ADVANCED MATERIALS & PROCESSES | APRIL 2024 58 SMJ HIGHLIGHTS 12 CHARACTERIZATION OF HYDROGEN THERMAL DESORPTION BEHAVIOR AND ENHANCEMENT OF HYDROGEN EMBRITTLEMENT IN Ni——Ti SUPER- ELASTIC ALLOY INDUCED BY CATHODIC HYDROGEN CHARGING IN THE PRESENCE OF CHLORIDE IONS Ryosuke Hayashi and Ken’ichi Yokoyama Abstract characterization of hydrogen thermal desorption behavior and enhancement of hydrogen embrittlement in Ni–Ti superelastic alloy have been investigated in terms of the type of cathodic charging in easy-to-handle 0.15 M NaCl, KCl, Na2SO4, and NaHCO3 solutions. Immediately after hydrogen charging at approximately 200 mass ppm, the amounts of hydrogen desorbed in the low-temperature region (150–400°C) for specimens charged in NaCl and KCl solutions are larger than those charged in Na2SO4 and NaHCO3 solutions. Even upon aging at room temperature after hydrogen charging, the shoulder in the low-temperature side (400–500°C) of the desorption peak remains for specimens charged in NaCl and KCl solutions. In cyclic tensile deformation in the stress plateau region caused by stress-induced martensite and reverse transformations, fracture occurs after 50–60 cycles irrespective of the type of solution immediately after hydrogen charging. Upon aging, the cycle numbers to fracture of specimens charged in NaCl and KCl solutions (800–900 cycles) Fig. 2 — FE-SEM images of fracture surfaces: general and magnified views of specimens subjected to tensile deformation after hydrogen charging for 1 h in NaCl, KCl, and Na2SO4 solutions and for 0.75 h in NaHCO3 solution. (a)–(d): non-aged and (e)–(h): aged specimens after hydrogen charging. DONATE NOW TO CASMART’S STUDENT DESIGN CHALLENGE The Shape Memory and Superelastic Technologies Society (SMST) is teaming with CASMART, the Consortium for the Advancement of Shape Memory Alloy Research and Technology, at SMST 2024 Conference & Exposition in Cascais, Portugal, for their 6th Student Design Challenge. The Student Design Challenge is intended for undergraduate and graduate students to consider innovative approaches to developing new materials and hardware using shape memory alloy (SMA) technology. Students will have the opportunity to showcase and present their creativity during the CASMART Student Design Challenge. SMST believes in inspiring young minds to pursue science, math, and technology education and careers. These subjects are critical in our economy, so let’s work together to raise money to excite students and drive them to fulfilling and productive career paths! For more information, visit https://www.asminternational.org/smst-2024/. Teams (finalists) include: 1. Team “EC Cube” (Saarland University, Germany): D. Zimmermann, L. Ehl, P. Molitor, J. Fehrenbach, N. Scherer (Advisors: F. Louia, Dr.-Ing. Paul Motzki) 2. Team “SMARTAN" (Iowa State University, USA): Masha Lebedeva, Roger Claude, Matthew Neilson, Josh Wo (Advisor: Dr. Jun Cui) 3. Team “InNova” (NOVA School of Science and Technology, Portugal): M. Sacramento, M. Pinto, M. Diaz, D. Pedreiro, D. Silva (Advisor: João P. de Sousa Oliveira) 4. Team “CASMARTIES” (University of Tulsa, USA): T. Valenzuela, K. Crouch, S. Free, M. Aurigemma, B. Charles (Advisors: E. Devine, Dr. William LePage) 5. Team “SMAckin” (University of North Texas, USA): Caleb McCoy, Kenneth Sanders, Natalia Vela (Advisors: A. Montagnoli, Dr. Marcus L. Young) 6. Team “Mean Green Chilling Machine” (University of North Texas, USA): D. Worrell, H. Patton, M. Jennings, S. Ruiz, B. Herrera-Alfaro (Advisors: Dr. Richard Zhang, Dr. Marcus L. Young) 7. Team “ShapeShifters” (Northwestern University, USA): Trevor Abbott, Darrel Chen, Paloma Lee, Linda Li, Rohan Luthra, (Advisor: Dr. Ian McCue) 8. Team “NiTi Jet” (University of Toledo, USA): Mohammad Pourshams, Pete Angelo Rocco, Timothee Cullaz (Advisor: Dr. Mohammad Elahinia) 9. Team “Metal Morphers” (Georgia Institute of Technology, USA): Alexa Brammer, António Ferreira, Zachary Haataja, Ella Parker, Tyler Knapp (Advisor: Dr. Aaron Stebner) are smaller than those charged in Na2SO4 and NaHCO3 solutions (approximately 1000 cycles). The present results suggest that hydrogen states, which strongly interact with martensite transformation, are charged to a greater degree in the presence of chloride ions, thereby enhancing hydrogen embrittlement (Fig. 2).
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