KR101882584B1 - Enhanced Corrosion Resistance Coatings by a Hybrid PVD/ALD Process and Manufacturing Method thereof - Google Patents

Abstract

According to the present invention, CrN is coated as a hard film on a base material by PVD method, and a nano-layered Al ₂ O ₃ / TiO ₂ (nanolaminate-Al ₂ O ₃ / TiO ₂ ) Thereby providing a multilayer coating film coated by the PVD method. That is, the layers stacked to the nano-thick _{Al 2 O 3 / TiO 2 (} nanolaminate-Al 2 O 3 / TiO 2) this provides a multi-layer coating film inserted in the middle of the rigid film layer CrN.

Description

TECHNICAL FIELD The present invention relates to a corrosion-resistant coating film comprising PVD and ALD,

The present invention relates to a technique for producing a high hardness coating film for improving corrosion resistance using CrN as a base material. More particularly, the present invention relates to a technique for producing a high hardness coating film as a multilayer film, To a coating film production technique.

Corrosion is a fatal disadvantage to metal parts which are widely used in industry. In aggressive environments, the technique of protecting metals from corrosion is a very important field, and forming the coating layer on metal surfaces is the most common form. A variety of coating layers have been developed and are exemplified by ceramic protective coatings such as nitrides, carbides, silicides and transition metal oxides, which exhibit relatively high corrosion resistance, abrasion resistance, and mechanical strength, Electronic, petroleum, chemical, mechanical, textile, and automotive industries.

On the other hand, CrN is a material which is attracting attention due to high hardness, high abrasion resistance and excellent corrosion resistance. Although these coating films have been produced by environmentally friendly PDV technology, there is a problem that the coating film by the PVD process contains many internal defects. That is, defects such as column structure, pinholes, pores, cracks, discontinuities, etc. have a significant influence on corrosion resistance. Especially, when the substrate is an active alloy such as iron, it is affected more by exposure to surrounding softening ions.

Recently, many researches for removing internal defects of such coating films have been conducted, and nanocomposites have been added or multi-layered structures have been formed.

On the other hand, ALD technology has been attracting attention due to its advantages such as uniformity of thin film, uniformity, low temperature process, and precise thickness control applied to thin film growth, and makes it possible to manufacture a high quality impermeable barrier layer.

Taking into consideration the advantages of PVD and ALD as described above, 10-1659232 discloses a multilayer coating film in which CrN is coated on a base material by PVD, Al ₂ O ₃ is coated on ALD, and CrN is coated on the base material to improve both corrosion resistance and mechanical properties I have provided it. In the above, Al ₂ O ₃ by ALD blocks pinholes and provides a passivation function with a low defect and an excellent insulating barrier. However, Al ₂ O ₃ is fundamentally vulnerable to corrosion by water. Therefore, it is not suitable in a high humidity environment or an environment in which water is flooded.

On the other hand, Al ₂ O ₃ Besides, TiO ₂ shows high strength, excellent oxidation and corrosion resistance. TiO ₂ shows excellent water resistance, and Al ₂ O ₃ To protect against erosion by water.

It is an object of the present invention to provide a coating technique for improving corrosion resistance, abrasion resistance and mechanical properties by providing CrN as a coating material to a base material, wherein an intercalation layer is formed between CrN coating layers made of PVD by the ALD method, And to provide a construction of a coating film capable of preventing erosion or penetration by water.

The present invention and to coat the CrN by a hard film on a base material by PVD method, an _{Al 2 O 3 / TiO 2 (} nanolaminate-Al 2 O 3 / TiO 2) stacked in a nano-thickness according to the purpose of a stacked ALD method Next, a multilayer coating film obtained by coating CrN with the PVD method was provided. That is, the layers stacked to the nano-thick _{Al 2 O 3 / TiO 2 (} nanolaminate-Al 2 O 3 / TiO 2) this provides a multi-layer coating film inserted in the middle of the rigid film layer CrN.

In the above, the thickness of the entire multi-layer coating film is 3 to 5 μm, and the thickness of the interposed Al ₂ O ₃ / TiO ₂ (nanolaminate-Al ₂ O ₃ / TiO ₂ ) layer is as thin as 15 to 50 nm.

According to the present invention, when the nano-laminated Al ₂ O ₃ / TiO ₂ layer was inserted into the middle of the CrN hard film, the grain size of the CrN hard film made of PVD was reduced by about 10 nm, while the crystal structure of the CrN hard film was It could be kept unchanged.

Due to the existence of the nano-laminated Al ₂ O ₃ / TiO ₂ layer, the penetration or erosion by water is prevented, the corrosion current I _corr is limited to about 6.26 10 ^-6 A / cm ² , and the corrosion potential E _corr The corrosion resistance is improved by setting the limit to about -2.145 V as a limit.

