Strengthening Mechanisms and Mechanical Properties of Palladium-Silver vs. High-Palladium Alloys

With the cost of palladium less than for gold, there is renewed interest in palladium-based alloys for metal-ceramic restorations. High-palladium alloys are substantially more expensive than Pd–Ag alloys. Objective: Compare tensile mechanical properties and scanning electron microscope (SEM) observations of microstructures for three Pd–Ag alloys (Ivoclar Vivadent) [IS 64 (59.9Pd–26.0Ag–7.0Sn–2.8Au–1.8Ga–1.5In), d.SIGN 59 (59.2Pd–27.9Ag–8.2Sn–2.7In–1.3Zn) and Aries (63.7Pd–26.0Ag–7.0Sn–1.8Ga–1.5In] with previous research (J Mater Sci Mater Med 2000:11;601-608) on two high-palladium alloys [Liberty, Heraeus Kulzer (76Pd–10Cu–5.5Ga–6Sn–2Au) and Protocol, Ivoclar Vivadent (75Pd–6Ga–6In–6Au–6.5Ag]. Methods: Cast specimens meeting dimensional requirements in ADA Specification No. 5 were prepared by torch melting, and loaded to failure in tension. Fracture surfaces and etched cross-sectioned specimens were observed with an SEM. Results: After simulated porcelain-firing heat-treatment, the high-palladium alloys had higher 0.2% offset yield strength (YS) and tensile strength (TS), and lower or comparable percentage elongation. SEM observations revealed ductile fracture processes, precipitates and casting porosity. While the three Pd–Ag alloys had the same YS to TS ratio (0.56), this ratio was higher (0.76 and 0.66, respectively) for the Pd–Cu–Ga alloy (Liberty) and Pd–Ga alloy (Protocol). Greater casting porosity was found in the Pd–Ag alloys. All alloys exceeded the minimum YS requirement in ADA Specification No. 38. Conclusions: Mechanical properties of both high-palladium and Pd–Ag alloys are controlled by palladium solid solution strengthening and dislocation interactions with precipitates, in agreement with previous transmission electron microscopy (TEM) observations, along with casting porosity. Tweed structure observed by TEM in high-palladium alloys, and absent in Pd–Ag alloys, does not have a primary role. Clinical selection may depend upon published reports about potential biocompatibility differences for these palladium alloys. Supported by NIDCR Grant DE10147.

.