Construction Of Low Frequency High Power Pulsed Electric Field And Its Effect On The Micro-structure Of Ion Plating

The DC magnetron sputtering ion plating,one of the two main technologies of PVD,has been widely used in optics and microelectronics industry.But it is difficult to deposit thick film coating,which limits its application in the field of precision transmission products.DC arc ion plating is easy to carry micro-droplets because of missed particles.Temperature tempering on the surface of low sensitive substrate results in its application limited to tools with temperincg temperatures above 450 degrees,such as cemented carbide and high speed steel.It is always difficult to extend the field of precision structural parts with medium or even low temperature tempering.High-power pulsed magnetron sputtering ion plating,which has become a research hot-spot gradually,is restricted by the cooling ability of magnetron target materials and the technology of avoiding the steady loss of power due to the avalanche effect in high-power mode.As a result,the peak conduction width of high-power pulsed current is always limited to the order of 100 microseconds,thus greatly reducing its effect on improving the coating structure and expectation of increasing deposition rate.In view of the bottleneck of the development of ion plating technology,a self-developed low-frequency and high-power dual-pulse ion plating power supply is used to construct a low-frequency and high-power pulsed electric field environment in which the peak current of magnetron cathode target can be independently modulated milliseconds in turn-on and turn-off period.The effects of electric field parameters such as pulse peak current and on-off ratio(Ton/Toff)on the miss mechanism,transient miss rate and coating structure of metal and compound coatings were investigated under the condition of transient high power density induced target overheating.The f’ollowing conclusions are obtained:1.Developed a low frequency high power double pulsed ion plating power supplyBased on the microsecond period of argon atom ionization recovery under negative pressure and the cascade enhanced plasma physics knowledge of electron collision escaping from magnetron cathode target surface,a double pulse ion plating power supply with different frequency and microsecond high frequency fluctuation of voltage is developed to keep the current steady at millisecond level.The sub-microsecond chop ping of the output voltage during the pulse conduction phase avoids the sharp increase of the electron escape rate of the target surface caused by the intense bombardment of the argon plasma on the target surface in the high power mode,and then causes the defects such as the grain boundary of the target surface to be subjected to the Joule heat(I2Rt).The pulse current conduction width can be extended to milliseconds to increase the transient deposition rate and improve the micro-structure of the coating.2.Determine the range of electric field parameters for the change of particle escape-target modeThe evolution of particle Miss mechanism in DC sputtering ion plating,DC arc ion plating and high power pulsed ion plating with transient peak output power up to 50KW was studied by using a self-developed low frequency and high power pulsed plasma power supply.The results show that in the DC sputtering ion plating environment with a target current of 4A,the discharge marks on the target surface appear as uneven craters,indicating that the escape-target mode of the plating particles is cascade collision caused by Ar+ ion bombardment,and in the DC arc ion plating environment with a target current of 100A,the discharge marks on the target surface appear smooth.The melting morphology of the plating particles,which is dense and contains a large number of micron arc spot splashes,indicates that the escape-target mode of the plating particles is the thermal emission miss of the micro-melt droplets.When the peak target current is 24A and the pulse width is 2ms,the gas discharge characteristic is between the glow discharge and the arc discharge region.From the combination of the target imprint and the first two,the mechanism of misalignment of the plating particles is changed into collision +thermal emission misalignment.3.The effect of millisecond pulse width on the structure of metal and compound coatings.The average deposition rate(the ratio of coating thickness to total deposition time)of metal Ti coating increases significantly with the increase of pulse width(coating thickness to total deposition time)when the conduction width of pulse current Ton increases from 700μs to 20ms(DC)under pulsed electric field with peak current and frequency of 7.5A and 50Hz.respectively.The ratio of degree to the sum of pulse conduction period)increases first and then decreases with the increase of pulse width,and the coating has the highest deposition rate when the pulse width is about 1.6ms.At the same time,the cluster particle size of the coating increases significantly with the increase of pulse width,indicating that the deposition mechanism of the coating particles is still in the cluster along the coating.Preferential crystalline growth is dominant,while for TiN composite coatings,the content of Ti increases first and then decreases slightly with the incr,ease of pulse width,resulting in the increase of micro-hardness from 21GPa to 25GPa and then drops back to about 23GPa;the specific internal stress(the ratio of internal stress to thickness)of TiN-based coatings is basically not changed with the pulse width.The influence of pulse width on the cluster size and internal stress of the coatings was compared with that of the corresponding power coatings.It was found that even if the pulse width of the target current was extended to 20ms under the condition of 7.5A low frequency electric field,the evolution of the coating particle escape-target mode from cascade collision to thermal emission could not be realized.4.The effect of peak current on the micro-structure of metal and compound coatingsIn the electric field with pulse width and frequency of 2ms and 50Hz,when the peak current increases from 6A to 60A,the average deposition rate of Ti and TiN coatings increases with the increase of the peak current,and the deposition rate increases rapidly from 6nm/min to 16nm/min before and after the peak current reaches 24A.The results show that the size of the clusters is not coarsened with the increase of the deposition rate,but is mainly composed of smooth and compact fine clusters,which indicates that the mechanism of the miss distance of the particles has begun to evolve from cascade collision to thermal emission.Ti:N in the corresponding TiN coating was gradually increased from 0.68:1 to 0.92:1,and the hardness was increased from 20GPa to 25.8GPa.Meanwhile,under equal thickness condition,the internal stress of Ti and TiN coatings decreases with the increase of peak current.Increasing the peak current can increase the deposition rate and reduce the internal stress of the coatings.The results show that increasing the peak current can easily lead to the evolution of the mechanism of particle escape-target mode from cascade collision to destargeting by thermal emission.