Advanced Electron Microscopy Characterisation of Important Precipitation and Ordering Phenomena in Shape Memory Systems

Abstract

The present paper discusses some important aspects of precipitation and ordering in alloy systems that show a martensitic transformation and can or are used as shape memory or superelastic metallic systems. The precipitates are investigated by a variety of conventional and advanced electron microscopy techniques, including atomic resolution, 3D slice-and-view, energy loss spectroscopy etc. Depending on the system, such secondary phases can decrease the probability of a displacive transformation by changing the phase stability in the system, such as in the case of Ni–Al or Ni–Ti–Pd, or can mechanically hinder the passage of the transformation interface, as in Ni–Ti–Nb. On the other hand, properly controlling the nucleation and growth of some precipitates can strongly improve the properties of some types of materials, as is the case for the well-known Ni4Ti3 precipitates.