Thick TiN Coatings Research Articles

Thick yet tough TiN coatings deposited by filter cathode vacuum arc technology

There are some high requirements for mechanical property to protective coatings of turbojet engine compressor blades as the appearance of extreme service conditions. The hard coating with high toughness, good adhesion, good wear resistance and excellent load carrying capacity is a potential coating for extreme service conditions in the future. Thick yet tough TiN hard coatings were successfully deposited on 304L stainless steel substrates by magnetic filtered cathodic vacuum arc technology. The morphology, structure and properties of the coatings were studied by SEM and XRD, etc.The results show that the continuous growth of TiN coatings attributed to periodic high energy ion bombardment which can suppress the large grain size and reduce the internal stress. The thickness of TiN coating can reach to 50 μm and the deposition rate was close to 0.2 μm/min. At the same time, the stable non stoichiometric TiN<sub>0.9</sub> can be formed by controlling the constant N<sub>2</sub> flow rate, which can improve the toughness of TiN coatings. All TiN ciatings belong to superhard coating and the max value of hardness and modulus of elasticity were 38.24 GPa and 386.53 GPa respectively. TiN coatings have good adhesion and excellent toughness.The highest <i> <inline-formula><tex-math id="Z-20200510122827-1">\begin{document}$ H/E^{*} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20200036_Z-20200510122827-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20200036_Z-20200510122827-1.png"/></alternatives></inline-formula></i> and <inline-formula><tex-math id="Z-20200510122827-2">\begin{document}$ H^3/E^{*2} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20200036_Z-20200510122827-2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20200036_Z-20200510122827-2.png"/></alternatives></inline-formula><sup> </sup>rate of TiN coating can reach to 0.0989 and 0.3742. Thick yet tough TiN hard coatings have excellent wear resistance with the lowest friction coefficient of 0.26.

Enhancement of Functional Ceramic Coating Performance by Gas Tunnel Type Plasma Spraying

A high-precision plasma system has been pursued for advanced thermal processing. The gas tunnel type plasma jet device developed by the author exhibits high energy density and also high efficiency. Among its various applications is the plasma spraying of ceramics such as Al2O3 and ZrO2. The performance of these ceramic coatings is superior to conventional ones. Properties such as the mechanical and chemical properties of the zirconia coatings were reported in previous studies. In this study, the enhancement of the performance of functional ceramic coatings by the gas tunnel type plasma spraying method was carried out using different powders. Results show that the alumina/zirconia composite system exhibited improvements of mechanical properties and corrosion resistance. The alumina/zirconia composite coating has the potential for use as a high functionally graded thermal barrier coating. Another application of the gas tunnel type plasma is for surface modification of metals. As an example, TiN films were formed in 5 s and, thick TiN coatings were easily obtained by gas tunnel type plasma reactive spraying.

Application of self-mixing interferometry for depth monitoring in the ablation of TiN coatings

Among possible monitoring techniques, self-mixing interferometry stands out as an appealing option for online ablation depth measurements. The method uses a simple laser diode, interference is detected inside the diode cavity and measured as the optical power fluctuation by the photodiode encased in the laser diode itself. This way, self-mixing interferometry combines the advantages of a high resolution point displacement measurement technique, with high compactness and easiness of operation. For a proper adaptation of self-mixing interferometry use in laser micromachining to monitor ablation depth, certain optical, electronical, and mechanical limitations need to be overcome. In laser surface texturing of thin ceramic coatings, the ablation depth control is critically important to avoid damage by substrate contamination. In this work, self-mixing interferometry was applied in the laser percussion drilling of TiN coatings. The ∼4 μm thick TiN coatings were drilled with a 1 ns green fiber laser, while the self-mixing monitoring was applied with a 785 nm laser diode. The limitations regarding the presence of process plasma are discussed. The design criteria for the monitoring device are explained. Finally, the self-mixing measurements were compared to a conventional optical measurement device. The concept was validated as the measurements were statistically the same.

