Gas turbine blade and rotor wear-protection system

Abstract

Sacrificial inserts for use in gas turbine engines to reduce friction and wear damage between compressor fan blades and the fan rotors are disclosed. The consumable metallic shims have low friction and reduce fretting and galling on fan blade roots and fan rotor dovetail slots thereby increasing their operating lives, as well as reduce engine noise and improve engine efficiency. The electroformed, compliant, multi-purpose shims may have variable thickness and, when positioned between the blade dovetail root and the rotor disk dovetail slot, prevent movement and slippage between air foil blades and the rotor.

Claims

1. An assembly for a gas turbine engine, comprising: (i) a fan rotor having multiple dovetail shaped slots in the circumference thereof, an outer surface of the fan rotor defining said dovetail shaped slots made of a first material; (ii) fan blades having dovetail shaped roots shaped to fit into the dovetail shaped slots of the fan rotor, an outer surface of each of the dovetail shaped roots made of a second material; and (iii) metallic shims disposed between the fan blade dovetail shaped roots and the fan rotor dovetail shaped slots to decrease air leakage, each metallic shim comprising: a variable thickness along a longitudinal cross-section and/or a transversal cross-section of the metallic shim to minimize a void space between each of the fan rotor dovetail shaped slot and the fan blade dovetail shaped root to decrease dovetail slot air leakage; an outer surface made, at least in part, of a third material; a shim core surrounded, in part, by the outer surface of the metallic shim and made of a fourth material; and wherein the outer surface of each metallic shim contacts the outer surface of the fan blade dovetail shaped root and the outer surface of the fan rotor dovetail shaped slots, the third material providing a lubricious and sacrificial surface layer on at least part of the outer surface of the metallic shim to a depth of at least 10 μm, the third material wearing preferentially when rubbed against the first material and/or the second material.

2. The assembly of claim 1, wherein the first material and/or the second material is selected from the group consisting of Ti, Al, Ni, Co and carbon comprising composites.

3. The assembly of claim 1, wherein the first material and/or the second material comprises Ti and the third material comprises at least one element selected from the group consisting of Co, Cu, Fe, Ni and P.

4. The assembly of claim 1, wherein the third material and/or the fourth material comprises at least one element selected from the group consisting of Co, Cu, Fe, Ni, Mo, F, C, N, S, Si and P.

5. The assembly of claim 4, wherein the third material and/or the fourth material comprises at least 0.5% per weight P.

6. The assembly of claim 4, wherein the third material and/or the fourth material comprises at least one particulate material selected from the group consisting of molybdenum disulfide, titanium nitride, boron nitride, a carbon based material, polytetrafluoroethylene, silicone, and inorganic oxides.

7. The assembly of claim 1, wherein the third material and/or the fourth material comprises Co.

8. The assembly of claim 7, wherein the third and/or the fourth material comprises between 0.05% and 3% per weight P.

9. The assembly of claim 7, wherein the third material and/or the fourth material comprises at least one particulate material selected from the group consisting of molybdenum disulfide, titanium nitride, boron nitride, a carbon based material, polytetrafluoroethylene, silicone, and inorganic oxides.

10. The assembly of claim 1, wherein the third material and the fourth material comprises at least 10% Co.

11. The assembly of claim 1, wherein the third material has a lower hardness than each of the first material, the second material and the fourth material.

12. The assembly of claim 1, wherein at least areas of contact between the first material, the second material, and the third material are covered with a lubricant film.

13. The assembly of claim 1, wherein the third material and/or the fourth material comprises Co in the range of 5-95% per weight, Ni in the range of 5-95% per weight and P in the range of 0.05-5% per weight.

14. The assembly of claim 1, wherein the third material comprises grain-refined Co and has a higher hardness than each of the first material and the second material, both comprising Ti.

15. The assembly of claim 1, wherein the first material and/or the second material comprise Ti and the third material comprises Co and a volume wear loss of the first material and/or the second material rubbing against the third material is less than 8 mm.sup.3/Nm×10.sup.−5 when subjected to an associated pin-on-disk testing in accordance with ASTM G99.

