ADVANCED MATERIALS & PROCESSES | OCTOBER 2024 45 12 References 1. J. Frenzel, On the Importance of Structural and Functional Fatigue in Shape Memory Technology, Shape Memory and Superelasticity, 6(2), p 213-222, 2020. 2. W.S. LePage, et al., Grain Size Effects on NiTi Shape Memory Alloy Fatigue Crack Growth, Journal of Materials Research, 33(2), p 91107, 2018. 3. J. Chen, H. Yin, and Q. Sun, Effects of Grain Size on Fatigue Crack Growth Behaviors of Nanocrystalline Superelastic NiTi Shape Memory Alloys, Acta Materialia, 195, p 141-150, 2020. 4. H. Yin, et al., Effects of Grain Size on Tensile Fatigue Life of Nanostructured NiTi Shape Memory Alloy, International Journal of Fatigue, 88, p 166-177, 2016. tomography (XCT) are presented in Fig. 4. This data clearly illustrates the significant reduction in damage generation during heating-limited actuation cycling compared to fully cycled samples. SUMMARY The actuation fatigue performance of NiTiHf HTSMAs is shaped by a complex interplay of factors, many of which remain underexplored. Significant progress has been made, particularly in understanding the effects of composition, impurities, and H-phase precipitation. However, further research is crucial, especially regarding the influences of grain size, texture, stress state, and heating/cooling rates on thermomechanical fatigue. This article provides a concise overview of the key factors affecting NiTiHf HTSMA performance, underscoring the need for continued investigation into the microstructural mechanisms behind both structural and functional fatigue during repeated partial phase transformations. Despite the challenges, the current understanding of these alloys offers confidence in their potential for critical applications. Moreover, the research has already contributed to the development of new ASTM test standards, such as those for constant force repeated thermal cycling (CFRTC)[31]. The ongoing refinement of these testing standards will be essential for advancing our knowledge of actuation fatigue mechanisms in NiTiHf HTSMAs and for expanding their practical applications. ~SMST For more information: A. Demblon, research assistant professor, Department of Materials Science and Engineering, Texas A&M University, 575 Ross St., College Station, Texas 77840, 979.845.0750, aldemblon@tamu.edu. Fig. 4 — Digital image correlation (DIC) and x-ray computed tomography (XCT) results of Ni50.3Ti29.7Hf20 samples during and after actuation fatigue testing specimens with a 300 MPa applied load. The red marks in the XCT images are cracks and voids formed after 1500 actuation cycles. FEATURE www.masterbond.com Need an adhesive for your MEDICAL DEVICE? Hackensack, NJ 07601, USA ∙ +1.201.343.8983 ∙ main masterbond.com Our products meet USP Class VI for biocompatibility & ISO 10993-5 for cytotoxicity We are ready to help with adhesive solutions for established and new medical device manufacturers We O er epoxies, silicones, light curing compounds for bonding, sealing, coating, potting & encapsulating
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