GB2267733A - Abrasion protective and thermal dissipative coating for jet engine component leading edges. - Google Patents

Description

ABRASION PROTECIlVE AND THERMAL DTSSIPATIVE COATING FOR JET ENGINE COMPONENT LEADING EDGES Background of the Invention The present invention generally relates to a jet engine component having a leading edge which has a gas flow passing thereover and more particularly to such component having a coating which is both a heat dissipative coating for thermal protection against a hot gas flow and an erosion-resistive coating for abrasion protection against a patticulate-laden gas flow The phrase "jet engine" includes gas turbine, ramjet, and scramjet engines. Such jet engines may be used to power flight vehicles.The gas turbine engine type of jet engine also may be used to power ships, tanks, electric power generators, pipeline pumping apparatus, and the likc. Jet engine components having a leading edge subject to a hot and/or particulate-laden gas flow include, for example, gas turbine engines fan and compressor blades and ramjet/scramjet engine cowls.

Ramjet and scramjet engines are known for powering aircraft at high supersonic or hypersonic velocitics of greater than about Mach 3. Both engines have no components therein which rotate due to air flow thereover, such as occurs in conventional tubofan and turbojet gas turbine engines. Instead, ramjet and scramjet engines utilize the supersonic movement of the aircraft in the atmosphere for compressing inlet air flow in the engine wherein it is mixed with fuel, and ignited for generating combustion gases for propelling the aircraft.

Ramjet engines and scramjet engines are different fundamentally in structure and function since a ramjet engine conventionally is designed to operate with subsonic fluid flow therethrough, whereas a scramjet engine conventionally is designed to operate with supersonic fluid flow therethrough. Rarnjet engines typically are effective for powering aircraft at supersonic speeds up to about Mach 6, whereas scramjet engines are designed for powering aircraft at flight velocities from about Mach 5 up to about Mach 18 and higher.

For purposes of illustration, the invention will be described with respect to a scrampt engine cowL However, it is understood that the invention is applicable equally to other types of jet engines as described above, as well as other types of jet engine components. Reference also is made to the following publications in this regard: Jones et al, 'Toward Scramjet Aircraft", Astronautics & Aeronautics, pp. 3848, February 1978, and U.S. Pats. Nos. 3,430,446 and 4,817,892, the disclosures of which are expressly incorporated herein by reference.

One of the most severe design conditions imposed on a hypersonic vehicle structure is the aerodynamic heating of the engine cowl leading edges. Nominal stagnation of heat fluxes can approach 2,000 to 8,000 BTU/ft2 sec. depending on mach number, dynamic pressure, and leading outer edge diameter which typically is about 0.100 inch to 0.250 inch. The nominal heat flux profile resembles a cosine distribution as location is traversed from the stagnation region at a() to the side of the leading edge at ago (a being the angular position about the leading edge diameter), thus the extreme heating rates are very localized.

Inlet compression performance is maximized when the vehicle bow shock is swallowed by the engine, resulting in maximum flow capture. The result, however, is a transient type IV shock interaction as the oblique shockwave from the vehicle bow passes over the cowl leading edge, impinging on the cowl leading edge normal shock. This transient condition can result in a local amplification of the nominal stagnation heat fluxes by a factor of 10 to 25, depending on the mach number and dynamic pressure at which shock capture occurs.

Transient "shock on lip" conditions, thus, can generate localized peak heating rates of approximaetly 40 to 75k BTU/ft2 sec. Internal cooling of the cowl leading edge by a variety of techniques is one solution to this design problem. If the heat build-up on the leading edge surface could be wicked away to other areas not subject to such high heat fluxes, cooling of the hypersonic cowl leading edge would be aided.

Broad Statement of the Invention The present invention is addressed to jet engine components which are subjected to exposure to gases which are hot and/or are laden with particulates. The inventive jet engine component comprises a surface having a gas flow thereover, which surface is coated with a layer of protective chemical vapor deposition (CVD) diamond. Advantageously, the jet engine component has an external hypersonic leading edge which is internally cooled and which leading edge bears the coating of CVD diamond.Preferably, the jet engine component comprises the leading edge of a scramjet engine cowl which is coated with a layer of heat dissipative CVD diamond. It will be understood, however, that a variety of jet engine components by virtuc of the hot gas flow path definition of the engine design, are subjected to exposure to hot gases and localized heating phenomena, and, accordingly, would benefit by being coated with a layer of heat dissipative CVD diamond in accordance with the precepts of the present invention. The same benefit is true for jet engine components that are subjected to particulate-laden gas flows and which require abrasion protection by the CVI) diamond coating.

