Mechanical And Cutting Performance Of DLC Composite Coated Tools

Diamond-like carbon（DLC）is a metastable amorphous material,which is formed by the combination of sp¹,sp² and sp³ hybrid bonds of coordinating carbon atoms,and contains C-H covalent bonds present in hydrogen-containing DLC.DLC coating has excellent properties such as low surface roughness,high hardness,self-lubricating characteristics,strong abrasion resistance and corrosion resistance,which are commonly used in the field of wear-resistant coating.DLC coated tools are suitable for machining various aluminum alloys and other non-ferrous metals.However,DLC coated tools have disadvantages,such as high internal residual stress,low toughness and poor adhesion strength,which severely limits the wide application of DLC coating.Adding transition interlayers can make the hardness and thermal expansion coefficient transition between the tool substrate and the DLC coating,which can effectively solve the above problems.In order to analysis the mechanical properties and cutting performance of DLC coated tools,the monolayer DLC coating,Cr/Cr N/DLC composite coating and Cr/W-DLC/DLC composite coating were prepared on YG8cemented carbide cutting tools by combining magnetron sputtering with plasma assisted chemical vapor deposition.The effects of Cr/x transition interlayer structure on the microstructure,mechanical properties and cutting performance about Al-Si alloy（AC9B）of DLC coating were studied.Compared with the monolayer DLC coating,the Cr/x transition interlayer structure in the Cr/x/DLC composite coating reduces the content of sp³ hybrid bonds,which in turn reduces the hardness and elastic modulus of the DLC coating.However,Cr/x transition interlayer contributes to the increase of sp²bonds content in the coatings,which can reduce the internal residual stresses of the coating.In addition,the coating/substrate matching performance of the Cr/x/DLC composite coating is better than the monolayer DLC coating.The test and analysis show that the Cr/W-DLC/DLC composite coating has the highest adhesion and the highest toughness.Cutting experiment research shows that Cr/W-DLC/DLC composite coated tool has the longest tool life in the machining of Al-Si alloys（AC9B）,which is 1.07 times longer than that of Cr/Cr N/DLC coated tool,1.15 times longer than that of DLC monolayer coated tool and 1.35 times longer than that of uncoated cemented carbide tool.The main wear mechanism of DLC coated tools is adhesion wear and abrasive wear.The Radar chart method was employed to comprehensively evaluate the mechanical properties and cutting life.The results show that Cr/W-DLC/DLC composite coating has the best comprehensive properties and is suitable for the machining of Al-Si alloy.The Advant Edge finite element simulation software was used to compare the Cr/W-DLC/DLC composite coating with three other commonly used coated tools（ie,Ti C-,Ti Al N-,Al₂O₃-）.The cutting performance parameters that are difficult to obtain in the actual cutting test are analysis carefully,such as the heat transfer coefficient of the rake face of the tool,the cutting deformation rate,the plastic deformation depth of the machined surface,and the interface temperature and stress of coating and tool.The effects of different cutting speed on the cutting performance of Cr/W-DLC/DLC composite coating are analyzed.The results show that the cutting temperature of Cr/W-DLC/DLC coated tool is the lowest compared with the other three coatings,but the calculated thermal distribution coefficient is higher than the other three coatings due to the large thermal conductivity coefficient of the coating.Cr/W-DLC/DLC coated tools also have lower cutting deformation rate,lower film-subatrate interface temperature and stress,which is conducive to the actual cutting process.With the increase of cutting speed,the cutting force and cutting temperature gradually increased,and the cutting deformation rate,the depth of plastic deformation on the machined surface and the thermal conductivity coefficient of the rake face gradually decreased.The successful preparation and analysis of mechanical properties of Cr/x/DLC composite coatings with excellent comprehensive properties provide a basis for the development of DLC composite coatings and provide a foundation for the application of DLC composite coatings in the field of cutting.The research of Cr/x/DLC composite coating provides a theoretical basis and technical guidance for the development and expansion of DLC coated tools with excellent comprehensive performance.