09-128 afs

Hoyt Memorial Lecture

Foundries: The Final Frontier the Next Thousand Years of Casting Technology

D. Weiss Eck Industries, Inc., Manitowoc, Wisconsin

Copyright 2009 American Foundry Society

ABSTRACT The future worlds of science fiction are built on advanced and sometimes fantastical materials and technologies. Star Trek s first starship Enterprise was built in the 2130s, a little more than one hundred years in our future. Can material science and advanced manufacturing methods turn fiction into fact? Will our foundries make parts for truly advanced transportation systems? This paper discusses the opportunities and challenges of the Star Trek universe for our industry. Part of that journey will explore materials imagined but never produced, and revisit the unrealized potential of materials we pour every day.

THE PAST The history of metalcasting is one of accidental discoveries, hard work, craftsmanship and the occasional blinding insight. The first metal casting may have been produced six thousand years ago when an Iranian potter accidentally dropped a piece of malachite into his kiln. The temperature would have been sufficient to reduce the mineral to metallic copper. Further experimentation may have led to putting a stone mold under the fire to collect the copper in a shape as a decoration. See

Figure 1. Craftsmen adapted the techniques and in short order began producing beautiful and intricate castings using lost wax.

What happened next was truly extraordinary. The (probably) accidental introduction of tin into copper to create bronze produced a material stronger than the base copper. The bronze was easier to cast since its melting point is 60 C less than

Figure 1-Bronze casting and mold (about 2000 BCE) on display at The Israel Museum, Jerusalem

Paper 09-128.pdf, Page 1 of 6AFS Transactions 2009 American Foundry Society, Schaumburg, IL USA

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that of pure copper. This led to the production of monumental bronze castings, including pillars weighing 100 tons for the Assyrian king, Sennacherib.1 The addition of tin into copper, carbon into iron and steel, copper and magnesium into aluminum, and aluminum into magnesium all produce alloys that are better than the base materials. Sophisticated alloying systems are the keys to the strength of the foundry metals that we pour today. Will manipulation of the periodic table continue to reward us with enough improvement in properties to meet the demands of the Star Trek universe?

THE FUTURE

Consider these materials from the future: Interon is a material that violates all known laws of physics and would be catagorized as a class III impossibility by Michio Kaku in his book Physics of the Impossible.2 Philip Nolan in Armageddon:2419 A.D. describes the material as follows:

Inertron is the second great triumph of American research and experimentation with ultronic forces. It was developed just a few years before my awakening in the abandoned mine. It is a synthetic element, built up, through a complicated heterodyning of ultronic pulsations, from "infra balanced" subionic forms. It is completely inert to both electric and magnetic forces in all the orders above the ultronic; that is to say, the sub-electronic, the electronic, the atomic and the molecular. In consequence it has a number of amazing and valuable properties. One of these is the total lack of weight. Another is a total lack of heat. It has no molecular vibration whatever. It reflects 100 percent of the heat and light impinging upon it. It does not feel cold to the touch, of course, since it will not absorb the heat of the hand. It is a solid, very dense in molecular structure despite its lack of weight, of great strength and considerable elasticity. It is a perfect shield against the disintegrator rays. 3

More plausible is the material scrith from Larry Niven s Ringworld as illustrated in Figure 2: Scrith is a milky-gray translucent, nearly frictionless material. The fairly thin layer of scrith that forms the floor of the

Ringworld blocks the passage of 40% of the neutrinos that encounter it, equivalent to almost a light year of lead. It also absorbs nearly 100% of all other radiation and subatomic particles and rapidly dissipates heat. The tensile strength of scrith is similar to the strong nuclear force. Due to its enormous strength, scrith is impervious to most weapons. A body (such as a comet or asteroid) striking with enough kinetic energy may be able to deform the Ringworld floor and punch a hole. The physical composition of scrith is unclear, but it appears to share some of the properties of a metal (albeit in a greatly exaggerated form): for instance, the high tensile strength, the ability to conduct heat and the ability to retain an induced magnetic field. Scrith is said to have been artificially produced through the transmutation of matter. 4 Kaku would call scrith a class II impossibility, since it is a material that sits at the very edge of our understanding of the physical world.

Most of what we see in Star Trek would be class I impossibilities. These are technologies that are impossible today but that do not violate the known laws of physics. Part of the appeal of Star Trek, indeed part of its design, is that the technology depicted is in the realm of possibility in the near future. Many of the materials necessary for the construction have already been discussed in terms of contemporary material science. Perhaps Star Trek's tritanium could be created by embedding diamond fibers in a titanium-alloy matrix.5 The warp coils for the Enterprise are cast of a material called verterium cortenide.6 The interaction between this material and hot engine plasma change the geometry of space surrounding the engine nacelles thereby creating a warped space in which the Enterprise travels. Within the warped space the Enterprise does not violate the local speed of light, thereby preventing the violation of the laws of special relativity.

