Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)
by Larry Zitko, ChromeTech, Inc.
Hard Chromium-Molybdenum Plating
I am interested in a prosses marketed as hard chrome containing molybdemum.Is the molybdeum co-deposited with the chrome or is it just another after plating prossess designed to enhance the surface finish of the chrome?I would appreciate any information you can provide on this process and or data to support claims of increased hardness and better ware characteristics.
I think you are referring to an alloy plating process in which molybdenum resides in the bath and is codeposited with the chromium. My understanding is that the moly takes the form of a dispersion of molybdenum oxide or trioxide in the chromium deposit.
I have read claims of increased hardness, wear resistance and abrasion resistance (200-300%) for the coating. For maximum wear resistance, the coating is electropolished after plating. For evidence supporting these claims, see pg. 63-64 of "The Properties of Electrodeposited Metals and Alloys - A Handbook, Second Edition", William H. Safranek. This book was published by AESF in 1986.
If you are an NMFRC subscriber, you can get a fax-back copy of MIL-C-85455, "Military Specification: Chromium-Molybdenum Plating (Electrodeposited)" at www.nmfrc.org. It's entry #4325 in the Technical Database.
I hope this helps.