Conclusion

In bringing this discussion to a conclusion, I would like to mention the pro­fessors who have had a major influence on my research and several mat­ters that I have kept in mind while carrying out my research.

Japanese wishing to see where the famous pioneer of solidification re­search, Professor Chalmers, had carried out his research often visited the University of Toronto where I was studying in about 1960. I frequently heard them say "There's nothing here. It's just like a senior high school in Japan." To be sure, there was not very much expensive equipment at that time. It was simple equipment, and most of the research involved solidifi­cation using Sn. Once I asked Professor Winegard "Why do you only use Sn here?" Taking his pipe from his mouth, he replied:

"Look, Sn can be melted in glass containers, we can see inside the containers, little power is necessary for heating, and measurement of the temperature is simple. If we used Al we would also have to consider its reaction with the container, and Fe would be even worse. What is impor­tant to us is to use Sn to pursue the study of solidification - study that can be applied also to Al and Cu and Fe."

Even now I can recall this scene. It occurred in a big empty room in an old building that was said to have been built in the days before electrici­ty. It was a room built a long time ago as a chemistry laboratory, and on top of the testing benches here and there lay zone melting equipment for obtaining Sn of a high purity. My research has been greatly influenced by Professor Winegard's words at that time to the effect that "Universities are for pursuing learning. Leave the application of this learning up to those with money."

When I commenced my research I had virtually no knowledge about casting solidification, merely what I had learnt from Professor Winegard's lectures on "Solidification". With my lack of experience in casting solidi­fication, the solidification theory in conventional theses was difficult for me to understand, so when starting my research into solidification I de­cided not to read past theses, but to begin from scratch. I thought that this might be a better approach, as I would not be influenced by existing con­cepts. Even when I read theses for reference sake, I always endeavored to place myself at a considerable distance from them so as not to be drawn in­to the thesis.

A. Ohno, Solidification© Springer-Verlag Berlin Heidelberg 1987

120 Conclusion

Instead of reading theses, I adopted the method of directly observing with frank eyes actual solidification phenomena in metal, without any preconceptions whatsoever. When I find a new phenomenon I imme­diately think it over myself and put together a theory, and try this out di­rectly on specialists who have presented solidification theories in the past and see their reaction. Towards this end I have travelled not only to Eu­rope and the United States, but even as far as Australia. I have attempted to learn the details of the circumstances under which these people carried out their research and how they performed their experiments and built up their theories, not from theses but from the authors themselves.

One method I have used in my research is to simplify as much as possi­ble apparently complex phenomena, and then to observe them. This is be­cause I thought that combining the several pieces of knowledge obtained would be extremely useful in the actual control of cast structures. For ex­ample, as I stated when discussing cast iron, in order to understand the ap­parently complex phenomenon of cast iron solidification, I adopted the method of not immediately using cast iron, but firstly regarding this as one eutectic alloy and using other simple eutectic alloys to investigate sol­idification phenomena common to all eutectic alloys. Based on this I then attempted to elucidate the complex phenomenon of cast iron solidifica­tion.

Another research method I have used is to firstly carry out macroscopic observations and then to observe on a microscopic basis. Before one knows whether the object is a cow or a horse, there is no point in looking only at the pores of the skin just because one has a microscope. I have adopted the method of first observing phenomena with the naked eye, and then if necessary I use a magnifying glass and then a microscope or elec­tronic microscope if further local magnification is necessary. This is be­cause I thought that discussing microscopic segregation within dendrites before a macroscopic understanding of the solidification phenomenon is obtained would not lead to the birth of any new techniques for solidifica­tion structure control.

Upon discovering under the microscope alien matter that differs from the surrounding matter, some people immediately jump to the conclusion that it nucleated at that site. Scholars formulate a theory to explain this, and finally this takes root as if it were Scripture. I have endeavoured not to be influenced by such "theories", and have tried not to apprehend solidified structures in one plane, but in terms of the whole casting, includ­ing the surface which is the cooled end. The reason that I observed the sol­idification of an ammonium chloride model in a transparent glass contain­er was also because I tried to grasp the whole picture of the solidification of the metal in the mould in macroscopic terms.

In the course of my research into solidification I have often been re­monstrated with - "Why don't you use numerical formulae?" I was afraid that if I got carried away by making numerical formulae and inserted

Conclusion 121

plausible-sounding hypotheses to no purpose without clearly grasping the phenomena, I would rather end up by merely giving listeners the impres­sion that solidification is a difficult matter.

I have often heard people say "Using only data that suits one's pur­poses results in such an explanation." On each occasion I have told myself "If my theory is correct, a day will surely come when they will accept it. It takes time for them to understand it." With my success in developing the O.c.c. process for the continuous casting of ingots in which single crystals are stretched out without limit, I feel that I have finally completed the sketch of the large picture of metal solidification that I have been drawing over the past two decades. I conclude here in the hope that read­ers will add beautiful colours to this sketch of mine and finish it off into a splendid painting.