FIG. 1 is a schematic view showing that an Al ₂ O ₃ layer, a TiO ₂ layer, and an Al ₂ O ₃ / TiO ₂ layer are inserted into a CrN coating layer as an intermediate layer when CrN is coated on a base material.
FIG. 2 is a graph showing (a) an XRD pattern and (b) an average grain size for the samples shown in the schematic diagram of FIG.
3 is a SEM photograph of the samples shown in the schematic diagram of FIG.
FIG. 4 shows the surface roughness of three-dimensional AFM images of the samples shown in the schematic diagram of FIG.
5 is a TEM / HRTEM / EDX analysis of pictures of the _{CrN-Al 2 O 3 / TiO} 2 coating.
6 is a case clad with _{CrN, CrN-Al 2 O 3} , CrN-TiO 2 and _{CrN-Al 2 O 3 / TiO} 2 coating on the SUS304, SUS304 3.5 wt. These are graphs showing the dynamic potential and the potential potential (Potentiodynamic and potential static) in the% NaCl solution, respectively.
FIG. 7 is a table showing conditions for manufacturing the CrN-Al ₂ O ₃ / TiO ₂ coating layer of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In this embodiment, it was examined for physical properties by forming three kinds of coating layers of _{CrN-Al 2 O 3 -CrN,} CrN-TiO 2 -CrN, and _{CrN-Al 2 O 3 / TiO} 2 -CrN the base material. CrN is deposited by the PVD method and interposed intermediate layers are deposited by the ALD method.

First, prepare the base material and apply CrN coating.

In this embodiment, the base material was SUS304, and a Cr adhesive layer was deposited on a monocrystalline Si wafer and an SUS304 substrate ultrasonically cleaned, which is intended to improve coating adhesion. CrN layers were deposited from a Cr target (99.99%) using a coating system using pulsed DC sputtering power in Ar and N ₂ gas. The thickness of the CrN layers was controlled by adjusting the deposition time. The deposition conditions of CrN are summarized in Table 1 in FIG.

Next, an ALD-intermediate layer is deposited.

ALD interlayers between 10 nm and 20 nm thick were deposited using a LUCIDA D100 ALD system on pre-deposited CrN. Each of Al ₂ O ₃ and TiO ₂ The intermediate layers were obtained using trimethylaluminium (Al (CH ₃ ) ₃ ), titanium isopropoxide (TTIP), and H ₂ O reactants, respectively.

Both depositions proceeded at a low temperature of 150 ° C. During the deposition of Al ₂ O ₃ and TiO ₂ , the tubes containing TMA, TTIP, and H ₂ O were stored at 25 ° C, 60 ° C, and 10 ° C to provide a uniform precursor.

The growth order of Al ₂ O ₃ is 0.5 s TMA pulse, 10 s N ₂ purge, 1 s H ₂ O pulse, and 10 s N ₂ purge. The growth order of TiO ₂ is 0.1 s TTIP assist and 1 s TTIP pulse, 10 s N ₂ purge, 1 s H ₂ O pulse, and 10 s N ₂ purge.

As mentioned above, the nano-laminated Al ₂ O ₃ / TiO ₂ interlayers laminated with nano-thickness were obtained by repeatedly subcycles of Al ₂ O ₃ and TiO ₂ , respectively. In both cases, the thickness of the vapor- 2 nm. The deposition cycles for each unit cycle were ~ 0.15 nm / cycle for Al ₂ O ₃ and ~ 0.03 nm / cycle for TiO ₂ , which is the growth rate per cycle (GPC) Respectively.

In general, the pure CrN coating and Al ₂ O ₃ , TiO ₂ and nanolaminate-Al ₂ O ₃ / TiO ₂ interlayer configurations were controlled through PVD deposition times and ALD deposition cycles. A schematic drawing of samples 1 to 4 is shown in FIG. 1, and deposition parameters are listed in Table 1 (FIG. 7). In FIG. 1 (d), the nanolaminate-Al ₂ O ₃ / TiO ₂ intermediate layer structure is formed by alternately laminating about 10 times of Al ₂ O ₃ and TiO ₂ each having a thickness of about ₂ nm.

The characteristics of the coating film produced by this example were analyzed and the following results were obtained.

The crystal structure of the films was confirmed with an X-ray diffractometer (XRD, D8-Discovery Brucker, 40 kV) using 1.54 Å Cu-Kα radiation. Surface and cross-sectional micrographs of the coatings were evaluated using a scanning electron microscope (SEM, Hitachi, S-4800, 15 KV).

