Moderate Temperature Chemical Vapour Deposition Research Articles

MT-CVD Ti(C,N,O) coatings controlled by CO: Microstructure evolution and its effect on the hardness

Incorporation of oxygen into Ti(C,N) coating by CO doping during moderate temperature chemical vapor deposition (MT-CVD) process is a promising strategy for enhancing the performance of cutting tools. In this work, Ti(C,N,O) coatings were prepared by MT-CVD in a hot-wall industrial-scale CVD reactor with increased CO volume fraction from 0 % to 8.0 % in the feed gas mixture. Microstructure evolution is revealed by high-resolution scanning electron microscopy, electron backscatter diffraction detector, and high-resolution transmission electron microscopy. Its effect on the hardness is investigated. The results show that as the CO fraction increases, the microstructure changes from columnar and large faceted grains to equilateral and nanoscale grains. An increasing density of plane defects including twins, especially Σ3 twin boundaries and stacking faults are identified in Ti(C,N,O) coatings with increasing CO fraction. The hardness of Ti(C,N,O) coatings increase from 26 GPa at 0 % CO to 34 GPa at 8.0 % CO, due to the grain refinement, solution strengthening, increased stacking faults, twins and {111} texture. A considerably lower rate of hardness increase is observed at CO fractions above 4.0 %, which is hypothesized to be related to grain boundary sliding, residual chlorine and excessive density stacking faults.

An innovative kinetic model allowing insight in the moderate temperature chemical vapor deposition of silicon oxynitride films from tris(dimethylsilyl)amine

An apparent kinetic model is developed for a novel chemical vapor deposition (CVD) process of silicon oxynitride (SiOxNy) films from tris(dimethylsilyl)amine (TDMSA) and O2, operating at moderate temperature (600–650 °C) and at atmospheric pressure. The definition of reaction pathways and the extraction of kinetic information is based on recently reported results of the gas phase composition, complemented by solid phase characteristics obtained by spectroscopic ellipsometry (SE) and ion beam analyses (IBA). Incorporation of carbon (up to 20 at.%) is considered alongside nitrogen (up to 25 at.%) for variable O2 flow rates (0.3–1.2 sccm). This combined gas- and solid-phase analysis is utilized to identify the main gaseous species and provide insight into the deposition mechanism. A silicon- and a nitrogen-centered radical intermediates are considered as the primary species of the mechanism, based on evidence from gas phase characterizations. A third, fictitious, nitrogen- and carbon-containing molecule is also conceptualized to account for carbon incorporation. Eight chemical reactions are defined alongside their respective kinetic parameters and are implemented in the ANSYS® FLUENT® computational fluid dynamics (CFD) code. Upon validation, the model allows for the successful prediction of local deposition rates and SiOxNy film composition containing non-negligible carbon, marking it as the first kinetic model able to represent the main chemical mechanisms involved in the CVD of a four-component material. The reported combined approach could be applied to other existing or new CVD chemistries forming multi-component thin films, favoring their implementation in original applications.

Effects of deposition parameters on the microstructure and mechanical properties of Ti(C,N) produced by moderate temperature chemical vapor deposition (MT-CVD) on cemented carbides

Using an industrial-scale chemical vapor deposition (CVD) system, a series of Ti(C,N) films were deposited from a TiCl4–CH3CN–H2–N2 gas mixture at 850–950 °C and 70–700 mbar with N2/H2 molar ratio varying from 0.27 to 3.77. Within the investigated temperature range, it is found that the growth rate of Ti(C,N) films is strongly dependent on the total pressure. Such behavior agrees with a diffusional limitation step. The lowest growth rate is measured at the N2/H2 molar ratio of 3.77, because of the low reduction rate of TiCl4 in a H2 deficient atmosphere. No significant influence of processing conditions on the carbon content of Ti(C,N) films could be found, as determined by X-ray diffraction and EPMA. The microstructure and mechanical properties were investigated and chiefly influenced by deposition conditions. In this work, the Ti(C,N) films deposited at 850 °C and 70 mbar with N2/H2 molar ratio of 0.27 exhibit a mixed texture with laminated facetted grains, the superior hardness reaching 30 GPa and the Young's modulus of 394 ± 32 GPa were measured. Furthermore, experimental results reveal that residual stresses could be thickness-dependent, due to the evolutionary film microstructure during film growth, and the stress relaxation is particularly attributed to cooling cracks.

