Study On The Relationship Between Microstructure And Properties Of TiAlN And TiSiN Ternary Films Prepared By PVD Method

With the extensive use of super hard materials,light metals and their alloys,green forming and high-efficiency processing have become the normal application means in manufacturing industry.Therefore,as a protective film,the improvement of quality and performance are also attracting more and more attention.Transition metal nitride film plays an important role owing to its structure and properties.It is one of the research hotspots in this field to introduce the third or more elements into the binary nitride film system represented by Ti N to improve its quality and performance.In this work,TiAlN and TiSiN coatings were prepared on the surface of high speed steel by using hollow cathode assisted multi arc ion plating technology in physical vapor deposition method.The strengthening mechanism of membrane was investigated;The influence of the residual stress on the coating/substrate adhesion was surveyed;The wettability of molten aluminum on high speed steel and film samples was analyzed;The electrochemical and chemical corrosion mechanism of coating samples at room temperature and high temperature were analyzed.Scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),transmission electron microscopy(TEM),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)were employed to detect the microstructure of the samples and determine the qualitative and quantitative analysis of the constituent phases and elements;Nanoindentation tester,micro nano mechanical testing system and laser confocal microscope(LSCM)were utilized for measuring the nanoindentation hardness,elastic modulus,friction coefficient,wear,surface roughness and coating/substrate adhesion of the samples;The micro strain of the film was calculated by XRD linear profile analysis;The surface wettability of the film was measured by the sessile drop method;The corrosion characteristics of the samples were evaluated by electrochemical impedance spectroscopy(EIS)and potentiodynamic polarization tests.The thermal stability of the coatings was analyzed by thermogravimetry(TG)and differential scanning calorimetry(DSC).The high temperature oxidation experiments were carried out in a box resistance furnace.The results show that the displacement solid solution Ti3 Al N based on Ti N is formed in the TiAlN film,and the hardness of the film is 44.8 Gpa,which is much higher than that of the Ti N film of 21 Gpa;Not only does the Ti N exist,but also there is independent nucleation and growth of Si3N4 phase in TiSiN film,which is different from TiAlN film.The hardness of the film is 34.8 Gpa.The calculated value of hardness / elastic modulus shows that the plasticity and toughness of the film are improved,and the mechanical properties of the original Ti N film are improved due to fine grain strengthening.However,the Si content in the film does not increase with the increase of Si content in the target due to the influence of the non-metallic Si element.Under the experimental conditions,the comprehensive performance of the film prepared by 15% Si target is the best.The above results are consistent with the influence of dislocation density on hardness obtained by XRD linear profile analysis.The friction coefficient and wear decreases along with the hardness of the films increase.The results show that the order is as follows: high speed steel > Ti N >TiSiN > TiAlN.The results show that the order of micro strain is TiAlN(1.309×10-3)>TiSiN(1.166×10-3)> Ti N(0.944×10-3).The results show that the order of coating/substrate adhesion is TiSiN(40N)> Ti N(39.5N)> TiAlN(33.5N),which is basically consistent with the tendency that the larger the strain is,the smaller the coating/substrate adhesion is.This could ascribe to Al atoms dissolved in Ti N will cause lattice distortion,and the existence of Ti N and Ti3 Al N in coherent or semi coherent way will also cause lattice distortion.In TiSiN coatings,the independent nucleation of Si3N4 phase and the combined effect of incoherent interface refine the structure of the coatings,slow down the increase of strain,and the optimal substrate bonding force was obtained.The experimental results show that good coating/substrate adhesion can be obtained without preplating Ti N substrate,which provides a theoretical and experimental basis for optimizing the preparation process,reducing the cost and improving the efficiency.The results show that the order of contact angle is as follows: high speed steel(9.8°)< Ti N(39.3°)< TiSiN(72.5°)< TiAlN(80.2°).The wettability is related to the chemical bond composition of each material.The high speed steel made of metal bond is most easily wetted,while the anti wettability of Ti N coatings with ionic bond and TiSiN and TiAlN coatings with covalent bond compounds is gradually enhanced.The results from electrochemical characteristic parameters of 304 stainless steel and coating samples show that the respective self corrosion potential is 304 stainless steel < Ti N < TiAlN < TiSiN,and the self corrosion current density and dimensional passivation current density are 304 stainless steel > Ti N > TiAlN > TiSiN.The resistance value of TiSiN film is 4306Ωcm2,which is much higher than that of other samples,showing the best corrosion resistance.The crystal defects caused by grain refinement of TiSiN film increase the electron scattering,and the difficulty of charge transfer is the main reason for the increase of impedance;The winding fine grain boundary hinders the penetration and diffusion of corrosive medium,and avoids the concentration of impurity elements caused by the coarse columnar grain boundary,and the high energy state of thermodynamics caused by crystal defects is easy to provide the driving force for the passivation process.The results based on high-temperature oxidation experiments at 600℃~900℃show that the Ti N film begins to decompose at the earliest time.At 800℃,Ti O2 has been formed in the film.Because of its poor protection,oxygen atoms are easy to diffuse through the columnar crystal boundary,resulting in the oxidation of the matrix.When the iron oxide film is formed,it will lose its protection.The high temperature oxidation resistance of TiAlN and TiSiN coatings is better than that of Ti N coatings due to the composition of phases and elements.The results show that both coatings are oxidized between 800 ℃ and 900 ℃,but the Ti3 Al N and Si3N4 phases in the coatings are not decomposed.The reason for the oxidation may be related to the thin film and the decomposition of Ti N phase in the film.