16. The assembly of claim 1, wherein the fourth material is grain-refined.

17. The assembly of claim 1, wherein the third material surrounds the entire outer surface of the shim.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to better illustrate the invention by way of examples, descriptions are provided for suitable embodiments of the method/process/apparatus according to the invention in which:

(2) FIG. 1 is a partial exploded perspective view of a rotor assembly including a fan rotor, and fan blade and a compliant shim contemplated by the present invention.

(3) FIG. 2 is a cross-sectional view of a portion of the assembled rotor assembly with the compliant shim positioned between the fan rotor and fan blade.

(4) FIG. 3 is a cross-sectional view of the compliant shim in a loaded contact region, contemplated by the present invention.

(5) FIG. 4 is a graph showing wear rates of a titanium pin when sliding against different metallic disk materials as determined by pin-on-disk testing in accordance with ASTM G99.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIG. 1 illustrates a fan assembly 10 including a section of a fan disk or rotor 12 of a gas turbine engine capable of receiving a plurality of fan blades 30 held in place by shims 50 according to the present disclosure. Specifically, the fan rotor 12 comprises, on it an outer periphery 16 made of a first material, a plurality of dovetail shaped grooves or slots 18. The slots 18 extend through the outer periphery 16 at an angle between the rotor's axial and tangential axes referred to as disk slot angle. The slots 18 are designed to receive the fan blades 30. Each fan blade 30 includes a radially upstanding airfoil portion 32 that extends from an airfoil leading edge 34 to an airfoil trailing edge 36. Each fan blade also comprises a root or root portion 40 made of a second material which is dovetail shaped to be received by the fan rotor slots 18. The fan rotor 12 and the fan blades 30 are typically made from Ti or Ti alloys, although the use of other materials is contemplated as well. Specifically, the fan blades 30 can be made of lightweight composite materials including carbon fiber reinforced polymers (CFRP) or CFRP cores coated with a metallic material layer, including, but not limited to, nanocrystalline metallic materials. The exemplary compliant shims 50 are used to firmly secure each fan blade 30 in its corresponding fan rotor slot 18.

(7) One of the fan blades 30 mounted in one of the slots 18 of the fan rotor 12 with the shim 50 there between is illustrated in greater detail in the cross-sectional view in FIG. 2. Each fan rotor slot 18 is defined by sloping side walls 22 diverging in a direction from the circumference toward the inward portion of the fan rotor, terminating at a bottom 24. Each fan blade 30 has at its lower end the root portion 40 with sides 28 sloping outward in a direction from the blade body to the dovetail bottom. The root portion 40 is configured and sized to slide into the fan rotor slot 18, as shown in FIG. 2.

(8) As indicated in FIG. 2 there is not a perfect fit between the fan blade root portion 40 and the fan rotor slot 18 creating a small air gap 60 between the side walls 22 and the sides 28 of the root portion 40 which is reduced by placement of the exemplary shim 50. The air gap 60 changes depending on whether or not the engine is operating and depends the rotation speed, and with increased operating time the air gap 60 tends to widen due to wear. The air gap 60 typically isn't uniform throughout its entire cross-section and typically is smaller at the sides and larger at the bottom which requires a perfectly conforming shim to be thinner at the sides and thicker at the bottom to achieve the best fit and minimize the air gap. Minimizing the air gap 60 therefore cannot be achieved with a conventional shim made of a rolled metal sheet of uniform thickness. In addition, an anti-fretting and/or anti-galling coating and/or layer, if applied, is placed at the sides increasing the overall thickness at the sides which limits minimizing the air gap.

(9) When the engine is not in operation, the bottom of the root portion 40 may contact the bottom of the fan rotor slot 18. When the jet engine operates, rotation of the fan rotor 12 generates a centrifugal force which results in movement of each fan blade 30 radially in an outward direction. Consequently, the side 28 of the root portion 40 applies forces against the side wall 22 defining the fan rotor slot 18. The sliding motion of the fan blade root portion 40 combined with the root portion contact pressure and the coefficient of friction (COF) produce shearing forces on both the side wall 22 and the root portion side 28 creating a loaded contact region over the area identified by numeral 32. In contrast, a non-contact region is formed in the area indicated by numeral 34 between the root portion side 28 and the bottom wall 24 defining the fan rotor slot 18 where the loaded contact, by comparison to the side walls in region 32, is small.

