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A D V A N C E D M A T E R I A L S & P R O C E S S E S | O C T O B E R 2 0 1 9 4 6 Fig. 7 — Some similarities of the iron-carbon phase diagram (left) and Ni-Ti phase diagram (right) suggest there could be potential for future developments in NiTi-based alloys. ble, hardened NiTi intermetallic structural alloys are a new class of materials for use in demanding mechanical engineer- ing applications. Fig. 5 — High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of hardened Nitinol 60 reveals microstructure containing complex Ni 4 Ti 3 platelets in a NiTi matrix. Magnification: 50,000x. Fig. 6— Optical microscopy images of Nitinol 60 (left) and NiTi-Hf (right) after heat treatment at 1000°C followed by water quenching to achieve high hardness. Magnification: 500x. Over the past 100 years, literally hundreds of steel com- positions have emerged from the basic iron-carbon phase di- agram (Fig. 7) and are in common use for bearings, gears, and other mechanical components. Looking at the history of the development of bearing steels, it is possible to extrapolate a parallel situation for NiTi when considering the NiTi phase diagram (Fig. 7). Today, there are just a few NiTi-based alloys for use inmechanical engineering applications. The landscape has plenty of room for more developments. ~SMST Acknowledgment The long-term, continuing support fromNASA’s Aeronau- tics Research Mission Directorate (ARMD), NASA’s Engineering and Safety Center (NESC), and NASA’s International Space Sta- tion (ISS) programs is appreciated. For more information: Christopher DellaCorte is senior tech- nologist, NASA Glenn Research Center, 21000 Brookpark Rd., Cleveland, OH 44135, 216.433.6056, christopher.dellacorte@ nasa.gov , www.nasa.gov/centers/glenn. References 1. W.J. Buehler, J.V. Gilfrich, and R.C. Wiley, Effect of Low- Temperature Phase Changes on the Mechanical Properties of Alloys near Composition TiNi, J. of Appl. Phys., Vol 34(5), 1963, p 1475-1477. 2. W.J. Buehler, “NITINOL Re- Examination,” White Oak Labo- ratory Alumni Association Leaf, Winter 2006, Vol VIII(I), www. wolaa.org. 3. C. DellaCorte, R.D. Noebe, M.K. Stanford, and S.A. Padula, “Resilient and Corrosion-Proof Rolling Element Bearings Made 8 FEATURE