Vickers microhardness

Wood, Wyedeven, and Tsuji [57] RFPECVD/ Hydrocarbon/N2 16 Vickers microhardness 0.4-0.8 10-20... 

Franceschini, Achek, and Freire [12] RFPECVD/CH4-N2 II Vickers microhardness 1.5-2.4 19-21... 

For the structural applications of materials, there is no more useful measurable property than mechanical hardness. It quickly and conveniently probes the strengths of materials at various scales of aggregation. Firstly, it does this at the human scale (Brinell hardness—millimeters to centimeters). Secondly, it does so at a microscopic scale (Vickers microhardness—1 to 100 microns). And thirdly, it does so at a nanoscale (nanoindentation—10 to 1000 nanometers). 

Hardness is essentially a measure of stiffness and in principle can be related to modulus. For plastics, the term hardness refers to resistance to indentation but depending on the test method the measurement is made either with the indentation load applied or after its removal when elastic recovery has taken place. The standard methods are given in ISO 868 (Shore) [6] and ISO 2039 (Ball indentation and Rockwell) [7]. However, Vickers microhardness is more satisfactory for monitoring degradation of rigid materials. 

In the second approach shown in Fig 3.12(b), a force is applied continuously using a Vickers microhardness indenter to compress the fiber into the specimen surface (Marshall, 1984). For ceramic matrix composites where the bonding at the interface is typically mechanical in nature, the interface shear stress, Tf, against the constant frictional sliding is calculated based on simple force balance (Marshall, 1984) ... 

Fig. 3.12. Schematic drawings of indentation (or liber push-out) techniques using (a) a spherical indenter (b) a Vickers microhardness indenter (c) on a thin slice. After Grande ct al. (1988).

Fig. 5.2. Effect of Cr203 content on Vickers microhardness in the system Cr203-Al2O3-O specimens sintered at 1870 K for 5 h in H2+H20 O specimens sintered at 1970 K for 5 h in air. (After Shinozaki et al., 1980)...

Table 1.3 Vickers microhardness (kg mm 2) of elements and compounds at room temperature...

Polish rate vs. Vickers microhardness in oil slurry. (From Ref. (3).)... 

Deformation induced by indentation. The deformation induced in single crystals of San Carlos (Arizona, USA) olivine around the in-denter in a Vickers microhardness test has been studied by Gaboriaud... 

Following the work of Loubet et al., Young s modulus ( ) and Vickers microhardness can be extracted from the unloading part of load-displacement... 

Depth-sensing microindentation allows the reliable determination of Young s modulus and Vickers microhardness of the different phases made of grains larger than 2 to 5 jm. Variations in chemical bonding and short-range order can be extracted from the intensity, wave number, and bandwidth of Raman peaks. The wave number shifts can be used to map the strain (and calculate the stress). Analysis of the bandwidth offers a tool to ascertain whether the wave number shift is strain induced or related to structural evolution of the Raman probe. 

As we have seen in Section 1.1, Vickers microhardness measurement uses as the indenter a square-based diamond pyramid about 100 qm in height. The included angles between opposite faces are a = 136°. This corresponds to the tangential angle of an ideal ball impression, considered to have a diameter equal to 0.375 times that of the ball (Tabor, 1951). The pyramid is pressed under a load P into the polymer surface to form a plastic deformation. When the indenter is removed the diameter of the indentation is measured and its area determined. The mean pressure p over the indentation is then... 

Figure 2.3. Sample size ratios for Vickers microhardness testing the correct ratio of the diagonal length d and the thickness of a layer for a cross-section measurement has to be 2d. (From Kleinhartepriifer DURIMET, Ernest Leitz GmbH, Wetzlar, Liste 72-5a, 1964.)...

The Vickers microhardness test gives a smaller indentation for a given force than the Knoop test and is less sensitive to material anisotropy. The Knoop test is easier to use because the impression is longer for a given load and usually only one measurement per test is required. The microhardness measurement with the Knoop diamond is quite sensitive to material anisotropy because of the twofold symmetry of indentation. Nevertheless, the Vickers diamond, as we shall show below, also detects anisotropy conveniently (Balta Calleja Bassett, 1977 Balta Calleja et al, 1980a). 

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. 

Fahad Hasan, Wang and Berndt (2014) investigated the Vickers microhardness of the cross- section as well as the top surface of plasma-sprayed polished hydroxyapatite coatings. The effects of applied load, measurement direction and indent location (Figure 7.55) on the microhardness were investigated. Indentation was performed on dense and porous areas of the coatings. After Vickers indentation,... 

Yovanovich et al. [140] and Hegazy [35] recognized the importance of the effect of work-hardened layers on the deformation of the contacting asperities. They proposed an iterative procedure to obtain the appropriate value of the contact microhardness Hc from Vickers microhardness Hv measurements [41,114]. Song and Yovanovich [102] reported the explicit expression for calculating the relative contact pressure ... 

S. Song and M. M. Yovanovich, Relative Contact Pressure Dependence on Surface Roughness and Vickers Microhardness, AIAA Journal of Thermophysics and Heat Transfer (2/1) 43-47,1988. 

PP-g-SBH copolymers cocrystallize completely with bulk iPP, which increases PP crystaUinity degree part of the SBH component (SBH grafts of PP-g-SBH copolymers and bulk SBH) enters the mutual amorphous phase of the blends, leading to a decrease of the intensity of the SBH peak. That means each part of the compatibilizer is miscible with the corresponding bulk phase of the blend. The compatibilized iPP/LCP blends display improved crystallization kinetics, enhanced degree of crystallinity, and improved interphase adhesion (37,38). Consequently, an improvement of the mechanical characteristics should be expected for these blends. In fact, the investigation of the Vickers microhardness of uncompatibilized and... 

Nitrides and carbides are also considered among the hardest materials. Table 5.2 shows data for the measured Vickers microhardness for these compounds. Such measurements are performed using a diamond indenter with square geometry. The indenter is forced towards the surface of the material and the diagonal of the microindentation is measured. In all cases, carbides and nitrides are significantly harder than the pure metals and are also comparable or superior to that of ceramic materials. 

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