Advantages of the present invention include the establishment of a coating that not only is effective in dissipating heat, but also is resistant to thermal shock and abrasion.

Another advantage is the very low thermal expansion coefficient possessed by the CvD diamond layer. A further advantage is the exceptional hardness of the CvD diamond coating which will minimize wear, erosion, and abrasion induced damage of the coated surface from impact with airborne particulates (e.g., dust, dirt, water, ice, etc.). These and other advantages will be readily apparent to those skilled in the art based upon the disclosure contained herein.

Brief Descngtlon of the Drawings Fig. 1 is a perspective, schematic view of a hypersonic aircraft including four sideby-side scramjet engines in accordance with a preferred embodiment of the present invention; Fig. 2 is a schematic, side view sectional representation of the aircraft illustrated at Fig. 1; Fig. 3 is an enlarged, sectional, schematic view of a portion of one of the scramjet engines taken along line 3-3 of Fig. 1.

Figs. 4-7 are partial cross-sectional elevational views through a scramjet engine cowl showing the layer of heat dissipative CVD diamond and internal cooling structures; Fig. 8 is a side elevational view of a chemical vapor deposition reaction chamber showing a set of filaments for use in creating a layer of heat dissipative CvD diamond for application to a seramjet cowl leading edge; and Fig. 9 is an overhead sectional view of the apparatus depicted at Fig. 8.

The drawings will be described in detail in connection with the description which follows.

Detailed Description of the Invention Illustrated in Fig. 1 is a schematic representation of hypersonic aircraft 10 including four side-by-side scramjet engines 12a-12d in accordance with a preferred exemplary embodiment of the present invention. Scramjet engines 12a-12d are effective for powering aircraft 10 at hypersonic velocities up to about Mach 18. Each scramjet engine 12a-12d is defined in part by cowl 14 spaced radially inwardly from midbody surface 16 of aircraft 10. Spaced-apart sidewalls 18a-18e extend between midbody surface 16 and cowl 14 for defining generallyrectangular scramjet engines 12a-12d.Each scramjet engine 12a-12e is substantially identical and further description may refer to only one of the engines, viz engine 12a, with the others being substantially identical.

Referring to Figs. 1 and 2, each scramjet engine also includes planar forebody surface 20 extending obliquely upstream from midbody surface 16 from throat 22 (Fig. 2) of minimum flow area defined between midbody surface 16 and cowl 14. In the embodiment illustrated, scramjet engines 12a-12d are alrcraft-integrated scramjet engines which utilize surfaces of aircraft 10 in part to define the scramjet engines. Such aircraft surfaces include midbody surface 16 and forebody surface 20. The surfaces also include planar bow surface 24 extending upstream from fore-body surface 20 at an inflection point 26 and at an obtuse angle 9 from forebody surface 20. Bow surface 24 extends at leading edge 28 of aircraft 10.The aircraft surfaces defining scramjet engines 12a-12d further include arcuate afterbody surface 30 extending downstream from midbody surface 16 at aft end 32 thereof.

As illustrated more particularly in Figs. 2 and 3, cowl 14 is spaced radially inwardly from midbody surface 16 and from portions of forebody surface 20 and afterbody surface 30, to define converging inlet 34 extending from leading edge 36 of cowl 14 to throat 22; a diverging combustor 38 extending downstream from throat 22, which also may be referred to as combustor inlet 22, to midoody surface aft end 32; and diverging exhaust nozzle 40 extending downstream from combustor 38 at aft end 32 and in part defined by aft end 42 of cowl 14 extending rearwardly from the plane of midbody surface aft 32 to trailing edge 44 of cowl 14. Scramjet engine 12a further includes means 46 for supplying fuel to combustor 38 at upstream end 48 thereof.

Fuel supplying means 46 includes one or more conventional fuel injectors 50 spaced transversely from each other at combustor upstream end 48. Conventional fuel conduits 52 join in flow communication conventional fuel supply 54 including a conventional fuel pump, to injectors 50. Fuel supplying means 46 is effective for supplying fuel 56 through injectors 50 into combustor 38. In a preferred embodiment, fuel 56 is liquid hydrogen which changes from its liquid state to its gaseous state upon injection into combustor 38 from injectors 50.

Scramjet inlet 34 is bounded further, in part, by both aircraft forebody surface 20 and bow surface 24 for providing extemal compression of ambient or free-stream air flow 58 in a manner well known. More specifically, inlet 34, including forebody surface 20 and bow surface 24, is predeterminately sized and configured for generating oblique bow shockwave 60 extending from aircraft leading edge 28 rearwardly down to cowl leading edge 36, and oblique forebody shock 62 extending downstream from inflection point 26 to cowl leading edge 36. Both bow and forebody shocks 60 and 62 provide external compression, which also is known as recompression, of ambient air flow 58 for increasing the static pressure thereof with a corresponding increase in static temperature thereof.

