Performances of PVD and CVD coated tools based on TiC_0.5N_0.5/Si₃N₄ composite ceramic matrix

Firstly, TiC_0.5N_0.5/Si₃N₄ composite ceramics were prepared by hot-pressing method using 15vol% or 25vol% TiC_0.5N_0.5 powders as conducting second phase. Then, CrAlN and TiN/Al₂O₃/TiN coatings were deposited on the surfaces of TiC_0.5N_0.5/Si₃N₄ ceramic tools by physical vapor deposition (PVD) and chemical vapor deposition (CVD) technologies, respectively. Finally, the effects of TiC_0.5N_0.5 content and coating type on tool wear characteristics were investigated by conducting continuous cutting experiments for gray cast iron on TiC_0.5N_0.5/Si₃N₄ tools, and the wear mechanisms of tools were also discussed. The results show that the increasing of TiC_0.5N_0.5 content is beneficial to enhance the matrix hardness and conductivity of TiC_0.5N_0.5/Si₃N₄ composite ceramic tools, but has little effect on wear resistance and cutting length. When depositing CrAlN coating by PVD technology, with TiC_0.5N_0.5 content increasing, the thickness, adhesion strength and hardness of coating increase, the wear performances of coated tools enhance significantly, and cutting length extends obviously. However, when depositing TiN/Al₂O₃/TiN coating by CVD technology, the variation of TiC_0.5N_0.5 content almost has no effects on coating thickness, adhesion strength and hardness, as well as the comprehensive cutting performances of TiN/Al₂O₃/TiN coated tools change little. Both of CrAlN coating and TiN/Al₂O₃/TiN coating can improve the wear resistance and cutting length of TiC_0.5N_0.5/Si₃N₄ composite ceramic tools significantly. Compared with TiN/Al₂O₃/TiN coating, CrAlN coating has higher coating hardness and adhesion strength; while TiN/Al₂O₃/TiN coated tool shows more excellent wear resistance and cutting length for TiN/Al₂O₃/TiN coating has larger coating thickness. The main wear mechanism of TiC_0.5N_0.5/Si₃N₄ composite ceramic tools is abrasive wear caused by mechanical friction, and associated with a small amount of adhesive wear.