Low Temperature Reactive Sputter Deposition Of ?-Al₂O₃ Film

With the development of mechanical processing industry oriented to high-speed,automation and precision,the requirements for cutting tools materials are higher and higher.Under the condition of precision,high speed and long life of cutting,Cutting tools require high hardness,good toughness and non reactive with machined material at high temperature,such as bonded,diffusion and oxidation reaction.The ?-Al₂O₃ coating material can satisfy the above requirements.?-Al₂O₃ can be obtained by high temperature chemical vapor deposition,but high deposition temperature limits the practical application.At the same time,there are metastable phases in the process of preparation of ?-Al₂O₃ by physical vapor deposition at low temperature,it is difficult to meet the industrial application.In this dissertation,Cr+?-Cr₂O₃ composite transition layer is used to improve binding force between film and substrate and reduce the deposition temperature of ?-Al₂O₃.The process of low temperature deposition of Al₂O₃ and the structure of the film were systematically studied.Cr films on the Si,Ni30 and Ni substrate were prepared by DC magnetron sputtering.Afterwards,the Cr+?-Cr₂O₃ composite was obtained by thermal oxidation method.The influences of deposition temperature,matrix material on the bonding force between the Cr layer and the substrate,and the effect of the oxidation time on the surface morphology and oxidation degree of the Cr₂O₃ transition layer were investigated,respectively.The results show that the compactness of the film increase with the increasement of substrate temperature.In the process of high temperature sputtering,the film/substrate binding force is improved owing to osmosis and metallurgical bond between the Cr and Ni30 substrate.When the oxidation time is 3 hours,the grain size of Cr₂O₃ is moderate,the surface smoothness of the film is the best and the oxidation degree of Cr layer is ideal.The process of depositing Al₂O₃ thin films on Si substrate by high power impulse magnetron sputtering was investigated.The results show that spark frequency ascends with increasing the substrate temperature and the Al₂O₃ is sputtered with smaller particles and deposited on the substrate surface.When the depositing temperature is 550?,the surface defects of the film are less and the overall flatness of the film is better.The reaction rate between Al target and oxygen,particles of Al₂O₃ and spark frequency of target increase with the increasement of oxygen flow.Finally,the Al₂O₃ thin films were deposited on the Cr +?-Cr₂O₃ composite transition layer by high power impulse magnetron sputtering and RF reactive magnetron sputtering,respectively.The results illustrated that Cr₂O₃ transition layer can reduce the deposition temperature of ?-Al₂O₃ thin films.The ?-Al₂O₃ phase can be obtained at 500 ?,while the ?-Al₂O₃ and ?-Al₂O₃ two phases can be obtained at 450 ? by using the high power impulse magnetron sputtering on the Cr+?-Cr₂O₃ composite transition layer with Al target,respectively.The single ?-Al₂O₃ phase was obtained at 500 ?,and ?-Al₂O₃ and ?-Al₂O₃ two phases can be obtained at 450 ? by RF-reactive magnetron sputtering on the Cr+?-Cr₂O₃ composite transition layer with Al target,respectively.While the ?-Al₂O₃ phase was obtained at 500 ? and ?-Al₂O₃ phase was obtained at 450 ? by RF-reactive magnetron sputtering on the Si substrate with Al target,respectively.