Ni-Silicon Carbide
Introduction
In industrial practice, particularly in the manufacture of industrial valves used in pipeline where wear resistance is very important, such where gas has an high percentage of sand, it has imposed the use of extremely hard deposits but which unfortunately do not have resistance to corrosion. Hence the need for a coating with a capacity of both corrosion resistance and an high hardness.
NiSiC assures a corrosion resistance and hardness to the covered items. These two qualities have permitted to use NiSiC as more than an effective alternative to many other coatings such as chromium or tungsten carbide.
Nickel - Silicon Carbide Codeposit
The process consists of suspending Silicon Carbide submicrons particles into an electroless nickel solution obtaining a layer where these submicrons particles are homogenously mixed in the final codeposit. The result is a co-deposit with an high surface hardness, due to the presence of silicon carbide particles even on the surface, and at the same time continues to exert its protective effect by its electroless nickel layer.
The result is an important resistance to wear and corrosion.
Electroless Nickel-Silicon Carbide (NiSiC) requires special techniques in conducting the process in order to ensure an homogenous dispersion in the array of chemical nickel deposit. This problem has been solved by Deltar with the possibility of a wide variety of supplies thanks to special equipments of its own design and construction.
This Co-deposit is based on the same principle of the Electroless Nickel plating (Enp1012), so the final thickness is absolutely homogeneous, avoiding any final grinding. In addition, NiSiC layer is continuous and uniform on all surfaces presenting the same characteristics throughout its extension, as opposed to ceramic and electrolytic deposits limited by the
geometry of the parts to be treated by Faraday cage, undercut, internal parts or blind holes.
Characteristics
The informations provided below are limited to some synthetic datas. Deltar is available to ‘test NiSiC caratheristic in according to the customer requirements on samples of various nature and geometry.
Table 1 below shows some indications of three different deposits: electroless nickel plating (Ni), Tungsten Carbide (WC) and co-deposit of chemical nickel + silicon carbide (SiC + Ni).
Therefore, we must consider the undereported datas in adhesion strength related to the following layers:
Electroless nickel plating ≥ 28.000psi
Tungsten Carbide ≥ 10.000psi
Hard chrome ≥ 10.000psi
NiSiC is currently used in applications requiring an high abrasion resistance, low coefficient of friction and corrosion resistance; for example in the chemical and petrochemical field, as a coating on metal-to-metal valve sealing, slab, expanding gate or butterfly valves.
The speed of execution, the total absence of any additional grinding combined with a very interesting cost, have decisively contributed to use it in large scale.
The hardness of silicon carbide (SiC) is higher than 2000Hv, the hardness of the final deposit is very high and it can easily exceeds the one of tungsten carbide (WC).
In synthesis Nichel chimico – Carburo di Silicio(Ni-SiC):
