Effect of low-temperature precipitation on the transformation characteristics of Ni-rich NiTi shape memory alloys during thermal cycling (bibtex)

by M.F.-X. Wagner, S.R.R. Dey, H. Gugel, J. Frenzel, C. Somsen, G. Eggeler

Abstract:
Thermal cycling of NiTi shape memory alloys is associated with functional fatigue: the characteristic phase transformation temperatures decrease with increasing number of cycles, and the transformation behavior changes from a single- to a two-stage martensitic transformation involving the intermediate R-phase. These effects are usually attributed to a gradual increase of dislocation density associated with micro-plasticity during repeated cycling through the transformation range. Here, these changes are shown to increase at a higher maximum temperature (in the fully austenitic state) during differential scanning calorimetric cycling of a Ni-rich alloy. Additional thermal cycling experiments without repeated phase transformations, and post-mortem microstructural observations by transmission electron microscopy, demonstrate that a relevant portion of functional fatigue is due to the formation of nano- scale Ni-rich precipitates of type Ni4Ti3 even at temperatures relatively close to the austenite finish temperature. These results show that both dislocation generation during the diffusion-less phase transformation, and diffusion-controlled nucleation and growth of Ni4Ti3 precipitates, can interact and contribute to the evolution of functional properties during thermal cycling of Ni-rich NiTi.
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Reference:
Wagner, M.F.-X., Dey, S.R.R., Gugel, H., Frenzel, J., Somsen, C., Eggeler, G.: Effect of low-temperature precipitation on the transformation characteristics of Ni-rich NiTi shape memory alloys during thermal cycling, Intermetallics 18, 1172-1179, 2010.
Bibtex Entry:
@Article{Wagner2010c,
  author    = {Wagner, M.F.-X. and Dey, S.R.R. and Gugel, H. and Frenzel, J. and Somsen, C. and Eggeler, G.},
  journal   = {Intermetallics},
  title     = {{Effect of low-temperature precipitation on the transformation characteristics of Ni-rich {NiTi} shape memory alloys during thermal cycling}},
  year      = {2010},
  issn      = {09669795},
  month     = jun,
  number    = {6},
  pages     = {1172--1179},
  volume    = {18},
  abstract  = {Thermal cycling of NiTi shape memory alloys is associated with functional fatigue: the characteristic phase transformation temperatures decrease with increasing number of cycles, and the transformation behavior changes from a single- to a two-stage martensitic transformation involving the intermediate R-phase. These effects are usually attributed to a gradual increase of dislocation density associated with micro-plasticity during repeated cycling through the transformation range. Here, these changes are shown to increase at a higher maximum temperature (in the fully austenitic state) during differential scanning calorimetric cycling of a Ni-rich alloy. Additional thermal cycling experiments without repeated phase transformations, and post-mortem microstructural observations by transmission electron microscopy, demonstrate that a relevant portion of functional fatigue is due to the formation of nano- scale Ni-rich precipitates of type Ni\textsubscript{4}Ti\textsubscript{3} even at temperatures relatively close to the austenite finish temperature. These results show that both dislocation generation during the diffusion-less phase transformation, and diffusion-controlled nucleation and growth of Ni\textsubscript{4}Ti\textsubscript{3} precipitates, can interact and contribute to the evolution of functional properties during thermal cycling of Ni-rich NiTi.},
  doi       = {10.1016/j.intermet.2010.02.048},
  keywords  = {Martensitic transformations, Multiphase intermetallics, Precipitates, Shape-memory effects},
  publisher = {Elsevier {BV}},
  url       = {http://www.sciencedirect.com/science/article/pii/S0966979510001366},
}
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