The surface morphology was observed using AFM (asylum research MFD-3D). The observation inside the CrN-Al ₂ O ₃ / TiO ₂ coating was confirmed by transmission electron microscopy (TEM, TALOS F200X) and energy dispersive spectroscopy (EDS) .

The electrochemical corrosion resistance of the coatings was investigated using a three electrode cell. Potential dynamics and potential static polarity test results of the samples were 3.5 wt. % NaCl aqueous solution.

A saturated calomel electrode (SCE) and a platinum (Pt) mesh were used as reference and counter electrodes, respectively.

The test results were as follows.

The exclusive coated with CrN and _{CrN-Al 2 O 3, CrN} -TiO 2 and the X-ray pattern of the multi-layer coating of _{CrN-Al 2 O 3 / TiO} 2 have been introduced in Fig. 2 (a). The diffraction pattern showed a cubic phase crystalline CrN with a mixed orientation of (111), (200), (220), (311), and (222) crystal planes. There was no XRD peak corresponding to another crystal phase, for example Al ₂ O ₃ , TiO ₂ or other CrN phases, because the intercalated interlayer had an amorphous amorphous structure and intercalation of the interlayer resulted in the phase of the CrN matrix It means that it did not cause metastasis. The grain size was calculated using Scherrer's formula, as previously found, because the formula provides a better approach to predicting D than the Williamson-Hall method. As shown in FIG. 2 (b), the grain size of the multilayer coating (approximately 24 nm) was significantly reduced after inserting the intermediate layer as compared to the single coated CrN (about 34 nm) And also inhibits new nucleation of CrN grains on the ALD-modified surface in the second deposition process.

Figure 3 shows the CrN and CrN-Al ₂ O _3, the multi-layer coating in top view and cross-section image of a TiO _2-CrN and _{CrN-Al 2 O 3 / TiO} 2 obtained by the SEM observation. As shown in FIG. 3 (a, e, i), the single-coated CrN showed a pyramid-like surface and a porous columnar structure consisting of long columnar grains and clear grain boundaries, ) Was like this.

On the contrary, multilayer coatings showed a denser and shorter columnar grain structure, and the location of the intermediate layer could be clearly identified.

The discontinuous morphology suggests the interstitial cracks along the columnar grains, and the fine grains are formed throughout the coating layer by the new nucleation of CrN formed on the intermediate layer. Hybrid coatings with different interlayers did not show definite morphology changes (see Fig. 3 (f, g, h and j, k, i). However, a reduction in the grain size of the multilayer coatings clearly occurred (Fig. 3 (b, c, d)) as compared to the CrN single coating, which also matches well with the calculation results shown in Fig. 2 (b).

CrN and subjected to AFM analysis to examine the surface roughness of the single coating and multilayer coating of _{CrN-Al 2 O 3, CrN} -TiO 2 and _{CrN-Al 2 O 3 / TiO} 2. As shown in FIG. 4, the surface topography of a 5 um x 5 um image of these coatings is shown, wherein the root mean square (RMS) value of all the specimens was approximately 60 nm and no significant change was observed after interlayer insertion.

The hybrid coating of _{CrN-Al 2 O 3 / TiO} 2 have been chosen in order to investigate a TEM / HRTEM / EDX after FIB stuffs, which is shown in Fig. As can be seen in FIG. 5 (a), the sharply contrasted bright line position appears to be the location of the nanolaminate-Al ₂ O ₃ / TiO ₂ interlayer, where a uniform ALD interlayer was deposited on the surface of the coarse CrN . Also, during the second PVD deposition process performed on the modified nanoraminate interlayer, new small and radial CrN sites were observed.

According to HRTEM observed (Fig. _{5 (b)), Al 2} O 3 And nano-laminates having an inner layer (sublayers) made of a _{TiO 2 - Al 2 O 3 /} TiO 2 is the middle layer can be clearly distinguished by the contrast of gray and white. As shown in FIG. 5 (ch), the EDX analysis of the intermediate layer showed that Al and Ti were uniformly distributed at the interface (interface) of the CrN matrix. Also, the presence of Al and Ti was also found along grain boundaries, suggesting that the ALD deposition completely covers the porous PVD CrN coating.

Potentiodynamic and potentialstatic polarization tests were conducted to investigate the corrosion characteristics.

Figure 6 shows the polarization curves and the current density according to the exposure time of corrosion current density ( I _corr ) versus corrosion potential ( E _corr ), pure CrN and multilayer coatings. As shown in FIG. 6 (ab), when compared with a pure SUS304 sample without CrN coating or a SUS304 sample with CrN coating, a high electric potential is observed after application of the hybrid coatings. I _corr values were obtained by extrapolation to the E _corr axis due to the asymmetrical polarization curves of the anode and cathode branches along a straight line extending along the linear portion of the cathode plot through a Tafel plot.

