Carbides Vickers hardness

Vickers Hardness 22 GPa (as opposed to other carbides, the hardness is maintained at high temperature with little change. 

Table 10.4 Comparison of Vickers hardness and fracture toughness for cemented carbide sintered with and without SiC-coated diamond particles...

The bulk densities of all the materials were determined using Archimedes method (AS 1774.5, 1979). The Vickers indentation technique was used to measure the hardness in each case. The applied load in the Vickers hardness tests was 10 kg for silicon nitrides and sialons. However, using the same load produced severe lateral cracking in silicon carbides around indents, which prevented the accurate measurement of the diagonals of indents. Therefore the load was reduced to 0.3 kg for silicon carbide samples. 

In order to improve the wear resistance of machining tools made of hard metals, steel, tungsten carbide cobalt, titanium aluminide, titanium and silicon substrates have been coated with SiBNsC via CVD of TABB [107, 108]. Layers produced in this fashion are dense and exhibit a Vickers hardness of 1000-2300 kg mm S depending on the specific process parameters. 

The MAX phases, unlike the MX carbides, are relatively soft and ecceedingly damage-tolerant. The Vickers hardness values of polycrystaDine MAX phases fall in the range of 2-8 G Pa thus, they are softer than most structural ceramics, but harder than most metals. The low hardness persists - at least in Ti3 iC2 - even at temperatures as low as 77 K [149]. 

In Fig. 1.56, graphs show the Vickers hardness variations for several refractory carbides under loads. These experiments were performed for a wide range of test forces, between 0.49 N and 196 N. All three graphs below show the same pattern... 

Tungsten powder is obtained by reduction of WO, with hydrogen gas at a temperature of800°C. The very hard, wear-resistant, tungsten carbide WC is prepared by reaction between W powder and carbon powder at a temperature above 1600°C. Tungsten carbide WC has a density of 15.72 g/cm and a Vickers hardness of 2350. 

A study of Vickers hardness of polycrystalline ceramics revealed that cracking may cause critical transition points in the Vickers ISE trends. The transition point was associated with extensive cracking in and around the indentation and a shift in the energy balance during indentation. Different ratios of the indentation work are expended on volumetric deformation and surface fracture processes above and below the transition point. The transition point was very distinct for brittle materials such as silicon carbide. The Vickers hardness transition point was related to a new index of ceramic brittleness defined as ... 

Among the studied carbides, the ternary Ti3SiC2 presents some interesting prospects. Indeed, in 1972 Nickl et al. remarked that this material, which was synthesized for the first time by a Viennese group in 1967 is abnormally soft for a carbide. Actually, Pampuch et al - and Lis et al demonstrated that this material is both stiff (Young s modulus of 325 GPa) and soft (Vickers hardness of 6 GPa). Moreover, like Goto et al some years before, they noted that the hardness of this carbide decreases as the applied load increases this property led them to qualify Ti3SiC2 as a ductile ceramic . 

Cubic boron nitride (cBN) is a very promising material that, after diamond, displays the highest hardness, excellent thermal conductivity, and important characteristic properties such as high electrical insulation and chemical and thermal stability. The cBN film can be deposited on a cemented carbide insert using activated reactive evaporation with a gas activation nozzle. Figure 20 shows the relation between the micro Vickers hardness (10 g load) of a BN film and its... 

High speed steels were discovered in 1868 and were developed from 1898 onwards. These derive their name from their capacity to preserve their hardness (until about 600°C) while cutting material at high speed. These are steels which can be hardened by heat treatment up to 1,000 HV (Vickers Hardness) or 65-70 HRC (Rockwell C Hardness). These steels are certainly not ceramics, but they cannot be ignored here on account of their properties, their operating techniques and the presence of reinforcing precipitates (carbides in particular). 

Hardness is measured by the Rockwell A-scale diamond cone iadentation test (HRA) or by the Vickers diamond pyramid iadentation test (HV). Although the Rockwell scale has been used for decades ia the carbide iadustry as a measure of hardness, a tme iadication of the resistance of the tool to deformation ia metal-cuttiag operatioas can be obtained only by measuting hardness at elevated temperatures. The hardness of cemented carbides decreases monotonicaHy with increasing temperatures. 

For erosive wear. Rockwell or Brinell hardness is likely to show an inverse relation with carbon and low alloy steels. If they contain over about 0.55 percent carbon, they can be hardened to a high level. However, at the same or even at lower hardness, certain martensitic cast irons (HC 250 and Ni-Hard) can out perform carbon and low alloy steel considerably. For simplification, each of these alloys can be considered a mixture of hard carbide and hardened steel. The usual hardness tests tend to reflect chiefly the steel portion, indicating perhaps from 500 to 650 BHN. Even the Rockwell diamond cone indenter is too large to measure the hardness of the carbides a sharp diamond point with a light load must be used. The Vickers diamond pyramid indenter provides this, giving values around 1,100 for the iron carbide in Ni-Hard and 1,700 for the chromium carbide in HC 250. (These numbers have the same mathematical basis as the more common Brinell hardness numbers.) The microscopically revealed differences in carbide hardness accounts for the superior erosion resistance of these cast irons versus the hardened steels. 

Kumashiro Y., Sakuma E., 1980, The Vickers micro-hardness of non-stoichiometric niobium carbide and vanadium carbide single crystals up to 1500°C, J. Mater. Sci., 15, 1321-1324. 

In the Brinell test (Brinell, 1900 Meyer, 1908) the indenter consists of a hard steel ball, though in examining very hard metals the spherical indenter may be made of tungsten carbide or even of diamond. Another type of indenter which has been widely used is the conical or pyramidal indenter as used in the Ludwik (1908) and Vickers (see Smith Sandland (1925)) hardness tests, respectively. These indenters are now usually made of diamond. The hardness behaviour is different from that observed with spherical indenters. Other types of indenters have, at various times, been described, but they are not in wide use and do not involve new principles. 

Figure 10.23 Hardness indenters (a) Brinell steel or tungsten carbide sphere (b) Rockwell A, C, D diamond cone (c) Rockwell B, F, G steel sphere (d) Vickers diamond pyramid and (e) Knoop diamond pyramid...

Knoop single crystal, 83 temperature effect, 78 Vickers single crystal, 93 toughness, 187 Titanium nitride (TiN), 297 hardness of thin film, 50 Titanium dioxide, TiOj, 124 Tolerance factor, 287 Topotaxy in ZrOj transformations, 272 Toughness, 145 mechanisms in Z1O2, 27 Transformation toughening, 273 Transition metal carbides, anisotropy in, 75 Transition metal nitrides, anisotropy in, 75 Trichloroborazine, 231 Tridymite, 236... 

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