Design Of Gradient Multi-layers Structure And Performance Of AlCrSiN Tool Coatings With High Strength And Toughness

AlCrN coatings have been widely used in the cutting process of cemented carbide and high speed steel tools.The addition of silicon into the coatings can effectively improve the hardness,wear resistance and high-temperature stability.In this paper,AlCrSiN coatings were fabricated on M42 high speed steel substrate and vertical end millings by multi arc ion plating equipment enhanced by ion source.The effects of the coating fabrication parameters including targets arc currents and deposition pressure,cycle multilayer structure and Si containing layers with gradient structure on the microstructure and properties were investigated.X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and X-ray photoelectron spectroscopy（XPS）were used to analyze the chemical composition and microstructure of the AlCrSiN coatings.Nano-indentation,scratchs tester,friction and wear tester and CNC machining center were used to reveal the mechanical properties,tribological behavior and cutting performance of the AlCrSiN coatings.The conclusions are as follows:Firstly,the adhesive strength can be effectively improved,the chemical composition of the coating can be adjusted and the internal stress of the coatings can be released by optimizing fabrication parameters including targets arc currents and deposition pressure of the AlCrSiN coatings.When the arc currents of Al Cr Si targets is 80 A and the pressure of deposition is 3.5 Pa,the performance including adhesive strength and mechanical properties of the AlCrSiN coating is better.The Si content in this coating is about 3.5 at.%,the surface roughness is lower than 101 nm,the adhesive strength is up to HF1 grade and the value of Lc2 is up to 60.4 N,the stress of the coating is reduced to about-5.3 GPa,the hardness of the coating is up to 32.5 GPa,the ratios of H/E and H3/E^*2 reach to 0.096 and 0.26 GPa respectively,the friction coefficient of the coatings is 0.6 and the wear rate is 5.5×10^-16m³/（N·m）and the cutting life of the coated M42 end millings is 4.7 m.Then,the introduction of cycle structure in the AlCrSiN multi-layer coatings can effectively prevent the occurrence of plastic deformation,crack growth and improve the toughness of the coatings.When the cycle number of the multi-layer AlCrSiN coatings is two,the surface roughness is lower than 205 nm,the value of adhesive strength Lc2 is as high as 62.7 N,the hardness is 30.2 GPa,the toughness characterization values reach to0.099 and 0.26 GPa,the friction coefficient is reduced to about 0.5 and the coatings wear rate is 4.2×10^-16 m³/（N·m）and the cutting life of the coated end millings was improved to7.3 m.Besides,the design of Si containing layers with gradient structure in the AlCrSiN multi-layer coatings can effectively refine the grain size and further improve the adhesive strength and enhance the toughness.In the AlCrSiN coating with the smoother Si content gradient structure,the grain size of the coatings decreased from 70-100 nm in the adhesion layer to10 nm in the working layer,the adhesion was at HF1 grade,the hardness increased as high as 33.1 GPa,the toughness characterization ratios H/E and H³/E^*2 were about 0.1 and 0.35GPa respectively,the wear rate decreased to 0.9×10^-16 m³/（N·m）and the service life of the coated end millings reached 14.0 m.Finally,the main failure mode of the AlCrSiN coatings or coated end millings is the combinations of abrasive wear,adhesive wear and oxidation wear during the process of wear test and milling test.The furrows or scratchs,adhesion debris can be clearly observed in the wear tracks of AlCrSiN coatings or the flank face of the coated end millings.EDS results showed that there are a lot of oxygen in the wear tracks and flank face.By optimizing the fabrication parameters,introducing the cycle structure and designing the Si content gradient structure in AlCrSiN coatings could effectively increase the adhesive strength,hardness,toughness,wear resistance and cutting performance.In this work,the gradient structure design of Si content played a more effective role than the multi-layer design in the cutting application.