Preparation And Investigation Of AlCrBn Hard Coating For High Speed Dry Cutting

In this thesis,AlCrBN coatings were prepared by arc ion plating technology.Scanning electron microscopy（SEM）,X-ray diffraction（XRD）,Raman spectroscopy（Raman）,X-ray photoelectron spectroscopy（XPS）,Transmission electron microscopy（TEM）,Profilometer,Microhardness tester,Rockwell indentation,Vacuum annealing,Ball-disc friction and wear,high speed dry turning and milling experiments were used to investigate the microstructures and properties of the coatings.By adjusting the deposition parameters,composition and structure of the coating,excellent AlCrBN tool coating was obtained,which effectively improved the high-speed dry cutting performance of AlCrBN coated tool.The main results are as follows:（1）AlCrBN coatings with different arc currents（60 A,80 A,100 A）and nitrogen partial pressures（3.0 Pa,3.5 Pa,4.0 Pa,4.5 Pa）were prepared by changing the two important deposition parameters of target arc current and nitrogen partial pressure.It was found that when the arc current of the target material was 80 A and the partial pressure of nitrogen was 4.0 Pa,the comprehensive properties of the AlCrBN coatings were better and it can withstand large alternating loads.Therefore,the arc current of80 A and nitrogen partial pressure of 4.0 Pa were selected as the main two deposition parameters in the subsequent preparation of AlCrBN series coatings.（2）AlCrBN composite coatings with different B contents were prepared,and their microstructure was closely related with the B content.XRD,Raman,XPS and TEM results show that addition of 1.5 at.%of B（T1 coating）results in the solid solution fcc-（Cr,Al,B）N and coherent fcc-BN/fcc-AlCrBN interfaces;addition of B content of 2.9 at.%（T2 coating）and 4.8 at.%（T3 coating）led to the composite structure comprising of nano-grains surrounded by amorphous a-BN_x,and the nano-grains decreased and amorphous layer thickness increased as the B contents further increased.The hardness results also showed that the AlCrBN coating with 1.5at.%B content obtained the highest hardness of 38.3 GPa due to the solution strengthening and coherent interface strengthening.While AlCrBN coating with 2.9at.%B content possessed the best toughness with higher values of H/E（0.073）and H³/E*²（0.169 GPa）.After vacuum annealing,the substrate elements were more likely to diffuse along the columnar crystals of the T1 coating to the surface of the coating,forming white particles on the surface.When the content of B was higher（2.9 at.%～4.8 at.%）,the phase structure and mechanical properties of the coating can be protected under high temperature vacuum annealing.In addition,take the AlCrBN coating with B content of 4.8 at.%as example,continuous Cr₂O₃film formed under400°C;continuous Al₂O₃ and Cr₂O₃ films accompanied by discontinuous B₂O₃ film appears with increasing to 600°C;as the temperature further increases to 800°C,discontinuous B₂O₃ film forms.High speed dry milling and turning results showed that the wear mechanism of coated tools were abrasive wear,adhesive wear and oxidative wear.Among them,the T2 coated cutter had better high-speed dry cutting performance（milling length of 8 m and turning time of 8 min）due to its better comprehensive performance.（3）AlCrN/AlCrBN multilayer coatings（1 layer,20 layers and 40 layers）were prepared by alternative deposition of AlCrN layers and AlCrBN layers.The surface roughness and microhardness of the multilayer AlCrBN coatings increased with the increase of the number of cycles.In addition,the adhesion strength of AlCrBN-1,AlCrBN-20 and AlCrBN-40 coatings reached HF1.After vacuum annealing,AlCrBN-20 and AlCrBN-40 coatings showed a special and complex multi-layer structure,which made the coating more prone to phase decomposition after vacuum annealing at 1000℃,and the substrate elements were easier to diffuse along the coating to form white large particles in coating surface,which the size of white large particles increased with the increase of the number of layers.In addition,the high temperature annealing hardness of AlCrBN coatings decreased obviously with the increase of the number of layers.It was found that the dry cutting wear mechanisms of coating tools were abrasive wear,adhesive wear and oxidative wear in high speed dry milling and turning experiments.Among them,the AlCrBN-20 coated cutter had better high-speed dry cutting performance（milling length of 13 m and turning life of13 min）due to its better comprehensive performance.