Originally Posted by SteveP

You have it mostly correct. It's not really wearing because it's thin. Both coatings will wear, but the nickel wears half as much as the chrome. Lets say for example that the NSC sleeve wears 3µm, then the hard chrome would wear about 6µm under the same conditions. The piston however, is where there's a big difference. In an engine with a hard chrome sleeve, this piston may wear 20µm, but the same piston under the same conditions with a NSC sleeve will probably wear 60-70µm. So, it's easy to see why the performance degrades more quickly in engines with NSC sleeves - it kills the piston.

If the NSC coating is applied via chemical process instead of electrochemical, it can be as thin as .3µm, whereas chrome starts about 2 to 3 times thicker, and gets multiple passes. So, the opportunity for the coating to wear through a NSC sleeve is greater if it's not applied thick enough. but the RATE of wear is still much lower when all other factors remain the same.