COATING FORMULATION

Abstract

The present invention relates to a coating formulation comprising at least one carbonaceous material and a coating material. The present invention also relates to a method for preparing a coating formulation comprising at least one carbonaceous material and a coating material comprising the step of dispersing the at least one carbonaceous material in the coating material.

Claims

1. A coating formulation comprising at least one carbonaceous material and a coating material.

2. The coating formulation of claim 1, wherein the at least one carbonaceous material is a carbon nanotube.

3. The coating formulation of claim 2, wherein the carbon nanotube is a single-walled carbon nanotube, a double-walled nanotube, a multi-walled carbon nanotube, an inorganic nanotube, a multibranched nanotube or combination thereof.

4. The coating formulation of claim 1, wherein the at least one carbonaceous material is surface-functionalized.

5. The coating formulation of claim 1, wherein the coating material is selected from the group consisting of tungsten carbide (WC), titanium carbide, titanium nitride, silicon carbide, boron nitrate, rhenium diboride, titanium diboride and combinations thereof.

6. The coating formulation of claim 1, wherein the at least one carbonaceous material is present in the range of 0.05 to 5 wt % based on the total weight of the coating formulation.

7. A method for preparing a coating formulation comprising at least one carbonaceous material and a coating material comprising the step of dispersing the at least one carbonaceous material in the coating material.

8. The method of claim 7, wherein the at least one carbonaceous material is a carbon nanotube.

9. The method of claim 8, wherein the carbon nanotube is a single-walled carbon nanotube, a multi-walled carbon nanotube or combination thereof.

10. The method of claim 7, wherein the at least one carbonaceous material is surface-functionalized.

11. The method of claim 7, wherein the coating material is selected from the group consisting of tungsten carbide (WC), titanium carbide, titanium nitride, silicon carbide, boron nitrate, rhenium diboride, titanium diboride and combinations thereof.

12. The method of claim 7 further comprising the step of milling the dispersion to reduce the particle size of the at least one carbonaceous material and the coating material to form a coating slurry.

13. The method of claim 12, wherein the milling step is undertaken for a period of at least 3 hours.

14. The method of claim 12, wherein the milling step comprises the step of using at least one grinding medium.

15. A substrate coated by a layer of a coating formulation, wherein the coating formulation comprises at least one carbonaceous material and a coating material.

16. The substrate of claim 15, wherein the coating layer has a thickness in the range of 0.5 to 5 mm.

17. The substrate of claim 15, wherein the hardness of the substrate coated by a layer of the coating formulation is at least 10 GPa.

18. The substrate of claim 15, wherein the Young's modulus of the substrate coated by a layer of the coating formulation is at least 220 GPa.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0108] The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0109] FIG. 1 is a picture of a scanning electron microscopy (SEM) image of the functionalized multi-walled carbon nanotube (MWCNT) of Example 1, with a magnification of 30,000.

[0110] FIG. 2 is a picture of a SEM image of the coating formulation prepared according to Example 2. The coating formulation comprises 0.5 wt % to 2 wt % of CNT and tungsten carbide (WC)-17 wt % Co, with a magnification of 5,000.

[0111] FIG. 3 is a number of pictures of cross-sectional SEM images of high velocity oxygen fuel (HVOF) spraying method for (a) WC-17 wt % Co coating, with a magnification of 200; and (b) CNT reinforced WC-17 wt % Co coating, with a magnification of 400according to Example 3.

[0112] FIG. 4 is a number of graphs depicting the XRD spectra of WC-17 wt % Co coating according to Example 3 with various concentration of CNT (0%, 0.5%, 1% and 2%).

[0113] FIG. 5 is a number of graphs depicting (a) the hardness of WC-17 wt % Co coating according to Example 4a with various concentration of CNT (0%, 0.5%, 1% and 2%) and (b) the Young's modulus of WC-17 wt % Co coating according to Example 4a with various concentration of CNT (0%, 0.5%, 1% and 2%).

[0114] FIG. 6 is a graph showing the erosion resistance of WC-17 wt % Co coating according to Example 4b with various concentration of CNT (0%, 0.5%, 1% and 2%).

EXAMPLES

[0115] Non-limiting examples of the invention and a comparative example will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1: Surface-Functionalization of CNTs

[0116] 0.8 g of the as purchased MWCNTs (obtained from mkNANO of Missisauga, Ontario of Canada) was refluxed in a mixture of 15 mL of concentrated nitric acid and 45 mL of concentrated sulfuric acid for a period in the range of 10 minutes to one hour.

[0117] The resulting surface-functionalized CNTs were washed several times by centrifuging in water until the pH of the CNTs suspension was about 7. Once the neutral pH is achieved, the CNTs were dried in a vacuum oven at 60 C. for about one hour.

[0118] The dried CNTs above were then subjected to SEM analysis. As can be seen from FIG. 1, the CNTs that have been surface-functionalized are well-dispersed and do not form clusters suggesting that surface functionalization of CNTs significantly reduces the agglomeration of CNTs.

