Effects of Porcelain-Firing and Annealing Heat Treatments on Palladium-Silver Alloys

Palladium-silver casting alloys have become more popular recently for metal-ceramic restorations because of the lower cost of palladium than gold. Objective: To study the microstructures and variation in Vickers hardness during simulated porcelain-firing and isothermal-annealing heat treatment in three Pd–Ag alloys (Ivoclar Vivadent): (a) IS 64, 59.9Pd–26.0Ag–7.0Sn–2.8Au–1.8Ga–1.5In; (b) d.SIGN 59, 59.2Pd–27.9Ag–8.2Sn–2.7In–1.3Zn; (c) Aries, 63.7Pd–26.0Ag–7.0Sn–1.8Ga–1.5In (wt%). Methods: Specimens meeting dimensional requirements in ADA Specification No. 5 were prepared using torch melting and recommended dental laboratory techniques. The specimens were sectioned into test sample disks with 1 mm thickness, using a slow-speed, water-cooled diamond saw. Except for as-cast samples, all other samples were subjected to either of two types of heat treatment: (1) the simulated porcelain firing process, including initial oxidation and subsequent six firing cycles recommended for IPS Classic dental porcelain (Ivoclar Vivadent); (2) isothermal heat treatments for 30 minutes from 450° to 950°C with intervals of 50°C. After standard metallographic procedures, microstructures were examined using an SEM. Bulk Vickers hardness and microhardness of single phase or multiphase regions were measured using loads of 1 kg and 10 g, respectively, with dwell time of 30 seconds. Results: During each step of the simulated porcelain-firing heat treatment, the Vickers hardness did not change greatly, even though there was variation in the microstructures. For individual annealing temperatures, the Vickers hardness and microstructures varied substantially, with highest hardness approximately in the region between 500° and 650°C. Conclusions: The microstructures and hardening behavior for these three Pd–Ag alloys are considerably different. Supported by NIDCR Grant DE10147 and Ivoclar Vivadent.