LAUSR

When metals are pulled in tension, they generally break after pulling out to only relatively small elongations. Nevertheless, it was reported in several early publications, dating back to the early part of the last century, that it may be possible under some conditions to achieve quite high elongations of the order of two or three hundreds of per cent. It is now known that very large elongations may be achieved in the process known as superplasticity in which metals pull out in tension with little or no necking and finally exhibit failure elongations that are in excess of 400 % [1]. The first direct example of true superplasticity was presented in the research of Pearson [2] conducted in England in the 1930s. In this work, it was reported that a two-phase Bi-Sn eutectic alloy exhibited an elongation of 1950 % in tensile testing and this example is shown in Fig. 1 where the sample is coiled to facilitate easy photography. Unfortunately, the remarkable results achieved by Pearson [2] in England were essentially overlooked in western countries but instead they led to very extensive experiments on superplasticity conducted by a number of prominent researchers in the Soviet Union. This research only became known in the west at a much later time in the 1960s as a result of the publication of a comprehensive review of the many reports then available describing this superplastic behavior [3]. This latter review effectively established superplasticity as a viable scientific area of considerable interest and industrial potential, especially because of the development of the superplastic forming industry for the fabrication of curved and complex parts for a range of commercial products [4]. Thereafter, an exceptional elongation of 4850 % was achieved in the Pb-Sn eutectic alloy [5] and reported in the Guinness Book of World Records [6] and later an even higher elongation of 7550 % was attained in the same alloy when testing at 413 K with a grain size of 11.6 μm as shown in Fig. 2 [7]. DOI: 10.22226/2410-3535-2018-4-506-509 PACS: 62.20fq, 6.60