Fundamentals and Theory
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Cambridge University Press 978-1-107-41004-6 - Materials Research Society Symposium Proceedings: Volume 196: Superplasticity in Metals, Ceramics, and Intermetallics Editors: Merrilea J. Mayo, Masaru Kobayashi and Jeffrey Wadsworth Excerpt More information PARTI Fundamentals and Theory © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-1-107-41004-6 - Materials Research Society Symposium Proceedings: Volume 196: Superplasticity in Metals, Ceramics, and Intermetallics Editors: Merrilea J. Mayo, Masaru Kobayashi and Jeffrey Wadsworth Excerpt More information © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-1-107-41004-6 - Materials Research Society Symposium Proceedings: Volume 196: Superplasticity in Metals, Ceramics, and Intermetallics Editors: Merrilea J. Mayo, Masaru Kobayashi and Jeffrey Wadsworth Excerpt More information OBSERVATIONS ON HISTORICAL AND CONTEMPORARY DEVELOPMENTS IN SUPERPLASTICITY Oleg D. Sherby* and Jeffrey Wadsworth+ * Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305 + Lockheed Missiles & Space Company, Inc., Research and Development Division, 0/93-10, B204, 3251 Hanover St., Palo Alto CA 94304 ABSTRACT The history of superplasticity is reviewed. The first scientific observation of superplasticity dates back to 1912. Sporadic reports of subsequent observations appear in the literature up to the review by Underwood in 1962. Since that time there have been a number of milestone achievements that have propelled the technology of superplasticity forward. These include commercial developments based on nickel, titanium, iron, and aluminum alloys. In more recent times the advent of superplasticity in ceramics and intermetallics has stimulated yet further interest in the field. At the present time there are major research efforts underway in the USA, USSR, Japan, China, and Europe to apply superplastic forming technology to the manufacture of complex components. HISTORICAL EVENTS It is often thought that superplasticity is a relatively recently-discovered phenomenon. It is intriguing to speculate, however, that the phenomenon may have had its first application in ancient times. For example, Geckinli [1] has raised the possibility that the ancient arsenic bronzes, containing up to 10 wt% As, used in Turkey in the early Bronze Period could have been superplastic. This is because the materials are two-phase alloys that may have developed the required, stable, fine grained structure during hand forging of intricate shapes. Furthermore, the ancient steels of Damascus, in use from 300 BC to the late 19th Century, are very similar in composition to modern ultrahigh carbon steels that have recently been developed, in large part, for their superplastic characteristics [2,3]. A perspective of the historical context of superplastic studies with respect to the modern time frame is shown in Fig. 1. Modern Study of Superplasticity \ Ancient Bronzes Damascus Steel Processing (Cu-As) (1.6-1.9%C Steels) J I I 3000BC 2000BC 1000BC BC/AD 1000 AD 2000AD Figure 1 Historical perspective of the development of superplasticity from possible ancient origins to the present time. We now believe that 1990 is the seventy-eighth anniversary of the first scientific report on superplasticity. During the course of our research into the history of Damascus steels we came across a paper published in 1912, by Bengough [4], that we believe contains the first description of superplasticity in a metallic material. Bengough describes how "a certain special brass which he had examined pulled out to a fine point, just like glass would do, having an enormous elongation." The quote (which even today represents a useful definition of superplasticity) was made by Bengough in a written discussion following a paper by Rosenhain and Ewen [5] on the "amorphous cement" theory. Examination of the original work by Bengough [4] shows that the special brass was an ct+p brass and exhibited a maximum elongation of 163% at 700°C; the original data from Bengough's paper is shown on the left hand side of Fig. 2. Considering the crude equipment (shown on the right hand side of Fig. 2), poor temperature control, large gage Mat. Res. Soc. Symp. Proc. Vol. 196. ©1990 Materials Research Society © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-1-107-41004-6 - Materials Research Society Symposium Proceedings: Volume 196: Superplasticity in Metals, Ceramics, and Intermetallics Editors: Merrilea J. Mayo, Masaru Kobayashi and Jeffrey Wadsworth Excerpt More information length, and probable relatively high strain rate of Bengough's experiment, his results are really rather remarkable. It is of interest to note that similar materials to those studied by Bengough have been processed to be superplastic in recent times. For example, Cu-40%Zn brasses have been developed for superplasticity in the temperature range 600-800°C [6]. 