The brittleness of Ag–25%Pd based dental alloys with S contamination

The effects of S and Ir on the microstructures and mechanical properties of a binary Ag–25%Pd alloy and a commercial alloy, A-2 (Ag–25wt.%Pd–2wt.%Au–2wt.%In–0.84wt.%Zn–0.5wt.%Ir) were studied. The segregation of S to the grain boundary was investigated by AES and EDS with varying S concentrations. The effect of the cooling rate on the microstructures and segregation was also investigated. The grain refining effect of Ir was obvious when the concentration of Ir was more than 0.1%. The degree of S-segregation to the grain boundary decreased slightly with grain refining. At 0.1% S, Ag2Pd3S-phase was formed at the grain boundary due to the S-segregation during solidification. Even at 0.01% S, the S-segregation to the grain boundary was confirmed, although, there were no Ag2Pd3S phases on the grain boundary. At 0.1% S, the ductility of the soft binary Ag–25%Pd alloy did not decrease much, but the elongation of the hard alloy A-2 decreased severely from 23 to 5%. The grain boundary brittleness caused by S-segregation came into effect, as the matrix became hard.