Letter 32039

Thin, Hard, Corrosion Resistant Coating for use in Saline Solution [Arizona] 

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I would like to know if anyone can point me in the right direction for coating a rather small metal part currently manufactured of 440C Stainless Steel (though open to better material suggestions). We are currently looking into PVD (physical vapor deposition) and CVD (chemical vapor deposition) for the relatively small coating thicknesses and quality of suface finish. The part to be coated has rather intricate wire EDM cut groves and needs to maintain these contours. Some coatings that we have looked at are CrN, TiN, AlTiN and TiC, though none of these are stated to have good corrosion resistance, which happens to be our most important reason for this coating. If anyone can direct me to a hard, tough, and highly corrosion resistant coating that is biocompatible (for use in testing medical equipment), then please do. The part will be constantly immersed in a saline solution at 37 degrees celsius and will be required to flex slightly.

Thanks!

Jason Mendoza
- Flagstaff, AZ, USA

Dear Sir /ref hand book/

The best up to boiling and high concentration of NaCL are titanium and its alloys. As well COPPER-NICKEL ALLOYS CORROSION SPEED 0.006MM/YEAR,Silver up to 20C .

hope this helps, good luck

Cair Shishani
aircraft maintenance - Abu Dhabi, UAE

I don't think PVD coatings will do the job. In fact, most PVD coatings will accelerate the corrosion by setting up a galvanic cell. The worst part is that you might think everything is ok, i.e., the rust will be hidden by the coating. I would suggest you consider changing base materials. Titanium should hold up, or you could look at a 300 series stainless steel.

Jim Treglio
- Gardena, California

I agree with Mr. Shishani-- investigate the use of a titanium alloy. Two surface treatments for titanium (one is nitriding the other is an oxidation process) can be used to improve the wear resistance if this is necessary. I would discuss this application with someone from Carpenter Technology, as they produce a number of high performance alloys including stainless steels, nickel alloys, and titanium alloys.

Toby Padfield
Automotive module supplier - MI, USA

I don't want this to sound like an ad, but we have been working on a halogen resistant surface for stainless steels, specifically for medical use, and meeting with success. I think we can help.

Dale Woika
- Bellefonte, PA

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