New results on the relationship between hardness and fracture toughness of WC-Co hardmetal

Growth and Microstructure‐Dependent Hardness of Directionally Solidified WC–W2C Eutectoid Ceramics

“…The thermal stability of WC is excellent due to its high melting point (~3000 K); however, because of its refractory nature, sintering of pure WC powder requires very high temperatures . Thus, cobalt and nickel are often added to WC as a second phase to enhance the sintering kinetics via a liquid phase, and the secondary metal phase also leads to enhanced fracture toughness . The mechanical properties of WC–Co composites have been studied, with hardness reported between 11 and 22 GPa, depending on Co concentration and grain size, and fracture toughness has been measured up to 20 MPa‐m 1/2 with 25 wt% cobalt .…”

Mechanical and tribocorrosion properties of HVOF sprayed WC–Co coatings

“…They range from about 21 MPa m 1/2 (E-W) and 15 MPa m 1/2 (L-F) for sample 1 increasing to 33 MPa m 1/2 (E-W) and 23 MPa m 1/2 (L-F) for sample 4, thus confirming the usual trend for microstructured coatings, which results in higher K Ic values with lower hardness values. 18 The value for the standard series 4 is quite high (about 50% higher than all the other samples) and it seems like being out of the typical range of these coating. Nevertheless, the calculated K Ic has to be related to the HVOF spray parameters and to the sample geometry, and can be strongly affected by compressive internal residual stresses generated within the deposit.…”

Application of ASTM C1421 to WC-Co fracture toughness measurement

“…Alternatively, a small crack may have formed, but it may then have been polished away during the subsequent material removal step, or the crack size may have been significantly reduced such that the naturally occurring flaws in the material remained dominant. Over the years, several studies [5,8,22,23,48] have shown that the surface region of WC-Co materials can contain a residual compressive stress and that the magnitude of this stress depends on the surface treatment. Residual stresses as low as a few hundred megapascals, but as high 2-3 GPa, have been measured.…”

“…Since then, many other techniques have been used to measure the toughness of WC-Co materials, including double torsion [3], double cantilever beam [4][5], chevron notch [6][7][8][9][10], notched beam techniques [11][12][13][14][15][16], the single-edge precracked beam method [17][18][19], the surface in crack in flexure method [14,20,21], and various techniques based on measuring cracks from Vickers indentations [9,14,[22][23][24][25][26][27][28][29][30][31][32][33][34]. Two standardized test methods are currently available for determining the toughness of cemented carbides.…”