WO2008052347A1

WO2008052347A1 - Use of cold spray to deposit coatings which improve fatigue life of a component

Info

Publication number: WO2008052347A1
Application number: PCT/CA2007/001967
Authority: WO
Inventors: George Kim; Bertrand Jodoin; Eric Sansoucy
Original assignee: University Of Ottawa
Priority date: 2006-11-03
Filing date: 2007-11-02
Publication date: 2008-05-08

Abstract

Cold Spray techniques show increasing potential for the production of corrosion-resistant components useful, for example, in vehicle or other heavy industry. Disclosed herein are methods of applying coatings, coatings themselves, and coated components, as well as methods to provide or improve characteristics of a component, such as fatigue strength.

Description

COATINGS, METHODS FOR THEIR PRODUCTION AND USE

FIELD OF THE INVENTION

The invention relates to the field of coatings generated by Cold Spray techniques, and their use.

BACKGROUND TO THE INVENTION

Aircraft or vehicle components, or components used in many other fields of industry, may be exposed to challenging conditions such as heat, chemicals, physical stress etc. Such conditions may result in component degradation, failure, or deterioration of component performance. Several techniques are known in the art for coating such components, for example to make them more corrosion resistant. Thermal Spray (TS) and Cold Spray (CS) techniques are just two examples.

Cold Spray techniques involve the use of a supersonic, high- velocity, or subsonic gas jet to accelerate solid particulate matter towards a substrate. In this way, the particles deform plastically upon impact with the substrate, and bond to form the desired coating. Cold Spray is an effective means for solid state material deposition.

Although Cold Spray holds much promise, the molecular mechanisms that underlie the techniques are poorly understood. Cold Spray remains an area of research in embryonic flux, and significant improvements in Cold Spray methodologies, applications, and resultant coatings are required for large scale industrial application.

SUMMARY OF THE INVENTION

It is one object of the present invention, at least in preferred embodiments, to provide a useful coating generated via Cold Spray.

It is another object of the present invention, at least in preferred embodiments, to provide a fatigue strengthened component.

It is another object of the present invention, at least in preferred embodiments, to provide a method to improve the fatigue-life of a component. Certain exemplary embodiments provide a method of increasing an ability of a component to resist damage or breakage due to fatigue, the method comprising the steps of: applying a coating to the component via Cold Spray, the coating material optionally being more anodic than a material of the component. In certain exemplary embodiments, the particulate feedstock material for Cold Spray comprises Aluminum or an alloy thereof, Magnesium or an alloy thereof, or Zinc or an alloy thereof. In certain exemplary embodiments, the alloy is amorphous, nanocrystalline, or conventional crystalline, or any combination thereof. In certain exemplary embodiments, the particulate feedstock material for Cold Spray comprises a metal-matrix composite (MMC). In certain exemplary embodiments, the alloy further comprises a transition element, and a rare-earth element. In certain exemplary embodiments, the transition element is Cobalt. In certain exemplary embodiments, the rare-earth element is Cerium. Certain expemplary embodiments provide a component having deposited thereon a coating applied by Cold Spray, the coating comprising a coating material suitable to an ability of the component to resist damage or breakage due to fatigue, the coating optionally being more anodic than a material of the component. In certain exemplary embodiments, the particulate feedstock material for Cold Spray comprises Aluminum or an alloy thereof, Magnesium or an alloy thereof, or Zinc or an alloy thereof. In certain exemplary embodiments, the alloy is amorphous, nanocrystalline, or conventional crystalline, or any combination thereof. In certain exemplary embodiments, the particulate feedstock material for Cold Spray comprises a metal-matrix composite (MMC). In certain exemplary embodiments, the alloy further comprises a transition element, and a rare-earth element. In certain exemplary embodiments, the transition element is Cobalt. In certain exemplary embodiments, the rare-earth element is Cerium. In certain exemplary embodiments, the component is suitable for use as a vehicle component or a structural component for structural or civil engineering. In certain exemplary embodiments, the vehicle is a watercraft, or an aircraft.

