Speaker
Description
Keywords: Hard chromium, tensile test, adhesion properties, coating
Hard chromium plating process is widely used in aerospace industry to enhance wear resistance of parts. The traditional process uses hexavalent chromium, a CMR classified substance which is submitted to authorization by the European REACh regulation since 21st September 2017. Such substances are meant to disappear in the upcoming years. The CHROMAERO project aim is to develop a new REACH-compliant electrolytic process with similar performances to those of the classical Cr(VI) process. Electrodeposited chromium deposits from several trivalent chromium electrolytes on unalloyed steel (2C45) are studied.
The intrinsic physico-chemical properties of chromium coatings as well as their adhesion are studied as a function of the operating parameters of the process. The hardness and rigidity of the deposits were determined by nanoindentation testing according to the bath formulation. In order to qualify the adhesion of these coatings, tensile tests on different scales are developed. Tensile tests on conventional specimen geometries, synchronized with an optical video device, allow an overall and statistical evaluation of adhesion to provide a response to industrial expectations. In situ tensile tests carried out on micro-samples in a scanning electron microscope make it possible to determine the elementary degradation mechanisms.
It is possible to obtain hard chromium coatings with a thickness greater than 50 microns with trivalent chromium baths. The hardness values of these new coatings (above 900 HV) are comparable to those classically obtained for deposits elaborated with hexavalent chromium baths. On unalloyed steel substrate, the micro tensile test made possible to relate the initiation of cracking to the passage of the Lüders bands. The crack density depends on both thickness and processing parameters.
| Speaker Country | France |
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