Study On The CrAl(Si)N Coatings Deposited By HiPIMS And Pulsed DCMS Techniques

The application of PVD coating technology have a significant influence on the development of high-performance cutting tool coatings.The machining quality and the life of the tool benefit a lot from coatings.CrAlN coating was widely applied to the surface protection of cutting tools due to its high hardness,oxidation resistance and wear resistance,induced by solid solution strengthening and nano composite strengthening.While the doping of Si into CrAlSiN nano composite coating will be more promising in cutting area.In this paper,CrAlN and CrAlSiN nanocomposite coatings were deposited by HIPIMS+Pulsed DC co-sputtering technique to prepare high-performance tool coating,combining the advantages of high ionization rate resulted from HIPIMS and high deposition rate resulted from pulse DCMS.The microstructures,mechanical properties as well as tribological behaviors of CrAlN and CrAl SiN coatings were studied respectively by varying substrate bias voltages,nitrogen/argon ratio and SiAl target power.The formation regularity of the microstructure of the CrAlSiN composite coating was revealed.The results indicated that:The substrate negative bias was able to adjust the internal stress of CrAlN coating and promote the phase transition interior the coating.With the increase of the substrate negative bias,all the as-deposited coatings showed the fcc-?Cr,Al?N phases,the peak of 111 orientation became gradually weakened and 200 orientation tend to be stronger.The residual compressive stress in the coating increased significantly,while a small amount of Cr dissolved in the AlN lattice,causing lattice distortion and grain refinement.The abrasion resistance of the coating was significantly enhanced due to the increasing substrate negative bias.The values of H/E and H³/E^*2 at-120v bias were 0.11 and 0.21Gpa respectively,and the maximum residual stress was-2.68GPa.The mechanical and tribological properties of the coating was greatly enhanced by the increasing negative bias.The friction coefficient of decreased gradually and the lowest coefficient of friction was 0.36 at-120v.The wear morphologies of the coating surface also demonstrated the lowest wear rate of 3.0×10^-16 m³/?N×m?.CrAlSiN nanocomposite coatings were prepared under high nitrogen content atmosphere with different N₂/Ar flux ratios.As the N₂/Ar ratio increased,the deposition rate of the CrAlSiN coating decreased due to the barrier effect of the nitride produced on the target surface.The increasing N₂/Ar flux ratio enhanced the crystallinity of CrAlSiN coating and the amount of nitrides in the coating increased.Large clusters of grains appeared on the surface of coatings under high N₂/Ar ratio.The sudden appearance of clusters was closely related to the surface mobility of deposition particles on the substrates.The increasing N₂/Ar flow rate failed in the improvement of the mechanical properties,but the friction and wear properties of the coating were greatly enhanced.And the wear rate decreased untill to 1.9×10^-16 m³/?N×m?reflecting the best wear resistance.The CrAlSiN coatings with different SiAl target powers were prepared by co-sputtering techneques.With the increase of SiAl target power,the content of Si in the coating increased significantly from 14.4 at.%to 22.7 at.%,which led to the increasing thicknes of amorphous layer,inhibited the nano-composite strengthening effect.When the SiAl target power was 0.7kw,the best mechanical properties and friction and wear properties were obtained.The wear rate was only 2.8×10^-16 m³/?N×m?.This demonstrated that too high Si content?more than 14.4 at.%?leads to the decrease of coating toughness and the abrasion resistance of the coating.