Investigation On Preparation And Performance Of AlCrN-based Coatings Using For Machining Of Difficult-to-cut Materials

In this thesis,we focued on the preparation and performance of the AlCrN-based coatings using for machining of difficult-to-cut materials such as hardended steel and superalloy.We achieved the improvement of mechanical propeties,high-temperature thermal stability and anti-oxidation performance of the AlCrN coatings via optimizing the deposition parameters,doping multi-components and introducing nanocomposite/multilayer structures.The composition,microstructure,high-temperature stability,mechanical and tribological properties of the AlCrN-based coatings were systematically investigated.The mechanisms of the coatings structure evolution and high-temperature friction-oxidation behavior were discussed.The main results were as followings.?1?The effect of oxygen content on the microstructure,mechanical properties and cutting performance of AlCrN/AlCrON coatings was studied by changing the O₂/?O₂+N₂?flow ratio of AlCrN/AlCrON coatings with different oxygen contents.The thermal stability and wear mechanism of the coatings at high temperatures were systematically studied.The results showed that with the increase of the oxygen content in the coatings,the coatings hardness value decreased while the adhesion of the coatings firstly increased and then decreased.With the increase of vacuum annealing temperature,the hardness of AlCrN coatings decreased,and hexagonal phase appeared at 950°C.The hardness value of AlCrN/AlCrON?O 7.41 at.%?coatings after vacuum annealing at 1100°C slightly increased,showing better high-temperature red hardness.At room temperature,600°C,and 800°C,the average friction coefficient rises first and then decreases with increasing oxygen content.The wear mechanism of Al CrN/AlCrON?O 0.96 at.%?coating is mainly abrasive wear and plastic deformation at room temperature.At 600 and 800°C,the coatings is mainly subjected to friction oxidation and adhesive wear at high temperature.The AlCrN/AlCrON?O 7.41at.%?coating is mainly abrasive wear and polished and lubricated at room temperature.At600°C and 800°C,the coatings is mainly abrasive wear with local adhesive wear.The turning life of coated tools is longer than that of uncoated tools,and the highest turning life of AlCrON?O 5.28 at.%?coated tools is about 6 times that of uncoated tool turning.AlCrN/AlCrON coated with oxygen tools have better turning performance than AlCrN coated tools.?2?In order to improve the strength and cutting performance of the coatings,a multi-component oxygen-containing AlTiN/AlCrSiN/AlCrSiON tool coatings was prepared by doping Si into the coatings.The microstructure and mechanical properties of AlTiN/AlCrSiN/AlCrSiON coatings were studied by the oxygen content.Influences on the thermal stability and wear mechanism of Al TiN/AlCrSiN/AlCrSiON coatings at high temperatures and the wear process of hardened steels and superalloys were systematically studied.The results show that with the increase of oxygen content in the coatings,the adhesion of the coatings increases first and then decreases,and the hardness value remains basically unchanged.At room temperature,the friction curve of low oxygen?O 0³0 at.%?coatings is stable,and the friction curve of high oxygen?42²5 at.%?coatings is drastically.Both the 600 and 800°C friction curves fluctuate.At room temperature,the plastic deformation and abrasive wear occurred in the coatings.The friction mechanism of the coatings at 600°C is abrasive wear followed by oxidation wear.The wear mechanism of the coatings at 800°C is mainly adhesive wear and oxidation wear.The high-temperature thermal stability of the coatings reaches 950°C.After vacuum annealing at 1100°C,the coatings phase decomposes and the hardness value decreases,but the oxygen-containing coatings can maintain a higher high temperature hardness.In the turning hardened steel experiment,the turning life of the coated tool increases first and then decreases as the oxygen content in the coatings increases.AlTiN/AlCrSiN/AlCrSiON coated tools exhibit better resistance to the sticking of the workpiece material than an oxygen-free coated tool.In the turning superalloy experiment,cutting friction oxidation basically did not occur,the coated cutter was mainly mechanical wear,and the AlTiN/AlCrSiN coatings showed the best cutting performance.?3?In order to further improve the performance of the AlCrN-based coatings tools,AlCrN/TiSiN multilayer coatings were deposited on cemented carbide substrates by arc ion plating.The microstructure,high-temperature thermal stability and tribological properties of the AlCrN/TiSiN coatings were investigated.The results indicated that the AlCrN/TiSiN coatings consist of c-Cr?Al?N and c-Ti?Si?N phases,exhibited a typical columnar microstructure.The AlCrN/TiSiN illustrated a hardness of 49.7±0.83 GPa and adhesion strength of⁸3 N.After vacuum annealing at temperatures form 800°C to 900°C,the coating microstructure became much more denser and the defect density decreased.However,both the coatings hardness and bonding strength were slightly changed.The high-temperature tribological tests suggest that the friction coefficient of the coatings increased as the temperature increases from RT to 400°C.The friction coefficient decreased with further increasing the temperature up to 600°C-800°C.The wear rate of the coatings increased monotonously as the test temperature increased.Both abrasive wear and plastic deformation produced the wear of the AlCrN/TiSiN coating at RT.However,both adhesive wear and abrasive wear dominated the wear occurre at 400°C.As the test temperature increased to 600°C-800°C,the wear of the AlCrN/TiSiN coatings was ascribed to the adhesive wear and the oxidation wear.