Novel Functional Behaviors: Beyond Shape Memory Effect & Superelasticity: Session 1
Program Organizers: Ibrahim Karaman, Texas A&M University
Monday 4:00 PM
July 10, 2017
Room: Water Tower
Location: Hyatt Regency Chicago
Session Chair: Huseyin Sehitoglu, University of Illinois
4:00 PM Invited
Strain Glass as Potential Smart Materials: Xiaobing Ren1; 1National Institute for Materials Science
For more than a century, martensite, a micro-sized microstructure, has played a central role in both structural materials (e.g., steels and Ti-alloys) and functional materials (e.g., shape memory alloys). The mechanical and functional properties of these materials stem from the micron-sized martensite and martensitic transformation. Contrasting with the martensite materials, over the recent 10 years there exists a new class of martensite-derived materials called “strain glass”, which is characterized by nano-sized martensite domains and a sluggish strain glass transition. The manipulation of these nano-domains by temperature and external field can lead to novel effects not found in conventional martensitic materials, such as nearly hysteresis-free superelasticity over a wide temperature range, Invar and Elinvar effect. In this talk I shall talk about the state-of-the-art of strain glass studies and its potential applications as novel smart structural materials.
Investigation of Precipitation Processes in NiTi Filaments: Ondřej Tyc1; Petr Sittner1; Jan Pilch1; 1Institute of Physics of the Czech Academy of Sciences
Precipitation in Ni-rich NiTi alloy is an influential process affecting material properties such as fatigue life, tensile strength or thermomechanical response. In this study, thin NiTi filaments (D=51 µm) were subjected to heat treatment at 350-520 °C for 2-120 min. A nonconventional method of direct electric current annealing was also employed and results of superelastic cycling and tensile tests of these methods were compared. Owing to the ultrafast direct electric current annealing it is possible to separate precipitation processes from recovery and recrystallization. The precipitation annealing allows a continuous and predictable adjustment of superelastic response. SANS data show that mean size of Ni-rich precipitates is approx. 8 nm after annealing at 350°C for 2h, which yields stable superelastic response and higher tensile strength. The wires annealed at 520 °C show significant instability in superelastic cycling and decrease of tensile strength and mean size of precipitates is approx. 0.5 µm.
The Elastocaloric Effect in the Shape Memory Alloys Exhibiting Weak and Typical First Order Martensitic Transformations: Fei Xiao1; Takashi Fukuda2; Tomoyuki Kakeshita2; Jian Liu3; Xuejun Jin1; 1Shanghai Jiao Tong University; 2Osaka University; 3Ningbo Institute of Material Technology and Engineering
We have investigated elastocaloric effects in a Fe-31.2Pd (at.%) alloy and a Ni50Fe19Ga27Co4 (at.%) alloy exhibiting a weak and a typical first order martensitic transformations, respectively. The adiabatic temperature change caused by the elastocaloric effect reached 3 K under a compressive stress of 200 MPa in the Fe-31.2Pd alloy, and the value reached 10 K under a compressive stresses of 300 MPa in the Ni50Fe19Ga27Co4 alloy. Although the main cause of the elastocaloric effect in the Ni50Fe19Ga27Co4 alloy is the latent heat of the martensitic transformation, which in the Fe-31.2Pd alloy is the large temperature dependence of elastic strain, which is caused by softening of elastic constant C'.
Isothermal Phase Transition in a Strain Glass Ceramic: Yaodong Yang1; 1Xi'an Jiaotong Universality
Isothermal process is very important to regulate the microstructure of steel (for different applications), but which is barely found in ferroelectric/ ferroelastic ceramic. However, here in a ferroelastic ceramic, we have found a ferroelectric/ ferroelastic phase transition induced solely by increasing waiting time at certain temperatures (isothermal phase transition). Through cooling, a unique metastable state between a strain glass and a ferroelastic is unveiled, which in essence is initially a short-range ordered glassy state and then can evolve into a long-range ordered state through the isothermal process. These features of isothermal phase transition can be understood by Landau theory with the consideration of random defects as a competition between the thermodynamically favored long-range ordered state and the kinetically frustrated short-range ordered glassy state from random defects. This finding may help to further clarify the intricate structure-property relationship of strain glass materials, and offer a new way to adjust the property.
5:30 PM Break