Article and method of manufacturing the same

Abstract

An article and a method of manufacturing the article is disclosed. The method includes providing the article including a substrate and a coating at least partially disposed on the substrate. The coating includes an outer surface. The coating further includes platinum and chromium. The method further includes applying cold work to the outer surface of the coating to produce a cold-worked layer extending from the outer surface of the coating to a cold work depth. The cold-worked layer includes approximately 45% cold work. The cold work depth is between about 30 microns to about 150 microns from the outer surface of the coating.

Claims

1. A method of manufacturing an article, the method comprising the steps of: providing an article comprising a substrate and a PtCr coating at least partially disposed on the substrate, the PtCr coating comprising an outer surface and a single gamma phase outer zone, the PtCr coating comprising platinum and about 8 wt. % to about 30 wt. % of chromium, wherein the PtCr coating is formed by a process comprising depositing a platinum layer having a thickness of 4 to 7 microns on the substrate and following formation of the platinum layer, a layer of chromium is deposited onto the platinum using a chemical vapor deposition process (CVD) to diffuse in the chromium which interdiffuses the chromium with the platinum to form a single gamma phase structure, the single phase structure forming the single gamma phase outer zone of the PtCr coating; and applying cold work to the outer surface of the PtCr coating to produce a cold-worked layer extending from the outer surface of the PtCr coating to a cold work depth, wherein the cold-worked layer of the article comprises approximately 45% cold work, and wherein the cold work depth is between about 30 microns to about 150 microns from the outer surface of the PtCr coating; wherein the article is a turbine blade.

2. The method of claim 1, wherein applying cold work further comprises shot peening the outer surface of the PtCr coating using shot.

3. The method of claim 2, wherein an intensity of shot peening is between about 2A to about 12A, and wherein the intensity of shot peening is imperial intensity such that 2A is equivalent to 0.002 inches and 12A is equivalent to 0.012 inches.

4. The method of claim 2, wherein the shot is between about 070H to about 330H conforming to at least one of AMS2431/1, AMS2431/2, AMS2431/3, AMS2431/4, AMS2431/5, AMS2431/5, AMS2431/6, AMS2431/7, and AMS2431/8 specifications.

5. The method of claim 2, wherein a coverage of shot peening is between about 95% to about 1200%.

6. The method of claim 1, wherein applying cold work further comprises deep cold rolling the outer surface of the PtCr coating.

7. The method of claim 1, wherein the cold-worked layer further comprises a chromia scale extending from the outer surface of the PtCr coating, and wherein a thickness of the chromia scale is less than the cold work depth.

8. The method of claim 7, wherein the thickness of the chromia scale is less than a thickness of the PtCr coating.

9. The method of claim 8, wherein the cold work depth is greater than the thickness of the PtCr coating.

10. The method of claim 1, wherein the turbine blade comprises an aerofoil, a platform, a shank and a root, and wherein the PtCr coating is disposed on the shank and the root of the turbine blade.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments will now be described by way of example only, with reference to the Figures, in which:

(2) FIG. 1 is a sectional side view of a gas turbine engine;

(3) FIG. 2 is a close up sectional side view of an upstream portion of a gas turbine engine;

(4) FIG. 3 is a partially cut-away view of a gearbox for a gas turbine engine;

(5) FIG. 4 is a schematic perspective view of a turbine blade mounted into a slot on a disc of the gas turbine engine;

(6) FIG. 5 is a schematic sectional view of a root and a shank of the turbine blade having a coating;

(7) FIG. 6 is a schematic view of a cold working process carried out on the turbine blade;

(8) FIG. 7A is a detailed schematic sectional view of the turbine blade depicting the coating and a cold-worked layer;

(9) FIG. 7B is a detailed schematic sectional view of the turbine blade depicting the coating, the cold-worked layer and a chromia scale;

(10) FIG. 8 is a flowchart of a method of manufacturing an article; and,

(11) FIGS. 9A, 9B, and 9C are images depicting corrosion-fatigue performance of various articles.