Certain exemplary embodiments provide a coating applied by Cold Spray, the coating being suitable to improve and ability of the component to resist damage or breakage due to fatigue, and optionally comprising a coating material being more anodic than a material of a component to which it is applied. In certain exemplary embodiments, the particulate feedstock material for Cold Spray comprises Aluminum or an alloy thereof, Magnesium or an alloy thereof, or Zinc or an alloy thereof. In certain exemplary embodiments, the alloy is amorphous, nanocrystalline, or conventional crystalline, or any combination thereof. In certain exemplary embodiments, the particulate feedstock material for Cold Spray comprises a metal- matrix composite (MMC). In certain exemplary embodiments, the alloy further comprises a transition element, and a rare-earth element. In certain exemplary embodiments, the transition element is Cobalt. In certain exemplary embodiments, the rare-earth element is Cerium. In certain exemplary embodiments, the component is suitable for use as a vehicle component or a structural component for structural or civil engineering. In certain exemplary embodiments, the vehicle is a watercraft, or an aircraft. Certain exemplary embodiments provide for a use of a component of the invention in the manufacture of a vehicle. In certain exemplary embodiments, the vehicle is an aircraft or a watercraft.

Certain exemplary embodiments provide for a use of a component of the invention for structural or civil engineering. Certain exemplary embodiments provide for a use of a coating of the invention, to coat a component. In certain exemplary embodiments, the component is a vehicle component. In certain exemplary embodiments, the vehicle is an aircraft or a watercraft. In certain exemplary embodiments, the component is for use in structural or civil engineering. Certain exemplary embodiments provide a method for performing a repetitive mechanical action involving a component, the method comprising the steps of: imparting resistance to the component to prevent damage or breakage due to fatigue, by coating the component with a coating via Cold Spray; applying mechanical forces to the component thereby to cause said component to undergo said repetitive mechanical action for a plurality of repetitive cycles without said damage or breakage due to fatigue of the component. Certain exemplary embodiments provide a method for performing a repetitive mechanical action involving a component, the method comprising the steps of: increasing the resistance of the component to damage or breakage due to fatigue, by coating the component with a coating via Cold Spray; and applying mechanical forces to the component thereby to cause said component to undergo said repetitive mechanical action for a greater number of repetitive cycles prior to damage or breakage of the component due to fatigue, than would be possible with an uncoated component.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 provides a scanning electronic micrograph (SEM) showing the morphology of the Al-13Co-26Ce powder particles.

Figure 2 graphically illustrates particle size distribution of the Al-13Co-26Ce powder.

Figure 3 illustrates a side or plan view of a cantilevered beam subjected to an alternating load.

Figure 4 illustrates a bending fatigue test sample. The gray region corresponds to the coated area. All the dimensions are in mm.

Figure 5 provides a graph to illustrate measured particle velocity of the Al-Co-Ce powder particles.

Figure 6 provides a graph to illustrate a mean number of cycles prior to failure as a function of the alternating stress obtained from the bending fatigue tests of the bare, Alclad and Al-Co-Ce.

Figure 7 provides a photograph to illustrate the bending fatigue specimen after the test. Failure occurred outside the coated area. Figure 8 provides a photograph of the bond strength specimens with a) the bonding agent and b) the remainder of the Al-Co-Ce coating after the test.

Figure 9 provides an SEM image of the cross-section of an Al-Co-Ce coating produced on a fatigue strength specimen.

Figure 10 provides a graph to illustrate XRD patterns for the Al-13Co-26Ce powder and the coating.

Figure 11 provides an SEM image of a zinc coating showing the thickness and the substate-coating interface.

Figure 12 provides a SEM image of a magnified view of Figure 11 showing a dense microstructure.

Figure 13 provides an SEM image of a zinc coating showing the thickness.

Figure 14 provides an SEM image of a magnified view of Figure 13 of the substrate- coating interface.

