Effect of Cryogenic Treatment on Improving the Fracture Toughness of TiN Coated Cemented Carbide

The 2 mu m thick TiN coatings were deposited by arc ion plating on YW2 cemented carbide substrate, and the system of TiN/YW2 was treated with cryogenic treatment at -196 degrees C for 30 hours. The change of the Rockwell indentation's morphology of the system (the form and density of cracks, the spalling state of the coating)before and after the treatment were investigated by means of the Rockwell hardness tester. With metallurgical microscope and SEM, the change of the microstructure of the substrate and its influence on the fracture toughness of the system were investigated. The results show that after the treatment, the density of the radiated cracks in the substrate were obviously reduced, but the main cracks hadn't any change, the spalling of the TiN coating along the indentation was lightened. After the cryogenic treatment the dispersed granular gamma phase obviously decreased or even disappeared, the pores became smaller and the microstructure of YW2 became more compact, and the microcracks were merged during the cryogenic treatment. These are beneficial to improve the fracture toughness of YW2 substrate and the coating/substrate system.