DETAILED DESCRIPTION OF THE DISCLOSURE

(12) Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art.

(13) As used herein, the terms “about,” “approximate,” or “approximately” with reference to a numerical value means +/− five percent of the numerical value. For example, a depth of “about” 100 microns refers to a depth from 95 microns to 105 microns, but also expressly includes any narrower range of depth or even a single depth within that range, including, for example, a depth of exactly 100 microns. In another example, “approximately” 45% cold work refers to a cold work percentage from 42.75% to 47.25%, but also expressly includes any narrower range of cold work percentage or even a single cold work percentage within that range, including, for example, exactly 45% cold work.

(14) As used herein, “chromia scale” refers to a stable oxidised layer of chromium extending from an outer or an exterior surface of an article. The chromia scale is typically formed due to exposure of the article to a corrosive contaminated environment for a predetermined time period.

(15) As used herein, “single phase gamma outer zone” of a coating refers to an outer zone that extends from an outer surface of a coating. Single phase gamma outer zone is substantially devoid of phase boundaries and includes almost exclusively the gamma phase of an alloy forming the coating. Single phase gamma outer zone may be enriched with a metal, for example, chromium.

(16) As used herein, “cold working” or “cold forming” refers to any metalworking process in which a metallic article is shaped below its recrystallization temperature, usually at the ambient temperature. Examples of cold working processes include shot peening and deep cold rolling. As used herein, “cold work” or “cold-worked layer” refers to a region, a layer or a portion of a given article that includes plastic strain induced by cold working. As used herein, “cold work depth” of a cold-worked layer is a depth or a thickness measured from an outer or exterior surface of a given article. Unless otherwise mentioned, plastic strain induced by cold working is present across the cold work depth. Plastic strain may also vary across the cold work depth.

(17) In the present disclosure, an amount of cold work in a given article has been characterised as cold work percentage (%). Cold work % refers to the absolute value of a true plastic strain in the sample expressed as a percentage. For example, 45% cold work refers to 45% true plastic strain. Cold work % may be measured by various methods, for example, X-ray diffraction techniques.

(18) Various parameters of shot peening process have been used in the present disclosure. Definitions of such parameters are provided below.

(19) As used herein, “coverage of shot peening” or “shot peening coverage” is expressed as a percentage which relates to a surface coverage of a given article. For example, 100% coverage equates to one complete coverage of shot peening indents. 2000% coverage equates to 20 complete coverages of shot peening indents.

(20) As used herein, “intensity of shot peening” or “shot peening intensity” refers to imperial Almen intensity consistent with Aerospace Material Specification AMS 2431 published by SAE International. Shot peening intensity is measured by peening a strip of Almen material, either A-type or N-type, for a sufficient length of time to achieve 98% coverage of the surface. The shot peening intensity is defined as the arc height of an Almen test strip measured at a coverage of 98% by using an Almen gauge. The amount of material deflection is measured in mils and the measure of the deflection is the peening intensity. Thus, if an A-type Almen strip is used, and deflection is measured to be 6 mils, then a 6 A peening intensity is achieved. In other words, 6 A is equivalent to 0.006 inches of deflection. The A-scale is the less severe peening scale as compared to the N-scale.

(21) In the present disclosure, peening media or shot is characterised by a numeral followed by the letter “H”. Further, “shot size” is given in inches. For example, 110H is equivalent to 0.011 inches and H denotes hard shot type. Peening media in the present disclosure conforms to at least one of Aerospace Material Specifications AMS 2431/1, AMS 2431/2, AMS 2431/3, AMS 2431/4, AMS 2431/5, AMS 2431/6, AMS 2431/7, or AMS 2431/8 published by SAE International. Details of these specifications are provided in Table 1 (provided below) of the present disclosure.

