The effect of recasting, up to four times, non precious Ni-Cr and Co-Cr commercial dental alloys on their corrosion behaviour in saliva and saline media was carried out. A potentiokinetic technique was utilised to analyse the electrochemical characteristics of the anodic polarisation curves of these alloys. A considerable anodic polarisation range (about 2.0 V vs SCE) was used to investigate the possibility of developing a passive regime at such high potential range. The most important feature noted was a rapid rise in current density above a certain critical potential called pitting potential, Ep. The experimental data show that the open circuit potential, Eoc does not enable differentiation between the corrosion resistance of the four alloys used in this study. However, Ep and the rupture potential Er does distinguish between them. Increasing the number of the successive recastings of Wirolloy leads to enhancing the pitting potential, thus, the corrosion resistance of Wirolloy (Ni-Cr) improves after remelting and recasting. It has been found that Wirolloy corrodes 26 times faster than Wironit alloy under the same solution. The alloys containing cobalt and molybdenum show higher corrosion resistance than those containing nickel. Additionally, their corrosion resistance was not affected by successive melting and recasting. In chloride solutions Ni-Cr alloys show a high susceptibility to pitting corrosion, while Co-Cr alloys show a noble behaviour. The corrosion resistance of the four non precious alloys were in the following order: Biocast > Wironit > Cobond > Wirolloy.
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"On the other hand, a significant problem is the lack of possibility of multiple alloy melting, due to the significant drop in the properties of these materials, which prevents their optimal use. There are also reports on their corrosion resistance being decreased as a result of their multiple casting  . The casting method (mostly lost wax casting) is used to produce crowns, bridges, clamps and entire frame dentures. "
[Show abstract][Hide abstract] ABSTRACT: The presented paper studies the effect of the casting technology on the corrosion resistance of Co-Cr-Mo alloy. The investigations were conducted on a commercial alloy with the brand name ARGELOY N.P SPECIAL (Co-Cr-Mo) produced by Argen as well as the same alloy melted and cast by the lost wax casting method performed by a dental technician. The corrosion behavior of the dental alloys in an artificial saliva was studied with the use of the following electrochemical techniques: open circuit potential and voltammetry. After the electrochemical tests, studies of the surface of the examined alloys were performed by means of a scanning electron microscope with an X-ray microanalyzer. The results of the electrochemical studies show that the dependence of the corrosion resistance on the microstructure associated with the recasting process is marginal. The results of the electrochemical studies of the considered alloy clearly point to their good corrosion resistance in the discussed environment.
Keywords: cobalt alloys, corrosion resistance, method of wasted wax, microstructure
Full-text · Article · Mar 2015 · Archives of Metallurgy and Materials
"However such comparison should be done very carefully, because chemical composition of Wirolloy and DUCINOX alloys differs in Ni and Fe content. The same authors  signalize that in case of other prosthetic alloys after 4th recasting the changes of corrosion resistance are negligible. Analogous conclusions Ozdemir et al.  have drawn for Wirolloy alloy. "
[Show abstract][Hide abstract] ABSTRACT: The effect of recasting, up to two times, Ni-Cr (DUCINOX) prosthetic alloy on its corrosion properties was carried out. The corrosion measurements were done in deoxygenated Fusayama Meyer artificial saliva solution at temperature of 37°C. In the study following electrochemical methods were used: measurement of free corrosion potential E cor in open circuit, measurement of polarization resistance according to Stern-Geary's method and measurement of potentiodynamic characteristic in wide range of anodic polarization. In general, it can be stated that casting number weakly influence on corrosion properties of investigated alloy. At free corrosion potential there is no monotonic dependence of corrosion parameters versus casting number. However, at extreme anodic potentials monotonic changes of corrosion parameters with increasing casting number is observed. Obtained results and drawn conclusions are partially compatible with literature data.
"Analogous to the present result, few reported works showed that commercial Co-Cr alloys possess more desirable corrosion resistance properties than Ni-Cr counterparts. According to results of KHAMIS et al, Wirolloy corroded 26 times faster than Wironit alloy. Their study suggested that increasing the times of successive remelting and recasting of Wirolloy enhanced the pitting potential and improved the corrosion resistance. "
[Show abstract][Hide abstract] ABSTRACT: The cast structures influencing the electrochemical corrosion behavior of Co-Cr and Ni-Cr dental alloys were studied using potentiodynamic polarization and AC impedance in 0.9% (mass fraction) NaCl solution at (37±1) ℃. The phase and microstructure of the alloys that were fabricated using two different casting methods viz. centrifugal casting and high frequency induction casting, were examined using X-ray diffraction analysis, scanning electron microscopy and energy dispersive spectroscopy. The roles of alloying elements and the passive film homogeneity on the corrosion resistance of Co-Cr-Mo and Ni-Cr-Mo dental cast alloys were reviewed. The results of electrochemical study show that the dependence of corrosion resistance on the microstructure associated with the casting methods is marginal. The Co-Cr alloy exhibits more desirable corrosion resistance properties than the Ni-Cr alloy. There is severe preferential dissolution of Ni-rich, Cr and Mo depleted zones in the Ni-Cr alloy.
Full-text · Article · Jan 2009 · Transactions of Nonferrous Metals Society of China