|Number of page(s)||10|
|Section||Principles, Simulations, Materials: Background|
|Published online||01 September 2009|
In-situ XRD Investigations Of Two Step R-phase Transformations In Aged NiTi Shape Memory AlloysK. Harikrishnan1, K. Chandra1, P. S. Misra1 and Vinod S. Agarwala2
1 Metallurgical and Materials Engineering Department, IIT Roorkee, Roorkee-247 667, India.
2 Air Vehicle Engineering Department, US Naval Air Systems Command, Patuxent River, Maryland, USA.
Published online: 1 September 2009
The characteristics of R-phase transformations in aged Ti-49.83 at% Ni (Nitinol) shape memory alloys at 300°C were explained with the help of Differential scanning Calorimeter (DSC) and In-situ X-ray Diffraction (In-situ XRD) studies. The solutionized and short duration aged samples (0 h and 48hrs) did not alter the B2-B19’ transformation path and medium aged samples (72 and 96 hrs) exhibit single-step R-phase with B2-R-B19’ transformation path and pro-longed aged sample (125 hrs) evolves two-step R-phase transformations with B19’↔R1↔R2↔B2. The carefully crafted in-situ XRD studies showed emerging of B2 (110) phase from merging of R (011) and R (-101) at 100°C and it is equal to the transformation temperature determined by the DSC experiments. The two-step R-phase transformation behavior is attributed to structural inhomogeneity of the matrix, both in terms of composition and of internal stress field, caused by the formation of Ni4Ti3 precipitates.
© Owned by the authors, published by EDP Sciences 2009