(10) As the jet engine operates from rest, through flight operations, and then again to rest, constituting what is generally referred to as a “cycle”, each fan blade 30 is pulled in the outward direction with varying loads. Therefore the side 28 of the root portion 40 and the side wall 22 repeatedly slide past each other by a small distance (<0.25 mm), however, that can nevertheless cause fretting fatigue damage with time. Of most concern is the damage to the fan rotor 12 as small cracks form after repeated cycles. Such cracks can extend into the fan rotor 12 from the side wall 22 and can ultimately lead to failure of the fan rotor.

(11) According to the invention, the wear and fatigue damage that would otherwise occur at the pressure faces because of the sliding motion at the sides 28 of the root portion 40 and the side walls 22 of the fan rotor 12 is reduced by inserting the exemplary shim 50 as reinforcement between the root portion 40 and the side wall 22 and the bottom wall 24 defining the fan rotor slot 18 as indicated in FIG. 2.

(12) The novel, compliant shim 50 is a thin metal sheet formed so that it attaches to the fan blade root portion 40 and is retained during service between the root portion 40 and at least the fan rotor slot side wall 22. The form of the shim 50 is generally a constricted U-shape, with the upper portion of the legs of the U turned slightly toward each other. The shim 50 is sufficiently long that it extends around the bottom of the root portion 40 and at least over the entire contacting surface 32 between the root portion 40 and the fan rotor slot side walls 22, completely separating the sides 28 and the side walls 22 so that they cannot contact each other along the contacting surface 32. The wall thickness of the conforming shim 50 varies to provide an excellent fit between the root portion 40 and the fan rotor slot 18, thereby minimizing the air gap 60 as stated. The fan blades are typically mounted in the fan rotor by first attaching a compliant shim onto each fan blade and sliding the blade/shim assembly into the fan rotor slot in the conventional manner.

(13) The surface of the shim 50 contacting the fan blade root portion 40 and the fan rotor slot 18 typically are softer than the respective materials of the root portion and fan rotor to ensure any material loss due to wear occurs preferentially on the shim preserving/extending the use of the expensive fan blades and rotor. As stated, frequently Ti alloys are used for both fan blades and fan rotors requiring the metallic shim contacting surface to be composed of a material which minimizes wear and friction with Ti and its alloys. The Applicants have surprisingly discovered that grain-refined Co and Co alloys are particularly suited to meet this requirement.

(14) In one embodiment, unlike prior art shims which are made of rolled metal sheet, the exemplary shims 50 are net-shaped electroformed to the exact shape and thickness required. The novel shims are an-isotropic across at least its cross-section and optionally along its length to meet the various material property requirements at various locations along the shims lengths and sides. For instance, an anti-fretting layer is formed in the mating areas of the root portion 40 and the fan rotor slot 18 as indicated as area 32 in FIG. 2 experiencing high forces during engine operation, subject to high wear. Optionally, the anti-fretting layer is also formed in the mating areas of the root portion 40 and the fan rotor slot 18 as indicated as area 34 in FIG. 2 experiencing less contact/friction and, as indicated, it may be beneficial to surround the entire outer surface of the shim with the anti-fretting layer.

(15) In one preferred embodiment the fan blade 30 is made of CFRP and encapsulated in grain-refined Ni and/or Co comprising metallic material (hardness ˜400-650VHN) whereas the side wall 22 and the bottom wall 24 defining the fan rotor slots 18 are made of a Ti alloy (hardness ˜300-400VHN). The shim core can also be made of a grain-refined Ni and/or Co comprising metallic material (10-100 nm grain-size, hardness 300-650VHN) and the sacrificial wear layers on both sides in areas 32 and 34 can comprise a coarser-grained Ni and/or Co metallic material (100-500 nm grain-size, hardness of ≥300VHN) with P as alloying element. Electroforming an isotropic shim and converting the outer surface to an oxide layer by chemical or electrochemical means is within the objects of this invention as well.

