One of the possible ways to improve performance properties of WC-Co cemented carbides for different applications is known to be adding insignificant amounts of tantalum carbide. Performance of mining tools is noticeably improved as a result of small additions of TaC, so that some companies produce WC-TaC-Co grades for mining applications. Despite clear experimental evidence of the positive influence of small TaC additions on the properties and performance of WC-Co cemented carbides, the mechanism of this influence is presently not understood. In the present work a new viewpoint of the influence mechanism of small TaC additions of performance of WC-Co cemented carbides was elaborated. It was established that small amounts of TaC added to WC-Co cemented carbides form an oversaturated solid solution of tantalum in cobalt when solidifying the liquid binder during cooling from sintering temperatures. This solid solution decomposes when further cooling in the solid state resulting in the formation of (Ta,W)C nanoplatelets and rounded nanoparticles embedded in the binder matrix. The effectiveness of cemented carbide with such a nanograin reinforced binder is assumed to be similar to that of the well-known cemented carbides with the binder reinforced by hard metastable W-Co-C nanoparticles implemented in industry about 20 years ago. The production of the cemented carbides with the (Ta,W)C nanograin reinforce binder is more economical and consistent, which ensures the more sustainable manufacture, and the nanoprecipitates are stable at elevated temperatures.

It was reported in the literature that the influence of grain growth inhibitors (GGIs) on the WC grain growth during sintering of cemented carbides is related to the formation of complexions at WC/Co interfaces at temperatures of liquid-phase sintering. However, this viewpoint was not confirmed experimentally, as such complexions were found upon cooling after sintering. The influence of different grain growth inhibitors on the kinetics of WC coarsening in WC-10 wt% Co cemented carbides was investigated. The presence of complexions having a thickness of nearly 1 to 3 nm at WC/Co interfaces was established by STEM, EDX and HRTEM as a result of adding VC, Cr3C2 and TaC to WC + Co. WC grains in WC-Co cemented carbides containing Mo2C was characterized by the presence of near-surface layers of (W,Mo)C having a thickness of about 100 nm and absence of complexions at the WC/binder interface. The values of activation energies for all the GGIs except for Mo2C lie in the range typical for the solid-state diffusion-controlled processes, therefore, the solid-state diffusion of W and C atoms through the nm-thick complexions is presumably a limiting stage of WC coarsening. Considering the activation energy and distribution of heavy elements in the binder for the samples doped with Mo2C, one can assume that in the liquid binder containing dissolved W, C and Mo atoms, molybdenum suppresses the diffusion of tungsten atoms. Therefore, the rate of the tungsten atoms' diffusion in the liquid binder is likely to be a limiting stage of WC coarsening.

A new express method for measurements of WC grain sizes in WC-Co hardmetals was developed. This method is as precise as the EBSD grain size measurement method but much faster and thereby less expensive. The new measurement method is based on a peculiar procedure of hardmetal samples' preparation, recording microstructure images and their segmentation followed by determining WC mean grain sizes by use of a specially developed software; the measurement error is less than +/- 3%. Dependencies of coercivity and hardness on the WC mean grain size of WC-10 wt% Co hardmetal samples were established by the new express measurement method. With the aid of this method the dependencies reported in literature were updated as a result of more precisely determined values of the WC mean grain size compared to those established in literature by conventional methods based on SEM measurements.

In this chapter, major properties of tungsten carbides and their structural characteristics are presented. The crystal lattice of tungsten monocarbide and the W–C phase diagram are reported. Unique properties of tungsten monocarbide, in particular, some degree of its plasticity before failure when applying loads at room temperature, are described. Characteristics of the crystal lattice of titanium carbide, in which W, Ta, and Nb atoms substitute Ti atoms forming cubic (W,Ti)C, (W,Ti,Ta)C, and (W,Ti,Ta,Nb)C carbides, are presented. A vertical section of the Ti–W–C phase diagram and a diagram indicating the temperature dependence of the solubility of WC in TaC are given and analyzed.

