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Poor adhesion of Electroless Ni with PTFE coating onto MIM parts

We are having difficulty with coating adhesion on the following substrate:

MIM 4620 and MIM 4650

The coating is a duplex coating, high phosphorous electroless Ni plate under a high phosphorous electroless Ni plate with PTFE. All components are bulk finished and baked at 375 degrees for 24 hours. The substrate has a very good surface roughness (around 10 Ra).

Any suggestions to increase the adhesion performance of the coating would be appreciated.

Thanks,

Jeff Thompson
manufacturing process engineer - Symsonia, Kentucky, USA
2004

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If you don't tell us what you're doing now, I doubt anyone is going to play the guess game. Guillermo Marrufo Monterrey, NL, Mexico 2004 I am not familiar with your substrate, but the most common adhesion problems are under or over cleaning, under or over etching, passivation of the metal before plate tank. There is a possibility that this metal will require a strike before the EN. I assume that you have checked and determined that the failure is between substrate and the first nickel and not between the nickels.(EN passivates extremely rapidly) James Watts - Navarre, Florida 2004

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By MIM do you mean Injection moulded metal? In that case copper plating before EN will help.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

2004

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I am not surprised that you have encountered adhesion problems in duplex coating. When you deposit duplex coatings, the sudden transition from EL Ni-P to EL Ni-P-PTFE coating is likely to cause adhesion failure.

To overcome the problem, you may try to deposit the EL Ni-P-PTFE coating with a steady gradation in the level of incorporation of the PTFE particles in the coating.

T.S.N. Sankara Narayanan
- Chennai, Tamilnadu, India
(ed.note Nov. 2017: The good doctor has a fascinating blog at https://advancementinscience.wordpress.com)
2004

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The 400 series alloys are usually chrome stainless steels. I do not know the composition of 46 series, but assume they too are chrome containing. Therefor a woods or sulfamate nickel strike is required, after proper cleaning and pickling, for good adhesion. It is not possible to achieve a high level of adhesion without a suitable nickel strike on these alloys.

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
           and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])
2004