Figure 15 provides an SEM image of an Al-Co-Ce coating showing the overall thickness.

Figure 16 provides a magnified view of a section of the coating of Figure 15.

Figure 17 provides another magnified view of the coating of Figure 15.

Figure 18 provides a photograph of a tested fatigue strength sample. Failure occurred outside the coated area.

DEFINITIONS:

Alloy: refers to any mixture of two or more metals, or of any one or more metals together with any one or more non-metal substances. Selected alloys may comprise Aluminum, Magnesium or Zinc, or a combination thereof. An alloy may be amorphous, nanostructured, nanocrystalline, or conventional crystalline. Alloy may also include amounts of transition and / or rare earth elements. Al-Co-Ce and nanostructured AA5O83 aluminium alloys are preferred, at least in selected embodiments.

Coating: refers to any coating applied to a substrate or component via coldspray. In selected embodiments, the coating may be more anodic than the substrate to which it is applied, for example to provide sacrificial cathodic protection for the substrate (e.g. against corrosion). Cold Spray: refers to any technique involving acceleration of particular matter in high- velocity, sub-sonic, or supersonic flows, for impact with a surface of a substrate at a temperature insufficient to cause significant melting or significant softening of the particles, such that impact causes plastic or other deformation of the particulate material for adhesion of the material to the surface, thereby to form a coating. Preferably, the impact speed and plastic deformation is sufficient for the particulate material to form an substantially non-porous coating with a high-quality or high-contact coating/substrate interface (for example substantially lacking gaps or regions of poor contact). The following patent documents include further non- limiting examples of Cold Spray techniques: United States Patents 6,365,222, 6,808,817, 6,780,458, 6,491,208, and 7,081,376, each of which is incorporated herein by reference.

Component: any item or article onto which a coating is applied via Cold Spray in accordance with the present invention. Such a component may also be referred to as a substrate, with a surface of the substrate being the surface onto which the coating is deposited. The component may comprise any material, including but not limited to: plastic, glass, resin, rubber, polymer, wood, stone, paint, etc., but more preferably comprises a metal or metal alloy, for example comprising Aluminum, magnesium, Zinc, or steel. Fatigue: refers to progressive and localised structural damage that occurs when a material is subjected to loading, such as cyclic loading. The maximum stress values are less than the ultimate tensile stress limit, and may be below the yield stress limit of the material. Fatigue strength: refers to a capacity of a component to avoid fatigue, or to resist breakage, damage, fracture, cracking or any other wear resulting from exposure of the component to a single or repeated physical stress or force from one or more directions or at one or more points. Metal matrix composite (MMC): refers to a composite material with at least two constituent parts, one being a metal. The other material may be a different metal or another material, such as a ceramic or organic compound.

Preferably: unless otherwise stated, the term preferably refers to preferred features of the broadest embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Cold Spray techniques show increasing potential for the production of corrosion-resistant components useful, for example, in vehicle or other heavy industry. Disclosed herein are methods of applying coatings, coatings themselves, and coated components, that further exhibit fatigue resistance. In selected aspects of the present invention, the inventors have unexpectedly discovered that selected Cold Spray coatings significantly enhance a fatigue-resistance and / or strength of a component. In selected embodiments, for example, gas atomized particles of an Al- 13 Co-

