Vickers scale

Figure 1.3 compares the Moh scratch scale with the more quantitative Vickers scale (Gilman, 1973). Clearly the two scales are not linearly related. Each has its own realm of application. For brittle minerals, and similar materials, the Moh scale is most useful. For ductile materials like metals the Vickers indentation scale can detect small differences more readily. Note that the range on the Vickers scale is large about 1000, while range of the Mohs scale is about 10. 

TABLE 8.1. Hardness Values of Various Materials on the Vickers Scale... 

The hardness of industrial hardmetal grades is characterized preferentially by the Rockwell A scale [1] in the USA [2] and by the Vickers scale [3] in Europe. Most research work, however, has been carried out, also in the USA, using the Vickers scale. Most of the results reported below were obtained using standard pyramidal Vickers indenters [3]. 

The hardness of the metal as deposited on the filament is typically 40 on the Vickers scale, although it varies from batch to batch according to the purity. 

The hardness of a material quantifies its resistance to permanent shape changes induced by applied mechanical forces such as fiiction or indentation by a sharp object. Scratch resistance is often measured on the Moh 1-10 scale and indentation hardness on the Vickers scale. Single crystal nonporous silicon has a Moh scale hardness of 6 (for comparison, diamond is 10, quartz is 7, calcium carbonate is 3, talc is 1). It has a Vickers hardness of 11.5 GPa. There have now been a few studies of the indentation hardness of porous silicon, with typical values for different types of porous silicon listed in Table 2. 

Percussion test The specimen shall be placed on a sheet of lead which is supported by a smooth sohd surface and struck by the flat face of a mild steel bar so as to cause an impact equivalent to that resulting from a free drop of 1.4 kg through 1 m. The lower part of the bar shall be 25 mm in diameter with the edges rounded off to a radius of (3.0 0.3) mm. The lead, of hardness number 3.5 to 4.5 on the Vickers scale and not more than 25 mm thick, shall cover an area greater than that covered by the specimen. A fresh surface of lead shall be used for each impact. The bar shall strike the specimen so as to cause maximum damage. 

Nanoskiving forms intact stmctures from films of relatively soft and compliant metals (softer than platinum, or those with bulk values of hardness < 500 MPa, Vickers scale), while hard and stiff materials tend to fragment (those harder than irickel, or >500 MPa). The Whitesides laboratory has successfully formed nanostmctures of aluminum, copper, silver, gold, lead, bismuth, palladium, platinum, nickel, germanium, silicon dioxide, all conducting and semiconduaing polymers tested, and films of lead sulfide nanocrystals. ... 

A HMT lathe (NH22) is used for turning EN8 steel of hardness number 190 on the Vicker scale (with a load of 20 kgs. using a pyramidal indentor). The uncoated carbide inserts used are - SPUN 120308, grade P20-P30, normal rake 6 deg., front clearance angle 11 deg., make WIDIA. 

Hardness, Mohs scale Hardness, Rockwell Hardness, Vickers ... 

Conversion to other hardness scales from Vickers is approximated for specific materials Hsted in ASTM E140 (2). Conversions outside the stated areas should be avoided unless supported by test data. 

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. 

Snccessful full-scale tests on quenching of deflagrations and detonations using expanded metal cartridge flame arresters were performed to USCG standards on Group C and D gases by Westech Industrial Ltd. (Lapp 1992, Lapp and Vickers 1992). 

Figure 1.3 Correlation between the Moh scratch hardness and Vickers indentation hardness scales.

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). 

Human studies and rodent experiments demonstrating the potential for CCM to reduce the risk of tooth enamel erosion are included in the patent of Andon et ah (1992). One experiment assessed rats provided with soft drink, soft drink with added CCM, or water as their only source of fluids for 21 days. Based on a predefined erosion scale, the average extent of dental erosion compared to the unfortified soft drink was 4.5 and sixfold less in water and soft drink + CCM, respectively. Another study used the Vickers hardness measurement to assess the mean ( SEM) reduction in surface hardness of human enamel specimens (n = 8 per group) immersed for 60 min in 15 ml of OJ (-101 8.7), OJ + CCM (0.9 5.8), grapefruit juice (-130 12.7), grapefruit juice + CCM (2.8 6.4), or... 

Mohs hardness is a measure of the relative hardness and resistance to scratching between minerals. Other hardness scales rely on the ability to create an indentation into the tested mineral (such as the Rockwell, Vickers, and Brinell hardness - these are used mainly to determine hardness in metals and metal alloys). The scratch hardness is related to the breaking of the chemical bonds in the material, creation of micro fractures on the surface, or displacing atoms in the metals of the mineral. Generally, minerals with covalent bonds are the hardest while minerals with ionic, metallic, or van der Waals bonding are much softer. 

Fig. 4.1.1. Comparison of Mohs hardness degrees with Vickers hardness logarithms for standard blocks of the Mohs scale. (After Bowden and Tabor, 1964)...

Ridgeway scale Vickers Bohme Friatester Equotip apparatus... 

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... 

Fig. 4.2.1. Comparison of old and new Mohs scale with Khrushchev hardness classes and Vickers hardness. (After Povarennykh, 1963)...

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... 

Hardness measured in units of Mohs scale Mineral Chemical formula Measured 1 Vickers Hv (with micro- measurement) lardness Rnoop hk. - H0 in nl >0 i Khrushchev tr° yC° hardness efficient. 1f classes A h = Ho Hl = 0.7 /Hv Htheor calculated by Pova-rennykh (1963) Optimum load of indenter P, mN ... 

Comparison of Rockwell hardness HRB with Rockwell (other scales), Brinell and Vickers hardness for soft metals... 

With the rapid advances now observed in hardness test methods (Vickers, Knoop, Grodzinski, Berkovich and Hanneman diamond indenters or Brinell and Rockwell hardness testers, etc.), the 10-degree Mohs scale poses a number of problems owing to the low distinction of hardness... 

The tests made with minerals of the Mohs scale (Section 4.4) revealed a close dependence of dynamic abrasiveness with the Mackensen blower on Vickers hardness of tested material. 

---