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Die Belastungsabhängigkeit der Knoophärte der SiC Keramik in einem breiten Belastungsbereich
Author(s) -
Majić M.,
Ćurković L.,
Ćorić D.
Publication year - 2011
Publication title -
materialwissenschaft und werkstofftechnik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.285
H-Index - 38
eISSN - 1521-4052
pISSN - 0933-5137
DOI - 10.1002/mawe.201100754
Subject(s) - knoop hardness test , indentation , materials science , ceramic , indentation hardness , composite material , silicon carbide , hardness , vickers hardness test , microstructure
Silicon carbide (SiC) ceramics is a material with increasing use, due to its excellent mechanical properties, especially high hardness. In order to integrate this material into design process, we need to know its hardness as precise as possible. The Knoop hardness number ( HK ) is calculated using the expression: HK = α·F/d 2 , where F is the applied load, d is the long diagonal of the resulting 1 0 indentation and a is the Knoop indenter geometrical constant. In this paper, the Knoop hardness of SiC ceramics was measured in the applied load range from 4.9 to 98.07 N. For some materials measured “apparent” hardness value decreases with increasing applied test load (normal indentation size effect – ISE), while for some materials measured “apparent” hardness increases with increasing applied test load (reverse indentation size effect – RISE). Obtained results show the measured hardness exhibits the ISE. In the literature several models are given for the phenomenon explanation. We used the following models: Meyer's law (F = K·d n ), proportional specimen resistance – PSR (F = a 1 ·d + a 2 ·d 2 ) and modified proportional specimen resistance – MPSR model (F = a 0 + a 1 ·d + a 2 ·d 2 ). Results of regression analysis for all applied models show they can all be used for ISE analysis. “True” hardness was determined based on the PSR and MPSR model (HK T = α·a 2 ). The obtained results were similar. If the specimen surface is carefully prepared and the range of loads is wide, the a 0 coefficient from MPSR model reaches small values and can be excluded. Therefore, for the calculation of SiC ceramics Knoop hardness, the simpler model (PSR) can be used.