800 700 / 600 i>00 o y 4oo N j / cot1PLEX BRA55 f 200 100 1 0 I 20 40 6o so IOO Figure 2 Data from the original paper by Bengough [4] in 1912 in which superplasticity was first scientifically documented are shown on the left hand side of the figure. The elongation to failure of an <x+p brass is plotted as a function of temperature and a maximum elongation of 163% is noted. On the right hand side is a photograph of the equipment used by Bengough. Other observations can occasionally be found in the early literature to viscous-like behavior in fine- grained metals (see, e.g., Refs. [7,8]). Jenkins achieved elongations of 300 to 400% in Cd-Zn and Pb-Sn eutectics after thermomechanical processing and provided the first photographic evidence of superplastic behavior in a tested sample in 1928 [8] as shown in Fig. 3. Interestingly, Jenkins did not find the observation to be important enough to include in either the synopsis or the conclusions of his paper. In 1934 Pearson [9] dramatically demonstrated, using a Bi-Sn sample that had been deformed to nearly 2000% and then coiled as shown in Fig. 4, that unusually large elongations could be achieved in certain fine-structured, two-phase materials. As a result he is often erroneously credited with having first demonstrated superplasticity. Although the results of Pearson were viewed in the West only as a scientific curiosity, work in the USSR specifically addressed the phenomenon and Bochvar and Sviderskaya [10] coined the term "sverhplastichnost" (ultrahigh plasticity) in their 1945 paper on superplastic alloys. Apparently the term "superplasticity" appeared for the first time in the English language in a 1959 paper by Lozinsky and Simeonova [11] on the subject of "Superhigh Plasticity of Commercial Iron under Cyclic Fluctuations of Temperature." A summary of the key observations and discoveries through this time period in superplasticity is shown in Fig. 5. Although occasional papers appeared on the subject after this date, the major increase in interest came with Underwood's [12] review article in 1962 on work in the USSR. In this review a Soviet graph, reproduced in Fig.6, was included which illustrated the ductility of Zn-Al alloys after quenching from 375°C. A ductility maximum of 650% was achieved at 250°C for a 20% Al and 80% Zn alloy (the monotectoid composition). This remarkable result, achieved on a sample that required only a quenching treatment, attracted the attention of Professor Backofen at M.I.T. With his students[13], Backofen studied details of the Zn-Al monotectoid alloy, as well as a Pb-Sn eutectic composition material. Of great significance is that Backofen and his colleagues showed © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-1-107-41004-6 - Materials Research Society Symposium Proceedings: Volume 196: Superplasticity in Metals, Ceramics, and Intermetallics Editors: Merrilea J. Mayo, Masaru Kobayashi and Jeffrey Wadsworth Excerpt More information Figure 3 The first published photograph of a superplastically deformed sample was by Jenkins[8] in 1928. The material is either a cadmium-zinc alloy or a lead - tin alloy (Jenkins does not specify which it is) and has undergone about 300% elongation. Figure 4 Famous photograph by Pearson [9] in 1934 of a Bi-Sn alloy that has undergone 1950% elongation. Note the undeformed specimen on the right hand side. © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-1-107-41004-6 - Materials Research Society Symposium Proceedings: Volume 196: Superplasticity in Metals, Ceramics, and Intermetallics Editors: Merrilea J. Mayo, Masaru Kobayashi and Jeffrey Wadsworth Excerpt More information Pearson publishes Sauveur discovers dramatic picture of internal stress 2000% deformed superplasticity sample of Bi-Sn alloy Jenkins Bochvar and colleagues carry out publishes Bengough research on superplasticity in first picture observes the USSR and coin the term of superplasticity superplasticity superplastic in a brass in Sverhplastichnost sample 1912 i 1910 1920 1930 1940 1950 1960 Figure 5 Key discoveries in the early and middle part of the 20th century prior to the major development of interest in the Western World in the 1960s. that the superplastic Zn-Al alloy could be formed into a practical shape, a hemisphere, by a simple air pressure forming operation, as in glass blowing. An example of such a hemisphere is shown in Fig. 7. This practical example, showing the spectacular formability of a superplastic metallic alloy, was probably the single biggest initiator of the rapid growth in the field of superplasticity that took place after the publication of the paper in 1964. By 1968, just four years after the Backofen demonstration of superplastic forming, the first review paper on the subject appeared by Chaudhari [14] and in the next year the first book was published by Presnyakov [15]. Since then, a number of monographs, by Western [6, 16-18], Soviet [19-24], and Chinese [25] researchers, have been published, as have numerous review articles [12, 26-41]. Two extensive reviews on the subject have also been presented by the present authors [16,42].