"Type II" Titanium Anodize

[Jabberwocky]

Hello all,

We have several vendors who will do this process which produces a dark grey sheen and is claimed to produce smoother surfaces, better galling properties, and improved fatigue strength in titanium alloy (Ti 6Al 4V)

Can anybody point me towards some non-proprietary papers that discuss the reason for this property change? I mean, surely we're dealing with a titanium oxide layer which is somewhat different than 'Type III' that gives pretty colors, but what else is actually changing?

I can only imagine it has something to do with porosity?

Thanks.

 

[vpl]

The OP has posted the identical question in the Mechanical Engineering Other Topics forum. See thread404-257702 . Please post all replies there.

Thanks

Patricia Lougheed

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[BiPolarMoment]

That thread seems to be deleted.


Foreword: Do not take as gospel; I am inferring the below hypothesis based on what information I have gathered from Tiodize.

From what I can gather from my Tiodize brochure I believe the mechanism is the fact that the Type II process also penetrates the surface (i.e. there is now oxide below the nominal original surface) compared to standard colored anodization which adds to the surface only. Afterwards they burnish the build up (i.e. oxide that was above the nominal original surface) back down to nominal dimensions. This decreases the surface roughness (and thus increases resistance to galling by reducing asperities) and plastically deforms the outer layer of the material (i.e. cold forming) and increases the fatigue resistance of the material. However, this doesn’t explain to me why the anodization is required—it seems that burnishing alone would accomplish the same thing.

I am very likely incorrect though , their literature seems to suggest that it’s a “converted layer” below surface level that is responsible for these properties; but I have no idea what it would be converted to aside from TiO2.

There is some information here, though I think the brochure I have is no longer found on their site:

http://www.tiodize.com/anodizing.html