Powder metallurgical processing of NiTi shape memory alloys with elevated transformation temperatures

Mentz, J.; Frenzel, J.; Wagner, M.F.-X.; Neuking, K.; Eggeler, G.; Buchkremer, H.P.; Stöver, D.

doi:10.1016/j.msea.2008.01.084

Powder metallurgical processing of NiTi shape memory alloys with elevated transformation temperatures (bibtex)

by J. Mentz, J. Frenzel, M.F.-X. Wagner, K. Neuking, G. Eggeler, H.P. Buchkremer, D. Stöver

Abstract:

The production of high quality powder metallurgical NiTi alloys with elevated phase transformation temperatures is challenging. During processing, an unavoidable pickup of impurity elements (especially oxygen and carbon) results in a decrease of phase transition temperatures and in the formation of brittle secondary phases. We introduce a processing route including melting, gas atomization and hot isostatic pressing for binary NiTi shape memory alloys which minimizes these problems. We demonstrate that the microstructure of the Ti-rich NiTi alloy contains precipitates of Ti₂Ni type which can be exploited to dissolve oxygen picked up during later process stages. In this study, three powder fractions with different grain sizes and impurity contents were subjected to hot isostatic pressing. The evolution of microstructures and material properties was studied by chemical analysis, microscopy, differential scanning calorimetry, and mechanical testing. Exploiting the solubility of oxygen in Ti₂Ni, the processing route presented in the present paper succeeds in producing powder metallurgical NiTi shape memory alloys with good structural and functional properties.

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Reference:

Mentz, J., Frenzel, J., Wagner, M.F.-X., Neuking, K., Eggeler, G., Buchkremer, H.P., Stöver, D.: Powder metallurgical processing of NiTi shape memory alloys with elevated transformation temperatures, Materials Science and Engineering: A 491, 270-278, 2008.

Bibtex Entry:

@Article{Mentz2008,
  author   = {Mentz, J. and Frenzel, J. and Wagner, M.F.-X. and Neuking, K. and Eggeler, G. and Buchkremer, H.P. and St\"{o}ver, D.},
  journal  = {Materials Science and Engineering: A},
  title    = {{Powder metallurgical processing of {NiTi} shape memory alloys with elevated transformation temperatures}},
  year     = {2008},
  issn     = {09215093},
  number   = {1-2},
  pages    = {270--278},
  volume   = {491},
  abstract = {The production of high quality powder metallurgical NiTi alloys with elevated phase transformation temperatures is challenging. During processing, an unavoidable pickup of impurity elements (especially oxygen and carbon) results in a decrease of phase transition temperatures and in the formation of brittle secondary phases. We introduce a processing route including melting, gas atomization and hot isostatic pressing for binary NiTi shape memory alloys which minimizes these problems. We demonstrate that the microstructure of the Ti-rich NiTi alloy contains precipitates of Ti\textsubscript{2}Ni type which can be exploited to dissolve oxygen picked up during later process stages. In this study, three powder fractions with different grain sizes and impurity contents were subjected to hot isostatic pressing. The evolution of microstructures and material properties was studied by chemical analysis, microscopy, differential scanning calorimetry, and mechanical testing. Exploiting the solubility of oxygen in Ti\textsubscript{2}Ni, the processing route presented in the present paper succeeds in producing powder metallurgical NiTi shape memory alloys with good structural and functional properties.},
  doi      = {10.1016/j.msea.2008.01.084},
  keywords = {Mechanical properties, Microstructure, Powder metallurgy, Processing, Shape memory},
  url      = {http://www.sciencedirect.com/science/article/pii/S0921509308001858},
}