26Ce alloy system were sprayed using the Cold Spray deposition technique. The coating microstructures were examined and the mechanical characteristics, in particular the bending fatigue and the bond strength, of Al-Co-Ce coatings are disclosed herein. The Al-Co-Ce coating improved the fatigue behavior of AA 2024- T3 when compared to uncoated and Alclad specimens. During the bond strength tests, the bonding agent failed and delamination of the coating from the substrate did not occur. The microstructural features of the initial powder were also found in the coatings. The coatings contained amorphous and crystalline phase contents similar to the ones found in the feedstock powder. The increase in fatigue properties was attributed to the residual compressive stresses induced in the coating and to the high adhesion strength of the coating to the substrate. Amorphous metals, also called metallic glasses, are characterized by their lack of defects such as grain boundaries and dislocations typically found in crystalline materials. The unique properties of these materials have pushed the industry towards the development of a new class of alloys. Aluminum-based amorphous alloys have demonstrated improved mechanical properties as well as significant enhancements to corrosion resistance compared to their crystalline counterparts [I]. For example, the addition of a late transition element such as cobalt, and a rare-earth element such as cerium, to an aluminum matrix, improves its corrosion protection abilities. When used as metallic coatings for aluminum components, an Al-Co-Ce alloy can act as a sacrificial anode and provides resistance to halide-induced pitting [2-4]. This superior pitting resistance is partly due to the amorphous structure and the presence of cobalt in the solid solution that limit the number of pitting initiation sites. The addition of cerium improves the amorphicity of the alloy and offers sacrificial anodic protection by decreasing the open circuit potential [2].

Typical thermal spray processes, such as plasma and high velocity oxy-fuel spraying techniques, may produce metallic amorphous coatings. The formation of the amorphous phase in the coating is attributed to the high cooling rates associated with these processes. Furthermore, the amorphous content within the coating depends on the spraying and depositing conditions. The critical cooling rate, for example, is influenced by certain chemical reactions such as the formation of intermetallic phases and oxidation [5]. Similarly, recrystallization of the amorphous phase can also occur during successive thermal spray passes. This causes localized reheating due to the deposition of molten droplets [6]. The presence of the crystalline phase and chemical changes represent inhomogeneities that affect the corrosion properties of the alloy.

In order to produce a fully amorphous coating, while avoiding chemical changes and recrystallization of the amorphous phase, the amorphous feedstock powder particles must undergo solid-state deformation in order to bond to the substrate. The Cold Gas Dynamic Spraying (CGDS) represents an emerging thermal spray technology in which the process temperatures are well below the melting point of the sprayed material. Consequently, the powder particles experience no significant heating and in-flight melting or softening. This absence of significant heating of the feedstock powder eliminates the possibilities of grain growth and chemical reactions. In CGDS, the particles are injected in a supersonic flow and accelerated above the material's dependant critical velocity [8]. Upon impact with the substrate, the particles undergo intense plastic deformation. The impact also disrupts the passivation layers, which provide intimate contact between the particles and the substrate [8-10]. In CGDS, the micro structure of the powder and the microstructure of the coatings are similar. For example, nanocrystalline [11-14] and amorphous [15, 16] coatings have been produced from nanocrystalline and amorphous feedstock powders, respectively. The CGDS process is capable of depositing a wide variety of aluminum alloys coatings [14, 17, 18].

In view of the aforementioned attributes of the CGDS process, Al-Co-Ce coatings produced by this technique constitute a promising application in the field of anodic protection of aluminum structures. Although the corrosion behaviors of Al- Co-Ce alloys have been explored, their fatigue performance as a coating has not been investigated. The objectives of this study are to produce Al-Co-Ce coatings using the CGDS process and evaluate their mechanical properties. The bond strength, the fatigue behavior, the hardness, and the microstructural features of the coatings are examined. Unexpected and profound improvements in fatigue strength and component durability are observed through the application of a coating by Coldspray. The results thus indicate the potential of Coldspray techniques in the manufacture of coated components suitable for use in mechanical, structural, and civil engineering including, for example, vehicle components that are subjected to repeated and significant mechanical forces.

This invention thus provides, in selected embodiments, for methods for performing a repetitive mechanical action involving a component, the methods comprising the steps of: imparting resistance to the component to prevent damage or breakage due to fatigue, by coating the component with a coating via Cold Spray; applying mechanical forces to the component thereby to cause said component to undergo said repetitive mechanical action for a plurality of repetitive cycles without said damage or breakage due to fatigue of the component. In this way, selected methods enable the use of the component in the step of applying mechanical forces, wherein the component would have been less suitable (or perhaps not suitable) for the method without the application thereto of a coating via Cold Spray.