Through-process modeling and experimental verification of titanium carbonitride coating prepared by moderate temperature chemical vapor deposition

In this work, the impact of temperature, pressure and gas flow on the chemical compositions, phases and deposition rates of MTCVD (Moderate Temperature Chemical Vapor Deposition) Ti(C,N) coatings is investigated by integrating thermodynamic calculations and computational fluid dynamics (CFD) simulations with key experiments. The thermodynamic calculations predict that both the C and the N contents of the films increase with increasing temperature under constant mixed gases and pressure, with the former increasing faster than the latter. CFD simulations indicate that the coating deposition rate decreases with increasing distance to the source gas for the hard metal samples loaded on the same tray. Subsequently, MTCVD-Ti(C,N) coatings were deposited at three different temperatures to verify the predicted chemical compositions and deposition rates. The experimental investigations are in reasonable agreement with the theoretical predictions. The present work applies a well-established strategy to meet the requirements of a controlled and robust process for MTCVD-Ti(C,N) coating with industrial applications.

Atom Probe Tomography investigations on grain boundary segregation in polycrystalline Ti(C,N) and Zr(C,N) CVD coatings

Atom Probe Tomography (APT) was used to obtain a direct evidence of chlor segregation and cobalt diffusion at the grain boundaries (GBs) of polycrystalline coatings deposited by moderate temperature chemical vapor deposition (MT-CVD) on a WC-Co cemented carbide substrate. Reasons behind segregations are discussed, and its effects are correlated to the micromechanical properties of Ti(C,N) and Zr(C,N). It is concluded that chlorine segregation is a relevant factor for explaining the low cohesive strength at the GBs of Ti(C,N) leading to intergranular failure during micro-compression testing, while its absence in Zr(C,N) along with Co diffusion contribute to grain boundary strengthening.

Development of a kinetic model for the moderate temperature chemical vapor deposition of SiO2 films from tetraethyl orthosilicate and oxygen

An apparent kinetic model for the chemical vapor deposition of SiO2 from tetraethyl orthosilicate (TEOS) and O2 was developed in a poorly investigated range of operating conditions, that is, at atmospheric pressure and between 350 and 500°C, based on literature survey and experimental results obtained in a hot wall tubular reactor. The kinetic model was implemented into the computational fluid dynamics code FLUENT and validated both in shape and value by comparison with experimental deposition rate profiles. It reveals that for the conditions tested, a possible mechanism of SiO 2 deposition involves two intermediate species formed from TEOS homogeneous decomposition, the first one being active from 300°C and the second one contributing to deposition for temperatures higher than 370°C. The calculated local profiles of gas flow, gas temperature, species mass fraction, and silica deposition rate indicate that the first intermediate species leads to marked film thickness gradients, the second one being more stable as producing uniform thicknesses. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3958–3966, 2018

Influence of annealing on the microstructure and mechanical properties of MTCVD TiC0.79N0.21 coating

TiC0.79N0.21 coating was deposited on WC-Co cemented carbide by moderate temperature chemical vapour deposition technique and then annealed in vacuum or air in the temperature range of 700–900 °C for 1 h. The morphology, composition, phase component, residual stress, hardness and plastic deformation resistance of the coating before and after annealing were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron probe micro-analyzer (EPMA), X-ray diffractometer (XRD) and nano-indentator. The results show that after annealing in low vacuum, the grain boundaries of the coating surface are still clearly visible and small capsule or granular oxide particles are uniformly distributed on the columnar surfaces of the coating. Coarse irregular particles enriched with W element are randomly located at the grain boundaries. After annealing in air, the coating is, however, oxidized to rutile TiO2 and oxidation rate increases with temperature. Dramatic coating oxidation is observed at 900 °C. With the increase of temperature, the residual tensile stress increases and compressive stress decreases after annealing in air and vacuum, respectively. The hardness and plastic deformation resistance on the cross section of coating are improved with temperature after vacuum annealing while opposite tendency is obtained for annealing in air.

