Indentation Size Effect for the Hardness of Refractory Carbides

Abstract

This study measured the Vickers hardness of the sintered refractory carbides B4C, Mo2C, NbC, TiC, V8C7, W2C, WC, WC–SiC, and ZrC over a wide range of test forces between 0.49 and 196 N. The results showed an indentation size effect (ISE), with hardness values that increased with decreasing test force for the carbides. The test force dependence of the hardness was analyzed by the proportional specimen resistance (PSR) model. The value of the a1 term that reflects the elastic resistance in the model was obtained for the carbides and compared with their measured elastic, shear, and bulk moduli. It was not clear what type of modulus related strongly to the a1 term. There was a strict correlation between the hardness at an infinite test force and at a test force of 9.8 N. However, the hardness at a test force of 0.49 N a little poorly reflected the hardness at an infinite test force. The hardness at low test forces must be corrected using the a1 value in comparing it with the hardness at a test force of 9.8 N recommended for the Vickers hardness test by the Japanese Industrial Standard.