The history of the invention of tungsten carbides by Henri Moissan in the end of the 19th century and cemented carbides by Karl Schröter in the beginning of the 1920s of the last century is described. First experiments on developing novel hard materials on the basis of WC and other refractory carbides with the objective to substitute diamond dies for drawing tungsten wires are briefly outlined. The discovery, patenting, and early production of WC–Co cemented carbides in Germany are described. The development and implementation of cemented carbides at various companies in different countries are outlined.

Kinetics of WC coarsening during sintering of WC-10 wt% Co cemented carbide grades was examined by use of submicron WC powders with a broad grain size distribution containing much nanograin fraction, medium -finegrain powders with a narrow grain size distribution containing little nanograin fraction and medium-grain powders with a very narrow grain size distribution not containing nanograin fraction. Based on the kinetic curves re-constructed in the Arrhenius coordinates, values of the apparent activation energy for each carbide grade were obtained, which allowed the limiting stage of the WC coarsening process to be evaluated. The limiting stage of the WC coarsening process for the medium-grain grade is related to the diffusion of W and C atoms in the liquid binder during sintering. For the submicron grade the limiting stage of the WC coarsening process is related to interfacial reactions at WC/liquid interfaces. In this case, the diffusion of W and C atoms dissolved in the liquid binder is fast due to a very significant difference between sizes of the fine/nano WC grains and coarser WC grains. When increasing the sintering temperature and time above a certain level, the significant acceleration of WC coarsening takes place indicating the transition of the process to the stage of anomalous grain growth, at which the formation of abnormally large WC grains in the microstructure determines the whole WC coarsening process. The limiting stage of the WC coarsening process for the medium-fine-grain grade is mainly related to diffusion of W and C atoms dissolved in the liquid binder.

Technological processes for fabrication of tungsten metal and tungsten carbide powders as well as those employed for fabrication of (W,Ti,Ta(Nb))C powders, powders of grain growth inhibitor, and cobalt powders are described. Typical images of powders of tungsten metal and tungsten carbide with different mean grain sizes are presented. Technological processes for fabrication of cemented carbide graded powders, including milling in attritor mills and ball mills, are described. Technological processes for granulation of the graded powders, including build-up granulation, fluidized bed granulation, and spray granulation, are described and compared. Technological processes for fabrication of cemented carbide green bodies, including pressing in dies, cold isostatic pressing, extrusion, and shaping green carbide compacts, are described, and their advantages and disadvantages are presented and analyzed. Technological processes for sintering cemented carbide articles comprising stages of dewaxing and presintering as well as final liquid-phase sintering are described. Theoretical bases of liquid-phase sintering, overview of physicochemical processes occurring during sintering of WC–Co cemented carbides, special features of sintering processes of WC–TiC–TaC–(NbC)–Co cemented carbides, and cemented carbides with alternative binders are presented with an emphasis on mechanisms of WC grain growth.

The W–C–Co, W–C–Ni, W–C–Fe, W–C–Fe–Ni, and W–C–Ti–Ta–C–Co phase diagrams are presented in this chapter. The comprehensive and simplified versions of the pseudobinary vertical section of the W–C–Co phase diagram between stoichiometric WC and cobalt as well as its vertical section through the carbon angle and horizontal section are given. The experimentally obtained vertical and horizontal sections of the W–C–Ni, W–C–Fe, W–C–Fe–Ni, and W–C–Ti–Ta–C–Co phase diagrams are reported and analyzed with respect to their applicability to the carbide production. Special features of the phase diagrams of each system are outlined.

General characteristics of cemented carbides are summarized with an emphasis on their exceptionally high combination of hardness, fracture toughness, wear resistance, and strength. Classification of different carbide grades with various WC mean grain sizes according to the ISO standard is given. Major properties of WC–Co cemented carbides in comparison with ceramics, stellite, cast iron, and steel are presented. Typical microstructures and application ranges of cemented carbides according to their Vickers hardness, WC mean grain size, and binder content are given. An estimate of the total world-wide cemented carbides' production and market shares of carbide grades for different applications are presented.

