places ‘theory and design of materials and processing’, clearly including computer simulation. His view of things is shown in Figure 15. I(b).

Figure 15.1. (a)  The four elements of materials science and engineering, (after Flemings). (b) The six elements of materials science and engineering (after Shi).

One should not be perturbed by different experts’ preferences for different kinds of polyhedra; after all, these are no more than a visual aid to understanding. The key thing is that different aspects are intimately related…in these figures, every point is linked to every other point. Each of these aspects, whether they be divided into four or six categories, needs a familiarity with some of the classical disciplines such as physics, chemistry, physical chemistry, and with subsidiary not-quite-independent sciences such as rheology and colloid science.

While I entirely agree with both Flemings and Shi about the crucial importance of the components in their diagrams, I persist in my conviction that microstructure is the central component that best distinguishes MSE from other disciplines; each　chapter of this book demonstrates this centrality. The other components in the diagrams themselves have microstructural features: thus self-assembled materials (a part of processing/synthesis) have carefully controlled microstructure, and composition, because of segregation, varies significantly from point to point - and all this intimately affects properties.

I recall my distinction, in Chapter 2, between emergence (of a discipline) by splitting and emergence by integration, and also my insistence that MSE is a prime example (together with geology) of emergence by integration. This is historically unusual. For instance, in a scholarly study of how chemistry and physics came to be distinct disciplines and then chemistry itself differentiated, Nye (1993) concludes (to simplify drastically) that around 1830 chemistry split decisively from experimental philosophy (or physique gCnCrale) by reference to its concern with molecules and their reactions and behaviour, and in doing so left physics behind. It is far harder to　reach an acceptable definition of physics than of chemistry, but that has not prevented physicists from driving their discipline forward during the past two centuries. Likewise, we materials scientists practice our mystery whether or not we can define it.

So. nearly half a century after the emergence of the concept, we its practitioners have in materials science and engineering a clearly distinct discipline which in practice doubles up as a multidiscipline, with a substantial number of independent academic departments and research institutes spread around the world, with its own multifarious journals and textbooks, and a large number of professionals, also spread around the world, who call themselves materials scientists and engineers and communicate with each other on that basis. We have a profession to be proud of.

REFERENCES

Cahn, R.W. (1965) What is materials science? Discovery (July issue, no page numeration).

Flemings, M. C. (1999) Annu. Rev. Mater. Sci. 29, 1.

Nye, M. J. (1993) From Chemical Philosophy to Theoretical Chemistry (University of

Shi. C. (1999) Progress in Natural Science (China) 9, 2.

    前面标记为红色的说明，是对形形色色的材料科学于工程学科内涵的“几面体”的一针见血的总结。

    至于说“组织”、“结构”的区别、使用，按照我们现在的使用习惯，应该没什么问题；至于区别，仁者见仁。

    上海交通大学材料学院的“导论”课程中的可下载课件不错。