Need process for 108 hours in CASS Test

We have plated 25 micron medium phosphorous electroless nickel as under coat and 10 micron micro cracked chromium as top coat. At CASS test it has failed after 44 hours against the requirement of 108 hours. Please advise us what process can withstand up to 108 hours in CASS test.

You should use an electroless nickel containing at least 10.5% P for severe corrosion services such those requiring CASS tests. Also, to obtain 104 hours resistance, you will probably have to increase the coating thickness to 50 or 75 microns.

The recommendation from Mr. Duncan seems correct, since high phos EN is more resistant to corrosion and has less pores or voids. Although, another thing to keep in mind, besides porosity or discontinuities is that EN is hard. This means that the microcracks in this particular chrome, which were developed for ductile electronickel or copper underplates, might propagate through a fragile layer to the base metal.