(16) FIG. 3 illustrates a cross-section of the novel shim 50 in the loaded contact region 32 of FIG. 2 displaying the wear layer 54 adjacent to the side wall 22 of the fan rotor and the wear layer 56 adjacent to the root portion 40 of the airfoil, made of a third material, and the core 52, made of a forth material. Wear layers 54 and 56 can be of similar or different thickness, and depending on the first material representing the outer surface of the fan rotor slot side wall 22 and the second material representing the outer surface of the root portion 40, can be of the same or different chemical composition. In addition, wear layers 54 and 56 can contain solid lubricants and/or comprise a surface oxide layer, e.g., formed by an appropriate surface oxidation treatment or formed with time by exposure to ambient air.

(17) FIG. 4 illustrates the unlubricated sliding wear loss of a 6 mm Ti ball against disks made from three materials: Ti6Al4V (polycrystalline, hardness: 350VHN), electrodeposited grain-refined Co-2% per weight P (average grain-size: 20 nm, hardness: 540VHN), and electrodeposited grain-refined Co (average grain-size: 20 nm, hardness: 400VHN). Specifically, the pin-on-disk testing was performed in accordance with ASTM G99 (“Standard Test Method for Wear Testing with a Pin-on-Disk Apparatus”) using the following testing parameters: (i) a 6 mm diameter ball (Titanium), (ii) an applied load of 10N, (iii) a sliding speed of 10 cm/s, (iv) a wear track radius of 10 mm, (v) a sliding distance of 100 m, (vi) no lubrication, and (vii) ambient atmosphere at room temperature.

(18) The volume wear loss (mm.sup.3/Nm×10.sup.−5) of both the Ti pin and the disk (shim material) was calculated from the input test parameters, the wear track area (measured in the plane perpendicular to the sliding direction), and the volume wear loss of the static partner. As is evident from the data in FIG. 4 the wear rate for electrodeposited metallic materials comprising Co is reduced by over 90% compared to Ti.

(19) Table 1 is a representation of the same and additional data also providing hardness information which reveals, that in the case of disks made from grain-refined Co materials, drastically reduced wear rates are measured although the hardness of the Co2P disk (540VHN) is 160VHN greater than the one of the Ti ball (380VHN). Pure n-Co of similar hardness than Ti causes even less wear on the Ti ball. Surprisingly, Ni containing materials of similar hardness behave much poorer than Co based materials. Table 1 data clearly demonstrate that the unlubricated Co comprising disk/Ti pin material pair results in a very low material wear loss on both the disk and the Ti ball. For the electroformed Co plates tested there was virtually no wear on the Ti pin compared to the other material pairs. The coefficient of friction of the Co materials was also the lowest although it did not vary much between the samples and ranged between 0.3 and 0.5.

(20) The data reveal unexpectedly that metallic materials comprising Co and/or P, even when their hardness exceeds the hardness of metallic materials comprising Ti these materials are mated with, surprisingly provide a superior material combination in any applications subject to wear, well beyond the use of shims as described herein. Such applications, include but are not limited to drive shafts, connector pins, gears, and brackets.

(21) TABLE-US-00001 TABLE 1 Wear loss of a 6 mm Ti ball (380 VHN) on disk materials (unlubricated) of various composition and hardness (10N load) Disk Material Ti6Al4V SS 304 n-Ni n-NiCo n-Co2% P n-Co Hardness 350 200 400 520 540 400 [VHN] Ti Pin Wear 9.1 43 62 46 0.3 0.1 [mm.sup.3/Nm × 10.sup.−5]

(22) Table 2 expands the wear data of FIG. 1 by providing the wear loss of the disks in addition to the wear loss of the Ti ball revealing that both the Ti pin and the unlubricated wear loss of disks comprising Co are drastically reduced compared to Ti pin/Ti disk wear loss. The data show that the volume wear loss of the Ti pin, representing the first material of the fan rotor slot 18 and/or the second material of the airfoil root portion 40 is lower than the wear loss of the third material of the disk comprising Co representing the consumable outer surface of the shim 50 as intended to achieve the desired extension of the rotor and/or airfoil life without the need of refurbishment or replacement.

