Tribo-Ellipsometric Study of the Repassivation Kinetics of a Ti 8Al-1Mo-1V Alloy

Abstract

The tribo‐ellipsometric technique allows one to distinguish between film growth and other reactions that occur after removal of a film from a metal surface in a given environment. This technique was used to study the relationship between repassivation kinetics and stress corrosion cracking (SCC) susceptibility for Ti 8A1‐1M0‐1V alloy. In these studies the effect of the rate of film growth on the amount of metal dissolution which occurs during the repassivation process was investigated by comparing the repassivation transient behavior in a 1.0N normalNaCl solution, where cracks have been found to propagate, to that in a 1.0N NaNO3 solution where SCC susceptibility has never been detected. Film growth kinetics in both solutions were consistent with a Fleischmann‐Thirsk mechanism of oxide patch nucleation and two‐dimensional growth, although the film growth rate was significantly slower in the 1.0N normalNaCl solution. Low film growth rate led to an increase in metal dissolution in a solution where crack propagation velocities have been measured, but at an apparent rate slower than necessary to propagate such cracks by metal dissolution alone.

Effects of Biological Factors on the Repassivation Current of Titanium

“…The J peak and Q w in the repassivation current increased with the charged potential. The J peak increased exponentially with the charged potential, expressed as the following equation: 19) I peak ¼ ðu=AÞ expðBV=XÞ ¼ I 0 expðBV=XÞ; ð3Þ where I peak is the peak current, X is the oxide thickness, u is a preexponential term incorporating various material parameters, A is a constant equal to M=nF, M is atomic weight, n is the number of electrons transferred, F is Faraday's constant, is density, B is the inverse field coefficient, and V is the voltage drop across the film. The I peak or J peak is governed by the exposed rate of the metal surface.…”

“…On the other hand, the thickness of the surface oxide formed on Ti-8Al-1Mo-1V alloy at 30 ms after removing an original surface oxide in 0.6-M NaCl solution at 0 V is about 0.2 nm. 19) In commercially pure titanium, large charge majority of charge passed goes into dissolution and not into oxide formation. 15) According to this discussion, approximate calculation of dissolution amount of metal ion from titanium during repassivation or when the surface oxide film is ruptured.…”

Oxydation Et Corrosionapplication of Ellipsometry to the Study of Corrosion Processes

“…This is so because of the localized nature of the attack, the production of patches of corrosion products of varying compositions and the problems of roughening. Nevertheless, by using qualitative ellipsometry, Ambrose and Kruger [20,21] have shown that changes in A and I , ! I can be used in a fruitful way to do the following : 1) compare the rate of repassivation of a bare surface for a given metal in different environments ; 2) measure the time during the course of a process when significant changes occur as indicated by abrupt changes in A and $ and to correlate the A, $ changes with others, e. g., electrochemical ones ;…”

“…(One can, however, measure changes in A and $ and relate these changes to thickness changes that are reasonable estimates even when the optical constants of the film are not well known [25]). To overcome the difficulties of inexact current density and film thickness measurements, a parameter has been defined [20,21] that allows one to compare the repassivation behaviors of a given metal in different environments and thus use it as a diagnostic tool for estimating which environment would have the greater likelihood to promote stress corrosion. This parameter Rp, the repassivation ratio, uses the experimentally measured variables of total current, i,, and film thickness, x, in the form of a ratio, designated R,, and is given by and -= id is the current consumed by metal disdt solution (I).…”

Repassivation of titanium and surface oxide film regenerated in simulated bioliquid

“…The repassivation kinetics of titanium alloys in an aqueous chloride solution has been investigated with various techniques, and the relationship between stress corrosion cracking and alloying elements have been discussed. [15][16][17] In the field of biomaterial research, studies using titanium specimens polished in water-in other words, the surface oxide film is regenerated in water-are common. Surprisingly, no research on repassivation and surface oxide film regeneration in a biological system has been performed in spite of the significance of such research.…”