In-situ observations of grain boundary migration

The X-ray Interface Continuous Tracking Device is introduced which is capable of on-line tracking of grain boundary motion and thus, provides information on grain boundary mobility. The grain boundary velocity was found to change in proportion to the driving force. The orientation dependence of mobility does not only affect the activation enthalpy of grain boundary motion, but also the preexponential mobility factor. This causes the exact Sigma 7 boundary to move fastest at low temperatures, however, the 40.5 degrees < 111 > boundary is most mobile at high temperatures. As expected, impurities were found to reduce the grain boundary mobility, but the mobility can also be enhanced by the addition of small amounts of Ga to pure Al. In-situ HRTEM observations of grain boundary motion in thin film Au bicrystals are presented, which reveal the mechanism of mass transfer across the grain boundary during its migration.