Mrs. Ruth Moshe, Ph.D. Candidate
Department of Materials Science and Engineering,
Technion – Israel Institute of Technology
Haifa 3200003, Israel
The microstructure of a sintered body strongly depends on the composition of the powder used for the sintering process, where dopants are also known to affect grain growth. In addition, second phase particles can act as grain growth inhibiters, inducing Zener drag on the grain boundaries. In this study, both solute drag and Zener drag were studied. While the concept of solute drag has been accepted, it is well known that several dopants induce grain growth instead. This phenomenological influence of dopants raises questions on the underlying assumptions regarding solute drag theory, and the mechanism for grain growth on which solute drag theory is based upon. This study examines solute drag in alumina doped with CaO, where the amount of dopant was confirmed by fully standardized wavelength dispersive spectroscopy.
Unlike segregating dopants which reduce grain boundary mobility by solute drag, CaO increases the rate of grain growth. The results show that this conflict with solute drag theory is systematic, rather than an exception. In addition, this study included the influence of Ni particles on the grain boundary mobility in alumina. The addition of Ni particles reduced the grain boundary migration rate as compared to CaO, thus enabling observation of the Zener drag force. The correlation between dopant concentration and mobility of grain boundaries was further examined to correlate the grain boundary mobility to changes of the chemical
composition at the grain boundary. Possible defect mechanisms by which the grain boundary mobility may be varied will be discussed.