Colmonoy® 88, a fully dense, complex carbide coating, can outperform two-phase NiCrSiB hardfacing materials with tungsten carbide in many slurry erosion applications.
The common solution against erosion wear in many applications that involve slurry or silt is the archetypal two-part blended NiCrSiB plus Tungsten Carbide applied by Spray & Fuse: FusewelderTM Torch, SpraywelderTM System, PTA or laser cladding systems.
However, these solutions often fail prematurely because the supposedly protective element, the tungsten carbide, is blended into the mix creating the two-part, two-phase deposit along with the matrix alloy (see Figure 1).
A slurry or silt erosion problem means that the surface is being attacked in many different directions, largely by very fine particles held loosely in a liquid which slowly destroys the NiCrSiB matrix alloy which cements the tungsten carbide particles into place. Once that “matrix” is lost, the harder tungsten carbide particles or grit fall away which, in enclosed equipment, exasperates the problem.
Protection against erosion is often better tackled using a single homogenous alloy rather than a two-part material whereby no large areas of less wear resistance are present. Colmonoy® 88 (US|UK) as an example, is a unique alloy because the alloy forms its own network of internally precipitated hard phases consisting of complex carbides, borides, and silicides which are closely spaced (see Figure 2). When the spacing of wear resistant phases is smaller than the diameter of the erosive slurry or silt the wear mechanism can be much more favorable than the conventional NiCrBSi-tungsten carbide composite blend.
Figure 1: NiCrSiB-tungsten carbide/cobalt blend – A matrix with relatively low wear resistance is susceptible
to attack from fine particle abrasion. Original at 300x, etched with marbles reagent.
Figure 2: Colmonoy® 88 provides a fully dense coating rich in wear resistant hard phases which are
uniformly distributed throughout the deposit. Original at 500x, etched with marbles reagent.
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