New approach for evaluating metal-porcelain interfacial bonding

Purpose: The purpose of this study was to evaluate the bonding characteristics of porcelain-fused-to-metal (PFM) systems by determining the strain energy release rate associated with interface fracture of porcelain and metals. Materials and Methods: Porcelain-veneered metal plates cast from commercially pure titanium and 3 metal alloys (gold, palladium, and nickel-chromium alloys) were made to dimensions of 25 mm x 8 mm x 2.5 mm with comparable thicknesses of porcelain and metal. The porcelain side of the specimens was notched to the interface with a thin diamond saw, and a small precrack was initiated at the metal-porcelain interface, The samples were subjected to a limited number (typically less than 4) of load-unload cycles under 4-point bending at a crosshead speed of 0.1 mm/min. The loading and unloading force displacements associated with stable crack extension were recorded. The strain energy release rate was calculated. The interfacial area was also examined under scanning electron microscope (SEM) after the test. Results: The mean strain energy release rates were 72.7 +/- 10.0 J/m(2), 58.5 +/- 13.5 J/m(2), 39.4 +/- 4.3 J/m(2), and 16.6 +/- 2.5 J/m(2) for the samples of gold, palladium, nickel-chromium alloys, and titanium, respectively. The SEM photographs showed that the crack occurred in the porcelain layer close to the interface. Conclusion: The bonding characteristics of PFM systems were determined with 3 types of metal alloys and commercially pure titanium by a fracture mechanics approach. The gold alloy and titanium are considered to obtain the greatest and least adhesion, respectively. The test system has proven to be a simple and reliable approach to determine the bonding in bimaterial systems.