Cobalt binder

Other wear mechanisms are flank wear and crater wear which occur mostly with cemented-carbide tools. Flank wear refers to the depression that is formed below the cutting edge on the side of the tool caused by the abrasive wear of the cemented carbide. TiC is particularly effective in reducing it. Crater wear occurs in the form of small depressions on the rake face behind the point of contact of the tool with the workpiece. Diffusion of the cobalt binder into the cutting chip usually occurs with crater wear. TiN is effective in reducing both diffusion and crater wear.PI... 

Thermal spray is a well-established, relatively low-cost, industrial processes which is used widely for the deposition of metals and compounds, including the refractory carbides and nitrides. Examples are coatings of tungsten carbide with a cobalt binder which are of major industrial importance. PI... 

Type 1 tungsten carbide—as required for service conditions, with cobalt binder (solid part, not overlay) ... 

Type 1 tungsten carbide- as required for service conditions, with cobalt binder (solid part, not overlay). Type 2 tungsten carbide-as required for service conditions, with nickel binder (solid part, not overlay) Type 3 tungsten carbide-sprayed overlay as required for service conditions. 

Fig. 3. Microstructures of cemented carbides, (a) 94%WC—6%Co alloy, coarse grain, (b) 85%WC—9%(Ta,TL>Nb)C—6%Co alloy, medium grain size. The gray angular particles are WC and the dark gray rounded particles are solid solution carbides. The white areas are cobalt binder.

These materials are extremely hard and wear resistant up to high temperatures (800 °C) and are used as high-speed cutting tools. They contain finely dispersed (l-3 J,m size) particles ofW, Ti, or Ta carbides (primarily WC) in a cobalt binder matrix (70 97.5% carbide). The direction of further development here is to produce and compound increasingly fine particulates, for example, by use of chemical precursor processes. ... 

Figure 4. Plot of the hardness of the cobalt binder in WC o alloys against A where A is the mean width of the binder layers, or binder mean free path. Adapted from reference [9].

However, Fig. 4 summarizes measurements by a number of investigators of the in situ hardness of the cobalt binder [9]. The hardness is plotted versus A being the thiekness of the cobalt layer where the hardness was measured, usually called the cobalt mean free path . The results in Fig. 4 satisfy the following Hall-Petch type relationship... 

Tungsten carbide (WC), the hard phase, together with cobalt (Co), the binder phase, forms the basic cemented carbide structure from which other types of cemented carbide have been developed. In addition to the straight tungsten carbide - cobalt compositions - cemented carbide may contain varying proportions of titanium carbide (TiC), tantalum carbide (TaC), and niobium carbide (NbC). These carbides are mutually soluble and can also dissolve a high proportion of tungsten carbide. Also, cemented carbides are produced which have the cobalt binder phase alloyed with, or completely replaced by, other metals such as iron (Fe), chromium (Cr), nickel (Ni), molybdenum (Mo), or alloys of these elements. 

Among the lefiactory carbides and nitrides, tungsten carbide with a cobalt binder is the most important material used widely in the coating of gas-turbine components for aircraft and industrial use, components of steam turbines and diesel engines, components for the oil and gas industry, paper and pulp industry, and chemical processing industry (see Ch. 16). 

Kentanium has better corrosion resistance than the cobalt binder tungsten carbides in salt solutions. 

Recent studies [3] on hot-pressed (binderless) NbC indicated, that pure niobium carbide has an intrinsic wear resistance, when bench marked against different ceramics, cermets, hard metals and thomally sprayed coatings. In consequence, because HP-NbC is still brittle, 8% of cobalt binder improved properties like toughness and strength as w ell as S PS reduced the sintering temperatures to 1,280°C and the dwell time to 4 minutes, as shown in the present paper. 

A direct comparison between WC>6Ni and HP-NbCl is difficult as nickel binder in WC-6Ni (6.4 wt.-% Ni + O.S wL-% Co) has a beneficial role in terms of tribo-oxidation (formation of double oxides [13]), the WC grain size being around 2 pm is much smallo than that of HP NbCl as well as the low content of the cobalt binder in NbC-8Co. The reasonable hardness of NbC compared to WC-6Ni makes die system wear (of both tribo-elements) less sensitive to demanding and cost intensive finishing (lai ied or polished ). 

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