Responses of pre-crystallized and crystallized zirconia-containing lithium silicate glass ceramics to diamond machining

Abstract

This paper reports on the responses of pre-crystallized and crystallized zirconia-containing lithium silicate glass ceramics (ZLS) to diamond machining in simulated dental milling and adjusting processes. Machining mechanics, tool wear and tribological characteristics, and surface and subsurface damage were investigated. Machining forces and coefficients of friction were measured using a force sensor and high-speed data acquisition system. Diamond tool wear and debris adhesion, and machining-induced surface and subsurface damage were examined using field emission scanning electron microscopy. The results show that both tangential and normal forces of crystallized ZLS were significantly higher than those of pre-crystallized ZLS (p < 0.05) while these forces for both materials significantly increased with the material removal rate (p < 0.05). Coefficients of friction in machining of crystallized ZLS were significantly higher than those in machining of pre-crystallized ZLS. In spite of the minimum wear of applied diamond tools in machining both materials, more crystallized ZLS debris adhesion on tool surfaces was observed. The principal removal mechanisms in machining of both materials were primary fracture and minor plastic deformation of pre-crystallized and crystallized ZLS. However, there was more severe fracture in machining of pre-crystallized ZLS than in machining of crystallized ZLS. Although machining-induced subsurface edge chipping damage in both materials remarkably increased with the feed rate (p < 0.05), such damage was significantly severer in pre-crystallized ZLS than in crystallized ZLS (p < 0.05). These microstructure-property-processing relations provide practical guidance of process selection for high-quality fabrication of ZLS materials.