| With the upgrading of national manufacturing and the arrival of the "14th five years plan" intelligent manufacturing plan,the national demand for high-precision and cutting-edge manufacturing technology increase,and the requirements for the properties and preparation technology of thin film materials are constantly improving.However,the research of thin film material preparation technology mostly focuses on the surface preparation of planar parts or the outer surface preparation of workpieces,while the research on thin films preparation technology for the inner surface of tube or the interior of complex components is relatively few.With the upgrading of the industry and the emergence of special application scenarios,the demand for high-quality films preparation or surface modification on the inner surface of tube or complex components is gradually increasing.How to effectively improve the plasma density deep inside the tube or complex components is an important technical index to improve the film preparation quality or surface modification effect on the inner surface of tube or complex components.In the field of magnetron sputtering technology,high power impulse magnetron sputtering(HiPIMS)technology is widely concerned for its advantages of high metal ionization ratio and high plasma density.Since the bipolar high power impulse magnetron sputtering(BP-HiPIMS)mode was proposed in 2018,it has become a research hotspot in the field of HiPIMS technology in recent years.Its technology is to apply a positive pulse to promote the acceleration of ions in front of target on basis of traditional HiPIMS.but there is a problem that the positive pulse has insufficient effect on the promotion of ions.Aiming at the problem of low plasma density deep inside the tube cavity in the deposition technology of film on the inner surface of tubes,this paper presents a plasma discharge method in tube using electric-magnetic field enhanced dual-pulse bipolar HiPIMS.Dual-pulse bipolar high power impulse magnetron sputtering(DBP-HiPIMS)mainly solves the problem that the positive pulse in traditional BP-HiPIMS has insufficient promotion effect on ions.DBP-HiPIMS discharge is carried out by using magnetron sputtering target outside the tube.Applying auxiliary anode near the tail of tube to "traction",and applying excitation coil behind the target to "push" plasma into deeper position inside the tube,to enhance the plasma discharge in tube and effectively improve the plasma density in the deep position of tube.Aiming at this method,the discharge characteristics of plasma in the tube,the transmission mechanism of ions in the tube and the deposition characteristics of Cr films on the inner wall of tube were studied.The substrate bias current and discharge spectral characteristics at various positions in tube under traditional BP-HiPIMS and DBP-HiPIMS were compared.It was found that DBP-HiPIMS with 100 V positive pulse voltage had higher substrate bias current integral value and higher Ar ion and Cr ion spectral intensity at various positions in tube than BP-HiPIMS,reflecting that DBP-HiPIMS can make more ions enter the deep position in tube.The influence of positive pulse parameters on substrate bias current integral value during the negative pulse end period at various positions in tube in DBP-HiPIMS was studied.It was found that,with the increase of positive pulse voltage,the substrate bias current integral value during negative pulse end period showed an increasing trend at various positions in tube,and this increasing trend was more obvious with the increase of position depth in tube.It showed that the positive pulse could promote more ions to reach the depth of tube.The effects of the auxiliary anode near the tail of tube and the excitation coil behind the target on the plasma discharge characteristics in tube were studied.It was fould that,under the condition of an auxiliary anode with a diameter of 80 mm and a distance of 35 mm from the tail of tube,when the auxiliary anode voltage was greater than the threshold of 15-25 V,due to the ionization enhancement caused by the collision between electrons and neutral gas particles enhanced by the auxiliary anode electric field,the plasma density in the depth of tube was sighnificantly increased.Various positions in tube,from the orifice to the tail,were divided into four positions equidistant according to the depth of position in tube,which are defined as Position 1,Position 2,Position 3 and Position 4,respectively.At Position 3 near the tail of tube,the substrate bias current integral value could increase from 7.2×10-6C at the auxiliary anode voltage of 0 V to 65.7×10-6 C at the auxiliary anode voltage of 35 V.When the auxiliary anode voltage was 35 V,the substrate bias current integral values at Position 2,Position 3 and Position 4 could account for 66.7%,76.0%and 62.1%relative to Position 1 at the nozzle.On the basis of increasing the number of ions at various positions in tube by applying auxiliary anode voltage,through the synergistic enhancement of electric-magnetic field,the increase of excitation coil current behind the target could further increase the number of ions at various positions in tube and increase the substrate bias current integral value at various positions in tube.By comparing the structure and properties of Cr films deposited on inner wall of tube at Position 2,it was found that,with the increase of DBP-HiPIMS positive pulse voltage,ions obtained higher energy,the surface roughness of films decreased,lattice constant increased,grain size decreased,and the lowest corrosion current density was obtained when the positive pulse voltage was 80 V.When the positive pulse voltage was 100 V,compared with BP-HiPIMS,the films deposited by DBP-HiPIMS had lower surface roughness,larger lattice constant,smaller grain size,higher hardness and better corrosion resistance.The increase of auxiliary anode voltage applied at tail of tube and excitation coil current applied behind target would increase the ion bombardment intensity of the films and increase the heat input,which would affect the structure and properties of the deposited Cr films.By comparing the corrosion resistance of Cr films deposited on inner wall of tube under traditional BP-HiPIMS mode,DBP-HiPIMS mode,DBP-HiPIMS+auxiliary anode mode and DBP-HiPIMS+auxiliary anode+excitation coil mode,it was found that,due to the high plasma density in depth of tube in DBP-HiPIMS+auxiliary anode+excitation coil mode,ion bombardment was enhanced and the films were densified.As a result,the Cr films deposited in depth of tube in this mode had the lowest corrosion current density,showing the best corrosion resistance. |
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