Preparation Of Carbon And Boron Doped AlCrSiN Composite Coatings And Study Of High Speed Dry Cutting Performance

In this thesis,AlCrSiCN coatings with different C contents（denoted as C0,C10,C20 and C30）and AlCrSiBN coatings with different B contents（denoted as B0,B5and B10）were prepared on cemented carbide tools by multi-arc ion plating technique.The lubrication C and B elements were selected to incorporated in to Al Cr Si N coating to improve the high temperature friction properties and high speed cutting performance of coating tools.The effects of C and B content on the structure,morphology,adhesion,microhardness,friction and wear properties of AlCrSiCN and AlCrSiBN coatings were investigated by X-ray diffractometer,scanning electron microscope（SEM）and energy spectrometer（EDS）,friction and wear experiment.High-speed near-dry milling and high-speed dry turning experiments against 20Cr Mo were conducted to study the effect of coating structure on its cutting performance,and the cutting mechanism was discussed in detail.The results were summarized as follows.With the increase of C₂H₂flows,the C content in AlCrSiCN coating increases and the Si content decreases;the phase structure of AlCrSiCN coatings with different C contents is solid solution（Al,Cr）N phase,and the C element exists mainly in the form of amorphous phase in the coating;the addition of C element can reduce the surface roughness of the coating,the surface roughness of C0 coating is the largest with Sa of 277±23 nm and Sq of 159±15 nm,with the surface roughness of C20coating is the smallest with Sa of 126±51 nm and Sq of 79±20 nm.The increase in C₂H₂flows reduces the hardness of the AlCrSiCN coating,the C0 coating shows the hardness of 3442±78 HK_0.05,while the C30 coating shows the low hardness of558±23 HK_0.05;Meanwhile,the adhesive strength of the AlCrSiCN coating firstly increases and then decreases with the increase in C₂H₂flows,with the best adhesive strength of 48.1 N for C20.The C content can effectively reduce the friction coefficient of the AlCrSiCN coatings and play a role in reducing wear,with the C30 coating having the lowest friction coefficient of 0.548;the wear mechanism of the C0 and C10 coatings is abrasive wear,while the wear mechanism of the C20 and C30 coatings is adhesive wear;the results of high-speed dry turning show that incorporation of C decreases the cutting force of the tools,reducing the adhesive wear of the front tool face.The C10coating has the best turning performance with a turning time of 17.5 min at a cutting speed of V_c=250 m/min.The main wear mechanisms for the rear face of the tool are abrasive wear and oxidative wear,while the main wear mechanisms for the rake face are abrasive wear and oxidative wear;the milling results show that the AlCrSiCN coating is not suitable for intermittent machining conditions in this work.The phase structure in AlCrSiBN coatings with different B contents is solid solution（Al,Cr）N and a small amount of Al N;B and Si elements mainly exist in the form of amorphous Si₃N₄and BN;amorphous BN can play a role in refining the grain;the higher the B element content result in the lower the surface roughness of the AlCrSiBN coating,and B10 coating has the lowest surface roughness;The B0 and B5coatings have the adhesion grade of HF-2 and the B10 coating has the adhesion grade of HF-3.The increase of B elements increases the microhardness of the coating,with the B10 coating having the highest hardness value of 3618±98 HK_0.05.The wear morphology of the B5 coating was relatively smooth with only slight furrows and adhesions,a few abrasive chips,slight wear and the low wear rate of0.28×10^-15m³·N^-1m^-1was revealled for the B5 coating.The wear rates of the coatings were in the order:B10>B0>B5;After annealing at 800°C,the diffraction peak intensity of the（Al,Cr）N phase enhanced and the micro-hardness showed a slight increase.After annealing at 1000°C,all the AlCrSiBN coatings started to decompose,among which the high temperature stability of B5 coating was the best;the results of high-speed dry turning showed that the main wear mechanism of the AlCrSiBN coating rear tool face was abrasive wear and adhesive wear,and the main wear mechanism of the rake tool face was oxidation wear,abrasive wear and adhesive wear;the B5 coating cutter showed the lower cutting force during high dry turing and had the longest cutting time of 17 min.The results of high-speed dry milling show that the main failure mode of AlCrSiBN coating tools are coating peel,adhesive wear and oxidative wear,and the B10 coating showed the poor adhesive strength.