(23) TABLE-US-00002 TABLE 2 Wear loss of 6 mm Ti ball on varius disk materials (10N load) Pin Material/ Ti Pin Wear Disk/Shim Disk/Shim Wear hardness [mm.sup.3/Nm × 10.sup.−5] Material/Hardness [mm.sup.3/Nm × 10.sup.−5] Ti (380 VHN) 9.1 Ti (380 VHN) 8.5 Ti (380 VHN) 0.3 n-Co2% P 1.4 (540 VHN) Ti (380 VHN) 0.1 n-Co (400 VHN) 2.9

(24) From the teachings of the present application, the person skilled in the art of electrodeposition/electroforming will know what metallic materials are suited for forming shims taking into consideration the material composition of the airfoil root portion and the fan rotor. Electrodeposition of metallic materials, including, but not limited to, nanocrystalline coatings is described by Erb et. al. in U.S. Pat. No. 5,352,266 (1994) and in U.S. Pat. No. 5,433,797 (1995), and Palumbo et. al. in U.S. Pat. Appl. No. 2005/0205425, all assigned to the Applicant of the present application.

(25) The person skilled in the art of electrodeposition/electroforming will also know how to conveniently form layered, nano-laminated and/or graded shims in a single electrolyte solution having an individual layer thickness between 1.5 nm and 1 μm, preferably between 25 nm and 500 nm, and more preferably between 100 nm and 250 nm, as described by Lashmore et. al. in U.S. Pat. No. 5,320,719 (1994), Schreiber et. al. in U.S. Pat. No. 6,547,944 (2003), and Tomantschger et. al. in U.S. Pat. No. 9,005,420 (2015), by suitably varying the electrodeposition conditions.

(26) Specifically, Tomantschger et. al. in U.S. Pat. No. 9,005,420 (2015), assigned to the Applicant of the present application, describes an elegant way to mass-produce a variable property deposit. The metallic layers formed can comprise fine-grained metallic materials, optionally containing solid particulates dispersed therein. The electrodeposition conditions in a single plating cell are suitably adjusted to once or repeatedly vary at least one property in the deposition direction and/or along the length of the workpiece. In one embodiment denoted multi-dimensional grading, property variation along the length and/or width of the deposit is described. Variable property metallic material deposits can be used to provide superior overall mechanical properties compared to monolithic metallic material deposits. This techniques also allows the preparation of an exemplary shim 50 with a soft, lubricious, anti-fretting and anti-galling surface including particulate matters on and near the outer surface while providing a strong, hard and particulate-free core, by using the degree of solution agitation to vary the particulate inclusion in the metallic layer and modulating the electrical current to adjust the composition, hardness and strength of the layer, all while using a single electrolyte and electroplating tank. Similarly, any suitable layering can be achieved to further optimize the physical properties of the electroformed shim as can be a non-uniform cross-section in the transversal or longitudinal direction of the deposited metallic layer by appropriate placement and use of ancillary anodes, current thieves and shields.

(27) Facchini et. al. in U.S. Pat. No. 8,309,233 (2012), assigned to the Applicant of this application, specifically discloses the electrodeposition of conforming, fine-grained and/or amorphous metallic layers, coatings or patches comprising Co onto suitable substrates or to electroforming free-standing, fine-grained and/or amorphous metallic materials comprising Co.

(28) Alloys comprising Co, Ni and P can be conveniently electroformed with Co and/or Ni contents ranging from 5% to 95% per weight, and a P content ranging between 0.05% and 5% per weight in average grain sizes ranging from 10 nm to 50 μm. In one preferred embodiment the Co content of the alloy is at least 50% per weight, preferably at least 60% per weight, more preferably at least 70% per weight and most preferably at least 80% per weight, the P content of the alloy is at least 0.05% per weight, preferably at least 0.1% per weight, more preferably at least 0.5% per weight and most preferably at least 1% per weight, and the hardness is at least 300VHN, preferably at least 350VHN, more preferably at least 400VHN and most preferably at least 500VHN. Accordingly, over the composition and grain-size range of interest the hardness can be in the range of 100VHN to 700VHN. The addition of particulates, e.g., lubricants, provides a further tool to dial in almost any material property desired.