Figure 2-Ringworld from Larryniven.org


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Many of these fictional materials may be newmatter as described in a new science fiction novel by Neal Stephenson, Anathem: A form of matter whose atomic nuclei were artificially synthesized and which therefore have physical properties not found in naturally occurring elements or their compounds. 7

A more plausible type of newmatter can be found in novelist and aerospace engineer Wil McCarthy s book, Hacking Matter.McCarthy proposes placing programmable dopants in the interior of bulk materials and controlling those dopants in real time through externals signals.8

The dopants are likely to be fibers cast in a matter similar to that used for selectively reinforced metal matrix composites.McCarthy has started a company, The Programmable Matter Corporation, to develop these ideas. Despite the technical challenges, McCarthy s speculations are taken seriously. In a 2000 column in Nature, McCarthy talks about one of his materials: Wellstone iron is weaker than its natural counterpart, less conductive and ferromagnetic essentially, less iron-like and if you bash it over and over with a golf club it will gradually lose any resemblance to iron, reverting to shattered silicon and emptyspace. On the other hand, it s feather-light, wholly rustproof, and changeable at the flick of a bit into zinc, rubidium, or even imaginary substances like impervium, the toughest superreflector known. 9

THE TRANSITION

There has been impressive progress toward some aspects of our science fiction universe. Cloaking technology, used by the Romulans in the original Star Trek series to prevent detection of their spacecraft, is rapidly becoming a physical reality.Controlling silicon morphology on the surface of a casting may make it optically invisible.10 We have yet to attain the full potential of metals and the castings that we make from them every day.

Pure metals are usually quite weak, but not theoretically so. In 1929 Yakov Frenkel used a simple atomic model to estimate the theoretical yield strength of a material at one tenth its Young s modulus. That would give theoretical yield strength of aluminum of one million pounds per square inch. Observed yield strengths are between one and two orders of magnitude less than that. The problem is that crystals of metals are not perfect, even when cast perfectly. They are filled with dislocations which will move under an applied load, weakening the material. This is true of other materials as well. Unique carbon configurations called carbon nanotubes have very high theoretical strengths. Even a single atom out of position will reduce the strength of a nanotube by 30% and atomic scale defects typical in manufacturing processes could reduce the strength by as much as 70%.11 Alloying was the initial answer to the weakening caused by dislocations. Precipitates at the grain boundaries induced by alloying additions will hinder the motions of dislocations. Reducing the grain size increases the number of barriers to dislocation motion as well. Perhaps we cannot further tackle atomic scale defects in castings for thenext few hundred years, but we may be able to make enough of an impact on macro defects to get us closer to the theoretical strength that would change the world of castings.

In order to make better castings, we need to improve their density. We work very hard to produce metals that are better than 99% dense. But consider a material that is 99.9999% dense (a density that cannot be physically measured by conventional techniques). Such a material has ~5 X 1016 pores/cm3 if the pores are 100 nm in diameter.12 In aluminum, using the best cleaning and de-gassing techniques available, inclusion sizes of .04 mm (40,000 nanometers) and overall metal densities of 99% are barely achievable in the foundry environment.13 Those numbers are even less encouraging after the metal is poured through the indignity of the typical gating system into a typical casting design. Good aluminum castings can show a variance between actual and theoretical densities of 1.5-2.0%.

The development in new metals is slow due to quality control and processing issues, according to Ivan Amato s book Stuff,The Materials The World Is Made Of14. Figure 3 is a reproduction of a chart from the book showing that the relative importance of metals peaked in the 1950s.


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Figure 3-The relative importance of materials over time

So what do we need to do to reconcile the past with the future? To make a significant impact on the mechanical properties of cast materials we need:

1) Reasonable financial support from the government. The funding for metal casting improvements is less that $5 million per year. This is .02% of the $25 billion requested for US automakers to retool for vehicles that are 25% more efficient than current models. However, the most effective means of achieving improved vehicle efficiency is by reducing the overall weight of the vehicle. Reducing weight through material strength improvement allows the automakers to produce big cars loaded with features -- the kind people want to buy. Increasing funding for cast metal research and development to $50 million per year (.1% of $25 billion) could improve properties of castings by 30%. That would go a long way to help the automakers meet their efficiency goals at a much lower cost. We can approach the funding problem differently and look at an X Prize type approach. The X Prize is a foundation funded program of high profile competitions to solve grand challenges. Perhaps the Department of Energy and the Department of Defense should post a $50 million reward for each castable metal system (aluminum, magnesium, iron, steel, titanium) that can demonstrate a yield strength improvement of 100% and a cost of no more than two times the current base alloy cost.