Cavitation erosion of TiN and CrN coatings deposited on different substrates

TiN and CrN coatings with various thicknesses deposited on X6CrNiTi18-10 and X39Cr13 steel by means of the cathodic arc evaporation method were tested in a cavitation tunnel with a slot cavitator and tap water as the medium. Steels were subjected to thermal treatment in order to obtain substrates of different properties. Present investigation shows that the properties of the substrate, especially the thermal properties, influence the properties of the TiN coatings. Deposition of hard TiN and CrN coatings on the steel substrates has caused the improvement of the cavitation erosion resistance. The increase of coating thickness decreases the positive effect of the TiN and CrN coatings deposition. The 8 and 12μm thick TiN and CrN coatings undergo degradation mostly via spalling by removal of the thin flakes of the coating. The resistance parameter, RCAV=(kc/ks)/(αc/αs)⋅(Hc⋅(1−vc2))/(Ec⋅(1+vc2))⋅(Es⋅(1+vS2))/(Hs⋅(1−vS2))⋅(LC2/pc⋅h), where k is thermal conductivity, α is the thermal expansion coefficient, H is the hardness in GPa, LC2 is the adhesion force in N obtained in the scratch tests, E is the Young’s modulus in GPa, pc is the number of phases in the coating phase composition, h is the coating thickness in μm, subscript c applies for coating, s is for the substrate, has been positively verified by present investigations. This indicates that not only the mechanical properties of the coating and of the substrate influence the cavitation erosion resistance of the PVD coating–steel substrate system, but also their thermal properties.

Effect of Cryogenic Treatment on Improving the Fracture Toughness of TiN Coated Cemented Carbide

The 2μm thick TiN coatings were deposited by arc ion plating on YW2 cemented carbide substrate, and the system of TiN/YW2 was treated with cryogenic treatment at -196°C for 30 hours. The change of the Rockwell indentation's morphology of the system (the form and density of cracks, the spalling state of the coating)before and after the treatment were investigated by means of the Rockwell hardness tester. With metallurgical microscope and SEM, the change of the microstructure of the substrate and its influence on the fracture toughness of the system were investigated. The results show that after the treatment, the density of the radiated cracks in the substrate were obviously reduced, but the main cracks hadn’t any change, the spalling of the TiN coating along the indentation was lightened. After the cryogenic treatment the dispersed granular γ phase obviously decreased or even disappeared, the pores became smaller and the microstructure of YW2 became more compact，and the microcracks were merged during the cryogenic treatment. These are beneficial to improve the fracture toughness of YW2 substrate and the coating/substrate system.

In Situ High Temperature X‐Ray Diffraction Reveals Residual Stress Depth‐Profiles in Blasted TiN Hard Coatings

AbstractHigh temperature X‐ray diffraction (XRD) is used to characterize residual stress depth‐profiles and volume‐averaged residual stresses in blasted 9 µm thick TiN coatings on WC/Co substrates in the temperature range of 25–1100 °C using a dedicated high temperature attachment from Anton Paar GmbH. Room temperature measurements reveal that the blasting process changes the almost constant tensile residual stress of 560 MPa across the coating to compressive stress which decreases exponentially within the coating surface region of 1–3 µm. The magnitude of the compressive stresses is dependent on the particle pressure used during the blasting process. Heating up results in rapid compressive stress relaxation already at relatively low temperatures and is accompanied by relaxation of stresses of II and III order. During cooling down from 1100 °C, tensile residual stresses are formed. After reaching the original stress value of about 560 MPa, the tensile stresses do not increase upon cooling anymore but are relaxed by cracks. The analysis of diffraction peaks shows that blasting results in anisotropic nano‐structural changes in the coating surface. In summary, the approach documents that HT‐XRD can provide important insights into the high temperature behavior of engineering components.

