Indentation Method to Measure Plating Ductility

Abstract

The ductility of a plating is an important measure of its durability. In the present paper an indentation test for thin platings is introduced. The test is based on the fact that tensile radial strains arising at the rim of the indentation crater tend to cause cracks in a material of insufficient ductility. By a quantitative knowledge of the radial strain the ductility – i.e., ultimate strain – of the material can be determined. We use a simple geometric analysis which assumes no tangential displacement in the contact area to determine the “average radial strain” across the indentation. In the experiments sharp conical indenters (typically having a 60 degree cone angle with a 0.025 mm (0.001 in.) tip radius) are used, and the plastically deformed crater is checked by electron microscopy (SEM) for cracks. If a crack is detected, its depth is further checked by an attendant X-ray procedure (EDX) for the presence of the underlying substrate material. If a “through-crack” is found, then the ductility of the plating has been exceeded; i.e., the ductility will be equated with the strain value measured for the last indenter loading not involving a crack.