Vickers hardness scale

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. 

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

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)...

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... 

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

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. 

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). 

The relation between Mohs hardness, M, and the Vickers hardness, V, is not a clear one. However, if diamond (M = 10) is omitted from the Mohs scale, the relationship... 

Mineral or material (in bold the original Mohs minerals) Mohs scale (1822) Rosival scale Ridgeway scale (1933) Povarennyk h scale (1962) Vickers hardness Knopp hardness ... 

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. 

Hardness. The resistance to indentation or deformation of a material is known as its hardness. There are many hardness scales and methods of measurement. Most methods involve indenting a test specimen by impressing a weighted diamond stylus of a prescribed shape on it, and measuring the area or depth of the indentation. The ratio of applied force to area of indention is defined as the hardness. The scales used most frequently for ceramic materials are Mohs, Vickers, Brinnell, Rockwell, and Knoop. These are discussed here. 

Arbitrary hardness scales have been established that allow some correlation between hardness and yield strength. There are a variety of different methods including Brinell, Rockwell, Vickers, and Knoop, each with its own hardness scale. The reader is referred to ASTM Standards ElO, E18, E92, and E384 for details. The primary value of hardness testing is that it provides a nondestructive method for assessing the strength of a material and is useful for certifying that the actual materials used for specific components in a system meet the required material specifications. 

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

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 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 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 ... 

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... 

---