A large number of electropolished copper parts showed evidence of discoloration (tinting) after electropolishing. Because these parts are used in a high-vacuum application, even trace amounts of organic materials would be problematic. Scanning electron microscopy of nondiscolored and discolored areas both showed trace amounts of residue in the form of adherent deposits. EDS, FTIR spectroscopy, XPS, and secondary ion mass spectroscopy (SIMS) analyses indicated that the discoloration to the copper components was due to the development of CuO at localized regions. It was recommended that process changes be made to completely remove residual processing fluids from the part surfaces...
S.J. Suess, Tinting of Electropolished Copper Parts, ASM Failure Analysis Case Histories: Processing Errors and Defects, ASM International, 2019, https://doi.org/10.31399/asm.fach.process.c9001629
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