Vickers hardness results

Sclerometer scratch and manual abrasion methods, considered impractical today because they involve tedious repetition of measurement to obtain the required mean, give values very close to Vickers hardness results. This... 

Hardness. The Knoop indentation hardness of vitreous sihca is in the range of 473—593 kg/mm and the diamond pyramidal (Vickers) hardness is in the range of 600—750 kg/mm (1 4). The Vickers hardness for fused quartz decreases with increasing temperature but suddenly decreases at approximately 70°C. In addition, a small positive discontinuity occurs at 570°C, which may result from a memory of quartz stmcture (165). A maximum at 570°C is attributed to the presence of small amounts of quartz microcrystals (166). Scanning electron microscopic (sem) examination of the indentation area indicates that deformation is mainly from material compaction. There is htfle evidence of shear flow (167). 

The influence of fillers has been studied mostly at hl volume fractions (40-42). However, in addition, it is instructive to study low volume fractions in order to test conformity with theoretical predictions that certain mechanical properties should increase monotonlcally as the volume fraction of filler is Increased (43). For example, Einstein s treatment of fluids predicts a linear increase in viscosity with an increasing volume fraction of rigid spheres. For glassy materials related comparisons can be made by reference to properties which depend mainly on plastic deformation, such as yield stress or, more conveniently, indentation hardness. Measurements of Vickers hardness number were made after photopolymerization of the BIS-GMA recipe, detailed above, containing varying amounts of a sllanted silicate filler with particles of tens of microns. Contrary to expectation, a minimum value was obtained (44.45). for a volume fraction of 0.03-0.05 (Fig. 4). Subsequently, similar results (46) were obtained with all 5 other fillers tested (Table 1). 

Results of the Vickers hardness of 15 inorganic and organic salts will be presented. The hardness-force dependency, and the effects of direction dependency were examined. The measured values of the Vickers hardnesses were taken for an attempt to prove a model to calculate the hardness. This model describes the hardness purely by physical properties of the substances. The use of such a model may be an approach for the description of the abrasion resistance of salts. Data describing the abrasion resistance could help in the understanding and interpretation of secondary nucleation phenomena. 

The force-dependency of the Vickers hardness was measured for several salts. This effect is shown in Figure 1 e.g. for sodium chlorate. With an increase of the indentation force the Vickers hardness decreases, e.g. up to 40 % for sodium chlorate. The photos of indentations by the Vickers pyramid in a sodium chlorate crystal are presented in Figure 2 and give an idea of resulting cracks and lift-offs. This cracks are due to too high indentation forces (the indentation force to be seen in the Figures are 2a, 2 10 N 2b, 4 10 2 N 2c, 0.25 N 2d, 0.6 N). 

In Table 2 the results are shown for the calculated volumetric cohensive energies of crystals with NaCl-type structure and their measured Vickers hardness. 

Going further in these attempts and analysing the results of Vickers hardness measurements (Hv) obtained for particular standard hardness blocks of the Mohs scale, Khrushchev (1950) tried to find a mathematical relationship between these values. To this end, he had to eliminate the existing discontinuities between particular degrees of Mohs hardness (Fig. 4.2.1, old scale). He attained this by augmenting the scale with five extra... 

According to the purpose of the measurement, we may take results expressed in measuring depth, reflecting the wearability of a material, or expressed in Mohs hardness units. The possibility of converting from depth measurement to H0 hardness classes conforming to the Mohs scale, consistent with Vickers hardness (Fig. 4.4.11), may provoke some reservations. For this reason, therefore, A. Szymanski and J. M. Szymanski (1976) tried... 

The influence of atmospheric air on the properties of mineral materials manufactured in thermal processes is generally known. An example of the nature of this phenomenon as regards hardness, is a series of Vickers hardness tests of a material made of sintered corundum modified with 0.6% MgO sintered at 1950-2050 K in various environments. The sintering process is accelerated in the presence of hydrogen and is slowest in air thus allowing a material with optimum parameters to be obtained at a significantly lower temperature. The results, specified in Table 6.2.4, show the gases used as... 

The Mackensen blower method is found to be harder to relate to Vickers hardness determined by diamond indenter, although analysing the results of tests carried out by the two methods on ceramic grinding wheels using alundum as the abrasive (A. Szymanski, 1968c), results qualitatively similar are observable (Fig. 4.5.12). Alundum grains, size 8 (3.15-2.50 mm), were moulded in a ceramic binder and fired at various temperatures ranging from 1470 to 1630 K, with one-hour time delay. Polished sections were... 

