Hardmetals applications

In most hardmetal applications it would be desirable to use the hardest possible grade. However, properties often have reciprocal relationships, i.e. an improvement in one leads to a deterioration in another. Therefore, in order to select the most appropriate grades for a specific application, it is desirable to know quantitatively the relationships between the various properties. So far, extensive work has been... 

Wear-resistant layers of transition metal carbides that have been deposited by CVD (see Chemical Vapor Deposition) and PVD processes on the surface of WC-Co hardmetals further reduce the wear in cutting applications. About 80% of... 

Table 5 Characteristics of hardmetal and cermet grades and their applications...

Since 1930, cemented carbides (also called hardmetals) steadily attained a greater share in tungsten consumption. It is of interest to ask why the demand for cemented carbide grew so rapidly. Table 2.9 shows a chronological table indicating the most important events in cemented carbide research and development, a process which is still under way today. We recognize that what we call cemented carbides or hardmetals are in reality a very wide palette of materials with different properties. Cemented carbide properties can be adjusted by several variations and combinations of the components, as shown in Table 2.10. Hence cemented carbides could be applied widely. Figure 2.10 presents a breakdown of the fields of application of cemented carbides. 

Besides tungsten metal, only those alloys which were described in Chapter 6 are treated in this chapter. Alloys produced by melting metallurgy as well as the cemented carbides (hardmetals) and their application are treated in Chapters 8 and 9, respectively. 

However, despite these changes in the tool industry, hardmetals have not lost their importance. On the contrary, larger amounts are produced than ever before and, in their various areas of application, their proportion is steadily increasing. The reason for this situation is manifold ... 

This chapter will follow the different stages of powder metallurgical manufacture. More emphasis will be put on the description of WC powder production methods and qualities, and the preparation of graded powders. Less emphasis will be put on sintering, hardmetal qualities, and applications. In this context, we refer to several excellent books and review articles dealing particularly with hardmetal technology, properties, and applications [9.1, 9.2, 9.4, 9.7-9.9]. 

Direct compacting. Direct compacting is applied for near-net shaping of parts. This means that the final hardmetal specimen after sintering already has the desired dimensions and only limited surface treatment is necessary afterward. For that purpose, semiautomatic or automatic mechanical or hydraulic presses are used. The pressure application is only from one direction, resulting in a slightly anisotropic density distribution in the green compact. 

Direct compacting is mainly used in producing mining tools, metal cutting inserts, and parts for construction applications. Around two-thirds of hardmetal production is compacted by this method. 

As mentioned earlier in the introduction to this chapter, tfie properties of WC-Co based hardmetals can be varied widely and consequently their applicability is extremely widespread. The properties are intimately connected with their microstructure (including micro- and macroporosity) and surface conditions (grinding cracks and excessive roughness). These can be influenced by several raw material properties and processing conditions ... 

As a result, by selecting appropriate combinations of cobalt contents and carbide grain sizes, the hardness of WC-Co can be varied from below 800 HV to more than 2000 HV. The most appropriate combination is determined by the properties which, besides hardness, are required for a specific application. The recent introduction of grain sizes of the order of 10 nm has extended the range of possible hardness well above 2000 HV [16]. However, nano-grade hardmetals are not included in the present review because they always contain grain refiners such as VC or Cr2C3, while this review is limited to two-phase V/C- Co alloys. 

A nozzle opening of a sandblaster may suffer severe wear during operation. This can be countered by using hot-pressed boron carbide (B4C), which is expensive but is very hard and has a long lifetime in this application. Sintered alumina or hardmetal (a cermet of tungsten carbide sintered with some cobalt or nickel metal) show more wear but are suitable as well and cheaper to make. 

A review on the most important models applicable to the mode I fracture of WC-Co hardmetals has been given in [1]. It was concluded that tremendous disagreement exists between different authors. Most of the models (e.g. [2]) rely on a plastic zone size ry comparable to the mean intercept length of the Co-binder Lco due to a linear relation between Lco and the toughness Kjc of WC-Co. Recent FE-calculations even yielded a much larger size of the plastic zone [3] while in [4] a smaller size was assumed ... 

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