[Ultra-structural study of Ni-Cr alloys used in joint prosthesis].

Ni-Cr alloys used in denture set, which have excellent mechanical properties, have a chemical and electrochemical inertia that depends on their composition and their microstructure. The objective of our work was to study the ultrastructure of the Ni-Cr alloy exposed to a free corrosion and a chemical analysis of surface depending on its composition. For this, five electrodes Ni-Cr alloy were prepared at the prosthesis laboratory by varying their composition. An analysis of the ultrastructure of the samples made by Scanning Electron Microscopy (SEM) samples was performed as well as a chemical analysis of their spectra. Prior to any manipulation, analysis by SEM of electrode number 5 (100% new metal) shows an altered surface. The electrode 3 (75% new metal) also presents an uneven surface. After a week in a free corrosion in Meyer solution at pH = 6.5, the electrode 5 shows a widespread intergranular and pitting corrosion. The same electrode 3 (75% new metal) after one week immersion in Ringer's solution at pH 7.9, shows a widespread intergranular and pitting corrosion. After electrochemical testing in Ringer's solution at pH 5, the SEM for electrode 1 (100% recovered metal) shows a very rugged structure with an important crevice corrosion. The composition and terms of shaping the Ni-Cr alloy influence its microstructure and at the same time its electrochemical behavior.