Comportement électrochimique et propriétés mécaniques de l'allige de Titane Ti6Al4V . Effet des traitements de surface.

Abstract

Titanium and its alloys are widely used in the aerospace sectors and the cars industry, especially the Ti6Al4V alloy, because of their interesting mechanicals and physico-chemicals properties, in particular their excellent corrosion resistant, low density and relatively high melting temperature. Moreover, their good biocompatibility with human tissues, the titanium alloys constitute materials of choice in orthopaedic and implantology. The objective of this work is to make an electrochemical and mechanical characterization of titanium alloy Ti-6Al-4V, in various corrosive conditions with knowing : an alkaline solution with 3% NaCl simulated to sea water, an acid medium decinormal of sulphuric acid (H2SO4 0.1N) and a physiological medium simulated with the human body (SBF). We also studied the influence of a salt bath nitriding treatment on the mechanical and electrochemical behaviour of this alloy in 3% NaCl, with a view to evaluate the mechanical behaviour of covered material of a nitride layer. Cyclic polarization curves show that the alloy is passivate in a large field of potential in the three corrosive conditions due to the formation of an oxide film generally of TiO2. The scanning rate has an influence on the passivation current. The impedance diagrams for the various imposed potentials on the passivation field are made up only of one simple loop, the behaviour is capacitive and the transfer resistance increase with the increase of applied potential. The microscopic observations enabled us to delimit the nitriding layer, the imagery by MEB showed the existence of porosity on the surface of nitrided material in salt bath. The nitriding treatment increase the surface hardness 1,3 times compared to that of the matrix following the titanium nitride formation (TiN and Ti2N). The stainless steel is known for its aptitudes of corrosion resistance in many mediums .However, the comparative study between Ti6Al4V and the stainless steel 304L, showed that the first presents a better electrochemical behaviour result of a large passivation field.