METHOD FOR GRAIN BOUNDARY ETCHING OF METAL SURFACE

摘要

PROBLEM TO BE SOLVED: To provide a method capable of evenly and surely forming a passive film while suppressing excessive metal corrosion of a crystal grain surface, and selectively breaking and metal-corroding a passive film in a grain boundary part without stopping or holding sweep at a re-passivation minimum potential.

SOLUTION: A potential is applied while a etching target part of a metal surface is brought into contact with an electrolyte, and the potential is swept upwardly from a natural potential 1 to a return point of an optional value exceeding a passivation potential 2 to form a passive film in the etching target part. The potential is thereafter inversely swept to the natural potential 1 through a re-passivation area and an active state area to selectively corrode the crystal grain boundary part. The sweep is performed at a high rate from the natural potential 1 to the passivation potential 2 to activate the etching target part while suppressing the corrosion of the whole crystal grain. When the potential is returned from the passivation potential 2 to the natural potential 1 through the return point R, the sweep is performed at a low rate at least up to the re-passivation minimum potential 8 in the inverse sweep to promote the dissolution of the grain boundary part.

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