In further selected embodiments there are provided methods for performing a repetitive mechanical action involving a component, the methods comprising the steps of: increasing the resistance of the component to damage or breakage due to fatigue, by coating the component with a coating via Cold Spray; and applying mechanical forces to the component thereby to cause said component to undergo said repetitive mechanical action for a greater number of repetitive cycles prior to damage or breakage of the component due to fatigue, than would be possible with an uncoated component. In this way, selected methods may prolong the life of the component in the step of applying mechanical forces.

Without the coating, the component would be expected to have a shorter lifespan, due to more rapid damage or breakage due to fatigue resulting from the mechanical action. The coating applied by Cold Spray thus confers, in such embodiments, greater fatigue strength to the component, so that it can undergo a greater number of cycles of the repetitive mechanical action prior to failure.

The following examples are merely illustrative of the methods, components, and coatings of the invention, and are in no way intended to be limiting with respect to the scope of the appended claims.

Example 1 - Powder preparation

The Al-13Co-26Ce powder was prepared by gas atomization. The various cooling rates encountered in the atomization process caused the powder to have an amorphous mixed with a crystalline phase. In addition, the particles have a spherical morphology, as illustrated in Fig. 1. The particle size distribution, outlined in Fig. 2, indicates that the powder has an average diameter of 12 μm. About 90% of the particles have a size below 23 μm. Example 2 - Particle velocity measurements

Particle velocities were measured using the DPV-CPS (Tecnar Automation Ltd., St- Bruno, Quebec, Canada), a laser in-flight diagnostic system. While a continuous laser illuminates a measurement volume, a dual-slit photomask captures the signal generated by individual particles passing in front of the sensor. The signal from the photosensor is then amplified, filtered, and analyzed. The in-flight diagnostic of each individual particle that crosses the measurement volume is performed by determining the time between two peaks of the particle signal. The particle velocities are then obtained by dividing the distance between the two-slits by the particle's flight time [21]. In this study, the velocity measurements were taken at a location 5 mm from the spray gun exit. In order to avoid particle build-ups and rebounds that could obstruct the sensor field of view, the particle velocity measurements were performed without the presence of a substrate at the exit of the spray gun.

Example 3 - Coating preparation

The aluminum alloy coatings were produced using the cold spray coating system developed at the University of Ottawa Cold Spray Laboratory. The system includes a spray chamber, a spray gun, a propellant gas heater, and a commercial powder feeder (Praxair Surface Technologies model 1264, Concord, NH, USA). The spray gun consists of a converging-diverging nozzle with an exit diameter of 7.3 mm. For the present work, helium was used as the propellant gas. The stagnation pressure and stagnation temperature used were 1.7 MPa and 320°C, respectively. The coatings were produced on grit blasted aluminum substrates at a stand-off distance of 10 mm.

Example 4 - Coating evaluation

The fatigue behavior, bond strength, and hardness tests were used to evaluate the properties of the coatings. The deposits were also analyzed based on a microstructural observation.

As an example, the effects of the Al-Co-Ce coatings on the bending fatigue behavior of AA 2024-T3 were examined following the ASTM Standard B 593-96 [20]. This test measures the ability of a material to withstand cyclic stress without developing cracks or other evidence of mechanical deterioration. The test specimens were supported in the same manner as a cantilevered beam at one end and were subjected to an alternating force at the other, as depicted in Fig. 3. The fatigue test specimen shown in Fig. 4, includes a triangular shape intended to produce a constant stress along the length of the test section of the specimen. This triangular region was grit- blasted and coated on one side only. Single passes, at 50% overlap, were used to cover the previously mentioned portion of the specimens with an Al-Co-Ce coating. In the current study, stress levels of 30, 40, and 50 ksi at a frequency of 30 Hz and a mean stress of zero, were used to test the samples. Two to three specimens were tested at each stress level. The number of cycles was automatically recorded until complete sample failure, characterized by the separation of the specimen into two pieces. The fatigue behavior of the coated test samples was then compared to uncoated AA 2024-T3 and Alclad specimens.

