The relationship between microstructure and wear of mica-containing glass-ceramics

A series of mica-containing glass-ceramics with three different mica platelet sizes were tested for wear against a harder alumina counterface in a pin-on-disk tribometer under distilled water lubrication. Under all test conditions (i.e. different loads and number of passes), the wear rate increased with the increase in mica platelet diameter. Examination of the wear scars on the glass-ceramic samples using a scanning electron microscope indicated that the wear process was dominated by a microfracture mechanism either along the mica cleavage planes or along the weak mica-glass interfaces. Three wear modes were observed. (1) At low loads and small number of passes, wear occurred by formation of isolated fracture sites on the wear track. No measurable wear took place during this 'localized fracture' wear mode. (2) The number of fracture sites increased and covered the entire contact width as the load or number of passes increased. This 'contact fracture' mode resulted in wear factors on the order of 10(-4) mm(3) Nm(-1). (3) At higher loads or after a large number of passes, accumulation of subsurface microfracture damage led to 'spallation' wear mode which resulted in wear factors on the order of 10(-2) mm(3) Nm(-1). The mica platelet diameter was found to be an important factor in controlling the wear modes and wear transitions. The transitions from 'localized fracture' to 'contact fracture' and to 'spallation' occurred at lower loads and smaller number of passes as the mica plate diameter was increased.