(29) The specifications of all disclosures above are incorporated herein by reference.

(30) The person skilled in the art of material science will appreciate that increased material strength can be achieved through grain-size reduction. Since some ductility is generally required in at least selected areas of the shims of this invention, microcrystalline or nanocrystalline coatings are generally preferred over amorphous deposits. Depending on the specific circumstance, however, graded, layered or nano-laminated sections may provide suitable mechanical properties. Incorporating a sufficient volume fraction of particulates can also be used to further enhance the material properties.

(31) The person skilled in the art will know that various DC and pulse electrodeposition plating schedules can be used. They include periodic pulse reversal, a bipolar waveform alternating between cathodic pulses and anodic pulses. Anodic pulses can be introduced into the waveform before, after or in between the on-pulse(s) and/or before, after or during the off time(s). The anodic pulse current density is generally equal to or greater than the cathodic current density. The anodic charge (Q.sub.anodic) of the “reverse pulse” per cycle is always smaller than the cathodic charge (Q.sub.cathodic).

(32) Table 3 below lists various properties of electrodeposited, grain-refined alloy groups commercially available from Integran Technologies Inc., of Mississauga, Ontario, Canada in comparison with a Ti-alloy commonly used in aerospace applications.

(33) TABLE-US-00003 TABLE 3 Properties of electroformed Co materials (compared to a popular Ti alloy) Nanovate Nanovate Nanovate Ti6Al4V N1200 R3000 R3010 Grade 5 Series Series Series Property/Material STA (n-NiCo) (n-Co) (n-CoP) Yield Strength (MPa) 1100 500-1200  800-1600 1500-1600 Tensile Strength 1170 800-1700 1400-2000 2000 (MPa) Elastic Modulus 114 150-160  130-140 130 (GPa) Ductility [%] 10 5-20  5-20 4-7 Hardness [VHN] 396 250-530  380-560 540 Service Temperature — up to 375 150-375 up to 375 [° C.]

(34) The net-shaped exemplary shims having a non-uniform thickness profile and anisotropic material properties can be formed using a reusable cathode mandrel by the appropriate selection and placement of consumable or inert anodes and the use of shields in the counter-electrode assembly notwithstanding post-plate machining and/or polishing operations may still be used to form the final product. The temporary mandrel used as cathode to electrodeposit the shim is shaped according to the desired form and dimensions of the shim. Shims are electroformed to the desired shape, thickness and composition as a solid piece and removed from the electroplating solution. Alternatively it may be practical to electroplate the shims directly onto airfoil roots. It is undesirable, however, to apply an intermediate bond coat to the airfoil root such as electroless Ni, as this may increase the wear with Ti parts compared to Co coatings as is evident from the data in Table 1.

(35) Optionally, the outer surface of the exemplary shim can be machined, ground, lapped and or polished while still attached to the reusable mandrel to prevent any deformation and maintain its shape before it is removed from the reusable mandrel. In contrast to conventional shims formed from sheet metal sheet feed stock, no bending/shaping is required as electroformed shims can be formed in the desired shape and form. The person skilled in the art will appreciate that it may be desirable to produce shims having a transverse cross-section which is slightly more bent than the corresponding air foil blade root in order for the shim to snap and hold onto the root.

(36) The cross-sectional thickness of the exemplary shims along its width (transverse direction) and/or length (longitudinal direction), depending, on the engine size and specific parts used, may range from about 0.025 mm to 2.5 mm, more typically in the range of 0.05 mm to 1 mm and, the minimum cross-sectional thickness may be ≤5%, ≤10%, ≤25%, ≤50% or as much as ≤75% of the maximum cross-sectional thickness.

(37) It is also possible in the practice of this invention to electrodeposit age-hardenable metallic shims, e.g., by adding P to the alloy. The strength and thermal stability of such shims may be increased by a subsequent heat-treatment according to known procedures.

VARIATIONS

(38) The foregoing description of the invention has been presented describing certain operable and preferred embodiments. It is not intended that the invention should be so limited since variations and modifications thereof will be obvious to those skilled in the art, all of which are within the spirit and scope of the invention.