Property Investigation Of TiAlSiN Nanocomposite Coatings Deposited By Modulated Pulsed Power Magnetron Sputtering

TiAlSiN nanocomposite coatings,as a new generation coating,have high hardness,good wear resistance and fatigue resistance properties,which can improve the work efficiency and service life of workpieces.However,the low touhness and high thermal conductivity limit the industrial application of TiAlSiN coatings.TiAlSiN coatings were deposited on Si(100)substrate by modulated pulsed power magnetron sputtering(MPPMS)technology.The average power was 1 kW,the working pressure was 0.5 Pa,and the partial pressure of nitrogen was 25%.TiAlSiN nanocomposite coatings with different characteristic structures were deposited by changing the peak power from 24.8 to 56.8 kW and the substrate bias from 35 to 130 V.The changes in the structure,fracture toughness and thermal conductivity of TiAlSiN coatings were studied,the mechanism of the changes in the toughness and thermal conductivity was analyzed,which provided theoretical basis and technical support for the industrial application of TiAlSiN nanocomposite coatings.When the peak power increased from 24.8 to 56.8 kW without bias,the TiAlSiN coating had a typical nc-TiAlN/a-Si3N4 nanocomposite structure,the thickness of the coating decreased from 2.6 to 2.1 ?m,and grain size decreased from about 10 to 6 nm.When the peak power was 24.8 kW and 35.2 kW,the microstructure of coatings was through-column structure(zone I in Thornton's model).When the peak power was 44.6 and 56.8 kW,the microstructure was dense defect-free zone T structure.The density and ioization rate of sputtering particles,which was calculated by global plasma model,increased by 40%and increased from 65%to 80%,repectly.That increased the bombardment energy Ebi and the surface mobility D of the incident species,led microstructural change from columnar structure to dense defect-free structure.With substrate bias of 100 V,the peak power increased from 24.8 to 56.8 kW,the thickness of coatings decreased from 2.3 to 1.8 ?m,the grain size was reduced from 18 to 5 nm,and the microstructure of all coatings was dense zone T structure.With increase of peak power at a high bias,the particle bombardment energy and migration energy were significantly improved,which caused microstructure of coatings to be dense zone T structure.With fixed peak power of 56.8 kW substrate bias increased from 35 to 130 V,the thickness of coating increased from 1.8 to 1.9 ?m,and the grain size decreased from about 16 nm to 6 nm.The microstructures were dense and defect-free zone T structures.Due to the high ionization rate of 80%and the added substrate bias,that led the microstructure of coatings to be a dense zone T structure.Under the conditions of peak power 24.8-56.8 kW and substrate negative bias 35-130 V,by using nanoindenter to test nanohardness(H)and elastic strain failure(H/E*)of TiAlSiN nanocomposite coatings.Hardness and H/E*of coatings were 23.6-37.5 GPa and 0.078-0.091.The compressive residual stress ? of coatings was 0.2-2.1 GPa.The fracture toughness of coating was characterized by using Vickers indentation at loads of 500 and 1000 mN.Under the floating potential,when the peak power increased from 24.8 to 44.6 kW,the effective elastic modulus ratio of the TiAlSiN coating and the Si substrate Ef/Es was lower than 1.95,indentation morphology of coatings was radial crack,crack length decreased from 15.1 to 9.7?m,the fracture toughness KIc increased from 0.96 to 1.77 MPa·ml/2.The coating of 56.8 kW was crack-free and had the highest fracture toughness.The toughening of the coating is due to the transformation of the microstructure.With a bias of 100 V,as the peak power was 24.8 kW,Ef/Es was about 2,the coating was without crack.At the peak power of 35.2 to 56.8 kW,indentation morphology of coatings was picture-frame cracks,the total length of crack increased from 15.2 to 36.2 ?m,KIC decreased from 1.94 to 0.96 MPa·m1/2.With the peak power of 56.8 kW,the substrate bias increased from 35 to 130 V,Ef/Es of all coatings was lager than 2.3,indentation morphology of all coatings was picture-frame crack,the total crack length increased from 28.2 to 49.4 ?m,KIC decreased from 1.64 to 0.91 MPa·m1/2.According to the elastic modulus ratio Ef/Es,the indentation morphology of coating was radial cracks when Ef/Es<2,and the indentation morphology was picture-frame cracks when Ef/Es>2,the coating had the highest fracture toughness with crack-free when Ef/Es was about 2.The thermal conductivity of TiAlSiN nanocomposite coatings was characterized using transient thermoreflectance technique,the relationship between thermal conductivity and structure of coatings was established.As peak power increased from 24.8 to 56.8 kW without bias,thermal conductivity of TiAlSiN coatings decreased from 9.1 to 4.8 W/mK.With bias of 100 V,as peak power increased from 24.8 to 56.8 kW,thermal conductivity of coatings reduced from 6.2 to 3.0 W/mK.With peak power of 56.8 kW,as substrate bias increased from 35 to 130 V,thermal conductivity of coatings reduced from 5.4 to 2.1 W/mK.The electric resistivity p of all TiAlSiN coatings was high,ranging from 147 to 173 k?·m,the electronic thermal conductivity of all coatings was 2.57-3.0×10-11 W/mK,which proved that electronic heat conduction had no contribution to the thermal conductivity,and phonon heat conduction was the main factor affecting the heat transfer.The phonon thermal conductivity was affected by the structure of TiAlSiN coatings-microstructure and nanometer size.The through columnar Zone I structure was very favorable for heat transfer from the surface of coatings down to the substrate,which caused high thermal conductivity of TiAlSiN coatings.But the dense zone T structure hindered heat transfer,at the same time with the grain size reduced,the interfacial density per unit volume was therefore increased,and leading to more interface scattering of the phonons in the heat transport progress,which was the key parameter to obtain low thermal conductivity of TiAlSiN nanocomposite coatings.