Amorphization and crystallization characteristics of TiNi shape memory alloys by severe plastic deformation

Abstract

Differential scanning calorimetry (DSC) was used to determine the crystallization fraction and rate in TiNi alloys by severe plastic deformation. Results showed that the reverse martensitic transformation peak was not observed during the first heating at the rate of 40 K/min in the as-rolled samples, but one exothermic peak was observed at 620 K, which was associated with the amorphous crystallization process. During the second heating, reverse martensitic transformation was recovered. The onset crystallization temperature was low in the initial stage of crystallization with lower heating rates, but the crystallization fraction was found to increase with increasing temperature. However, the crystallization fraction was almost constant in the initial stage of crystallization with a relatively high heating rate. In all heating rates, the amorphous crystallization rates almost always reached maximum as the volumetric fraction of amorphous crystallization rose to 50%.

Keywords

shape memory alloy / cold deformation / nanocrystallization / amorphization

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Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant No. 50471021) and Research Foundation for the Doctoral Program of Higher Education (Grant No. 20050425002).

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg