ADVANCED MATERIALS & PROCESSES | OCTOBER 2025 38 SMA INDUSTRY’S BIG EVENTS W e all know the history of the development of Nitinol based on the hard work and keen observations from William J. Buehler (1923-2014) and later in partnership with Frederick E. Wang (1932-2022) at the U.S. Naval Ordnance Labora- tory (NOL). Once discovered, they were focused in their belief that this shape memory effect could change the world. And they were right: Lives continue to be changed through this technology. Since the initial development of Nitinol in the late 1950s, the shape memory alloy (SMA) growth has been shaped by a number of Big Events. I often think of these events and how they have affected my career as well as the world at large. From the inception, SMA found a home with aerospace. One of the first commercial applications was the Raychem Cryofit couplings. Who would have thought that SMA could be drilled out from 0.25-in. to over 2-in. diameter bars, cooled in liquid nitrogen, and then expanded by 8% in one shot and then shipped to the various airfield in liquid nitrogen for installation? Constrained recovery is simply an amazing technology. By 1971, these couplings were installed success- fully on hydraulic lines in Grumman F-14A aircraft. This event is significant by itself, but perhaps more importantly, the material and application passed stringent specifications and inspections of the military as well as at NASA. For these and many more applications for airframes, engines and space, reliability and reproducibility are of paramount importance for safety. The past decade has produced a mind-blowing array of aerospace applications. The next decade was an exciting time to be a Nitinol metallurgist as boutique alloy compositions were retired to focus on thermomechanical processing wire of a few binary compositions—namely Ti-rich shape memory for orthodontic applications as well as early implants and Ni-rich for superelastic applications such as guidewires and surgical instrument components. And then another Big Event occurred. Dr. Julio Palmaz, along with Dr. Richard Schatz, developed and patented a balloon-expandable stent to treat coronary artery disease (U.S. Patent No. 4,733,665, 1985). This life-saving medical device used no SMAs but rather 316 stainless steel tubes; the pertinent claim in the patent reads as follows: “…by expanding a portion of the catheter associated with the prosthesis to force the prosthesis radially outwardly into contact with the body passageway, by deforming a portion of the prosthesis with a force in excess of the elastic limit of the portion of the prosthesis…”. In other words, in practice the stent is balloon expanded to induce plastic deformation to maintain patency and allow blood flow. Johnson & Johnson eventually fully purchased the Palmaz-Schatz stent and it was soon approved by the FDA with the reward of a whopping 90% market share. So how could other medical device companies compete without infringing this clever Palmaz patent? Simple: Use Nitinol instead of 316 stainless steel! As we now know, Nitinol stents are self-expanding and do not require plastic deformation to function. For these self-expanding implants to be manufactured, however, another Big Event was required: production of seamless Nitinol tubes with exacting dimensions and tolerances. Nitinol tubing was developed in the early 1990s and required many trials and errors to determine the exact methods to achieve the correct dimensions with optimal mechanical and thermal properties. But once the tubing was ready for medical device use, one more essential Big Event was then necessary: laser equipment capable to machine fine features on the shape-changing tubes. Whereas lasers were already in use for the balloon-expandable stents, additional technologies were required for Nitinol tubing. Fortunately, these two essential ingredients of high-quality tubing and lasers dovetailed together at nearly the same time to allow the development of a wide variety of Nitinol implants. There were many more hurdles to cross before FDA acceptance, of course, but the pathway was paved with these early developments that encouraged formation of many start-up companies, and more importantly, the health of millions of people to be improved. Academics held the premier International Conference on Martensitic Transformations (ICOMAT) in 1976 to discuss all aspects of martensitic transformations in steel, ceramics, and of course SMAs. In 1992, while attending ICOMAT in Monterey, Calif., a small international group sat down to discuss a more product-focused SMA-specific conference. The inaugural Shape Memory and Superelasticity (SMST) conference in Pacific Grove, Calif., in 1994 was another Big Event. Conferences are now held approximately every three years around the world with up to 500 attendees. Together with ICOMAT and other more local (Europe, Asia, North America) conferences, SMST strives to disseminate both scientific and engineering aspects of SMAs to a broad audience and to train students. The development of SMA devices mentioned above: Pipe couplings and other space applications, orthodontic wires, stents, and many other devices and components were developed primarily by industries with very little GUEST EDITORIAL 2 Pelton (continued on page 15)
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