Letter | Published:

Indentation Hardness of Diamond



RECENTLY, S. Tolansky and V. R. Howes1 published some data on indentation compression strength with a diamond ball (0.39 mm. radius) on differently orientated diamond faces. They obtained values for the pressure which caused cracking on different diamond faces ranging from 1.2 to 1.8 × 1011 dyne-cm.−2 (1,200–1,800 kgm./mm.2). By comparing these values with those quoted in the literature it appears that they are extremely low : F. Auerbach2, absolute hardness of diamond 2,200 kgm./mm.2; Knoop, hardness3 of diamond 6,500–8,500 kgm./mm.2; Russian tests with triangular pyramids4 and my own tests5 with the same type of indenter indicated hardnesses greater than 14,000 kgm./mm.2. Recent tests with double cone indenters (radius 2 mm., included angle 154°) showed that diamond surfaces could be loaded to well over 3,000 kgm./mm.2 without showing any form of cracks even when investigated with the electron microscope (by courtesy of Mr. M. Seal, Cambridge).

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  1. 1

    Howes, V. R., and Tolansky, S., Proc. Roy. Soc., A, 230, 294 (1955).

  2. 2

    Auerbach, F., Smithsonian Report, 4, 207 (1891).

  3. 3

    Knoop, Indust. Diamond Rev., 4, 103 (1944).

  4. 4

    Khrushchov, M. M., and Berkovich, E. S., Zavodskaya Lab., (2), 193 (1950); Indust. Diamond Rev., 11, 42 (1951).

  5. 5

    Grodzinski, P., and Stern, W., Indust. Diamond Rev., 11, 48 (1951).

  6. 6

    Hertz, H., “Miscellaneous Papers”, (London, 1896).

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