Crystallograply of Ni-Ti Shape Memory Alloy by X-Ray Diffraction and Diffraction Pattern Simulation

Abstract

The martensitic transformation of Ni-Ti shape memory alloy was investigated by X-ray diffraction analysis aided X-ray diffraction pattern simulation. Using the wire shape samples the X-ray diffraction patterns were measured at every 10 from 0 to 80 . The software that simulated the X-ray diffraction patterns using by the data of already known lattice constants was developed on the basis of the Bragg's law and the intensity laws. First we confirmed that the X-ray pattern measured by arranging wire samples and attaching the sample holder coincided that of the powder method. Next the X-ray pattern at austenite phase (80 ) was compared with the simulated pattern of B2 crystal structure by the program and the state was identified as B2 structure. On the other hand at martensite phase (0 ) B2 and B19' structures were mixed in the crystal. Although the shape memory effect was expressed at this environmental temperature, it is considered that not only B19' structure but B2 structure is also related to the effect of shape memory effect.

Low temperature polytetrafluoroethylene (PTFE) coating improves the appearance of orthodontic wires without changing their mechanical properties

“…7A). In Ni-Ti wires, specimens heated to 380°C, which diminished superelasticity, exhibited a martensitic phase instead of an austenite phase at a 42° diffraction angle in unheated and 200°C heated specimens 24,25) Ti-Mo; Ti-11.5Mo-6Zr-4.5Sn, Ti-Nb; Ti-23Nb-0.7Ta-2.0Zr-1.2O, Non; intact products without PTFE coating or heating Superscript letters denote statistically significant differences (p<0.01) within each material of each measurement item. 7B).…”

“…For Ni-Ti wires (Ni-Ti; CaCl type-B2 structure), we first expected that the heating condition of the PTFE coating (200-400°C) would not change the crystal structure or the mechanical properties, based on the equilibrium diagram of Ni-Ti, and because Ni-Ti wires were usually heated at 400-500°C for a few minutes to a few hours to achieve shape fixity 25) . Ni-Ti wire heated to 380°C exhibited a martensitic phase instead of an austenite phase at a 42° diffraction angle in unheated and 200°C heated specimens 24,25,34) , which could be a cause of the diminishment of its superelasticity as revealed by the three-point bending test (Fig. 7B).…”