(22) FIG. 1 illustrates a gas turbine engine 10 having a principal rotational axis 9. The engine 10 comprises an air intake 12 and a propulsive fan 23 that generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 comprises a core 11 that receives the core airflow A. The engine core 11 comprises, in axial flow series, a low pressure compressor 14, a high pressure compressor 15, combustion equipment 16, a high pressure turbine 17, a low pressure turbine 19 and a core exhaust nozzle 20. A nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass exhaust nozzle 18. The bypass airflow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low pressure turbine 19 via a shaft 26 and an epicyclic gearbox 30.

(23) In use, the core airflow A is accelerated and compressed by the low pressure compressor 14 and directed into the high pressure compressor 15 where further compression takes place. The compressed air exhausted from the high pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel and the mixture is combusted. The resultant hot combustion products then expand through, and thereby drive, the high pressure and low pressure turbines 17, 19 before being exhausted through the core exhaust nozzle 20 to provide some propulsive thrust. The high pressure turbine 17 drives the high pressure compressor 15 by a suitable interconnecting shaft 27. The fan 23 generally provides the majority of the propulsive thrust. The epicyclic gearbox 30 is a reduction gearbox.

(24) An exemplary arrangement for a geared fan gas turbine engine 10 is shown in FIG. 2. The low pressure turbine 19 (see FIG. 1) drives the shaft 26, which is coupled to a sun wheel, or sun gear, 28 of the epicyclic gear arrangement 30. Radially outwardly of the sun gear 28 and intermeshing therewith is a plurality of planet gears 32 that are coupled together by a planet carrier 34. The planet carrier 34 constrains the planet gears 32 to process around the sun gear 28 in synchronicity whilst enabling each planet gear 32 to rotate about its own axis. The planet carrier 34 is coupled via linkages 36 to the fan 23 in order to drive its rotation about the engine axis 9. Radially outwardly of the planet gears 32 and intermeshing therewith is an annulus or ring gear 38 that is coupled, via linkages 40, to a stationary supporting structure 24.

(25) Note that the terms “low pressure turbine” and “low pressure compressor” as used herein may be taken to mean the lowest pressure turbine stages and lowest pressure compressor stages (i.e. not including the fan 23) respectively and/or the turbine and compressor stages that are connected together by the interconnecting shaft 26 with the lowest rotational speed in the engine (i.e. not including the gearbox output shaft that drives the fan 23). In some literature, the “low pressure turbine” and “low pressure compressor” referred to herein may alternatively be known as the “intermediate pressure turbine” and “intermediate pressure compressor”. Where such alternative nomenclature is used, the fan 23 may be referred to as a first, or lowest pressure, compression stage.

(26) The epicyclic gearbox 30 is shown by way of example in greater detail in FIG. 3. Each of the sun gear 28, planet gears 32 and ring gear 38 comprise teeth about their periphery to intermesh with the other gears. However, for clarity only exemplary portions of the teeth are illustrated in FIG. 3. There are four planet gears 32 illustrated, although it will be apparent to the skilled reader that more or fewer planet gears 32 may be provided within the scope of the claimed invention. Practical applications of a planetary epicyclic gearbox 30 generally comprise at least three planet gears 32.

(27) The epicyclic gearbox 30 illustrated by way of example in FIGS. 2 and 3 is of the planetary type, in that the planet carrier 34 is coupled to an output shaft via linkages 36, with the ring gear 38 fixed. However, any other suitable type of epicyclic gearbox 30 may be used. By way of further example, the epicyclic gearbox 30 may be a star arrangement, in which the planet carrier 34 is held fixed, with the ring (or annulus) gear 38 allowed to rotate. In such an arrangement the fan 23 is driven by the ring gear 38. By way of further alternative example, the gearbox 30 may be a differential gearbox in which the ring gear 38 and the planet carrier 34 are both allowed to rotate.

