Fracture of WC–Ni cemented carbides with different shape of WC crystals q A.V. Shatov a,b, * , S.S. Ponomarev a , S.A. Firstov a a Frantsevich Institute for Problems of Materials Science, 3 Krzhizhanovsky St., 03680 Kiev-142, Ukraine b Mercer Management Consulting, Inc., 125 Village Boulevard, Suite 270, Princeton, NJ 08540, USA Received 25 February 2007; accepted 18 March 2007 Abstract The dependences of fracture toughness and crack propagation on the shape equiaxiality of WC crystals are studied on WC–Ni cemen- ted carbides with small addition of TiC. The fracture toughness K 1C linearly correlates to mean linear path in binder phase regardless of the shape and contiguity of WC crystals as well as despite of the fracture path change in studied WC–Ni cemented carbides. It is exper- imentally shown that the fracture toughness K 1C does not correlate versus contiguity of carbide crystals on WC–Ni cemented carbides when shape of WC crystals is changed. The relative amount of trans-crystalline fracture through the carbide crystals and the total area of fracture through the carbide phase increase, whereas, the relative amount of inter-crystalline fracture along carbide–carbide boundaries decrease on WC–Ni cemented carbides with flatter WC crystals and lower values of contiguity of WC crystals. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Cemented carbides; Fracture toughness; Crack path; Shape of carbide crystals 1. Introduction The fracture of cemented carbides is believed to be a two-step process. The brittle inter- and trans-crystalline fracture of carbide phase is followed by the ductile rup- ture of binder phase and carbide–binder interfaces [1– 12]. The area fraction of crack path through the carbide phase accounts for at least 50–80% of the fracture surface area of cemented carbides and increases with the amount of carbide phase V C V in the alloy [5–7,13–17]. The increas- ing value of the mean linear intersect d of WC crystals causes the increase of the ratio of the surface area of trans-crystalline fracture through the carbide crystals (C) versus the inter-crystalline fracture of the carbide phase (C/C) and at the same time the increase of the ratio of the surface area of the fracture through the binder phase (B) versus the fracture along the carbide–binder interfaces (B/C) regardless of the volume fraction of the carbide phase V C V in the alloy [5–7,13–17]. However, it is believed that the rupture of the carbide phase makes a minor con- tribution to the fracture toughness of the cemented car- bides due to relatively low value of the critical strain energy release rate of carbides (for WC G 1C  50 J/m 2 ) compared to that of the cemented carbides (200–500 J/m 2 ) [4,5,7,18–20]. The major contribution is made by the plastic deformation and rupture of the binder phase ligaments and carbide–binder interfaces. Despite the theoretical estimations of fracture energies, two experimental correlations of fracture toughness versus the mean linear path in binder phase k and versus the car- bide crystals contiguity G are observed simultaneously (Fig. 1) [1,17]. The fracture toughness K 1C increases line- arly with k (Fig. 1a) but decreases with the contiguity G (Fig. 1b). 0263-4368/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijrmhm.2007.03.002 q This paper was partially presented at the 16th Plansee Seminar, Reutte, Austria, May 2005. * Corresponding author. Address: 8 Parkside Drive, Jamesburg, NJ 08831, USA. Tel./fax: +1 732 605 0416. E-mail address: alex_shatov@hotmail.com (A.V. Shatov). www.elsevier.com/locate/IJRMHM Available online at www.sciencedirect.com International Journal of Refractory Metals & Hard Materials 26 (2008) 68–76