Design,Preparation And Performance Study Of Zr-B-N/ZrO₂ Multilayer Composite Tool Coatings

The rapid development of the contemporary manufacturing and aerospace sectors has led to progressively higher requirements for tool performance.Coated tools substantially improve machining quality and extend tool life due to their high strength,good wear resistance and heat resistance.In order to solve the problem of easy wear and short life of carbide tools when cutting high temperature alloys at high speed,this paper proposes the"reverse design of coating composition"method.Development of high purity,high performance Zr-B-N coatings using a reducing atmosphere to remove residual O2 from the coating chamber,reducing the process requirements for vacuum coating equipment.The Zr-B-N/ZrO₂ nanomultilayer coatings were developed by high power pulsed magnetron sputtering and pulsed DC magnetron sputtering composite techniques with periodic implantation of ZrO₂ layers as thermal and chemical barriers.Optimising the mechanical and tribological properties of nano-multilayer coatings by modulating the heterogeneous interface of the multilayer structure to improve the service life and machining efficiency of coated carbide tools.In this paper,we systematically investigate the mechanisms affecting the mechanical properties,microstructure and frictional properties of ZrO₂ coatings,Zr-B-N coatings prepared under reducing atmosphere and Zr-B-N/ZrO₂ nanomultilayer coatings,and prepare coated tools for cutting experiments.The specific findings of the study are as follows:High purity Zr-B-N coatings were prepared by introducing a reducing gas into the vacuum chamber to fully reduce the oxygen impurities and mitigate the damage to the nano-scale interface of the coating by the oxygen impurities.At a flow rate of 6 sccm of N2+H2,the dense nanostructure of the coating effectively prevents slippage between grain boundaries,refines the grains and presents a glassy microstructure with no obvious features inside the coating.At this point the hardness reaches a maximum of 23.22 GPa,the modulus of elasticity is at a maximum of 308.63 GPa,the critical load is approximately 33 N and the coefficient of friction is at a minimum of 0.839.The process parameters of the ZrO₂ coating were designed.When the O2flow rate was 6 sccm,the XRD analysis showed that the Zr O phase in the coating had been transformed into stable ZrO₂,the coating structure was stable and the coating was dense.The hardness of the coating reaches 24.21 GPa,the modulus of elasticity is 329.3 GPa,the crystalline ZrO₂ resists wear better than Zr O,the coefficient of friction is lower at 0.455 and the wear rate is lighter at 8×10^-10 mm³/(N·mm).Development of Zr-B-N/ZrO₂ nanomultilayer coatings using a combination of high power pulsed magnetron sputtering and pulsed DC magnetron sputtering techniques,which exhibit a glassy structure without distinctive features.Mainly due to the diffuse distribution of nanocrystals(nc-Zr N)in the Zr-B-N modulation layer in the amorphous(a-BN),the nanocrystals slip in the amorphous under external forces to release strain.At the same time,the presence of the multilayer coating breaks the grain growth structure in the ZrO₂ modulated layer,and the applied load is buffered at the nanostructure and multilayer interface to prevent crack intrusion,improving the mechanical properties of the Zr-B-N/ZrO₂ nanomultilayer coating.When the multilayer coating modulation period was 80 nm and the modulation ratio was 7:1,the hardness of the nanomultilayer coating was up to 30.2 GPa,compared to the single component Zr-B-N coating(hardness 23.2 GPa)and ZrO₂ coating(hardness 24.2 GPa),the hardness of the Zr-B-N/ZrO₂ nanomultilayer coating was increased by 29.8%and 24.7%respectively,when the coating had the highest resistance to wear,with a wear rate of 5.0×10^-7 mm³/(N·mm).When the heat treatment temperature was increased to 900°C the coating flaked off extensively.A comparative study of the cutting performance of Zr-B-N/ZrO₂ nano multilayer coated end mills with uncoated carbide end mills and Zr-B-N coated end mills for continuous dry cutting of 45#steel and quenched steel.It was found that the Zr-B-N/ZrO₂ nano multilayer coated end mill had the lowest cutting temperature and the longest service life,with a maximum cutting temperature of 408°C and a service life of 38 min for quenched steel,and the best relative tool integrity.