09.01.2019 | SPECIAL ISSUE: HTSMA 2018, INVITED PAPER
On the Oxidation Behavior and Its Influence on the Martensitic Transformation of Ti–Ta High-Temperature Shape Memory Alloys
- Zeitschrift:
- Shape Memory and Superelasticity
Wichtige Hinweise
This article is an invited paper selected from presentations at the 2nd International Conference on High-Temperature Shape Memory Alloys and has been expanded from the original presentation. HTSMA 2018 was held in Irsee, Germany, May 15–18, 2018 and was organized by the German Materials Society (DGM).
Abstract
In the present work, the influence of oxidation on the martensitic transformation in Ti–Ta high-temperature shape memory alloys is investigated. Thermogravimetric analysis in combination with microstructural investigations by scanning electron microscopy and transmission electron microscopy were performed after oxidation at 850 °C and at temperatures in the application regime of 450 °C and 330 °C for 100 h, respectively. At 850 °C, internal oxidation results in the formation of a mixed layered scale of TiO2 and β-Ta2O5, associated with decomposition into Ta-rich bcc β-phase and Ti-rich hexagonal α-phase in the alloy. This leads to a suppression of the martensitic phase transformation. In addition, energy dispersive X-ray analysis suggests an oxygen stabilization of the α-phase. At 450 °C, a slow decomposition into Ta-rich β-phase and Ti-rich α-phase is observed. After oxidation at 330 °C, the austenitic matrix shows strong precipitation of the ω-phase that suppresses the martensitic transformation on cooling.
