Microstructure and martensitic transformation behavior of crystallized Ti-36Ni-7Sn (at%) alloy ribbons

Abstract

Amorphous Ti-36Ni-7Sn (at%) alloy ribbons prepared by melt spinning were annealed at various temperatures for crystallization and then microstructures and transformation behavior were investigated by means of electron microscopy, X-ray diffraction and differential scanning calorimetry. Crystallized Ti-36Ni-7Sn alloy ribbons consisted of Ti3Sn, Ti2Ni and TiNi phases. Size of Ti3Sn phase was in the range of 50-850 nm depending on annealing temperature. Average size of TiNi phase increased from 25nm to 100nm with raising annealing temperature from 8731( to 1073K. Volume fraction of Ti2Ni phase decreased by raising annealing temperature through decomposition reaction of 3T(i)2Ni+Sn (solved in TiNi phase) -> 3TiNi+Ti3Sn and then Ti2Ni almost disappeared by annealing at 1173K. The TiNi phase in crystallized Ti-36Ni-7Sn alloy ribbons showed the B2-R-B19' transformation behavior. DSC peak temperature associated with the B2-R transformation (T*(R)) decreased from 303K to 292K with raising annealing temperature from 973K to 1173K, while DSC peak temperature associated with the R-B19' transformation (M,*) increased from 187K to 237K with raising annealing temperature from 1073K to 1173K and thus the temperature gap between Tit* and M,* decreases from 112K to 55K. (C) 2012 Elsevier B.V. All rights