Effect of chemical composition on the corrosion behavior of Ni-Cr-Mo dental casting alloys.

Abstract

The objective of this investigation was to study the compositional influence on the corrosion behavior of Ni-Cr-Mo dental casting alloys in acidic artificial saliva. Cyclic potentiodynamic and potentiostatic tests were used to evaluate the corrosion behavior of different Ni-Cr-Mo dental casting alloys in deaerated artificial saliva with pH 5 at 37 degrees C. Optical microscope observations were made following the cyclic potentiodynamic tests. Surface chemical analyses were characterized by X-ray photoelectron spectroscopy and auger electron spectroscopy following the potentiostatic tests. The results show that the corrosion resistance of the Ni-Cr-Mo casting alloys investigated is associated with the formation of passive film containing Ni(OH)(2), NiO, Cr(2)O(3), and MoO(3), on the surface. The pitting potential and passive range, respectively, were statistically different among the different Ni-Cr-Mo alloys. The Ni-Cr-Mo alloys with higher Cr ( approximately 21%) and Mo ( approximately 8%) contents had a much larger passive range in the polarization curve and were immune to pitting corrosion due to the presence of high Cr (maximum approximately 31-35%) and Mo (maximum approximately 12%) contents in the surface passive film. The presence of Ti lower than 4% in the Ni-Cr-Mo casting alloy had no effect on corrosion resistance. A pitting resistance equivalent (PRE) of about 49 could provide the Ni-Cr-Mo alloy with a good pitting corrosion resistance.