Microstructural influence on damage-induced zirconia surface asperities produced by conventional and ultrasonic vibration-assisted diamond machining

Zirconia surface asperities associated with machining-induced damage and deformation jeopardize the quality of zirconia products. Conventional and emerging ultrasonic vibration-assisted machining processes are used to shape zirconia materials. However, a deep understanding of how zirconia microstructures and ultrasonic vibration amplitudes affect material removal mechanisms and surface quality in these processes is missing, rendering the proper mechanical process selection challenging. This paper reports on the 3D characterization of damage-induced surface asperities and the investigation of material removal mechanisms of pre-sintered porous and sintered dense zirconia materials in conventional and ultrasonic vibration-assisted diamond machining processes. 3D white light profilometry was used to measure surface asperities in terms of texture parameters, together with scanning electron microscopy (SEM) for imaging damage and deformation morphologies. The results show that removal mechanisms and damage-induced zirconia surface asperities depended on material microstructures and ultrasonic vibration amplitudes. Both porous and dense zirconia materials had a brittleductile mixed removal mode in conventional and ultrasonic vibration-assisted diamond machining processes. However, brittle fracture was dominant for the porous state and ductile deformation was presiding for the dense state. Thus, there were significantly higher fracture damage area ratios with much higher average and maximum roughness values, and maximum peak and valley heights on machined porous surfaces than dense ones. Ultrasonic assistance at an optimal vibration amplitude promoted brittle-ductile transitions on both porous and dense zirconia surfaces, resulting in reduced brittle fracture damage areas with reduced surface asperities. This microstructure-process-surface quality relation provides insights into manufacturing processes for zirconia products.