Improvement of mechanical properties and cutting performance of modified MT-TiCxN1−x coating by moderate temperature chemical vapor deposition

Abstract To improve the cutting performance, a modified MT-TiCxN1 − x coating (x = 0.63) that adheres well to carbide substrates was developed by introducing C2H4 gas to a TiCl4–CH3CN–H2 precursor system on a TiN base layer during moderate temperature low pressure CVD. Glow-discharge optical emission spectroscopy and X-ray diffraction analyses reveal an increase in the incorporated carbon content. Electron backscatter diffraction analysis shows a highly preferred orientation [(422) plane] with a very fine columnar grain size of 0.17 ± 0.06 μm. The increase in hardness and the decrease in friction coefficient for cutting AISI: 51200 and AISI: 316 at room temperature and 600 °C with the modified MT-TiCxN1 − x coating result in a 30% longer tool life for continuous cutting of carbon steel (AISI: 1055) and alloyed steel (AISI: 4137) and a 60% longer tool life for stainless steel (AISI: 316). The modified MT-TiCxN1 − x coating resistance to failure was determined by four-groove intermittent cutting of AISI: 4137, and it shows a 30% increase in the average number of impacts compared with a conventional MT-TiCxN1 − x coating.

A self-modification approach toward transparent superhydrophobic glass for rainproofing and superhydrophobic fiberglass mesh for oil⿿water separation

A method employing one kind of material both for the construction of rough morphology and the chemical modification is called self-modification by us, which has not been reported in fabricating superhydrophobic surfaces so far. In this paper, taking candle soot as an intermediate, we created rough, superhydrophilic and transparent surfaces on glass trough calcination of polydimethylsiloxane (PDMS) at 550°C. Subsequently, a novel chemical vapour deposition (CVD) modification was conducted by heating PDMS at 330°C in air to give the surfaces a water contact angle (WCA) of 170°±0.5° and a sliding angle (SA) of 0°. This CVD modification is expected to be a valuable way of modification because of its simple operation, low cost and short time consumption. Results indicate that the high temperature calcination and the moderate temperature CVD modification can drastically improve the stability of the surperhydrophobic surfaces through controlling the morphology and the surface chemical composition. The as-prepared glass surfaces are capable of bearing heavy rains, keeping the sight clear in the rain and being used at a high temperature (<400°C) or in water. Besides, superhydrophobic fiberglass mesh was prepared and applied in oil⿿water separation.

Microstructure, mechanical properties, and cutting performance of TiCxN1 − x coatings with various x values fabricated by moderate temperature chemical vapor deposition

TiCxN1−x composite coatings on carbide substrate are important modern coating systems for cutting tools. The hardness, adhesion, and wear resistance of these coatings are determined by their structure and chemical composition. Therefore, TiCxN1−x coatings with varied x values were deposited on carbide tools via moderate temperature low pressure chemical vapor deposition using a mixed TiCl4–CH3CN–C2H4–H2 precursor system at 840°C and 9kPa. Furthermore, the effect of the x value on their mechanical properties and cutting performance was investigated. Deposition of the TiCxN1−x coatings with various x values was achieved by changing the molar ratio of C2H4 relative to CH3CN from 0 to 30. The x value of the TiCxN1−x coatings, defined as the atomic concentration ratio C/(C+N), was determined using X-ray photoelectron spectroscopy and observed to increase as the C2H4/CH3CN molar ratio increased until saturation at x=0.75. The crystallite sizes of the TiCxN1−x coatings were determined from X-ray diffraction analyses, and the microstructures were observed using a scanning electron microscope and an optical microscope. Additionally, the hardness and adhesion of the TiCxN1−x coatings were evaluated by indentation and scratch tests. Indentation hardness increased with the x value because of a decrease in the crystallite size and reached a maximum of 28.6GPa at x=0.69. Contrarily, the adhesion of the TiCxN1−x coatings to carbide substrates decreased as the x value increased because of a change in the morphology and formation of a discontinuous bonding interphase. Longitude turning operation test using ductile cast iron (AISI:100-70-03) was also performed on TiCxN1−x (10μm)/Al2O3 (5μm)-coated carbide inserts with different x values (x=0.59–0.74). It was observed that the TiC0.69N0.31/Al2O3-coated carbide insert exhibited a significant increase in tool life of 30%–50% compared with that of a commercially available TiC0.59N0.41/Al2O3-coated carbide tool.

