Diamond hardness anisotropy

Ceramics with cubic F structures and lllKHO) slip systems exhibit the same hardness anisotropy as fluorite structure solids with 001 (110) slip systems in the sense that the hardest directions on 100 are (100) and the softest are (110). Thus in order to determine which system is operative, a combination of the analysis given in Section 3.6.1 and other techniques, such as slip line analysis, is necessary. Ceramics with the diamond cubic structure have this slip system, and the parallel of their hardness anisotropy with that of fluorites can be seen by comparing the results for cubic boron nitride, BN, with the InP data in Figure 3.7. 

Radiation damage can, in some samples, introduce a degree of plasticity for example, in diamond the overall hardness is reduced after irradiation but there are no data showing what this does to the Knoop hardness anisotropy. We can, however, note that radiation damage in MgO increases the overall hardness but does not affect the anisotropy, a fact that seems to be general for the rock-salt structure. ... 

Because this is not a commonly encountered indenter and because of the restricted type of plane that it can usefully investigate, there are very few results from which to draw conclusions. However, for cubic crystals the difference between those having 001 (011) slip systems and the other types is evident in the symmetry of the hardness anisotropy curves as it was in the case of the Knoop indenter and the Vickers diamond. 

Barium titanate (BaTi03), strength after indentation, 185 Barrel indents, 44-126 BeBg Knoop hardness, 303 Beevers-Ross sites, 280 Berkovich hardness anisotropy, 94 diamond, 11, 39-40 equation, 11... 

Penetration depth hardness scale, 46-47 and Rockwell scales, 47 and scratch hardness, 62-63 of various diamonds, 41 Penny crack growth, 156, 170 Penny shaped flaw, 150-161 Periclase, 264 Perovskites, 286-290 cracked indent in, 66 hardness anisotropy, 77, 93, 288-289 structure, 286-287 tolerance factor equation, 287 Peters equation, 176 pH... 

The most striking feature of the collected data in the tables in this chapter and in Chapter 6 on anisotropic indentation hardness values for crystalline ceramics is its dependence on the relevant active slip systems. This has been extended by observation to encompass materials beyond ceramics. Thus, the nature of anisotropy for a soft, face-centered cubic metal may be the same as for hard, covalent cubic crystals like diamond, since they both have lll (lTo) slip systems. Consequently it is natural that, in order to develop a universal model, we should first look for explanations based on mechanisms of plastic deformation. 

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