Plasma State And Structural Properties Of Cr-based Coatings Deposited By Arc Ion Plating

As one of the most commonly used physical vapor deposition methods,arc ion plating has been widely concerned.And the research on the arc ion plating process and materials has been relatively systematic.The state of the discharge plasma has a great influence on the coating quality.However,few studies have mentioned it,and how does the process affect the plasma state is still unclear.In view of the above problems,this paper uses optical emission spectroscopy to diagnose the plasma state in the chamber during the deposition of CrN and CrAlN coatings,and investigates the effect of process parameters on the plasma state.The main parameters include arc current,working pressure,electromagnetic frequency,temperature and Cr Al target ratio of CrAlN coating.According to the results of plasma diagnosis,the process parameters of coating deposition were selected,and CrN and CrAlN coatings were prepared by cathodic arc ion plating,respectively.The morphology,structure and intrinsic properties of the coatings were characterized and analyzed in depth.Then the relationship between deposition conditions and plasma state,as well as coating structure and properties was studied.The main findings are as follows:（1）The plasma mainly includes excited atoms and primary ionized particles.The plasma density of the Cr target is over 7.5×10¹⁴/cm^-3,and which of the Cr Al target is over 6×10¹⁴/cm^-3,both of which satisfy the local thermodynamic equilibrium state.The plasma temperature of the Cr target reaches more than 7500K,while that of the Cr Al target reaches 8800K.For the Cr target,the spectral intensity of each particle showed good agreement with the plasma density and temperature.The plasma states under different parameters are different.The intensity of emission spectrum rises with the increase of pressure,arc current,electromagnetic frequency and temperature,and then decreases.The maximum values were got at 4Pa,90A,16.7HZ,and 350℃.The change trend of plasma state of Cr Al target with parameters is similar to that of Cr target,but the parameters of the maximum emission spectrum intensity are different,which are 3Pa,90A,16.7HZ,and 350℃.With the change in the atomic ratio of the Cr Al target,the highest spectral intensity,plasma density and temperature of each particle were got at the target ratio Cr/Al5:5.（2）The effects of parameters on the phase structure are not obvious for CrN coating,and the preferred orientation of the coating is（200）.The number of macro-particles in coatings was affected by the plasma density and the process parameters.The minimum value is got at 0.5Pa,70A,16.7HZ,and 350℃,which differ from the parameter with the highest emission spectrum intensity.The hardness of the coating is affected by the number of macro-particles,coating density and residual stress,and which also deviates from the optimal parameters of the plasma state.It shows that the plasma state is not the only factor that directly determines the intrinsic properties of the coating.The influence of the process on the plasma density and energy further affects the morphology and microstructure of the coating.Combined with the influence of different processes,the coating properties are jointly determined.For the CrAlN coating,the hardness is mainly affected by ion bombardment on the coating density and residual stress.The coating with3Pa,90A,16.7Hz,and 350℃has the highest density and the highest hardness,reaching 33.29GPa.And the coatings at these parameters also had the lowest residual stress which is 1.59GPa and the lowest number of macro-particles.The plasma state matches the structural properties of the coating.The change in the target ratio has a greater impact on the coating properties.The atomic ratio of Cr and Al in the coating is consistent with the change trend of it which in the target,but the atomic ratio is not the same.The coating of Cr/Al5:5 has the highest density.But the coating of Cr/Al3:7 has the highest hardness due to the most dissolved Al atoms.The coating roughness of Cr/Al3:7 and Cr/Al7:3 is much larger than that of Cr/Al5:5.Therefore,the coating deposited under the target ratio of Cr/Al5:5 has the best comprehensive properties.