Structure-property Characterisation at Nanoscale using In-situ TEM and SEM
In-situ electron microscopy is an emerging technique for real time visualisation of micro-structural changes of a specimen under some applied constraints inside microscope. In this study, in-situ nanoindentation experimentation on a carbon nanocoil inside transmission electron microscope has been reported. The elastic modulus of the carbon nanocoil is found to be 177 GPa. Similar experiments are also carried out on carbon nanotubes, but force response of carbon nanotubes is beyond the limit of sensors presently available. The present study also reports the in-situ dissolution behavior of the secondary phases of a 7xxx series aluminum alloy under high vacuum condition in scanning electron microscope (SEM) in the temperature range of 350 °C to 400 °C. We report for the first time using in-situ SEM technique that dissolution of the MgZn2-base phase present as eutectic and divorced eutectic forms could start at a temperature as low as 300 °C, although the usual homogenisation temperature of such alloys is always > 450 °C. Furthermore, the kinetics of dissolution of such phases, particularly when present in fine eutectic phase mixture, is significantly faster than what is observed under atmospheric pressure. It has been found that modification of surface composition under high vacuum condition plays a key role in the low temperature dissolution processes. It has further been found that the dissolution process does not start with the thinning of the IDC phase as proposed for Al-Zn-Mg-Cu alloys, rather it occurs by a combination of ‘spheroidisation’ and thinning process called ‘the thinning, discontinuation, and full dissolution’ (TDFD) mechanism. Results of the in-stu experiments under high vacuum are compared with the ex-situ dissolution experiments under normal atmospheric pressure.
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