(28) It will be appreciated that the arrangement shown in FIGS. 2 and 3 is by way of example only, and various alternatives are within the scope of the present disclosure. Purely by way of example, any suitable arrangement may be used for locating the gearbox 30 in the engine 10 and/or for connecting the gearbox 30 to the engine 10. By way of further example, the connections (such as the linkages 36, 40 in the FIG. 2 example) between the gearbox 30 and other parts of the engine 10 (such as the input shaft 26, the output shaft and the fixed structure 24) may have any desired degree of stiffness or flexibility. By way of further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts from the gearbox and the fixed structures, such as the gearbox casing) may be used, and the disclosure is not limited to the exemplary arrangement of FIG. 2. For example, where the gearbox 30 has a star arrangement (described above), the skilled person would readily understand that the arrangement of output and support linkages and bearing locations would typically be different to that shown by way of example in FIG. 2.

(29) Accordingly, the present disclosure extends to a gas turbine engine having any arrangement of gearbox styles (for example star or planetary), support structures, input and output shaft arrangement, and bearing locations.

(30) Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate pressure compressor and/or a booster compressor).

(31) Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in FIG. 1 has a split flow nozzle 18, 20 meaning that the flow through the bypass duct 22 has its own nozzle 18 that is separate to and radially outside the core exhaust nozzle 20. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct 22 and the flow through the core 11 are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example. In some arrangements, the gas turbine engine 10 may not comprise a gearbox 30.

(32) The geometry of the gas turbine engine 10, and components thereof, is defined by a conventional axis system, comprising an axial direction (which is aligned with the rotational axis 9), a radial direction (in the bottom-to-top direction in FIG. 1), and a circumferential direction (perpendicular to the page in the FIG. 1 view). The axial, radial and circumferential directions are mutually perpendicular.

(33) FIG. 4 illustrates a turbine blade 100 mounted in a root slot 102 of a turbine disc 104. The gas turbine 10 (shown in FIG. 1) includes the turbine blade 100. Specifically, a turbine of the gas turbine engine 10 includes the turbine blade 100. The turbine can be the high pressure turbine 17 and/or the low pressure turbine 19.

(34) The turbine blade 100 includes an aerofoil 106, a platform 108, a shank 110 and a root 112. The aerofoil 106 extends radially outward from the platform 108. The shank 110 and the root 112 extend radially inward from the platform 108 opposite to the aerofoil 106. The root 112 is at least partially received in the root slot 102 of the turbine disc 104. The turbine blade 100 may have internal cooling passages which carry cooling air in use to allow the blade to operate at high temperatures. In some embodiments, a coating 200 (shown in FIG. 5) is at least partially disposed on a substrate of the turbine blade 100. In some embodiments, the coating 200 is disposed on the shank 110 and the root 112 of the turbine blade 100.

(35) FIG. 5 shows a detailed view of the coating 200 of the turbine blade 100 according to an embodiment of the present disclosure. The coating 200 is at least partially disposed on a substrate 114 of the turbine blade 100. In the illustrated embodiment, the substrate 114 includes the shank 110 and the root 112. The coating 200 extends over at least the whole exterior surface of the root 110 and the shank 112. The coating 200 includes an outer surface 202. The outer surface 202 forms the exterior surface of the coating 200.

(36) In some embodiments, the coating 200 includes platinum and chromium. In some embodiments, the coating 200 includes between about 8 wt. % to about 80 wt. % of chromium. In some other embodiments, the coating 200 includes between about 8 wt. % to about 30 wt. % of chromium. In some other embodiments, the coating 200 includes between about 9 wt. % to about 50 wt. % of chromium.

(37) The turbine blade 100 may be manufactured from a metallic material, for example, a nickel based superalloy, a cobalt based superalloy, or other based superalloy that comprises a gamma prime phase matrix and a gamma prime phase in the gamma phase matrix. The substrate 114 may therefore be manufactured from a superalloy.

(38) A platinum layer may be deposited using a standard electroplating process. Alternatively, chemical vapour deposition, physical vapour deposition, e.g., sputtering, plasma assisted chemical vapour deposition, or any other suitable process may be used provided a thickness of the deposited coating is above a defined minimum and is conformal without pores or blistering.

