Measurement of Microhardness

Metallographic investigations and determination of microhardness testify that upon titanium oxidization the dissolution of oxygen in the surface layer of metal occurs simultaneously with formation of oxide film. The results of measuring of microhardness of surface layer, metallic matrix and depth of gas saturation show that the layer of metal adjacent to the scale has the increased hardness. Microhardness of surface layer is considerably more... 

The only reported measurement of microhardness was made by Kempter and Krikorian (1962). ThCo.99 and ThC2 gave 850kg/mm and 600kg/mm (200 g DPH), respectively. 

Fig. 14, p. 74, shows the phase diagram based on X-ray and thermal analyses, microstruc-tural investigations, and measurements of microhardness. The diagram reveals the existence of five intermetallic phases LaSe, a solid solution phase between the compositions La3Se4 and... 

Microhardness was measured at room temperature up to 30% overall relative deformation, e (when fracture occurs). As in the aforementioned measurements of microhardness under strain, in the present case also a deformation step of = 5% was adopted. 

Ber] Amorphous ribbons and crystallized samples of compositions (Cr Fci c)83Bi7 and (Cr,Fei ,)goB2o (0 < x < 25) were examined with DSC, XRD and measurements of microhardness. Crystallization behaviour and microhardness were studied. 

Testing. Chemical analyses are done on all manufactured abrasives, as well as physical tests such as sieve analyses, specific gravity, impact strength, and loose poured density (a rough measure of particle shape). Special abrasives such as sintered sol—gel aluminas require more sophisticated tests such as electron microscope measurement of a-alumina crystal si2e, and indentation microhardness. 

Ultrasonic Microhardness. A new microhardness test using ultrasonic vibrations has been developed and offers some advantages over conventional microhardness tests that rely on physical measurement of the remaining indentation size (6). The ultrasonic method uses the DPH diamond indenter under a constant load of 7.8 N (800 gf) or less. The hardness number is derived from a comparison of the natural frequency of the diamond indenter when free or loaded. Knowledge of the modulus of elasticity of the material under test and a smooth surface finish is required. The technique is fast and direct-reading, making it useful for production testing of similarly shaped parts. 

The wide use of microhardness testing recently prompted Oliver (1993) to design a mechanical properties microprobe ( nanoprobe would have been a better name), which generates indentations considerably less than a micrometre in depth. Loads up to 120 mN (one mN 0.1 g weight) can be applied, but a tenth of that amount is commonly used and hardness is estimated by electronically measuring the depth of impression while the indentor is still in contact. This allows, inter alia, measurement... 

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

The Knoop test is a microhardness test. In microhardness testing the indentation dimensions are comparable to microstructural ones. Thus, this testing method becomes useful for assessing the relative hardnesses of various phases or microconstituents in two phase or multiphase alloys. It can also be used to monitor hardness gradients that may exist in a solid, e.g., in a surface hardened part. The Knoop test employs a skewed diamond indentor shaped so that the long and short diagonals of the indentation are approximately in the ratio 7 1. The Knoop hardness number (KHN) is calculated as the force divided by the projected indentation area. The test uses low loads to provide small indentations required for microhardness studies. Since the indentations are very small their dimensions have to be measured under an optical microscope. This implies that the surface of the material is prepared approximately. For those reasons, microhardness assessments are not as often used industrially as are other hardness tests. However, the use of microhardness testing is undisputed in research and development situations. 

Durometer hardness is defined as the measure of resistance to indentation using either a macro- or microhardness tester. To the pharmaceutical drug manufacturer, hardness is important because of its relationship to ultimate mechanical properties— particularly modulus. In general, softer compounds of the same elastomer base have better coring and reseal properties, whereas harder compounds tend to process better on high-speed filling lines. 

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. 

Up to today it has been impossible to measure reproducible microhardness data of non-metallic crystals. This was due to the too high indentation forces of commercial available hardness testing devices. Today with the new ultra-microhardness devices, which allow to reduce the indentation force down to 5 - 10 N, it is no longer the limiting problem to measure the Vickers hardness of such brittle crystals. 