Effect of coating thickness on the deformation mechanisms in PVD TiN-coated steel

The deformation mechanisms of a range of TiN coatings with different thicknesses, deposited on a V820 steel substrate following nanoindentation were characterized using focused ion beam (FIB) cross-sectioning and imaging, as well as cross-sectional transmission electron microscopy (TEM) of the indented region. Four TiN coatings were examined, including a cathodic arc evaporation (CAE) coating with a thickness of ∼ 0.7 μm and low voltage electron beam (LVEB) evaporation coatings with thicknesses of ∼ 2.0, ∼ 3.7 and ∼ 4.0 μm. Based on a model developed by Xie et al., the intercolumnar shear stresses were calculated to be approximately 2.20, 3.05, 3.50 and 3.55 GPa in the ∼ 0.7, ∼ 2.0, ∼ 3.7 and ∼ 4.0 μm thick TiN coatings respectively, that is, increasing as the coating thickness increases. Columnar cracking and shear steps at the coating/substrate interface were observed more frequently in the thinner TiN coatings indicated that these coatings deformed predominantly by shear along the columnar grain boundaries. In contrast, inclined cracking was the more dominant fracture type in the thicker TiN coatings. It is suggested that increased grain boundary strength occurs together with a lack of direct crack path along the grain boundaries through the thicker coatings due to the more equiaxed grain structure. Clearly, the grain structure and/or thickness of the TiN coating play a highly significant role in the deformation mechanisms.

TEM study of TiN coatings fabricated by mechanical milling using vibration technique

A mechanical milling method was used for the deposition of TiN coatings. The principle of this method is that a substrate and powder were placed along with balls into the vibration chamber that was vibrated by a mechano-reactor. During mechanical milling process, the substrate surface was impacted by a large number of flying balls. The TiN particles trapped in between the balls and the substrate became cold welded to the surface. The repeated substrate-to-ball collisions forged TiN particles into a coating on the substrate surface. The process allowed the thick TiN coatings to be produced at room temperature in an ambient atmosphere. TEM study of the as-fabricated coatings was carried out. The coating formation depended on the size of the initial TiN particles. The 50-nm TiN nanoparticles were more easily cold welded than 1.5-μm microparticles. The nanoparticles had a tendency to consolidate and densify into the bulk material under the applied compressive loading. The TiN particles better consolidated and densified on the hard Ti surface than on the soft Al one.

The effects of pre-implantation of steel substrates on the structural properties of TiN coatings

We have studied the effects of nitrogen pre-implantation of AISI C1045 steel substrates on the microstructure and microhardness of deposited TiN coatings. The substrates were implanted at 40 keV, to the fluences from 5 × 1016 to 5 × 1017 ions/cm2, which was followed by deposition of 1.3-μm thick TiN coatings by reactive sputtering. Structural characterization of the samples was performed by standard and grazing incidence X-ray diffraction analysis, Rutherford backscattering spectroscopy and transmission electron microscopy. Microhardness was measured by the Vicker’s method. Nitrogen implantation up to 2 × 1017 ions/cm2 induces the formation of Fe2N phase in the near surface region of the substrates, which becomes more pronounced for higher fluences. Microstructure of the deposited TiN coatings shows a strong dependence on ion beam pre-treatment of the substrates. The layers grown on non-implanted substrates have a (200) TiN preferential orientation, and those grown on implanted substrates have (111) TiN preferential orientation. The change in preferred orientation of the layers is assigned to a developed surface topography of the substrates induced by ion implantation, and possible effects of distorted and altered crystalline structure at the surface. Ion implantation and deposition of TiN coatings induce an increase of microhardness of this low performance steel for more than eight times.

Corrosion Resistance of High Hardness TiN Coatings Prepared by Gas Tunnel Type Plasma Reactive Spraying

Thick titanium nitride coatings, which have high hardness, were obtained by gas tunnel type plasma reactive spraying. In this study, the corrosion behavior of the thick TiN coatings was investigated using the electrochemical polarization measurement in 1 M hydrochloric (HCl) solution at room temperature of 295 K. The polarization curve of stainless steel (SUS304) was also measured in order to clarify the effect of corrosion resistance of TiN coatings on the substrates as protective layer. The results showed that the TiN coating could protect the substrate surface from corrosion. It also revealed that the corrosion resistance of TiN coatings was improved as the thickness of TiN coatings was increased.

