Research on the mechanical and tribological properties of multilayer toughened cBN/NCD tool coatings
摘要
In the paper, the cBN/NCD (nano-crystalline diamond/cubic boron nitride) multilayer coatings with varying modulation ratios (defined as the thickness ratio of NCD to cBN layers) were fabricated via alternating deposition of NCD and cBN layers. The microstructure and mechanical properties of cBN/NCD multilayer coatings were systematically characterized as a function of modulation ratio. The prepared coatings are dense and the thickness is uniform. Residual stress are compressive stresses in all coatings, and have a significant reduction as the modulation ratio increased. Fracture toughness shows a gradually increasing trend. The bonding strength between the coatings and substrates are significantly enhanced. When the modulation ratio is increased to 7:3, residual compressive stress is only 0.43 GPa and the fracture toughness rises to 4.98 MPa m1/2. The reason for improvement of fracture toughness is attributed to the increased number of interfaces and higher NCD proportion, which can inhibit crack propagation and effectively prevent coating delamination. Besides, although the friction coefficient increases slightly, the wear resistance were significantly improved and the wear rate is as low as 1.19 × 10−6 mm3/N m. The research results will provide a theoretical basis for the preparation and industrial application of high-performance cBN coating tools.