Five to ten rows of microhardness intentations, typically at a load of 0.196 N (20 g), were put onto the surface of any Ni-Bi cross-section in the direction of diffusion at different places of the Ni-Bi interface. The layer thickness at each annealing time was thus taken as the average of five to ten measurements. The experimental results were treated using standard statistical methods. 

For initial alloy and the hydrogenation products the values of microhardness are measured, which have appeared equal 337 50 and 565 51 kg/mm2, accordingly. The microhardness of the samples which have stayed after realization... 

Teeth fulfill very specific functions and it can be safely assumed that the tooth structure is finely tuned for this purpose. The dentin structure is clearly anisotropic, with all the mineralized fibrils being located on one plane, and all the tubules oriented perpendicular to this plane. It is therefore most surprising that in terms of microhardness, dentin is isotropic. This has recently been confirmed in a careful study in which root dentin microhardness was measured at the same precise location in three orthogonal directions [33],... 

An attractive method to produce single crystals (in the dimension range from pm to several nun) is the high-temperature solution (flux) method, becanse of its simphcity and the low temperature required. The elements are dissolved in the solvent metal (often Al) and subseqnently the solntion is slowly cooled to room temperature. A prerequisite is, of course, that the solubility of the used solvent in the desired boride is insignificant. The solubility of Al in most boron-rich binary borides has been found to be extremely small. Crystals prepared in this manner are suitable for measurement of physical properties, for instance, microhardness, electrical resistivity, and so on. 

The measurement of local mechanical properties is an important step in understanding of the macroscopic behavior of multiphase materials. The indentation hardness test is probably the simplest method of measuring the mechanical properties of materials. Figure 12.2b shows the evolution of the microhardness as a function of the thermal treatment temperature of a Nasicon sample. The use of load-controlled depth-sensing hardness testers which operate in the (sub)micron range enables the study of each component of the composite more precisely. 

Freitag F, Kleinebudde P. How do roll compaction / dry granulation affect the tableting behaviour of inorganic materials Microhardness of ribbons and mercury porosimetry measurements of tablets. Eur Pharm Set 2004 22 325-333. 

Another motivation for measurement of the microhardness of materials is the correlation of microhardness with other mechanical properties. For example, the microhardness value for a pyramid indenter producing plastic flow is approximately three times the yield stress, i.e. // 3T (Tabor, 1951). This is the basic relation between indentation microhardness and bulk properties. It is, however, only applicable to an ideally plastic solid showing no elastic strains. The correlation between H and Y is given in Fig. 1.1 for linear polyethylene (PE) and poly(ethylene terephthalate) (PET) samples with different morphologies. The lower hardness values of 30-45 MPa obtained for melt-crystallized PE materials fall below the /// T cu 3 value, which may be related to a lower stiff-compliant ratio for these lamellar structures (BaM Calleja, 1985b). PE annealed at ca 130 °C... 

Scratch tests have been used for microhardness measurements of polymeric materials (Bierbaum Scratch Hardness Test (ASTM D 1526)). These tests are related to cuts and scratches, and, to some extent, to the wear resistance of materials. Scratch tests are not always related to the resistance to local deformation and they are now being replaced by the preferred indentation test. 

In the last two decades the value of microhardness measurement as a technique capable of detecting a variety of morphological and textural changes in crystalline polymers has been amply emphasized leading to an extensive research programme in several laboratories. This is because microindentation hardness is based on plastic straining and, consequently, is directly correlated to molecular and supermolecular... 

Microindentation hardness is currently measured by static penetration of the specimen with a standard indenter at a known force. After loading with a sharp indenter a residual surface impression is left on the flat test specimen. An adequate measure of the material hardness may be computed by dividing the peak contact load, P, by the projected area of impression (Tabor, 1951). The microhardness, so defined, may be considered as an indicator of the irreversible deformation processes which characterize the material. The strain boundaries for plastic deformation below the indenter are critically dependent, as we shall show in the next chapter, on microstructural factors (crystal size and perfection, degree of crystallinity, etc.). Indentation during a microhardness test permanently deforms only a small volume element of the specimen (V 10 -10 nm ) (non-destructive test). The rest of the specimen acts as a constraint. Thus the contact stress between the indenter and the specimen is much larger than the compressive yield stress of the specimen (about a factor of 3 higher). 

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