(39) The deposited platinum layer may be subsequently heat treated at a temperature between 1000° C. and 1200° C. for 1 to 6 hours. This may produce a two phase (gamma-gamma prime) coating. The heat treatment of a 7 micron thick layer of platinum into the nickel base superalloy may result in a platinum enriched outer layer between about microns to about 30 microns thick.

(40) The heat treatment of a 4 micron thick layer of platinum into the nickel based superalloy may result in a platinum enriched outer layer between about 12 to about microns thick. In some embodiments, a layer of platinum that is deposited is between about 5 to about 11.5 microns and generates an outer layer that is between about 5 and about 30 microns.

(41) Following formation of the platinum layer, a layer of chromium may be deposited onto the platinum using a chemical vapour deposition process (CVD) to diffuse in about 8 to 80 wt. % chromium which interdiffuses the chromium with the platinum to form a single gamma phase structure. To achieve the desired interdiffusion, the CVD process may be run at 875° C. to 1200° C. for 1 to 12 hours. Further, the single phase structure forms a single gamma phase outer zone of the coating 200.

(42) An example of the coating 200 is disclosed in United States patent application US 2014/0271220 A1, the disclosure of which is incorporated herein by reference in its entirety.

(43) In the illustrated embodiment of FIGS. 4 and 5, the coating 200 is provided on the turbine blade 100. However, a coating similar to the coating 200 may be provided on any other article that may be used in the gas turbine engine 10 of FIG. 1. In some embodiments, the article is an aerofoil or a vane. In some other embodiments, the article may be used in boilers, such as biomass boilers. In some other embodiments, the article may be used in oil and gas industry. In some other embodiments, the article may be used in a nuclear reactor.

(44) The article includes a substrate. The substrate may be made of a high performance alloy, such as nickel based superalloy. The article further includes the coating that is at least partially disposed on the substrate. The coating includes an outer surface. Specifically, the coating is disposed on at least a portion of an exterior surface of the substrate. In some cases, the coating may cover the whole exterior surface of the substrate.

(45) In some embodiments, cold work is applied to the outer surface of the coating to produce a cold-worked layer. The cold-worked layer extends from the outer surface of the coating to a cold work depth. The cold-worked layer includes approximately 45% cold work to the cold work depth. In some embodiments, the cold work depth is between about 30 microns to about 150 microns from the outer surface of the coating. In some embodiments, the cold-worked layer further includes a chromia scale extending from the outer surface of the coating. In some embodiments, a thickness of the chromia scale is less than the cold work depth. In some embodiments, the thickness of the chromia scale is less than a thickness of the coating. In some embodiments, the cold work depth is greater than the thickness of the coating.

(46) In some embodiments, applying the cold work includes shot peening the outer surface of the coating using shot. In some embodiments, an intensity of shot peening Is between about 2 A to about 12 A. In some embodiments, the shot is between about 070 to about 330 conforming to at least one of AMS2431/1, AMS2431/2, AMS2431/3, AMS2431/4, AMS2431/5, AMS2431/5, AMS2431/6, AMS2431/7, and AMS2431/8 specifications. In some embodiments, a coverage of shot peening is between about 95% to about 1200%.

(47) In some other embodiments, applying the cold work includes deep cold rolling the outer surface of the coating.

(48) The coating and the cold-worked layer may be applicable to articles made of superalloys, such as nickel based superalloys. Such articles may operate in a temperature range from 400° C. to 750° C. in corrosive contaminated environments.

(49) FIG. 6 shows a cold working process carried out on the turbine blade 100 in accordance with an embodiment of the present disclosure. In the illustrated embodiment, the cold working process is a shot peening process. Shot peening includes impinging the outer surface 202 of the coating 200 of the turbine blade 100 with shot 300. Shot peening the outer surface 202 of the coating 200 may produce cold work at the outer surface 202. The shot 300 is discharged by a shot peening machine 302.

