Hardness testing on advanced technical ceramics

To validate the European standard ENV 843-4 for hardness measurements on ce ramics, three classes of ceramic materials, silicon nitride, silicon carbid e, and aluminium oxide: involving 19 ceramics in total, were tested using t he traditional techniques Vickers (HV1), Knoop (HK2), and superficial Rockw ell (HR45N). The use of new ceramic reference blocks certified according to the standards ISO 4547 and ISO 6507-1 for metallic materials was studied. If the hardness response of the tested materials does not involve chipping and cracking the application of high hardness reference blocks for training users to obtain hardness values comparable with the certified HV1 and HK2 values improves the reproducibility from about 10% to 1 to 3%. The scatter between the laboratories is similar to the scatter within the laboratories. The measurement of the indentation geometry on typical commercial ceramic materials call be made only with higher scatter and reduced reproducibility compared with typical metallic materials, which is caused by the stochasti c indentation response. For such materials involving chipping and cracking (for instance SiC), the application of reference blocks with well-shaped in dentations does not provide improved comparability of results between the l aboratories, The actual indentation response of the ceramic material tested must be considered before selecting the appropriate hardness technique and test force. There is no significant difference between the abilities of th e hardness techniques HV1, HK2, and HR45N to discriminate sensitively betwe en materials of closely similar properties. (C) 2001 Elsevier Science Ltd. All rights reserved.