Effect of cryogenic treatment on mechanical properties of TiN coated cemented carbide

TiN coatings with thickness of 2 μm were deposited on YW2 cemented carbide substrate by arc ion plating. The YW2 cemented carbide was then cryogenically treated at -196°C for 30 h. The phase structure and hardness of the coatings before and after the treatment were investigated by XRD and microhardness tester. The morphology of the indentation for hardness tests of the cemented carbide before and after the treatment was observed. Microstructure of the substrate and its influence on fracture toughness of the cemented carbide with TiN coatings were investigated by means of metallurgical microscope and SEM. The results show that after the treatment, the hardness of the material is enhanced because of the preferred orientation along (111) plane of TiN that caused by torsion of grains during cryogenic treatment. After the treatment, the number of the radia cracks formed during hardness tests in the substrate is obviously reduced and the massive spalling of the TiN coatings along the indentation is lightened. The dispersively distributed granular γ phases obviously decrease or even disappear, the porosity becomes smaller and the microstructure of YW2 cemented carbide becomes more compact, and the microcracks are merged during the cryogenic treatment. These are beneficial to improve fracture toughness of YW2 substrate with and without TiN coatings.