Experimental study of indentation fracture toughness in HVOF sprayed hardmetal coatings

In this study, indentation fracture toughness in HVOF-sprayed WC-12%Co, WC-17%Co, Cr3C2-25%NiCr, Cr3C2-25%CoNiCrAlY and WC-CrC-7%Ni coatings was determined by the Vickers indentation test for various loads. Relations proposed by Chicot were used to calculate the value of KIc under conditions of the Palmqvist, intermediate and radial-median cracking modes. The loads for transition between the cracking modes were determined, and the potential for an intermediate cracking mode was demonstrated. The intermediate cracking mode equation proposed by Chicot successfully removed strong load dependence that was present in equations for Palmqvist and radial-median cracking mode. On the other hand, the substantial assumption of his equation was shown not to be valid for tough HVOF sprayed hardmetal coatings.