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PVD adhesion issue on hard chrome  

April 30, 2009

Adhesion is one of the critical problems in PVD coating. I find good adhesion on stainless steel, HSS etc. But electroplated (Ni or Ni chrome) substrates like brass, zinc, etc. always give problems. Coatings are patchy with poor adhesion in some places. In fact any electroplated surface has such problems. However on one test sample of electroless Ni plated brass did not show any problem! It appears some people use a palladium interface coating after the usual Ni. Is there a simpler solution?
Has any one tried PVD Ti/TiN on hard chrome plated mild steel? How good is the adhesion?

H.R.Prabhakara

H.R. Prabhakara H.R. Prabhakara
Coater - Bangalore, Karnataka, India

We've also had a significant amount of problems applying a PVD coating to a plated surface. I believe one of the issues is stress. You're applying a PVD coating with high residual compressive stress onto a surface with residual tensile stress. Not good. When you apply the PVD coating, you heat the parts up, maybe as high as 450 C. If the substrate has any voids under the plating, you get bubbles (or maybe even holes). Any junk coming out of the plating will cause delamination of the PVD coating. Then you face the mismatch in coefficient of thermal expansion.

So there are no tricks here. You need to keep stress in the plating and coating as low as possible, make sure the plating is clean, and avoid zinc or similar low melting point, high vapor pressure metals.

Jim Treglio
- San Diego, California

Thank you Dr.Treglio. I deposit the coatings at ~ 250 C by arc. Comressive stresses are there but less compared to at 450 C. Electroplating is done by the customer and unfortunately we do not have any control.
I would like to know if any one could share his/her experience of PVD coating on hard chrome.

H.R.Prabhakara
- Bangalore, Karnataka, India