High ultimate tensile stress in nano-grained superelastic NiTi thin films

✍ Scribed by H. Rumpf; T. Walther; C. Zamponi; E. Quandt

• Book ID: 103840933
• Publisher: Elsevier Science
• Year: 2006
• Tongue: English
• Weight: 467 KB
• Volume: 415
• Category: Article
• ISSN: 0921-5093
• DOI: 10.1016/j.msea.2005.09.089

✦ Synopsis

NiTi-films were fabricated by dc magnetron sputtering from melt-cast disc targets. The freestanding films revealed superelastic properties in tensile tests. At 37 • C superelastic properties were achieved showing a closed-loop hysteresis and a plateau of more than 5% strain. The ultimate tensile strength exceeded 1180 MPa for the sputtered films at a maximum strain of 11.5%. This remarkable improvement in mechanical properties over those reported in previous studies correlates with a textured, fine grained (50-200 nm), single phase microstructure, confirmed by transmission electron microstructure. Moreover, these grains revealed a texture which was not found in earlier studies concerning sputtered films. Finally, the prepared specimens did not reveal any evidence of disc or lens shaped Ti 3 Ni 4 precipitates but a relatively homogeneous chemistry.