Nickel in Tungsten Carbide

In the former article, we talked about cobalt in tungsten carbide. In manufacturing tungsten carbide products, cobalt is not the only metal used for the binder phase. Nickel, iron, and other metals can also be the binder phase for manufacturing tungsten carbide.

There are several reasons why choose metal as cement for carbides, for instance, Nickel:?

a) High melting point (nickel 1453oC);?

b) Form a liquid phase with tungsten-carbide at a suitable temperature (nickel does at 1310 oC). his liquid pulls the sintered parts together by surface tension and eliminates voids;?

c) Dissolve WC (nickel forms a eutectic with at ~1310 oC and dissolves 4% WC at that temperature);?

d) On cooling, the binder should reprecipitate WC, leaving a tough matrix with dispersed carbides (nickel can produce particles around 1-2μm).?

e) No structural defects (pores, etc), and a good surface roughness showing a mirror appearance.?

f) High resistance to corrosion and oxidation;?

g) High hardness and strength;

These are the advantages of nickel and explain the paramount importance it has in cemented carbides. Because of these excellent mechanical properties, it is effective in applications requiring high resistance to corrosion, even under conditions where conventional cemented carbide tools are used.

It is known that nickel is not present in the hard metal in pure form but as a solid solution with tungsten and carbon because of its ability to solve considerable amounts of tungsten carbide at sintering temperature.

HARDNESS determines the resistance of a material to abrasion and wear. It is affected not only by composition but also by the level of porosity and microstructure. For normal WC-Ni alloys of comparable WC grain size, hardness decreases with increasing nickel content. However, because both composition and microstructures affect the hardness, nickel content, and grain size must be considered. At a given nickel level, hardness improves with decreasing WC grain size.

DENSITY, or specify gravity, of WC+Ni, is very sensitive to composition and porosity in the sample and is widely used as a quality control test. Density values of WC+Ni range from 14,97g/cm3 for low-nickel WC-Ni alloy to about 10 or 12 g/m3 for highly alloyed carbide grades.

POROSITY - The properties of a WC+Ni, hard metal, are dependent on its density, which in turn is critically dependent on composition and porosity. Porosity is evaluated on the as polished material.

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