Once tested, the coated regions of the fatigue specimen were sectioned, and prepared for scanning electron microscopy (SEM) of the coating microstructure, following standard metallographic techniques. Secondary electron and backscattered electron images of the coatings' cross-sections were used to evaluate the microstructural features. Porosity and oxide contents were measured by optical microscopy and analyzed using a commercial metallographic software. A grey scale delineation technique was used to quantify the area fraction of oxides, porosity, and aluminum. X-ray diffraction (XRD) were carried out using a Scintag XDS-2000 diffractometer using Cu Ka radiation at 50 steps per degree and a count time of 5 sec per step.

Bond strength evaluations were conducted using the ASTM Standard C 633-01 [19]. Coatings were produced on grit-blasted standard test samples having a 25.4 mm diameter and an overall length of 38.1 mm. Several passes were carried out to cover the entire surface of the sample. The top portion of the coating was machined flat and glued to an uncoated test sample, using an adhesive (Master Bond EP- 15, Hackensack, NJ, USA). The assembled parts were cured at 17O⁰C for 90 minutes in a V block device that ensures proper alignment. Before testing the coatings, the bonding agent was tested separately on uncoated test samples, and failed at 82 MPa, which conforms to the product specifications.

Example 5 - Particle velocity measurements Prior to producing the Al-Co-Ce coatings, particle velocity measurements were performed under the test conditions listed above. The measured particle velocity distribution is shown in Fig. 5. The particle velocities varied between 600 and 1000 m/s, with an average of 842 ± 80 m/s. This high average particle velocity was due to the small average particle size. A narrow particle velocity distribution was obtained as a result of the slender particle size distribution.

Example 6 - Mechanical properties evaluation

The experimental results of the fatigue tests for the bare, Alclad coated and Al-Co-

Ce coated specimens are presented in Fig. 6. At all three stress levels, the specimens with CGDS deposited Al-Co-Ce outperformed the bare and the Alclad coated specimens. At a stress of 50 ksi, the Alclad and the Al-Co-Ce coated specimens failed at about the same number of cycles. However, as the stress amplitude decreases, the Al-Co-Ce coatings significantly improve the fatigue performance of the substrates. At 30 ksi, the Al-Co-Ce coatings outlasted the bare and the Alclad specimens by over an order of magnitude. The fatigue curve for the coated samples indicates that the Al-Co-Ce coatings give rise to a significant increase in fatigue properties of the coated substrates in comparison with the uncoated substrates at all stress levels. It is interesting to note that during the tests, delamination of the Al-Co- Ce coatings from their substrates did not occur and failure occurred outside the coated area, as shown in Fig. 7. The Al-Co-Ce coatings remained completely attached to the substrates.

The adhesion level the of Al-Co-Ce coatings was evaluated through bond strength tests. The coatings produced on standard adhesion strength specimens failed at an average strength 61 ± 4 MPa. The failures occurred partly in the coating (cohesive) and partly in the adhesive (the bonding agent). Figure 8 illustrates the mixed failure mode between the glue and the coating. Consequently, the adhesive strength of the Al-Co-Ce coatings is larger than the reported value since the coating remained attached to the coated specimen.

The present results can be explained on the basis of two important factors: the existence of residual compressive stresses, and the high adhesion of the coatings to the substrate. In CGDS, compressive stresses are induced in the coatings. The high velocity impacts of particles cause plastic deformation of the underlying layers and generate compressive residual stresses [22]. Herein, evidence is provided to illustraste that such stresses can play a significant role in improving the fatigue behavior of materials by delaying crack initiation and propagation. However, the stresses that exist within a cold-sprayed coating are mainly beneficial if the coating remains attached to the substrate. Hence, the appropriate adhesion of the coatings to the substrates also contributed in improving the fatigue properties of the AA 2024- T3 substrates.

