Antiphase boundary-like stacking fault in α″-martensite of disordered crystal structure in β-titanium shape memory alloy

Abstract

The ordering and antiphase boundary (APB)-like fault found in the α″-martensite of β-Ti shape memory alloys are studied. Long-range chemical ordering was not found, but APB-like faults were observed in every martensite plate studied by transmission electron microscopy. These faults have morphology similar to the APBs observed in ordered phases. The superlattice reflections observed in some previous works were a consequence of multiple diffractions. APB-like faults were not observed in the parent phase, leading to the conclusion that the faults were introduced by the martensite transformation. The fault took the form of a wavy tube running perpendicular to the habit plane. The fault was a ‘transformation-induced APB’ with an additional small displacement due to the pre-existing athermal ω phase. The displacement vector was determined to be [–3/50, −23/50, 1/2]. Geometrical aspects of the formation of APB-like faults are also discussed.

Keywords:

• biomaterials
• shape memory alloys
• superelasticity
• titanium alloys

Acknowledgements

This work was partially supported by the foundation Hattori-Hokokai, a Grant-in-Aid for Fundamental Scientific Research Kiban B (No. 20360310 (2008-2010)) and the Global COE Program from the Ministry of Education, Culture, Sports, Science and Technology, Japan. TI would like to thank Emeritus Professor A. Sato (Tokyo Institute of Technology) for his valuable comments on the manuscript.