Ti-Ni Alloy Thin Films Research Articles

Electrochemical Properties of Multilayered Sn/TiNi Shape-Memory-Alloy Thin-Film Electrodes for High-Performance Anodes in Li-Ion Batteries.

Sn is a promising candidate anode material with a high theoretical capacity (994 mAh/g). However, the drastic structural changes of Sn particles caused by their pulverization and aggregation during charge–discharge cycling reduce their capacity over time. To overcome this, a TiNi shape memory alloy (SMA) was introduced as a buffer matrix. Sn/TiNi SMA multilayer thin films were deposited on Cu foil using a DC magnetron sputtering system. When the TiNi alloy was employed at the bottom of a Sn thin film, it did not adequately buffer the volume changes and internal stress of Sn, and stress absorption was not evident. However, an electrode with an additional top layer of room-temperature-deposition TiNi (TiNi(RT)) lost capacity much more slowly than the Sn or Sn/TiNi electrodes, retaining 50% capacity up to 40 cycles. Moreover, the charge-transfer resistance decreased from 318.1 Ω after one cycle to 246.1 Ω after twenty. The improved cycle performance indicates that the TiNi(RT) and TiNi-alloy thin films overall held the Sn thin film. The structure was changed so that Li and Sn reacted well; the stress-absorption effect was observed in the TiNi SMA thin films.

Formation of multilayer structure and evolution of shape recovery characteristics in proton irradiated TiNi alloy thin films

TiNi thin films have attracted wide attentions as actuator materials in the micro-electro-mechanical systems (MEMs) for aerospace craft. However, multiple irradiation, such as the proton, was generally considered as an essential expired factor for the materials used in the aerospace. The present paper focused on the microstructure, martensitic transformation and shape recovery property of TiNi thin films after being irradiated by proton. A single layer structure B19′ phase to a dual-phase (B2 and B19′) with multilayer structure after proton irradiation have been revealed through a combination technique of grazing incidence (GI) XRD and TEM. As-formed irradiated films with amorphous layer and B2 austenite phase displayed a two-step martensitic transformation behavior, which occurred in the irradiated and the unirradiated layer. In contrast, the unirradiated counterparts just exhibited a single-step martensitic transformation. In addition, some defects could be seen after the TiNi films being irradiated. Such defects could induce a stress field that produces the R phase in the B2 phase. Furthermore, the synergistic effect of preferential sputtering effect and inverse Kirkendall effect induced the GP zones in the irradiated layer after 120 keV proton irradiation. The existence of amorphous phase and precipitation significantly deteriorated the shape recovery property.

Effect of low-energy proton on the microstructure, martensitic transformation and mechanical properties of irradiated Ni-rich TiNi alloy thin films

Effect of low-energy proton on the microstructure, martensitic transformation and mechanical properties of irradiated Ni-rich TiNi alloy thin films

Dependence of compositions and crystallization behaviors of dc-sputtered TiNi thin films on the deposition conditions

TiNi alloy thin films, whose properties are very sensitive to the composition, were prepared using a dc sputter deposition technique. Effects of major deposition parameters on the resulting thin film properties were investigated. The atomic percent of Ti was found to increase with increasing working distance or pressure. The deposition rate was found to increase with the dc power but decrease with the working distance and pressure. The activation energy was also determined and compared to that of bulk TiNi alloys.