Microhardness of known abrasives

- May 21, 2018 -

    Microhardness of common abrasives


The hardness of abrasives is now expressed in terms of microhardness. Microhardness is a type of indentation hardness that reflects the ability of a measured object to resist pushing into from another hard object. The measuring instrument is a microhardness tester, which is actually a microscope equipped with a loading device having an eyepiece micrometer. Before the measurement, the abrasive to be measured is made into a reflective polishing sample, placed on the micro-hardness tester's stage, and the quadrangular pyramidal diamond indenter is pressurized by a loading device. The amount of the load can be increased or decreased depending on the hardness of the material being tested. After the diamond indenter was pressed into the specimen, a pit was created on the surface of the specimen. The microscope reticle is aligned with the pit and the length of the diagonal of the pit is measured with an eyepiece micrometer. Based on the applied load and the diagonal length of the pit, the microhardness value of the measured substance can be calculated.


Due to the different diamond indenters used, the microhardness is subdivided into Vickers microhardness and Knoop microhardness.


The Vickers microhardness is a 130° diamond quadrangular pyramid for the press head. The value is calculated as follows:




Where: HV-Vickers hardness, Mpa;


P-load, kg;


D-dimple diagonal length, mm.


The Knoop hardness is made using a diamond quadrangular pyramid with a corner angle of 170°30′ and 130° as its insertion point. The value is calculated according to the following formula:


In the formula:

HK-Knoop hardness, Mpa

P-load, kg

L-dimple diagonal length, mm.

Vickers hardness is used in countries in China and Europe, and Knoop hardness is used in the United States. Megapascals (MPa) is the legal unit of measurement for microhardness, and kg/mm2 is the previously used hardness calculation unit. The conversion formula between them is 1 kg/mm2 = 9.80665 Mpa. The microhardness of commonly used abrasives is shown in the table below.


Abrasive             Vickers Microhardness/Mpa(kg/mm2)


Brown fused alumina         19,600~21,600 (2,000~2,200)

White corundum         21,600~22, 600 (2,200~2,300)

Chrome corundum 21,600~22,600 (2,200~2,300)

Monocrystaline corundum 21,600~23,500 (2,200~2,400)

Microcrystalline corundum 19,600~21,600 (2,000~2,200)

Bauxite sintered corundum 16,700 (1,700)

Zirconia                 14,700 (1,500)

Diamond         78,500 (8,000)

Boron carbide         49,000 (5,000)

Silicon carbide         30,400~3,330 (3,100~3,400)

Garnet                 13,300 (1,360)

Silicon                 8,000 (820)