Example 7 - Coating microstructure

The cross-section of the coated region of a tested fatigue specimen is shown in Fig. 9. The coating thickness of approximately 160 μm and its microstructure were consistent throughout the sample. The coating remained well adhered to the substrate during fatigue testing, which confirms the absence of any delamination of the coating from the substrate. The coating remained structurally intact as neither damages nor cracks as a result of the fatigue test were found in the coating.

A quantitative analysis of the SEM samples revealed that oxide content was below 0.3%. The coatings exhibited porosity levels below 0.03%. An average oxygen content of 1.29% was obtained by EDS. A Vickers hardness value of 340 was also measured, which is approximately 1.5 times harder than the AA 2024-T3 substrate.

A fully amorphous coating was not achieved in this study since the original feedstock contained amorphous and crystalline particles. A crystalline phase precipitated during the gas atomization in the larger particles. As the particle size increases, the cooling rates decrease and crystallization occurs during the solidification process [15]. Figure 10 shows the XRD patterns for the Al-13Co-26Ce powder and a cold sprayed coating. These results indicate that no microstructural changes occurred during the deposition process. The amorphous regions found in the coating are attributed to the deformation of amorphous particles that preserved their initial microstructure after their impact. Correspondingly, the crystallized particles also kept their original microstructure and constitute the crystalline zones in the coating. Hence, the coating's microstructure and amorphous content reflect the features and quality of the initial feedstock powder. A fully amorphous coating may be synthesized from a feedstock powder consisting of amorphous particles only.

The CGDS process was used to produce coatings of a partially amorphous Al-Co-Ce alloy system. The mechanical properties of the deposits were evaluated based on the fatigue behavior, bond strength, and hardness. The oxide, porosity, and oxygen contents within the coatings were obtained from a microstructural analysis.

The Al-Co-Ce coatings give rise to a substantial increase in the fatigue properties in comparison with the uncoated and the Alclad coated substrates. It was proposed that any crack propagation in the coating was hindered by the residual compressive stresses contained in the coating. In addition, an excellent adhesion prevented delamination of the coatings from the substrates. Bond strength tests of Al-Co-Ce coatings confirmed their high degree of bonding to substrates. During these tests, fracture occurred within the coating and within the adhesive and not the substrate- coating interface. A microstructural examination of a tested fatigue sample indicated that the coatings remained structurally intact, which was supported by the absence of any damage in the coating.

Consequently, it is shown that the use of Al-Co-Ce coatings on aluminum alloys may provide improved corrosion resistance as well as increased fatigue resistance of the coated component.

Example 8 - Further SEM analysis The following images were obtained from scanning electron microscopy (SEM). Figure 11 shows the thickness and the substrate-coating interface of a zinc coating. In Figure 12, a magnified view of Figure 11 that demonstrates the dense microstructure of the coating. Figures 13 and 14 depict another zinc coating.

Further images are scanning electron microscopy (SEM) images of Al-Co-Ce coatings. Figure 15 displays the overall thickness of the coating. The substrate- coating interface is also shown at the bottom of the figure.

Figures 16 and 17 are magnified views of the coating. The different grey contrast represent different phase that were produced during the gas atomization of the powder.

A tested fatigue strength specimen is shown in Figure 18. The coated region is the dark grey zone on the specimen. This specimen shows that failure occurred outside the coated region. During the fatigue strength tests, all the specimens coated with an Al-Co-Ce coating failed in the same manner.

Whilst the invention has been described with reference to specific embodiments of methods, components, and coatings, these embodiments are in no way intended to be limiting. Further embodiments other than those actually presented are within the scope of the present invention.

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Claims

CLAIMS:

1. A method of increasing an ability of a component to resist damage or breakage due to fatigue, the method comprising the steps of: applying a coating to the component via Cold Spray, the coating material optionally being more anodic than a material of the component.