Major methods for controlling industrial cemented carbides in the manufacture are described in this chapter. Main methods employed for the examination of cemented carbide microstructures including different etching techniques are reported. Typical images of cemented carbides' microstructures containing inclusions of free carbon and ղ-phase are given. Advanced techniques employed for examining cemented carbide microstructure on the micro-, nano-, and atomic level (transmission electron microscopy and electron backscattering diffraction) are briefly described. Techniques for examining magnetic properties of cemented carbides including coercive force and magnetic saturation/magnetic moment are reported. Major methods employed for controlling mechanical properties of different cemented carbide batches in the manufacture are described. Main wear tests of cemented carbides according to the ASTM standards are presented. Procedures for the examination of high-temperature properties of cemented carbides are briefly outlined.

Mechanisms of wear and degradation of cemented carbides in the major application fields are described. The major wear mechanisms of coated indexable cutting inserts in metal cutting are reported with an emphasis on the influence of wear-resistant coatings on wear patterns on different stages of the wear process during metal cutting. Wear mechanisms of WC–Co cemented carbides employed for mining and oil-and-gas drilling applications are described with an emphasis on micromechanisms of material removal from the near-surface layer of carbide inserts during percussive drilling. Special features of wear and damage of carbide inserts during rock- and coal cutting as well as road-planing are outlined. Mechanisms of abrasive wear and degradation of cemented carbides employed for the fabrication of wear parts are described. Typical carbide grades employed for the fabrication of stamping tools are reported. Major mechanisms of wear and degradation of cemented carbides used for rolling and drawing of wires and bars at room and elevated temperatures are reported and analyzed. Photos showing typical fracture surfaces of carbide high-pressure high-temperature components including cubic and belt anvils and dies are presented.

Technological processes of final processing carbides articles after sintering and deposition of wear-resistant coatings are described in this chapter. Physical principles, technological parameters, and different methods of grinding are reported. Major methods used for brazing carbide components to steel articles, including furnace brazing, induction brazing, and flame brazing, are presented. Main techniques for assembling different tools and wear-resistant articles comprising steel and carbide components, including shrink fitting and adhesive joining, are described. Chemical vapor deposition (CVD) and physical vapor deposition (PVD) techniques employed for obtaining wear-resistant coatings on indexable carbide cutting inserts are reported with an emphasis on advantages and disadvantages of different deposition technologies with respect to each concrete application of metal-cutting. Different compositions and architectures of advanced CVD and PVD hard coatings are briefly outlined.

Advanced uncommon industrial grades of cemented carbides fabricated by different carbide manufacturers are presented in this chapter. These grades include functionally graded cemented carbides (functionally graded WC–Co cemented carbides and functionally graded cemented carbides with cubic carbide depleted near-surface layers), nanostructured cemented carbides, cemented carbides with nanograin reinforced binder, cemented carbides with alloyed binder phases, cemented carbide substrates in combination with layers of polycrystalline diamond, and cemented carbides with Co-enriched surface layers. Technological processes employed for the fabrication of such advanced industrial carbide grades are briefly described.

Different technologies of recycling cemented carbides, including the full chemical recycling technique, technique based on leaching carbide binders, zinc reclaim process, and cold stream process, are described in this chapter. Major features as well as advantages and disadvantages of each recycling technology are outlined, compared, and analyzed. Schematic diagrams illustrating the different recycling procedures are presented.

Major properties and structures of Co-based, Ni-based, and Fe-based binders of cemented carbides are presented. Vertical sections of the calculated W–C–(Fe, Co, and Ni) phase diagrams through the carbon angle at a binder content of 20 wt.% are reported, compared, and analyzed. Unique properties of Co-based binders, in particular, their increased work-hardening rates due to the fcc-hcp martensitic transformation occurring as a result of fatigue are described. The results of experiments on the cobalt binder dispersion hardening in WC–Co cemented carbides due to their annealing are reported. Processes of the formation of nanoparticles consisting of different W–Co–C phases in the binder phase of cemented carbides are outlined. Advantages and disadvantages of alternative binders of the Co–Fe–Ni system are described and analyzed.