Quantitative analysis of potentiometric dynamic curves reveals the inverse relationship between I _corr and E _corr . E _corr continuously increases after pure CrN coating, whereas I _corr slightly increases. Also, I _corr decreased with formation of the ALD intermediate layer of CrN, suggesting that the excellent corrosion resistance of such a hybrid coating is derived from the ALD-interlayer having excellent passivation performance.

Hybrid coatings with nano-laminate-Al ₂ O ₃ / TiO ₂ interlayers showed the best corrosion performance at the lowest I _corr of ~ 6.26 × 10 ^-6 A / cm ² and at the highest E _corr of -2.145 V. This demonstrates that the nano-laminate -Al ₂ O ₃ / TiO ₂ intermediate layer is formed after applying a hybrid coating more efficiently against corrosion in the corrosive medium. Figure 6 (c) the CrN-Al ₂ O _3; CrN-TiO _2; Current of the _{CrN-Al 2 O 3 / TiO} 2 - there are listed the time curve, this experiment the stability of the protection for a specified time for the fitting area potential (E = 0.4 V vs. SCE) in a given (the pitting region) To find out. At first, they all showed a downward current density. CrN showed a stable current density of 5 ~ 6 × 10 ^-5 A / cm ² . However, after interlayer insertion, the lowest and most stable current density in the nano-laminate-Al ₂ O ₃ / TiO ₂ , especially 6 to 9 × 10 ^-6 A / cm ² , reversed the superior corrosion resistance results of the coatings.

According to microstructure and corrosion performance studies, it was discussed that the mechanism of hybrid coating prevented the attack of corrosive media. The intermediate layer of the CrN coating showed an improved effect on the corrosive behavior was interpreted largely for two reasons.

First, the dense intermediate layer served as a complete insulating layer to prevent electron transport in the coating, and also acts as an insulating layer against the current flow from the anode to the cathode, reducing the corrosion current density, and the electrons of the anode metal ions Exchange rate and dissolution rate were also reduced.

Second, a continuous intermediate layer with low defect also served as an excellent barrier to cover the porous walls of CrN, for example, to prevent the diffusion of corrosive materials such as chlorine ions. Chloride ion plays an important role in the corrosion process, because it has the ability to damage the passive film formed spontaneously to increase corrosion resistance. Thanks to the small diameter of the ions, chlorine ions can easily diffuse through defects in the pore grain boundary, internal pinholes, and coatings and react with metal ions and soluble compounds. The nano-laminate-Al ₂ O ₃ / TiO ₂ interlayer showed the best internal performance when compared to other multilayer coatings, which is interpreted to be due to the synergy of Al ₂ O ₃ and TiO ₂ . That is, it is presumed that the multi-layered structure of ALD-Al ₂ O ₃ and TiO ₂ , which are highly resistant to water, which effectively cover the defects of CrN due to the fine size, gives strong overall corrosion resistance. Al ₂ O _3, which is relatively finer in grain size, is controlled on the basis of atomic layer on the CrN surface to thoroughly cover the defects. TiO ₂ , which is slightly larger in particle size than Al ₂ O ₃ , _It is predicted that the pores that can be formed by TiO ₂ can be completely buried by laminating Al ₂ O ₃ of ₂ in atomic layer unit and Al ₂ O ₃ of minute particle size again on the surface where TiO ₂ is formed.

It is to be understood that the invention is not limited to the disclosed embodiment, but is capable of many modifications and variations within the scope of the appended claims. It is self-evident.

No reference symbol.

Claims (3)

A method of forming a coating film for improving the corrosion resistance of a base material,
CrN layer is formed by a PVD (Physical Vapor Deposition) method,
By the TiO ₂ layer and the Al ₂ O ₃ layer on the CrN layer formed on the ALD (atomic layer deposition), but forming a nanolaminate -Al ₂ O ₃ / TiO ₂ layer, a nano-laminate -Al ₂ O ₃ / TiO ₂ layer is Al ₂ O ₃ and TiO ₂ layers are alternately repeatedly laminated using the ALD method,
To form a CrN layer formed by PVD over nanolaminate -Al ₂ O ₃ / TiO ₂ layer,
Nanolaminate -Al ₂ O ₃ / TiO ₂ by the insertion of the layer covering the defect of the CrN layer, CrN / nano-laminate, characterized in that to prevent the grain growth and to improve the corrosion resistance -Al ₂ O ₃ / TiO ₂ / CrN multilayer coating film. delete The method according to claim 1, wherein the nanolaminate-Al ₂ O ₃ / TiO ₂ layer is formed to a thickness of 10 to 20 nm.

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