2. The method of claim 1, wherein the particulate feedstock material for Cold Spray comprises Aluminum or an alloy thereof, Magnesium or an alloy thereof, or

Zinc or an alloy thereof.

3. The method of claim 2, wherein the alloy is amorphous, nanocrystalline, or conventional crystalline, or any combination thereof.

4. The method of claim 1 , wherein the particulate feedstock material for Cold Spray comprises a metal-matrix composite (MMC).

5. The method of claim 2, wherein the alloy further comprises a transition element, and a rare-earth element.

6. The method of claim 5, wherein the transition element is Cobalt.

7. The method of claim 5, wherein the rare-earth element is Cerium.

8. A component having deposited thereon a coating applied by Cold Spray, the coating comprising a coating material suitable to improve the ability of the component to resist damage or breakage due to fatigue, the coating optionally being more anodic than a material of the component.

9. The component of claim 8, wherein the particulate feedstock material for Cold Spray comprises Aluminum or an alloy thereof, Magnesium or an alloy thereof, or Zinc or an alloy thereof.

10. The component of claim 9, wherein the alloy is amorphous, nanocrystalline, or conventional crystalline, or any combination thereof.

11. The component of claim 8, wherein the particulate feedstock material for Cold Spray comprises a metal-matrix composite (MMC).

12. The component of claim 9, wherein the alloy further comprises a transition element, and a rare-earth element.

13. The component of claim 12, wherein the transition element is Cobalt.

14. The component of claim 12, wherein the rare-earth element is Cerium.

15. The component of claim 8, suitable for use as a vehicle component or a structural component for structural or civil engineering.

16. The component of claim 15, wherein the vehicle is a watercraft, or an aircraft.

17. A coating applied by Cold Spray, the coating being suitable to improve the ability of a component to resist damage or breakage due to fatigue, and optionally comprising a coating material being more anodic than a material of a component to which it is applied.

18. The coating of claim 17, wherein the particulate feedstock material for Cold Spray comprises Aluminum or an alloy thereof, Magnesium or an alloy thereof, or

Zinc or an alloy thereof.

19. The coating of claim 18, wherein the alloy is amorphous, nanocrystalline, or conventional crystalline, or any combination thereof.

20. The coating of claim 17, wherein the particulate feedstock material for Cold Spray comprises a metal-matrix composite (MMC).

21. The coating of claim 18, wherein the alloy further comprises a transition element, and a rare-earth element.

22. The coating of claim 21 , wherein the transition element is Cobalt.

23. The coating of claim 21 , wherein the rare-earth element is Cerium.

24. The coating of claim 17, suitable for use as a vehicle component or a structural component for structural or civil engineering.

25. The coating of claim 24, wherein the vehicle is a watercraft, or an aircraft.

26. Use of a component of claim 8, in the manufacture of a vehicle.

27. Use of claim 26, wherein the vehicle is an aircraft or a watercraft.

28. Use of a component of claim 8, for structural or civil engineering.

29. Use of a coating of claim 17, to coat a component.

30. Use of claim 29, wherein the component is a vehicle component.

31. Use of claim 30, wherein the vehicle is an aircraft or a watercraft.

32. Use of claim 29, wherein the component is for use in structural or civil engineering.

33. A method for performing a repetitive mechanical action involving a component, the method comprising the steps of: imparting resistance to the component to prevent damage or breakage due to fatigue, by coating the component with a coating via Cold Spray; applying mechanical forces to the component thereby to cause said component to undergo said repetitive mechanical action for a plurality of repetitive cycles without said damage or breakage due to fatigue of the component.

34. A method for performing a repetitive mechanical action involving a component, the method comprising the steps of: increasing the resistance of the component to damage or breakage due to fatigue, by coating the component with a coating via Cold Spray; and applying mechanical forces to the component thereby to cause said component to undergo said repetitive mechanical action for a greater number of repetitive cycles prior to damage or breakage of the component due to fatigue, than would be possible with an uncoated component.