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Galvanic deposition of nano dispersion coatings
W.E.G. Hansal(1), S. Hansal(1), M. Halmdienst(1), W. Siegert(2) (1) Happy Plating GmbH, Berndorf, Austria (2) Collini Skolnik GmbH, Wien, Austria E-mail: wh@happyplating.eu |
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Engineered tribocoatings offer a significant opportunity as they enhance component reliability and reduce life cycle costs of materials and tools. One way for producing high performance tribocoatings is the electrochemical co-deposition of hard or functional particles with a metal matrix. While such dispersion coatings consisting of micro particles co-deposited in a direct current (DC) process proofed their abilities in various industrial applications this work focuses the next major step in the development of high performance dispersion coatings by integrating nanoparticles into a enhanced metal matrix by using pulse plating or electroless processes.
The type of particle, the actual particle size and the distribution in the metal matrix are affecting the hardness of the produced composite material and thus the wear properties. Dispersion coatings using micro particles and direct current processes for the deposition yield in hard durable coatings but show limitations in the practical use. It is reported that larger particles show a greater strain hardening effect in the matrix metal but the actual particle size should be optimised for the optimum wear resistance. The pull out of the particles during the wear process should be prevented by a homogenous dense and hard metal matrix occluding them. Therefore, to additionally reduce the average particle size into the nano scale it is of major importance that the metal matrix is adjusted respectively. This can be only realised using pulse plating for electrolytic processes or special adjusted electroless systems.
The incorporation rate of the WC particles depends on the electrolyte system investigated. The incorporation of the particles led, when combined with pulse deposition, to a significant increase of the micro hardness and an improvement of the wear resistance. Due to the complex composition of the electroless system only small amounts of particles could be added with only small effects on the resulting layer properties.
The wear rates, measured in terms of mass loss after abrasion, were widely following the micro hardness of the coatings. The DC reference materials lost between 1.6% (sulfamate) and 2.0% (sulfate) weight after the wear cycle. Particle incorporation reduced this value to below 1.0%. The pulse plated nickel systems without particles were slightly better than their DC counterparts. The mass loss measured was 1.4% for the sulfamate and 1.7% for the sulfate system. The electroless nickel system including the WC particles led to a mass loss of 0.9% without thermal treatment and 0.5% after heating the sample at 250°C for 1 hour. The pulse plating systems including the WC particles had the best performance in this test series: 0.3% mass loss was found for the sulfate and 0.2% for the sulfamate system. The nickel-cobalt alloy system was comparable with 0.2% mass loss measured.