Letter 9178

HOW TO REMOVE OXIDE FILM ON TITANIUM ALLOY??? 

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Hi experts,

My trouble is quite specific, but I rely anyway on your help!

Try to imagine a complex shape part made in Titanium alloy (6Al-4V, B348 gr.5). It has an extremely polished surface, very very smooth, in spite of its complex geometry. Due to a previous electrochemical process (no way to modify it), it results anodized. Its color ranges light brown to golden brown.

Hard to believe: I need to remove most of this anodic film, restoring Titanium to its original silver appearance! Obviously, I need to avoid any damaging/modification (both morphological and chemical) of the polished surfaceÖ That ís why any mechanical approach (tumbling, brushing, sanding and similar) appears to be unfeasible.

Are we dealing with science fiction???

Thanks in advance,

Giovanni Righini
- Italy

Giovanni,

You can use solution: Chromium oxide (CrO3) - 100g/l Hydrofluoric Acid 40% - 20ml/l. Rinse in this solution until stains disappear. You can also try electropolishing titanium in salty solution. For more information contact Dan Weaver at Global Stainless in Georgia.

Good luck.

Anna Berkovich Russamer Lab Pittsburgh, Pennsylvania

What if you etch your part carefully, I mean etch it just enough to strip the oxide film off? Do you think your part will loose the shine?

Mark Camilleri
- Malta

I think that a room temperature dip in nitric-HF acid will do quite nicely. Time and concentrations are important. Ratio needs to be about 14 to 1 and not lower than 10-1 or it will eventually pit, possibly from tramp ions.

James Watts
- Navarre, Florida

Dear friends,

Many thanks to all of you for your help. I really appreciated it. At the moment I'm testing an acid mixture HNO3-HF characterized by a very very low ratio, about 60 to 1, otherwise the brightness of the polished surface is lost (etching of the surface, resulting in a "butter finish" appearance). This ratio seems to be promising, also if time is still a critical parameter.

Thanks again,

Giovanni Righini
- Italy

The time is not so critical, but for us one minute was sure enough.

Anna Berkovich Russamer Lab Pittsburgh, Pennsylvania

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