Process optimisation of non-cyanide Ag-PTFE metal matrix composite plating for threaded connections

Abstract

Silver-PTFE metal matrix composite coatings were deposited onto ANSI 304 stainless steel to assess the potential of using a novel non-cyanide electroplating process to produce a corrosion resistant, self-lubricating composite coating. During this study, 32 different bath parameter sets, derived from 5 variables were used to develop the non-cyanide electroplating process without the use of a surfactant or strike. SEM/EDS as well as XPS microscopy equipment was used to analyse the samples. In addition, the functional characteristic and adhesion strength of the coating was assessed using a bi-directional tribometer (to measure the coefficient of friction) and a pull-off test conducted on an Instron tensile test machine. The experimental results revealed that a friction coefficient of 0.23 was achievable (62% improvement over pure silver coating) where adhesion strength is not a primary consideration. For solid lubrication applications requiring high coating adhesive strength, the maximum adhesion strength achieved for the silver-PTFE composite coating was 2.5MPa (44% reduction over pure silver coating) with a friction coefficient of 0.32 achieved (47% improvement over pure silver coating).