Example 2: Dispersion of Functionalized CNTs in WCCo Powder

[0119] The surface-functionalized CNTs obtained in Example 1 were dispersed in WC powder via roller milling with grinding media. The amount of CNTs used to form the coating formulation was varied from 0.5 wt % to 2 wt %, whereas the coating precursor used was WC-17 wt % Co powder. The formulation containing the surface-functionalized CNTs and WCCo was then subjected to roller milling for about five hours with grinding media. The resulting formulation was subjected to SEM and Raman analyses.

[0120] From the SEM image of FIG. 2, it can be seen that the CNT is well dispersed in the WCCo matrix. More remarkably, some of the CNT particles appear to lie in between the WCCo powders forming bridges with other powder particles. Further, as can be observed from FIG. 2, the size of the WCCo powders are reduced upon roller milling that facilitates in the creation of a homogeneous mixture. Raman spectroscopy of the formulation powders at several spots reveals the homogeneity of the CNT dispersion and negligible damage for the CNTs during the mixing process.

Example 3: Preparation of the Substrate Coated by a Layer of Coating Formulation of Example 2

[0121] The formulation powders obtained in Example 2 were deposited on Inconel 718 coupons via HVOF.

[0122] It is well known that deposition of WCCo powders with small powder size via HVOF results in decarburization of the coating by the formation of W2C phases. The decarburization leads to a poor adhesion between the WC particles which then increases the inter-lamellar defects and reduces the density. This will in turn reduce the hardness and resistance to abrasive wear.

[0123] Hence, in addition to SEM analysis, additional characterization such as XRD was also used to examine the structure of the coatings.

[0124] As can be seen from the XRD spectra in FIG. 4, W2C phases were not formed in the CNT reinforced WCCo coating, suggesting that there was minimal or no decarburization. This lack of decarburization may be due to the short duration of milling, which did not significantly reduce the size of the WCCo powders.

Example 4: Mechanical Properties of the Coating Formulation of Example 2

[0125] a. Hardness and Young's Modulus

[0126] Mechanical properties of the coatings were measured by the nano-indentor. As can be seen from FIG. 5, the CNT reinforced WCCo coating (referred as the inventive coating formulation in the present disclosure) possessed higher hardness and modulus values. The higher hardness is a result of the denser structure with the addition of the MWCNT while the increased modulus could be due to the addition of MWCNT which possesses superior modulus and the appearance of MWCNT in between the WCCo particles.

[0127] b. Erosion Resistance

[0128] To evaluate the erosion resistance, the initial and final coating thickness and coating weight of the films were measured after bombarding the coatings with Al.sub.2O.sub.3 media for 75 seconds at 60 psi. Results in Table 1 below show that after the bombardment, the reduction of the coating thickness and weight of MWCNT-reinforced WCCo coating was lesser as compared to the WCCo coating. This indicates that the addition of MWCNT increases the erosion resistance. Erosion rate can be reduced as low as 2.5 fold as shown in the table (2% CNT+WCCo vs. pure WC).

[0129] By comparing the erosion resistance to the microhardness measurements in FIG. 6, it can be concluded that the addition of CNT enhances the hardness of the coatings and that the enhanced erosion resistance is due to the increased hardness.

TABLE-US-00001 TABLE 1 Erosion Resistance (thickness) of WCCo and MWCNT-reinforced WCCo coatings Coupon thickness Change in (inch) thickness Sample Before After (inch) Time (s) PSI Pure WC (M73) 0.071 0.061 0.010 75 60 0.5% CNT + WCCo 0.071 0.065 0.006 75 60 1% CNT + WCCo 0.071 0.066 0.005 75 60 2% CNT + WCCo 0.074 0.070 0.004 75 60

[0130] c. High Cycle Fatigue (HCF) Testing

[0131] High cycle fatigue testing was also conducted on the CNT-reinforced WCCo and WCCo coatings according to ASTM E466-07. The following parameters were used: frequency of 29 Hz, stress ratio of 0.1, sinusoidal waveform and a maximum stress of 76.87 ksi. The results indicate that the WCCo coating lasted for 7235 cycles while the CNT-reinforced coating lasted for 9236 cycles. This result suggests that the incorporation of CNT increases the HCF lifetime by 27.66%.

INDUSTRIAL APPLICABILITY

[0132] Owing to the advantages of the CNT reinforced WCCo coating as described in the present disclosure, for example high impact resistance, high HCF lifetime, high fracture toughness and no decarburization observed at high temperature, the coating formulation as defined herein may therefore be useful when applied onto a suitable substrate such as a part or component exposed to extreme environment (high temperature, corrosive). Hence, it is expected that the part or component coated by a layer of the coating formulation as defined herein may be used for various application such as in gas-turbine engines used in transportation, energy and defence sectors.

[0133] Further, since the CNT reinforced WCCo coating as defined in the present disclosure exhibits excellent impact resistance, the part or component coated by the coating formulation as defined here may not undergo erosion due to ingestion of debris thus requiring minimum service and maintenance cost for the coated part or component. In addition, since the layer of the coating formulation also displays increased lubricity and increased temperature capability, the part or component coated by the coating formulation as defined herein may also be suitable for application in aviation, aerospace, automotive and marine and offshore.

[0134] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.