Heterointerface and grain boundary energies, and their influence on microstructure in multiphase ceramics

Heterointerface energy measurements for multiphase systems are rarely reported in the scientific literature in contrast to grain boundary energies for single phase systems. Hence, thermal groove dimensions on the surfaces of single-phase (YSZ, Al2O3, MgAl2O4), two-phase (YSZ/MgAl2O4, YSZ/Al2O3), and three-phase (YSZ/MgAl2O4/Al2O3) ceramics were measured using atomic force microscopy to calculate relative energies for six different types of interfaces. Average grain boundary and interfacial energies were estimated from relative values calculated using previously published surface energies. Our results show that relative areas of interfaces in a multiphase composite are governed by relative interface energies. We show that Al2O3-Al2O3 homointerfaces occur less frequently in the multiphase systems studied, attributed to their higher grain boundary energies compared to YSZ-YSZ and MgAl2O4-MgAl2O4 boundaries. Using the complex three-phase ceramic system as a model, we also show that heterointerface energies are intermediate between the grain boundary energies of each of the two associated phases. Grain boundary and heterointerface energies for any specific type of boundary were similar for single phases versus multiphases, but the influence of grain boundary chemistry variations is reflected in the energy distribution. Our findings contribute novel insights on grain boundary and heterointerface energies that can inform materials design due to their strong influences on microstructural evolution.