Metal finishing Q&As since 1989

Laser etch survival during passivation

My company routinely etches various types of stainless and titanium for the medical industry. As you are aware, survival of etch quality after passivation is an ongoing issue. We will often test the settings of our laser on one or more parts in various types of passivation (hot nitric, cold nitric, Stellar Solutions [a finishing.com supporting advertiser] CitriSurf (citric) prior to passivating the entire order. On more than one occasion, the initial part survives but when the entire order is processed to the exact same conditions with the exact same laser settings... we lose some or all of the etch. This happens in all types of our passivation. We have not been able to establish a cause of this due to the lack of "linear" results. Our solution has been to full passivate before etch with an abbreviated passivation after etch. Have you experienced this result before? Can you provide me with any new information on the whole etch survival issue? Thank you for your time and consideration.

In laser marked stainless, the black color comes from Fe(+2) in the oxide, which properly should be removed via passivation for best corrosion resistance. Topics 19343 and 2030 mention using a ceramic or glass frit, which is fused by the laser and resists passivation solutions.

You mentioned "Our solution has been to full passivate before etch with an abbreviated passivation after etch."

This is our usual recommendation to people who want the black mark of the laser etch to remain but still get some measure of corrosion protection on the etch area.

Dear Sir:
Do you make the stainless and titanium parts in electrical contuct in your solution if so you may have a galvanic over etching for some parts-may be !
Good luck

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