The hardness of SiC ceramics plays a significant role in their performance as armormaterials.Different hardness measurement techniques and loads,however,substantiallyinfluence the hardness values of ceramics,making it difficult to make material comparisons andrelate these to performance.In this study hardness tests were performed with:(ⅰ)monocrystallinealpha-and beta-SiC crystals,(ⅱ)polycrystalline,sintered (pressureless/gas-pressure sintered)alpha-SiC materials,and (ⅲ)hot-pressed (uniaxially/isostatically)alpha-SiC materials.Hardnessnumbers were measured by indentation with Knoop and Vickers diamonds in the load rangefrom 0.245 N to 4.9 N on a Leitz Miniload-2 tester.At loads over 0.98 N hardness decreasedwith increasing load.Highest values for Knoop and Vickers hardness at constant load wereobtained with the SiC single crystals.In most cases it was found that Vickers hardness is higherthan Knoop hardness.In the hot isostatically pressed SiC (encapsulated HIP-SiC)the Vickersand the Knoop numbers were found to be identical.Furthermore,it was observed that dopingelements like Al and B have an effect on hardness.Al-doped SiC ceramics exhibited lowerhardness numbers than pure or B-doped materials and,additionally,in these materials the Knoophardness is higher than the Vickers hardness.Liquid phase sintered SiC showed lowest hardnessnumbers due to the secondary phase and solubility of Al in the SiC-lattice.
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