2) An attitude adjustment by foundries and their suppliers. Cleaning and degassing technologies that leave 40,000 nanometer inclusions and 99% density are inadequate to meet the casting demands of the future. We need an order of magnitude improvement in inclusion size and density. Clearly some new thinking is required. In the 1960s, when cleaning up lake pollution was a major issue, breakthroughs occurred when the Canadian government funded research into understanding how lakes became polluted.15 Do we really understand how metal gets dirty? If not, perhaps that is a prerequisite to understanding how to get it clean. Even the measurement techniques, such as reduced pressure test in aluminum foundries, are inadequate to take metal cleanliness to the next level.

3) Recognition that casting simulations are inadequate to meet the demands of 21st century castings. These simulations do not take into account metal/mold interactions, gas generated from cores and corewashes, or grain refining. Casting simulations have revolutionized how foundries do business and have significantly improved the average product coming out of the foundry. They have replaced the gating guru in many situations and can help the foundry produce castings mostly free from shrinkage and significant oxides. However there is much work to be done. In many alloys, the fundamental physical inputs are still not available. Modeling of composites is in its infancy and the modeling of gas flow out of cores and molds is unavailable. Figure 4 is an illustration of a core gas defect that cannot be modeled using current software.


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Figure 4-Core gas defects in aluminum castings

4) Research on castable, high strength composites for all metal systems. Recent work at the University of Wisconsin-Madison and elsewhere has shown that sub-micron size reinforcements can improve the yield strength of aluminum and magnesium by 50%.16 In general castable composites offer major weight savings due to higher strength-to-weight ratios, exceptional dimensional stability, higher elevated temperature stability and significantly improved cyclic fatigue characteristics.17 After a burst of activity in the 1990s, composite research has been underfunded by both industry and government.

Why is any of this important? Not so that we can just play out our science fiction fantasies. The progress of civilizations has been paced by the development of materials and ways to manufacture them. In 1865 the mechanical properties of cast iron were typically13 to 26 ksi depending on the manufacturing technology used.18 Today those properties are typically 25 to 135 ksi or even higher in specialty irons. It should be clear that advancements in everything from agriculture to transportation are tied, in part, to improvements in the properties of iron and other structural cast materials. The great industrial metallurgist and essayist Cyril Stanley Smith said: Much of the history of materials has been rather dull, for man has usually been satisfied to make do with what he had, but there are three periods in which sharp change occurred. These correspond to the first discoveries of the principal alloys and ceramic materials, the beginning of scientific explanation, and the very recent realization that, by control of their structure, materials that possess almost any property in high degree can be designed and produced for special applications. 19In an era of pending energy shortages and the potential catastrophic effects of global warming, making do is probably not an option; the design and production of improved materials can help solve the problems of the present and lead us into a brighter future.

REFERENCES

1. Sass, Stephen: The Substance of Civilization. Arcade Publishing, 1998, pp. 49-67 2. Kaku, Michio: Physics of the Impossible. Doubleday, 2008, pg XVII 3. Nowlan, Philip Frances, Armageddon: 2419 A.D., Amazing Stories, 1928 4. Wikipedia entry on Ringworld 5. Bormanis, Andre, Needed: Materials for 24th Century Starships-Considering the Materials Demand of the Star Trek

Universe. Journal of Materials 48 (6), 1996, pp 12-14. 6. Sternbach, Richard and Okuda, Michael: Star Trek, The Next Generation Technical Manual. Pocket Books, 1991, pp 22-

23 7. Stephenson, Neal: Anathem. William Morrow, 2008, pg 902 8. McCarthy, Wil: Hacking Matter. Basic Books, 2003, pp 185-207 9. Nature, Vol. 407, 5 October 2000, pg 127 10. MRS Bulletin, Vol. 33, June 2008, pg 579 11. Kaku, pg 168


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12. Science, 17 October 2008 13. R. Gallo: Cleaner Aluminum Melts: A Critical Review and Update , AFS Transactions, Vol. 116, pp. 195-220 (2008). 14. Amato, Ivan: Stuff, The Materials The World Is Made Of. Avon, 1997, pg 7 15. Canada s Experimental Lakes , Science, 28 November 2008 16. Li, X.; Yang, Y.; Weiss, D.Ultrasonic Cavitation Based Dispersion of Nanoparticles in Aluminum Melts for

Solidification Processing of Bulk Aluminum Matrix Nanocomposite: Theoretical Study, Fabrication and Characterization, AFS Transaction, Vol. 115, Paper 07-133

17. Chawla, Nikhilesh and Chawla, Krishan: Metal Matrix Composites. Springer, 2006, pg. 1 18. Fairbairn, William: Iron, It s History, Properties and Process of Manufacture. Edinburgh, 1865, pp 225-227 19. Smith, Cyril Stanley: A Search for Structure. The MIT Press, 1981, pg 112


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