(50) The shot peening may be carried out with predetermined values of various parameters, for example, shot size, shot hardness, intensity of shot peening, coverage of shot peening etc. In some embodiments, an intensity of shot peening is between about 2 A to about 12 A. In some other embodiments, an intensity of shot peening is between about 4 A to about 10 A. The intensity of shot peening is expressed as imperial intensity such that 2 A is equivalent to 0.002 inches, 4 A is equivalent to 0.004 inches, 10 A is equivalent to 0.010 inches, and 12 A is equivalent to 0.012 inches. In some embodiments, the shot 300 is between about 070 to about 330 conforming to specifications as per AMS2431. In some other embodiments, the shot 300 has 070H to 330H shot size with Vickers hardness of 45-62 Hv. In some other embodiments, the shot 300 has shot size between about 110H to about 230H as per AMS2431 specifications. In some embodiments, the coverage of shot peening is between about 80% to about 2500%. In some other embodiments, a coverage of shot peening is between about 95% to about 1200%.

(51) Some exemplary AM S2431 specifications are provided in Table 1 below.

(52) TABLE-US-00001 TABLE 1 Peening media and identification codes Specification Description Code AMS243 1/1 Cast Steel Shot, Regular Hardness ASR (45 to 52 HRC) AMS243 1/2 Cast Steel Shot, High Hardness ASH (55 to 62 HRC) AMS243 1/3 Conditioned Carbon Steel Cut Wire Shot, AWCR Regular Hardness (45 to 52 HRC) AMS243 1/4 Conditioned Stainless-Steel Cut Wire Shot AWS AMS243 1/5 Peening Balls APB AMS243 1/6 Glass Shot AGB AMS243 1/7 Ceramic Shot AZB AMS243 1/8 Conditioned Carbon Steel Cut Wire Shot, AWCH High Hardness (55 to 62 HRC)

(53) Some exemplary combinations of shot peening parameters are provided in Table 2 below.

(54) TABLE-US-00002 TABLE 2 Shot peening parameters Shot Size (H) Intensity (A) Coverage (%) 070 1-5  100-2000 110 2-10 100-2000 230 4-12 100-2000 110-230 4-10  95-12000

(55) FIG. 7A illustrates a schematic sectional view of the coating 200 and a cold-worked layer 400 of the turbine blade 100 in accordance with an embodiment of the present disclosure. The cold-worked layer 400 and the coating 200 without cold work are both shown for illustrative purposes. Referring to FIGS. 4, 5 and 7A, the substrate 114 of the turbine blade 100 includes the coating 200 and the cold-worked layer 400. The substrate 114 may include the shank 110 and/or the root 112 of the turbine blade 100. The coating 200 is disposed on an exterior surface of the substrate 114. The coating 200 includes the outer surface 202 that defines the exterior surface of the coating 200. The coating 200 has a thickness T1. The cold-worked layer 400 may be formed due to cold working of the outer surface 202 of the coating 200. In some embodiments, the cold-worked layer 400 may be formed by shot peening as described above with reference to FIG. 6. In some other embodiments, the cold-work layer 400 may be formed by deep cold rolling of the outer surface 202 of the coating 200.

(56) The coating 200 further includes a single gamma phase outer zone 204. The single gamma phase outer zone 204 may be enriched with chromium. The coating 200 may further include a platinum enriched inner zone (not shown) adjacent to the single gamma phase outer zone 204. A thickness T2 of the single gamma phase outer zone 204 may be a fraction of the thickness T2 of the coating 200. The single gamma phase outer zone 204 may be substantially devoid of phase boundaries. This may avoid regions at which the atomic structure can change and can cause strain due to in part to a mismatch in elemental makeup. Absence of phase boundaries may improve the corrosion resistance of the coating 200.

