In situ determination and imaging of physical properties of metastable and equilibrium precipitates using valence electron energy-loss spectroscopy and energy-filtering transmission electron microscopy

The physical (elastic, cohesive, and electronic) properties of precipitates are important in determining factors such as their equilibrium shape, coarsening, and strengthening behavior in alloys. In this work, we use valence electron energy-loss spectroscopy (VEELS) and energy-filtering transmission electron microscopy (EFTEM) to determine quantitatively and image the elastic moduli, cohesive energy, and interstitial electron density of both metastable and equilibrium precipitates in two different metal alloys. We show that the elastic properties of θ′ and θ precipitates in Al–Cu alloys can be measured in situ as a function of temperature and during transformation from θ′ and θ phases. We also measure and image in situ the elastic and cohesive properties of metastable TiHx precipitates in a Ti–H alloy. These results demonstrate the capability of VEELS∕EFTEM for real-time nanoscale determination and imaging of multiple physical properties of precipitates in solid-solid phase transformations.