Quasimartensitic Modulations: Session 1
Program Organizers: Avadh Saxena, Los Alamos National Laboratory
Monday 4:00 PM
July 10, 2017
Location: Hyatt Regency Chicago
Session Chair: Avadh Saxena, Los Alamos National Laboratory
4:00 PM Invited
Precursors, Strain Glass and Avalanches in Martensitic Transitions: Antoni Planes1; Teresa Castán1; Marcel Porta1; Pol Lloveras2; Avadh Saxena3; 1Universitat de Barcelona; 2Universitat Politècnica de Catalunya; 3Los Alamos National Laboratory
Martensitic transitions are often preceded by nanoscale, modulated textures associated with local symmetry breaking effects. Disorder and long-range anisotropic interactions are the essential ingredients for these precursors to occur. In some circumstances due to the screening of long-range correlations the martensitic transition is kinetically arrested and the system becomes frozen into a strain glass phase. We will demonstrate that the properties of martensitic systems are controlled by the combined effect of the amount of disorder and elastic anisotropy. We will discuss a phase field model that reproduces such behavior and reveals that the response of these systems to an applied stress should occur intermittently through avalanches. A crossover from a super-critical to a sub-critical distribution of the avalanche sizes is predicted when the amount of disorder is increased (or the elastic anisotropy decreased). Criticality is found for the amount of disorder and elastic anisotropy at which the transition is suppressed.
Re-entrant Glass Transition in Ferroelastics: Wenjia WANG1; Shuai REN2; Dong WANG2; Xiaobing REN1; 1National Institute for Materials Science; 2Xi'an Jiaotong University
Demanded by the thermodynamics, systems always tend to form a state of minimum energy, thus resulting in a large class of disorder-order transition, disorder-glass transition, and spontaneous or isothermal glass- long range order (LRO) transition. Nevertheless, it is unexpected that LRO stable phase can further transform into a metastable glassy state (i.e., the re-entrant glass transition). Here we report for the first time the existence of re-entrant glass transition in Ti-Ni-based ferroelastic system: upon cooling, the system firstly transforms from B2 parent phase to B19 martensites, and then transforms to a glass state. This unusual transition can be attributed to the competition between the thermodynamic driving force of a lower-symmetry stable phase than existed B19 and the frustration caused by doped point defects. This discovery may not only contribute to a deeper understanding on the re-entrant phenomena in ferroic materials, but also produce unique properties.
Dislocation Induced Strain Glass in Ti50Ni45Fe5 Alloy: Jian Zhang1; Dezhen Xue1; Xiaoying Cai1; Xiangdong Ding1; Xiaobing Ren1; Jun Sun1; 1Xi'an Jiaotong University
Strain glass (STG) appears when kinetic limitation is strong enough to suppress martensitic transition, where point defects and precipitates have been proven to be effective. Dislocations can also introduce the random stress field down to atomic scale, however the effectiveness of which remains unknown. We will present the first experimental finding of dislocation induced STG in Ti50Ni45Fe5 alloy with over 20% plastic deformation (Acta. Mater. 2016). Being different from point defects and precipitates, dislocations do not change the chemical composition of matrix and consequently do not vary the transition temperature too much. Our finding verifies the effectiveness of local randomness on the crossover from martensite to STG transition and suggests that global effect of defects is not a necessary condition for STG. The present finding may promote the application of STG alloy by assisting on the tuning of functional temperature range in STG alloy through adding the randomness of dislocations.
Ti-Ni-Hf-Cu High Temperature Shape Memory Alloy Ribbon with a Large Completely Recoverable Strain: Xianglong Meng1; Xiaoyang Yi1; Wei Cai1; Liancheng Zhao1; 1Harbin Institute of Technology
Ti-Ni-Hf alloys are promising shape memory alloys (SMAs) for high temperature applications due to its high martensitic transformation temperatures and low cost. However, their completely recoverable strain is only about 3%, which has severely hampered their practical applications. In our previous papers, it has been found that the addition of Cu into Ti-Ni-Hf alloys changes the martensitic transformation temperatures slightly and improve the amorphous forming ability. In the present study, nano-scale particles precipitate in Ti-Ni-Hf-Cu SMA ribbons during the crystallization process. the microstructure evolution of Ti-Ni-Hf-Cu ribbons were investigated by TEM. During deformation, the nano-scale particles change the deformation mechanisms of Ti-Ni-Hf-Cu ribbons and result in a remarkable increase of completely recoverable strain. A maximum completely recoverable strain of about 6% is obtained in Ti-Ni-Hf-Cu high temperature SMA ribbons.