(57) The cold-worked layer 400 may be formed due to plastic strain induced by cold working. The cold-worked layer 400 extends to a cold work depth CD from the outer surface 202 of the coating 200. In the illustrated embodiment, the cold work depth CD is greater than the thickness T1 of the coating 200. However, in some other embodiments, the cold work depth CD is less than or equal to the thickness T1 of the coating 200. In some embodiments, the cold work depth CD is between about 30 microns to about 150 microns from the outer surface 202 of the coating 200. In some other embodiments, the cold work depth CD is at least 10 microns, at least 50 microns, at least 70 microns, at least 100 micros, or at least 120 microns. In some other embodiments, the cold work depth CD is about 150 microns. In some embodiments, the cold-worked layer 400 includes approximately 45% cold work to the cold work depth CD. In some other embodiments, the cold-worked layer 400 includes approximately 10%, approximately 50%, approximately 60%, or approximately 80% cold work. The cold work may be uniform or variable across the cold work depth.

(58) FIG. 7B illustrates the cold-worked layer 400 further including a chromia scale 402 extending from the outer surface 202 of the coating 200. Referring to FIGS. 4, 5 and 7B, the chromia scale 402 may be a stable oxidised layer of chromium formed in the single gamma phase outer zone 204 of the coating 200. The chromia scale 402 may also include other metal oxides. The chromia scale 402 may provide oxidation resistance in an oxidising environment. The chromia scale 402 may be formed due to exposure of the turbine blade 100 to a corrosive contaminated environment for a predetermined time period. For example, the chromia scale 402 may be formed due to exposure of the turbine blade 100 to an environment within the gas turbine engine 10 (shown in FIG. 1) for a predetermined time period of engine operation.

(59) A thickness T3 of the chromia scale 402 may be less than or equal to the thickness T2 of the single gamma phase outer zone 204 of the coating 200. In the illustrated embodiment, the thickness T3 is less than the thickness T2. Therefore, the thickness T3 of the chromia scale 402 is less than the thickness T1 of the coating 200. Further, the thickness T3 of the chromia scale is less than the cold work depth CD. The comparison between the different thickness is mathematically represented as: T3<T2<T1<CD.

(60) FIG. 8 illustrates a method 600 of manufacturing an article. Referring to FIGS. 2-7B, the article may be the turbine blade 100. The turbine blade 100 will be interchangeably referred to as the article 100.

(61) At step 602, the method 600 includes providing the article 100 including the substrate 114 and the coating 200 at least partially disposed on the substrate 114. The coating 200 includes the outer surface 202. The coating 200 further includes platinum and chromium. In some embodiments, the coating 200 further includes the single gamma phase outer zone 204. In some embodiments, the coating 200 includes between about 8 wt. % to about 80 wt. % of chromium.

(62) At step 604, the method 600 further includes applying cold work to the outer surface 202 of the coating 200 to produce the cold-worked layer 400 extending from the outer surface 202 of the coating 200 to the cold work depth CD. In some embodiments, the cold-worked layer 400 includes approximately 45% cold work to the cold work depth CD. In some embodiments, the cold work depth CD is between about 30 microns to about 150 microns from the outer surface 202 of the coating 200.

(63) In some embodiments, applying cold work further includes shot peening the outer surface 202 of the coating 200 using the shot 300. In some embodiments, the intensity of shot peening is between about 2 A to about 12 A. In some embodiments, the shot 300 is between about 070 to about 330 conforming to at least one of AMS2431/1, AMS2431/2, AMS2431/3, AMS2431/4, AMS2431/5, AMS2431/5, AMS2431/6, AMS2431/7, and AMS2431/8 specifications. In some embodiments, the coverage of shot peening is between about 95% to about 1200%.

(64) In some embodiments, applying cold work further includes deep cold rolling the outer surface 202 of the article 100.

(65) In some embodiments, the cold-worked layer 400 further includes the chromia scale 402 extending from the outer surface 202 of the coating 200. The chromia scale 402 may be formed due to exposure of the article 100 to a corrosive contaminated environment for a predetermined time period. In some embodiments, the thickness T3 of the chromia scale 402 is less than the cold work depth CD. In some embodiments, the thickness T3 of the chromia scale 402 is less than the thickness T1 of the coating 200. In some embodiments, the cold work depth CD is greater than the thickness T1 of the coating 200.

