Electroless Nickel-Silicon Carbide (NiSiC) co-deposition endows the coated item with increased hardness while maintaining high corrosion resistance properties. These properties have made it possible to use Electroless Nickel – Silicon Carbide (NiSiC) co-deposition as a perfectly valid alternative to many other coating procedures, such as Chromium or Tungsten Carbide.
Indeed, in industrial practice, and in particular in the fabrication of valves intended for systems where wear resistance is important, such as with fluids or gasses heavily loaded with particulates such as sand and the like, the use of extremely hard deposits has become necessary, but unfortunately these generally do not have great corrosion resistance. This has resulted in the requirement to use a coating method characterised by high hardness, while in any case retaining high corrosion resistance properties.
High abrasion resistance
High corrosion resistance
Reduced costs, compared to a ceramic-like coating
Rapid delivery times
No additional processing, such as grinding, polishing and lapping, required
General description of the process
Suspending submicron Silicon Carbide particles in a Electroless Nickel bath solution gives a deposit where a Electroless Nickel matrix incorporates finely dispersed particles of Silicon Carbide. . The result is a co-deposit with high surface hardness, thanks to the presence of protruding Silicon Carbide particles, and excellent corrosion resistance. The latter being a native characteristic of high phosphorus Electroless Nickel deposits. Specifically, Electroless Nickel-Silicon Carbide (NiSiC) co-deposition requires particular techniques for the execution of the process so as to ensure uniform dispersion in the Electroless Nickel matrix. The problem has been resolved technically by Deltar, with the ability to offer an extensive range of supplied products thanks to highly specialised equipment, all designed and manufactured in-house. Since the co-deposit obtained is based on the same principle as the high phosphorus electroless nickel-plating (Enp1012) deposition process, the thickness that will be obtained is constant, thus avoiding uncoated areas or zones subject to Faraday cage phenomena. Therefore, post deposition rectification treatment processes are avoided, guaranteeing the possibility of the coated article being passed directly to the assembly stage.
The Electroless Nickel-Silicon Carbide (NiSiC) co-deposit is continuous and homogeneous over all “bathed” surfaces, exhibiting the same characteristics over its entirety. On the other hand, this is not so in the case of ceramic and electrolytic deposits, limited by the geometries of the articles to be treated, by "Faraday Cage” type phenomena and/or areas of undercutting and problems related to inner parts or blind holes.
The indications available are limited to certain summary data. Obviously, Deltar makes the implementation of test procedures available, with the agreement of a program allowing improved knowledge through the attainment of test values from specific sample products. Being limited to certain salient characteristics, Table 1 below illustrates several indications pertaining to three different deposition types: Electroless Nickel (Ni), Tungsten Carbide (WC) and Electroless Nickel + Silicon Carbide (Ni + SiC) co-deposit.
Type of deposit
Deposit thickness µ
Final grinding/polishing required
Final thickness µ
Hardness without H.T. Hv
Final hardness Hv
Cost ratio %
It should also be considered that the adhesion of ceramic deposits on a carbon steel substrate is:
Electroless Nickel ≥ 28,000 psi
Tungsten Carbide ≥ 10,000 psi
Hard Chromium ≥ 10,000 psi
Deposition on any substrate
Available thicknesses of up to 30 – 50 µ (in specific cases, it is possible to obtain much greater thicknesses
Hardness > 1100 Hv
Corrosion: optimal resistance (ASTM B117)
Adhesion > 28,000 psi/mm2
Taber abrasion index 0.2
Friction under lubricated conditions: 0.13
Friction under non lubricated conditions: 0.3
The Electroless Nickel-Silicon Carbide (NiSiC) co-deposition process is currently used in applications where high wear resistance, a low friction coefficient and corrosion resistance are required; e.g. in the chemical and petrochemical sectors, it is used as coating on metal-to-metal sealing valves, typically being ball, gate, slab or expanding, shutter or butterfly valves. The speed of execution, the complete absence of additional mechanical processing, together with very competitive costing and above all the quality of the coating, have definitively contributed to its large scale use. In summary, the process consists of the immersion of the articles in high phosphorus Electroless Nickel solutions into which Silicon Carbide is dispersed. Articles immersed in the bath emerge with a coating of Electroless Nickel co-mixed with particles of Silicon Carbide. The hardness of Silicon Carbide (SiC) is in excess of 2000 Hv, giving the hardness of the deposit extremely high values with high wear and corrosion resistance, both being present in this individual and unique treatment.
Some processing examples
Electroless nickel plating
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DELTAR CO-DEPOSITION SRL
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