The corrosion resistance and wear resistance of thick TiN coatings deposited by arc ion plating

Thick TiN coatings were successfully deposited onto A3 mild steel by the arc ion plating process. The influence of the coating thickness on phase constitution of the coating and growth orientation of the crystallites was investigated using X-ray diffraction analysis. The results show that the lattice constant of the TiN coating decreased with the increase of the coating thickness from 6 to 12 μm. The wear resistance of thick TiN coatings was also studied, and results show that the arc ion plated thick TiN coatings exhibits excellent wear resistance and good adhesion to substrate. Investigation on the corrosion resistance of thick TiN coatings was performed in 450 ml of 1 N H 2SO 4 corrosion media by means of an electrochemical potentiodynamic polarization. The AIP TiN coatings with thickness of 12 and 18 μm show excellent corrosion resistance, and no clear corrosion pit was found on the surface of the coatings.

Wear mechanism maps for TiN-coated high speed steel

Dry sliding wear experiments were conducted on PVD TiN-coated high speed steel (HSS) discs over a range of contact loads (5-200 N (0.25-10 MPa nominal contact pressure)) and sliding speeds (0.25-2.5 m s -1 ) against HSS pins using a pin-on-disc test configuration. Friction heating effects were monitored by recording bulk pin surface temperatures and correlated with wear rates and mechanisms for 3 μm thick TiN coatings. Steady state wear rate, wear mechanism and bulk temperature data were summarized on load versus sliding speed axes in the form of wear and bulk surface (T b ) temperature maps. Four TiN wear regimes were identified: (i) tribochemical polishing and rapid removal of the TiN by oxidation of TiN at loads below 10 N and sliding speeds below 0.5 m s -1 ; (it) mild wear of TiN coating asperities at loads below approximately 100 N and where T b remained below approximately 150 C; (iii) mild wear of TiN coating asperities at high sliding speeds and loads where severe wear, softening and transfer of the opposing HSS pin occurred at a critical T b of approximately 300°C, thereby minimising coating damage; (iv) rapid wear of TiN at T b between 150 and 200°C where sliding speeds remained below approximately 1.68 m s - 1 and loads were above 100 N.

A study of rolling-contact fatigue of bearing steel coated with physical vapor deposition TiN films: Coating response to cyclic contact stress and physical mechanisms underlying coating effect on the fatigue life

The effect of physical vapor deposition (PVD) TiN coatings of different thicknesses on the rolling-contact fatigue (RCF) life of coated specimens is studied experimentally. Based on the results of conventional three-ball-on-rod testing, the optimum film thickness is found to be about 0.75 μm. Thinner coatings do not significantly affect the fatigue life, while much thicker ones have a negative effect on it. These trends agree with the findings of prior studies. Using a progressive testing technique, the mode of localized damage experienced by thick TiN coatings under cyclic contact stress conditions is established. The fatigue life reduction observed with such coatings is explained by comparison of the coated surface roughness in the damaged and the intact portions of the rolling track. Progressive testing results also indicate that the stress-affected material volume plays an important role in near-surface initiated rolling-contact fatigue. By modifying fatigue test conditions, the fatigue life enhancement observed with some PVD TiN coatings is demonstrated to result from loading ball polishing by the hard coating. The present experimental observations agree with the predictions of a companion theoretical study.

Scratch Induced Subsurface Deformation Behaviour of Thin Ceramic Coatings

Transmission electron microscopy has been used to study the subsurface deformation structures induced in ceramic coatings subjected to scratch testing. CVD TiN, CVD TiC (both ∼ 5 μm thick), and ∼ 2 μm thick PVD TiN coatings, all deposited on steels, were investigated. For behavioural comparison, a relatively soft, thicker ‘coating’ - an aluminised KEA28 steel of reacted layer (Al2O3) thickness ∼ 30 μm - was also studied. For the TiN and TiC samples, both grain boundary decohesion and in grain plasticity were found to feature prominently both in response to subsurface stresses and in contributing to friction by dissipating energy. For the coating on the aluminised steel, plasticity alone appeared as the dominant deformation mechanism. The results are discussed in relation to coating microstructure and wear performance.