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Residual stresses and strength of hard chromium coatings

: Pfeiffer, W.; Koplin, C.; Reisacher, E.; Wenzel, J.

Preprint urn:nbn:de:0011-n-1725359 (226 KByte PDF)
MD5 Fingerprint: 2196d762adf44c452b47a7257243ca17
Created on: 20.4.2013

Scardi, P.:
Residual Stresses VIII. Selected, peer reviewed papers from the 8th European Conference on Residual Stresses, ECRS 2010 : June 26-28, 2010, Riva del Garda, Italy
Stafa-Zurich: Trans Tech Publications, 2011 (Materials Science Forum 681)
ISBN: 978-3-03-785085-5
European Conference on Residual Stresses (ECRS) <8, 2010, Riva del Garda>
Conference Paper, Electronic Publication
Fraunhofer IWM ()

Experimental and numerical investigations have been performed on the relationships between coating parameters, residual stresses, micro-cracks and the near surface strength of electrochemically deposited hard chromium coatings. The experimental investigations included: X-ray measurements of residual and externally-applied stresses; crack density measurements using microscopy; and load-bearing measurements using ball-on-plate tests. The numerical investigations in combination with analytical conclusions focused on the influence of different crack lengths and densities on the effective elastic modulus of the chromium coating and the stress-enhancing or shielding effect of micro-crack networks respectively. The results show that the residual stresses and crack networks are influenced by the current density used during deposition. Coatings with high tensile residual stresses have low crack densities. This correlation is associated with stress relaxation by formation of micr o-cracks and, to a lesser extent, to a direct reduction in residual stresses due to the deposition process. The load bearing capacity is dominated by the crack density and can be significantly increased by shot-peening-induced compressive residual stresses. Thus, optimization of hard chromium deposition parameters for applications needing high surface strength should predominantly focus on minimizing the crack density.