Oxide adherence and porcelain bonding to titanium and Ti-6Al-4V alloy

The bonding of an experimental low-fusing porcelain to titanium and Ti-6Al-4V was evaluated by an x-ray spectrometric technique that measures the area that remains covered with porcelain following a controlled deformation of the metallic substrate. Oxide adherence strength values for titanium and Ti-6Al-4V oxidized at 750 degrees and 1000 degrees C were measured in tension with use of high-strength adhesives. The effect of further oxidation that would occur during porcelain firing was evaluated via simulated porcelain firings without actual porcelain application. Interface cross-sections of the titanium-porcelain and Ti-6Al-4V-porcelain bonds were examined in a scanning electron microscope (SEM). The porcelain was found to delaminate completely from the metal substrate, leaving less than 1% of the surface covered with porcelain. The oxide adherence of the specimens oxidized at 750 degrees C was good, but those oxidized at 1000 degrees C exhibited significantly lower oxide adherence (p = 0.001). The simulated porcelain-firing oxidation treatments also produced a significant decrease in oxide adherence (p = 0.004). The 750 degrees C oxidation treatments produced oxide films too thin to be visualized in the SEM, whereas the 1000 degrees C oxidation treatments produced oxide films approximately 1 micron thick. The lower oxide adherence of the 1-micron-thick oxide films is consistent with reports in the titanium literature of oxide delamination when the oxide film reaches 1 micron in thickness.