It is known that Ni replacement of Cu in ZrCu high temperature shape memory alloy (HTSMA) results in the increase of the temperatures of the martensitic transformation (MT) [1]. Once the Ni content reaches 20 at.%, the temperatures of MT are becoming higher than the temperature of crystallization of the amorphous alloy with the same composition [2] and crystallization from the amorphous state in this case takes place through formation of B19` phase without any visible signs of the nanoscale phase separation.

Transmission electron microscopy (TEM) in the present study revealed that once the Ni content is not sufficient to increase the MT temperatures above crystallization one, the nanoscale phase separation plays important role. The increase of MT above crystallization like in [2], indeed, results in the preferential formation of B19` upon crystallization. DSC and X-ray diffraction were used to find a correspondence between kinetics of the crystallization and structural phase formation qualitatively detected by TEM.

References

[1] Koval Yu.N., Firstov G.S., Delaey L., Van Humbeeck J., Scr. Met. et Mat., v.31, No. 7, 1994, pp.799-802.

[2] Firstov G.S., Koval Yu.N., Van Humbeeck J., Portier R., Vermaut P., Ochin P., Materials Science and Engineering: A, Volumes 438-440, 25 November 2006, Pages 816-820

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