The relationship between microstructure and wear rate in polycrystalline aluminas

A range of dense polycrystalline liquid phase aluminas was prepared by hot-pressing . and pressureless sintering methods with calcium silicate additions of 0.5, I, 5 and 10% by weight. The CaO:Si02 ratio varied betWeen 1:10 and 10:1. The microstructures wer~ systematically studied using analytical scanning electron microscopy (SEM) and' transmission electron microscopy (TEM) combined with energy dispersive X-ray (EDX) spectrometry and electron energy loss spectrometry (EELS). These techniques . allowed the direct imaging of' secondary· crystalline phases and amorphous films at grain boundaries and at triple pockets as well as both a qualitative and semiquantitative determination of their composition and chemistry. The, specific composition of the glassy phase ([Ca]:[Si]:[AI] atom ratios) was found to vary from grain boundary to triple pocket and also with the exact additive composition. Wet erosive wear rates, Vickers hardness and impedance spectroscopy measurements were investigated along with residual stress measurements caused by thermal expansion coefficient mismatches between alumina grains, glassy and secondary and crystallised phases observed in the microstructures. Silica rich samples were found to exhibit greater wear resistances, and residual stresses. The varying wear resistance obs'erved between specimens may also be attributed to dislocation arrays, strain and microcracks observed within the microstructure along with the intergranular film composition and additive chemistry. Grain size was also found to be a controlling factor of wear rate and hardness. Silica phases also acted to increase the resistance and capacitance of the grain boundaries as measured by, impedance spectroscopy.EThOS - Electronic Theses Online ServiceGBUnited Kingdo