Microstructure Studies Of Cemented Carbide Tool Coatings

The hard alloy with WC,TiC and other hard phases and Co and Ni binder phase as the main components has excellent performance,high strength,high hardness,good anti-flaking performance and chemical inertness.It is widely used as a high-performance tool in the modern machining field.With the complex processing and diversification requirements of processing efficiency,environmental protection and processing materials in the modern processing field,coated tools with cemented carbide as the substrate have been rapidly developed,and fine-grained cemented carbide substrate with functionally graded structure is deeply studied and applied.The diversity of coating materials has continuously optimized the performance of cemented carbide tool coatings,and is the core technology of contemporary high-performance tools.At present,the preparation methods of cemented carbide tool coatings mainly include chemical vapor deposition(CVD),physical vapor deposition(PVD),plasma chemical vapor deposition(PACVD),and sol-gel methods(Sol-Gel).The properties of the coating material mainly depend on the microstructrure of the material.Based on the above research background,the morphology and elemental diffusion behavior of cemented carbide tool coatings are observed and analyzed,and the microstructure of cemented carbide tool coatings is analyzed.In this paper,the microstructure of cemented carbide tool coatings was characterized by metallographic microscope,scanning electron microscope,transmission electron microscope and X-ray diffractometer,and the results were analyzed.Experimental results show:(1)The Ti element in the inner TiN coatings hardly diffuses into the matrix,and the Ti element in the TiAlCNO hardly diffuses into the Al₂O₃,but the Ti element in the outer TiN diffuses to the Al₂O₃ in a small amount,and A small amount of Al diffuses into the outer TiN coatings.The Co and W elements diffuse from the substrate to the inner TiN coatings,and the TiCN and the C elements in the substrate diffuse simultaneously into the inner TiN coatings.(2)The fine WC and Co raw material powder can greatly improve the hardness and strength of the cemented carbide substrate.The TiN coatings deposited on the substrate are dense,the grains are fine and uniform,have good strength and hardness,and the thickness should be within 0.5 ?m.The TiCN coatings increase the impact toughness of the coatings and reduce the overall internal stress of the coatings,improving the service life and overall performance of the tool coatings.A TiAlCNO transition layer with a suitable thickness should be deposited between the TiCN and Al₂O₃ coatings to increase the bond strength between the coatings,increase the corrosion resistance of the coatings,and refine the grains of the Al₂O₃ coatings.(3)The enrichment of the Co phase on the surface of the substrate in the cemented carbide coatings can obtain the fine-grained polycrystalline TiN coatings with different orientation.The TiCN grains deposited on the TiN change with the orientation of the deposition.The grain size gradually becomes larger and the uniformity is lowered.Dislocations occur in the grains of the upper layer of TiCN,and the internal stress becomes large.It is necessary to control the TiCN coatings so that the thickness thereof is not too large.When the outermost TiN coatings are deposited on ?-AlO3,?-Al₂O₃ is not formed as much as possible by controlling the deposition atmosphere,thereby obtaining the TiN coatings having different grain orientations.