Many thanks Dr.D for your information.There are numerous methods to plate or coat materials with things such as gold, silver, platinum, rhodium, nickel, etc. Some methods provide better results than others. The bottom line is most of the plated/coated materials are subject to wear. Some suppliers provide lifetime warrantees for their top of the line coatings, some do not.
I have from time to time worked with and consulted for platers - some using gas vapor, some using liquid solutions, with or without electrodes. All I can say as to durability of the coating/plating comes from over 60 years experience with firearms. Chrome wears, nickel wears, gold really wears. The toughest, most wear resistant materials I have found for firearms are some of the ceramics; Titanium nitride, also known as tenite or TiN offers some of the best durability available to man.
PSI is, from my experience, a very reputable company. If they offer a lifetime warranty
I'm sure they will back it up. Read the terms and conditions to understand coverage.