Porcelain veneered on pure titanium with an intermediate plasma-sprayed ZrO 2 bond coat layer was investigated in this study. The pure porcelain coating veneered on Ti was used as a control. The specimens were subjected to four-point bending test to measure the bonding strength. The fractograph, microstructure, surface roughness, and phase of plasma-sprayed ZrO 2 bond coat were examined. The phase constituents at the location of adhesive failure of the fractured specimens were investigated by thin-film X-ray diffractometry. Experimental results reveal that the bonding strength of the coating with the intermediate layer was increased by 55.7% that was accompanied by a significant decrease of the area of adhesive failure in the fracture. The ZrO 2 provided a higher surface roughness to enhance the mechanical bond at the interface of porcelain/ZrO 2 , meanwhile it acted as a sufficient oxygen diffusion barrier at 800 C to prevent the oxidation of Ti at the interface of ZrO 2 /Ti.
The interfacial characteristics between porcelain coating and titanium under vacuum firing at 800 C have not been well documented. The cross-sectional variations in microstructures and compositions at the porcelain/Ti interface were investigated with a SEM and an EPMA equipped with WDS. The phase constituents of the porcelain bulk coating and the nearby porcelain/Ti interface were analyzed by X-ray and thin-film X-ray diffractometry respectively. In addition, a TEM equipped with EDS was used to examine the porcelain/Ti oxide interface. The experimental results revealed that the oxidation of Ti occurred at the porcelain/Ti interface, and it is reasonable to deduce that the Ti reduces the SnO 2 and SiO 2 components of the porcelain and becomes Ti oxide. Furthermore, redox reactions and chemical bonding occur at porcelain/Ti interface during firing and thus prevent the initiation of fracture from occurring at this interface. Subsequently, the fracture initiation tends to be located near the interface of newly formed Ti oxide and Ti substrate and/or slightly inside the Ti.
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