The hardness number is usually combined with the name of the method used, to indicate how the value was obtained. The commonly used tests are the Brinell, Rockwell, and Vickers hardness tests. The results of these tests are presented as the HB or Brinell hardness number, or the HV, and so on. 

Today, Vickers hardness is the most common method of determination. Table 1.9 compares the results of Vickers microhardness measurements obtained from two differently produced types of single crystals and several polycrystalline tungsten samples. 

A plot of typical microhardness data is given in Fig. 7.11. Results revealed an increase in hardness from approximately 340 Vickers hard-... 

It is found that the steady state C 7 is about 2.08x10" ar and 1.81x10" ar for the ion-irradiated Fe-9at%Cr alloy and Fe-12.5at%Cr alloy, respectively. In Heintze et al. (2011) correlation between Vickers-hardness/yield stress of neutron-irradiated materials and indentation hardness of both ion-irradiated Fe-9at%Cr and Fe-12.5at%Cr alloys was found, and the assumption that the SANS results can be transferred to the ion-irradiated materials, if the dpa-values agree, was manifested. According to this statement CD modeling of kinetics of a -phase in ion-irradiated Fe-9at% and Fe-12.5at%Cr alloys has been carried out. The value of that provides the best fit of CD results to SANS data is found to be about 3.4 x 10" J/m vs. 0.17 J/m in Gokhman et al. (2011), where TEM data for the neutron-irradiated Fe-12.5at%Cr alloy are taken. 

Other common hardness tests involve the use of diamond pyramids. In the Vickers hardness test, a square pyramid is used and in the Knoop hardness test, the pyramid is elongated. The area term in the former test is the actual indentation area and in the latter, the projected area. From the impression geometries, shown in Fig. 6.30, the Vickers Hardness Number (VHN) and Knoop Hardness Number (KHN) can be shown to be VHN=1.854F/a and KHN=14.2F/L, respectively. A common hardness test in the USA is the RockweO hardness test, which uses various indenter types and loads. The result of these tests is a dimensionless number and leads to the use of various hardness scales (e.g., Rockwell B, Rockwell C). 

Figure 3. Conventionally measured Vickers hardness on sapphire ((1210) surface, Vickers diagonals parallel with the traces of (1012) and (1102) planes) fl31 The interrupted line is the fit according to Eq. (3) with a constant (average) ratio (fie/ i) resulting in = 15.40GPa and (4A) = 1.119. An only slightly different fit results with the varying of Eq. (3a)...

Figure 9 shows Vickers hardness measurements carried out on the identical surfaces as used for the residual stress measurements. At an indentation time of ti = 20 s, an indentation force of F = 300 mN was used. The results are depicted in. Each data point is the average of at... 

For hardness determination, different methods are possible scratching the surface, penetration of an indenter with static or dynamic loads, or rebound as a result of elastic material behavior. The methods with a penetrating indenter are the most important ones. The applied methods are distinguished, e.g., by the shape of the indenter. Brinell hardness is determined by a ball-shaped indenter, while Vickers hardness applies a pyramid-shaped one. After the indenting test with a certain load, the surface area of the indentation is measured which delivers a value for material hardness. Determination of Rockwell hardness uses the depth of the indentation instead of the surface area (Bargel and Schulze 1988). Independent of the method, the so-called surface hardness... 

The hardness of metals is generally expressed in terms of their resistance to indentation. A hard indenter is pressed into the surface under the influence of a known load and the size of the resulting indentation is measured. A widely used instrument is the Vickers indenter, which gives a pyramidal indentation, and the results are expressed as a Vickers hardness number (kgf mm ). Other... 

The strengths of the Pb-Ag-Ca alloys were experimentally examined using tensile and Vickers hardness tests. The results were compared to the data for a conventional Pb-Ag alloy used as anode material for zinc electrowinning. 

Figure 15 shows the Vickers hardness test results for various alloys. The increase in the Ca content of the Pb-0.5 wt% Ag - Ca alloy was considered to increase the Vickers hardness of the alloy. The rolling rate increased the hardness of the Pb-0.5 wt% Ag - Ca alloy, but after annealing, the hardness decreased. Because the Vickers hardness shows a constant value after annealing at 200 C for 48 h, it was considered that the strain in the anode material could be removed by annealing at 200 C for 48 h. The Pb-0.5 wt% Ag - Ca alloy annealed at 200 C for 48 h after rolling showed the same or better mechanical properties relative to the conventional Pb-1.0 wt% Ag alloy. 

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