Quasimartensitic Modulations: Session 2
Program Organizers: Avadh Saxena, Los Alamos National Laboratory

Tuesday 2:00 PM
July 11, 2017
Room: Gold Coast
Location: Hyatt Regency Chicago

Session Chair: Ryan Elliott, University of Minnesota

2:00 PM  
Slow Dynamics of Strain Glass: Aging, Scaling, Memory and Rejuvenation: Dezhen Xue1; Yumei Zhou1; Xiangdong Ding1; Turab Lookman2; Xiaobing Ren1; 1State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China; 2Los Alamos National Laboratory
     We report that the slow dynamics, a critical slowing down of the relaxational process, occurs in the strain glass (STG) with short-range strain ordering. The features of slow dynamics including physical aging, scaling, memory and rejuvenation, which are the crucial evidence for glassy behavior, support the glassy nature of STG. Our focus on the structural degreeof freedom provides a basis for understanding the slow dynamics of other ferroic glass systems, including cluster spin glasses and relaxors, in which the defects induce lattice distortion in the matrix as well.

2:20 PM  
Crystallization of Strain Glass:Introducing Time as a Variable for the Future Martensitic Design: Yuanchao Ji1; Dong Wang1; Xiangdong Ding1; Kazuhiro Otsuka1; Xiaobing Ren1; 1Xi'an Jiaotong University
    Time plays a crucial role in diffusional transformations and different kinds of microstructures and metastable phases may appear with the time evolution, which are used to achieve desired physical properties of materials (steel is the best known example). On the other hand, time-independence is a primary characteristic of martensitic transformations. It is believed that time is not essential for achieving a stable phase and determining a diffusionless equilibrium phase diagram, because the rapid transformation rate in the growth process provides little time window for the existence of metastable states. Here, we report a surprising discovery, a normally “non-existent” martensite isothermally appears through a gradual growth with time. This provides evidence for the existence of time-dependent phase evolution in martensitic systems. Our study suggests a new mechanism of the isothermal phase formation in martensitic systems, which provides an approach to find new phases and novel properties.

2:40 PM  
Stress-induced Transition from Modulated 14M to Non-modulated Ni-Mn-Ga Martensite Studied by In situ TEM: Yanling Ge1; Niva Za´rubova´2; Oleg Heczko2; Simo-Pekka Hannula1; 1Aalto Univeristy; 2Institute of Physics of the Czech Academy of Sciences
    In situ TEM straining was utilized to study stress induced intermartensitic transformation from seven-layered (14M) to non-modulated (NM) martensite and the detwinning in non-modulated (NM) martensite. We found that in NM martensite both detwinning of nanosized deformation twins and formation of new twins occurred via movement of twinning dislocations along the twin boundary, which has a Burgers vector close to 1/12[101]. However, during stress induced intermartensitic transformation the leading partial dislocation was moving along the basal plane of 14M having a Burgers vector of type 1/6[1-10]. High resolution TEM investigation revealed that the moving partial at the edge of the fault is actually a pair of partial dislocations resulting in two-layered fault on the basal plane. This two-layered fault is twin related to adjacent five-layered plane forming a complete seven-layered nano-twinned structure. Thus the fault can be considered as doublelayered nanotwin and the intermartensitic transition is two-layered fault detwinning process.

3:00 PM  
The Strain Glass Transition in Fe-Ni-Cr Elinvar Alloy: Fangyu Qin1; Xiaobing Ren2; Xinqing Zhao1; 1Beihang University; 2 Xi’an Jiaotong University
    The first Elinvar alloy with invariant elastic modulus over a wide temperature range was discovered almost 100 years ago. And it has been well accepted that the physical mechanism for this anomaly (elastic invariable) in FeNi-based Elinvar could be attributed to magnetic phase transitions, while some relative models explaining the anomaly are controversial. However, recent studies indicated that non-magnetic alloy could possess the Elinvar effect by strain glass transitions. The mechanism is validated by simulation method computing a magnetic Fe-Ni Elinvar lately. Nevertheless, direct experimental evidence for traditional magnetic Elinvars is still lacking. In the present work, the micro-structural evolution of a Fe-Ni Elinvar were intensively characterized by dynamic thermal mechanical analysis, high resolution microscopy and magnetic measurement. Our results evidently suggested that the continuous formation of nano-sized martensite results in a gradual softening of the elastic modulus over a wide temperature range, leading to the Elinvar phenomenon.

3:15 PM  
New Strain Glass Transition with Unique Properties in Deformed NiTi Alloys: Qianglong Liang1; 1Xi'an Jiaotong University
    Strain glass is a new strain state with randomly distributed martensitic nanodomains in ferroelastic/martensitic system, which have shown many novel properties due to its unique glass characteristics. However, the small transformation strain of the local structure of martensitic nanodomains in current reported strain glass systems limits its applications. Here we report a new kind of strain glass state with new local structure with large transformation strain. This strain glass has been proved by the continuous decrease of electrical resistivity and TEM observations. Furthermore, this new strain glass performs unique properties such as quasi-linear elasticity with a large recoverable strain (>4%) and high strength (>2GPa), tunable elastic modulus. Our work expands the strain glass field and may shed light on the design of new strain glass materials with novel properties.

3:30 PM Break