Characterization and oxidation behavior of MTCVD Ti–B–N coatings

In this work, Ti–B–N coatings have been prepared by moderate temperature chemical vapor deposition (MTCVD). The effect of a varying boron concentrations (9.6 and 55.4at.%) on the chemical composition and the oxidation behavior was investigated by XRD, SEM, WDS, XPS and Raman spectroscopy. The results clearly demonstrate a good correlation between the different techniques. The same transition trends were observed in the examined Ti–B–N system in the progression from TiN to TiB2 by the addition of boron. At boron concentrations ≥18at.%, the coatings reveal a two phase structure comprising a nanocrystalline TiN phase embedded in an amorphous TiB2 matrix. In Ti–B–N coatings with boron concentrations ≤18at.%, the high sensitivity of Raman spectroscopy enabled the identification of an amorphous TiB phase.The oxidation behavior of Ti–B–N coatings was found to be affected by the boron concentration as well. Boron concentrations ≤18at.% improve the thermal stability compared to TiN, most likely due to the TiB phase present in these coatings. Ti–B–N coatings with a high boron concentration show a higher degree of oxidation compared to TiN manifested in a higher oxide layer thickness. In addition, these coatings tend to form boron oxides on their surface, which lead to the formation of metastable anatase rather than the thermodynamically stable rutile.

Characterization and properties of MTCVD Ti(C,N) coated cemented carbide substrates with Fe/Ni binder

Two developments, including the deposition of hard chemical vapour deposition (CVD) coatings on cemented carbides and the use of innovative binders instead of Co for cemented carbides, have attracted worldwide interest. In this paper, ISO grade P30 cemented carbides with Fe/Ni and Co binders are prepared as the substrates, and adherent Ti(C,N) coatings are deposited on them by moderate temperature chemical vapour deposition (MTCVD) technique. The microstructure and properties of both the substrates and coated cemented carbides are studied.

Adherent Ti(C,N) Coatings on Cemented Carbide Substrates with Fe/Ni/Co Binder

Both hard CVD coatings deposited on cemented carbides and the use of innovative binders for Co-bonded cemented carbide attract worldwide interest. In this article, ISO grade P30 cemented carbides are prepared with Fe Ni and Co binder, and adherent Ti(C,N) coatings are deposited on all the substrates by moderate-temperature chemical vapor deposition (MTCVD). The microstructure and properties of the cemented carbides before and after coating process are studied. The results show that Ti(C,N) coatings on all the substrate show compact and well-developed columnar structures, and high adhesion strength can be achieved.

Effect of ultra-fine TiC 0.5N 0.5 on the microstructure and properties of gradient cemented carbide

To increase the performance of cemented carbide, it was common to coat the wear surfaces with thin layers of hard materials. Cemented carbides with surface zone depleted of hard cubic phase and enriched in ductile binder phase were commonly used as the substrates. At the present, the so-called “gradient cemented carbides” were usually prepared by adding TiN or medium-sized TiCN, and a two-step sintering process including pre-sintering in nitrogen and gradient sintering in vacuum was usually adopted. In this paper, gradient cemented carbide based on WC–5.19 wt.%Ti–9.2 wt.%Co was prepared by simple vacuum sintering with the addition of 0.13 μm ultra-fine TiC 0.5N 0.5, compared with medium-sized TiN or TiCN. The result showed that gradient cemented carbide prepared with 0.13 μm ultra-fine TiC 0.5N 0.5 had better properties. With the increase of ultra-fine TiC 0.5N 0.5 content, the thickness of gradient surface zone decreased. TiCN coatings were deposited on gradient substrate and conventional substrate by moderate temperature chemical vapor deposition (MTCVD), respectively. Gradient substrate resulted in better adhesion and cutting performance.