Major modern trends in the research and development of novel cemented carbides are briefly outlined in this chapter. One of such trends is the grain boundary design of WC–Co materials at WC/Co and WC/WC interfaces, which can potentially result in significantly improved mechanical and performance properties of cemented carbides. Another general trend in modern materials science is related to in situ examinations of deformation and thermal processes in different materials, particularly, in cemented carbides, directly in transmission electron microscopes. One more general trend in modern materials science, which becomes more and more popular for examining cemented carbides, is micromechanical testing of various materials by use of micropillars and other articles obtained by the focused ion beam technique. Different techniques of additive manufacturing, which is a powerful tool for rapid prototyping and fabricating metal articles with a complicated geometry, are presently investigated and optimized with respect to fabrication of cemented carbide parts. Development of diamond-enhanced cemented carbides is presently a topic of great importance, as such materials could potentially possess an exceptionally high combination of hardness, fracture toughness, and wear resistance.

Different approaches to modeling of the cemented carbides' structure and properties are described in this chapter. Results of modeling the cemented carbide structure on the micro-, nano- and atomic level by ab initio calculations are presented, analyzed, and compared with the experimentally obtained results. Methods of modeling mechanical properties of and degradation processes in cemented carbides are described. Methods and results of modeling of the stress distribution in cemented carbide articles based on the Finite Element Analysis or Finite Element Method are reported with respect to different applications of carbide articles and tools.

The influence of the composition and microstructure on properties and applications of WC–Co cemented carbides is reported. The major special features of cemented carbides are summarized and analyzed with respect to their influence on the microstructure, properties, and performance of cemented carbides in different applications. These features include the cobalt content and mean WC grain size, uniformity of cemented carbide microstructure, total carbon content, composition and state of the binder phase, origin of tungsten carbide powders, inhibitors of WC grain growth, shape and contiguity of WC grains, and impurities and contaminations.

New impact-abrasion tests allowing one to evaluate performance of hardmetals operating in conditions of intensive abrasion, severe fatigue and high impact loads can be of great importance for many industrial applications. A new test for studying wear behaviour of hardmetals under high impact loads was developed and employed for evaluation of performance of different hardmetal grades in comparison with polycrystalline diamond (PCD). The wear behaviour of the same hardmetal grades and PCD was also examined in the standard ASTM B611 test, which was employed as a control. A significant difference between wear rates of near-nano and submicron hardmetals on the one hand and medium-coarse and ultra-coarse hardmetals on the other hand in the new impact-abrasion test was established. The wear of PCD in the impact-abrasion test was found to be close to zero. Examinations of wear surfaces of the tested hardmetal samples allowed wear mechanisms of the different hardmetal grades to be evaluated. The wear mechanism of the near-nano and submicron grades in the impact-abrasion test comprises phenomena of wear and flattening of WC grains, partial removal of Co from binder interlayers in a thin surface layer and formation of shallow holes on the worn surface as a result of detachment of relatively small WC-Co fragments. The wear mechanism of the medium-coarse and ultra-coarse grades in the impact-abrasion test includes phenomena of full removal of the binder phase from thick Co interlayers among WC grains leaving them unsupported. This leads to cracking, damage and breakage of the WC grains as well as detachment of large WC-Co fragments resulting in significantly higher wear rates of the medium-coarse and ultra-coarse grades in comparison with the near-nano and submicron grades.

Nanostructured WC-Co hardmetals, also known as near-nano-hardmetals, are characterized by fine and uniform microstructure with the WC mean grain size of about 150 nm. The near-nano hardmetal with 10% Co has a significantly improved combination of hardness, wear-resistance and fracture toughness in comparison with a conventional ultra-fine hardmetal grade with 10% Co. The wear-resistance of the novel near-nano hardmetals is exceptionally high due to their high hardness, extremely fine microstructure and consequently a low Co mean free path among WC grains. (C) 2019 Elsevier B.V. All rights reserved.