New production of (Ti, W)C-based cermets toughened by in-situ formed WC and twinned (Ti, W)C platelets: Carbonization of the Nix(Ti0.6, W0.4)4C-type η phases

Toughening of (Ti, W)C-based cermets is one of the most important field to expand their application in cutting, Wear-resistant materials and equipment used in harsh environment. Modifying the morphology and composition of the ceramic grains is a highly effective measure. Here, we demonstrate a promising cermet toughened by in-situ formed WC or twinned (Ti, W)C platelets with large size around 5-8 μm. A new method is established by carbonization of synthesized η phases, via sintering of the high-energy crushed TiWNiC powders. Results showed that higher Ni/C ratio and temperature could boost the carbonization process, resulting in more Ni6(W1-x, Tix)6C. Only when Ni/C ratio was higher than 1.0, could WC platelets appeared in the cermets. TiC doped WC platelets with no planar defect began to be precipitated at a low temperature by two-dimension growth, along with the formation of fine spherical (Ti, W)C particles. Plate-like twinned (Ti, W)C was only formed by carbonization of Ni2(W1-y, Tiy)4C above 1200 °C, through the twin-assisted growth along {111} planes at a low supersaturation. Platelets could enhance the strength and toughness with slightly decreased hardness, via crack deflection and platelet pull out mechanisms. Compared to the conventional cermets, (Ti, W)CNi with high fracture toughness (15.80 MPa mm1/2), satisfactory strength (1885 MPa) and hardness (88.3 HRA) were achieved. This work provided not only a new method for preparing the (Ti, W)CNi cermets, but also a new insight to modify the final microstructure with controlled properties.