Thermal aging of the high temperature shape memory alloy 50.3Ni-29.7Ti-20Hf (at.%) introduces a novel precipitate phase, which plays an important role in improving shape memory properties. The precipitate phase was investigated by conventional electron diffraction, high resolution scanning transmission electron microscopy (STEM) and three dimensional atom probe tomography. An unrelaxed orthorhombic atomic structural model is proposed based on these observations. This model was subsequently relaxed by ab initio calculations. As a result of the relaxation, atom shuffle displacements occur, which in turn yields improved agreement with the STEM images. The relaxed structure, which is termed the “H-phase”, has also been verified to be thermodymanically stable at 0 K.
Revised: June 25, 2013 |
Published: March 22, 2013
Citation
Yang F., D.R. Coughlin, P.J. Phillips, L. Yang, A. Devaraj, L. Kovarik, and R.D. Noebe, et al. 2013.Structure Analysis of a Precipitate Phase in an Ni-Rich High Temperature NiTiHf Shape Memory Alloy.Acta Materialia 61, no. 9:3335-3346.PNNL-SA-91683.doi:10.1016/j.actamat.2013.02.023