(66) The cold-worked layer 400 imparted by the method 600 may improve corrosion-fatigue performance of the article 100. Specifically, the cold-worked layer 400 may provide improved resistance of the article 100 to Type IV corrosion-fatigue attack. Imparting cold work to the outer surface 202 of the coating 200 may provide retardation of coating cracks in early stages of an attack mechanism associated with Type IV corrosion-fatigue attack. The chromia scale 402 may provide additional corrosion resistance. Since the corrosion kinetics at temperatures below 600° C. are typically very slow, the cold-worked layer 400 along with the chromia scale 402 may provide an improved combined resistance to Type IV corrosion-fatigue attack. The cold-worked layer 400 may therefore protect the coating 200 against Type IV corrosion-fatigue attack that could otherwise cause embrittling of the coating. The coating 200 may therefore continue to protect the substrate 114 from environmental degradation.

(67) The coating 200 including platinum and chromium may also be referred to as a PtCr coating. The PtCr coating may also include the single gamma phase outer zone 204.

(68) FIGS. 9A, 9B and 9C depict images of articles 900A, 900B and 900C, respectively. The article 900A includes a coating that has undergone cold working, i.e., shot peening. The coating is a PtCr coating. The article 900B includes a coating that has not undergone any cold working. The article 900C does not include any coating. The articles 900A, 900B, 900C were subjected to 560° C. notched corrosion-fatigue testing. It may be apparent from the images that articles 900B and 900C displays cracks in the PtCr coating. However, the article 900A that has been subjected to shot peening does not display any cracks. The addition of the cold-worked layer to the PtCr coating may therefore provide improved resistance against Type IV corrosion-fatigue attack as compared to PtCr coatings without any cold work.

(69) The images depicted in FIGS. 9A, 9B and 9C were generated using scanning electron microscope (SEM) high magnification imaging.

(70) Applying cold work to an outer surface or an exterior surface of a PtCr coating may improve corrosion-fatigue of an article including the PtCr coating. Specifically, a cold-work layer formed due to cold working may improve resistance of the article to Type IV corrosion-fatigue attack. Imparting shot peening to the outer surface of the coating may provide retardation of coating cracks in early stages of an attack mechanism associated with Type IV corrosion-fatigue attack. Cold working may also aid in the formation of a chromia scale extending from the outer surface of the coating. The chromia scale may be formed due to the chromium enriched outer zone (i.e., the single gamma phase outer zone) of the PtCr coating. The chromia scale may provide additional corrosion resistance. The combination of the cold-worked layer and the PtCr coating may therefore provide an improved corrosion resistance and crack retardation. Specifically, the cold-worked layer along with the chromia scale may provide an improved combined resistance to Type IV corrosion-fatigue attack. The corrosion-fatigue performance of the combination of the cold-worked layer and the PtCr coating may therefore be better than only cold work or only PtCr coating.

(71) The various parameters of PtCr coating, the cold-work layer and shot peening can be measured using various methods. Some exemplary measurement methods are provided below.

(72) Alicona surface roughness or SEM high magnification imaging may be used to measure shot peening dimple size. This can be cross correlated to the shot size used in the shot peening process.

(73) Energy-dispersive X-ray spectroscopy (EDM) analyses may be used to determine a composition of the PtCr coating. SEM imaging may be used for microstructure and thickness measurements. Such analysis may be carried out on a cross-section of an article.

(74) Cold work percent (%) can be measured using X-ray diffraction. Electron back scatter diffraction can be used to measure the depth of cold work. Nano-indentation can also be used to measure the depth of cold work. Micro-hardness tests can be used to measure residual stress and cold work depth profile. Cold work comparison between short peened articles and unpeened articles may be carried out using electron back scatter diffraction and kernel misorientation spread analysis. Electron back scatter diffraction may also be used to measure the chromia scale. Such measurements can be carried out on a cross-section of an article.

(75) It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.