Enhancing Surface Hardness of Titanium Alloy Ti-6Al-4V by Combined Nitriding and CVD Coating

Titanium alloys show a relatively high strength to density ratio and good corrosion resistance. Their main disadvantage in many applications is the low hardness and hence low resistance to abrasive wear. The wear resistance of titanium alloys can be enhanced by nitriding, but the compound layer thickness is limited. The requirement of thicker compound layers could be fulfilled by a combination process. The duplex process of nitriding plus moderate temperature chemical vapour deposition (MTCVD) TiCN coating of titanium alloys appears promising. Either pressure nitriding or gas nitriding can be applied to Ti-6Al-4V. With pressure nitriding, homogeneous compound layers can be produced on complex shaped components; however, the combined process must be carried out discontinuously in two reactors, due to the different process parameters. When using gas nitriding, the combined process can be performed continuously in the CVD equipment. With the combined nitriding +MTCVD coating route, thick compound layers could be produced in relatively short process times. The surface microstructures consist of a nitrogen diffusion layer, an intermediate layer, a compound layer, and a TiCN coating. The Ti-6Al-4V surface was characterised by high hardness and good layer adhesion.

Microstructure and properties of Ti(C,N) coatings produced by moderate temperature chemical vapour deposition

In this work, Ti(C,N) coatings produced by moderate temperature chemical vapour deposition (MTCVD) were investigated and compared with Ti(C,N) coatings produced by conventional CVD. Detailed characterisation of the microstructure was made using transmission electron microscopy in combination with electron diffraction and electron energy-loss spectroscopy. The mechanical properties of different Ti(C,N) coatings were also dealt with. The deposited Ti(C,N) coatings had a twinned columnar microstructure with strong [112] texture. Large {001} crystal faces result in a rough and facetted surface. MTCVD coated tools have higher transverse rupture strength values than CVD coated ones, due to reduced decarburisation of the cemented carbide substrates and lower residual tensile stresses. Reduced decarburisation and the absence of the reversible η-phase reaction lead to improved edge strength.

Wear characteristics of TiC, Ti(C,N), TiN and Al 2O 3 coatings in the turning of conventional and Ca-treated steels

The wear characteristics of single layers of TiC, Ti(C,N), TiN and Al 2O 3 were investigated during turning of conventional and Ca-treated quenched and tempered Al-killed steels. The experimental coatings were deposited using chemical vapour deposition (CVD) or moderate temperature CVD (MTCVD) on cemented carbide substrates of a single composition and the coatings were of similar thicknesses (7 ± 1 μm). The wear mechanisms and layer formation were studied using scanning electron microscopy, optical microscopy and X-ray diffraction. Inclusion modification appeared to be an effective means of enhancing machinability and all experimental coatings exhibited about 20% better performance as a result of Ca-treatment. In particular, the crater wear of the experimental coatings — excluding Al 2O 3 — was clearly reduced. Comparative cutting tests revealed important differences between the coating materials. Wear mechanisms of the experimental coatings are discussed in detail.

New developments in chemically vapour-deposited coatings from an industrial point of view

Abstract The present paper gives an overview of the development of hard and wear-resistant coatings obtained by chemical vapour deposition (CVD), ranging from single layers of TiC, TiN, Ti(C x N y ), HfN and Al 2 O 3 to complex multilayer systems using a combination of the hard materials mentioned above. The progress of the performance in general by these and new coatings applied at reduced temperatures is discussed. The introduction of new CVD coating techniques at reduced temperatures and of special substrate materials has improved the performance and increased the application range in dry- and wet-milling and turning operations for Ti(C x N y ) and new Al 2 O 3 coatings. A comparison of the performance of moderate temperature CVD Ti(C x N y ) coatings vs. different coatings obtained by physical vapour deposition (PVD) in milling applications is given. The wear and the thermal crack behaviour are studied for different cutting conditions and different workpiece materials. For given milling conditions, Ti(C x N y ) coatings obtained at moderate temperatures are found to have superior performance. Further improvements to PVD and plasma-assisted CVD can be expected in the near future that will allow exotic materials to be machined by coated tools.