Ambient air flow 58 when so compressed, results in supersonic compressed air flow 64 which is channeled into inlet 34 generally parallel to forebody surface 20. Air flow 64 obliquely impinges cowl 14 and generates oblique cowl shock 66 extending at an acute angle rearwardly from cowl leading edge 36.

In accordance with a preferred, exemplary embodiment of the present invention, a method of operating scramjet engine 12a for powering aircraft 10 includes the steps of providing supersonic compressed air flow 64 from inlet 34 to combustor 38 at a predetermined static temperature and static pressure. As described above, the recompression of ambient air flow 58 from bow and forebody shocks 60 and 62 supersonically compress air flow 58 to a predetermined static pressure with a corresponding predetermined static temperature. In the embodiment of the invention illustrated at Figs. 1-3, inlet 34 comprises a supersonic diffuser which additionally increases the static pressure and correspondingly increases the static temperature of ambient air flow 58 by internal contraction for providing supersonic compressed air flow 64 to combustor 38.Providing supersonic compressed air flow to a scramjet combustor at predetermined static pressure and temperature is conventional. A conventional inlet, forebody and bow of a hypersonic aircraft is sized conventionally and configured for generating the predetermined static pressure and static temperature of the air flow for providing a relatively large increase in static pressure from aircraft leading edge 28 to combustor 38 and a correspondingly high static temperature for obtaining spontaneous ignition of the fueVair mixture in the combustion.

Thus, it will be appreciated that leading edge 36 of cowl 14 will be subjected to a variety rugged conditions inlcuding airborne particulate matter which causes wear, erosion, and abrasion; and extremely high localized heating stresses which require, not only unique materials of construction, but also unique methods of heat removal. Not only is leading edge 36 subjected to high localized heating, but temperature differences between leading edge 36 and adjacent areas of cowl 14 place high thermal stresses additionally on leading edge 36. A layer of CVI) diamond has the advantageous effect of dissipating high localized heating at leading edge 36 to adjacent areas which are much cooler.Such heat dissipative characteristic of the CvD diamond layer reduces localized heating at leading edge 36 and additionally reduces thermal stresses placed on the leading edge as described above.

The heat dissipative properties and extremely high thermal shock capabilities of CVD diamond layers will be applicable to the majority of leading edge cooling concepts.

All cooling concepts have one common feature: flow path definition. The geometric configuration of a typical engine cowl is a 10--13* wedge with a 0.100 inch to 0.250 inch diameter leading edge. Oblique shocks formed from compression surfaces upstream bounce their way through the engine, reflecting off internal walls of the engine. An interaction between a reflecting shockwave and the local flow path boundary layer occurs whereby the nominal sidewall heat flux is locally magnified due to the shoclbboundary layer interaction. Similarly, because hypersonic engines generally involve rectangular cross-sections, recirculation effects in the corners also can locally magnify the nominal sidewall heat fluxes.A CVI) diamond layer would be useful in dissipating the heat in these zones, thus minimizing the formation of local hot spots.

An overcoat or outer layer to aid in preventing oxidation of the CVI) diamond layer may be applied if necessary, desirable, or convenient. The overcoat should be relatively thin so as not to prejudice the heat dissipating function of the CVI) layer. The overcoat additionally should have a coefficient of thermal expansion not too different from CvD diamond in order to prevent thermal stresses between such materials. Oxidative protective coatings include, for example, silicon (which will form stable silica oxides), silicon carbide, and fused silicide coatings. As noted, these coatings should be only thick enough to effect an oxidation protection function, which thickness generally translates into about 10 microns minimum on up to several hundred microns.Such overcoatings also aid in providing additional abrasion resistance which the CVD diamond coating already provides.

With respect to the layer of CvD diamond providing a thermal flow path on the leading edge of a cowl and alternative internal cooling schemes, reference is made to Figs.

4-6. Leading edge 80 is the parent metallic structure which may be a refractory alloy of tungsten or molybdenum for strength, temperature capability, and modest thermal conductivity. Copper alloys also are candidates for an appropriate materials of construction. CVD diamond layer 82 is attached to edge 80 via braze line 84. Optionally, outer surface coating 86 of silicon, silicon carbide, or other thin coating may be applied to shield diamond layer 82 from the oxidizing effects of free stream air flow. Additionally, heat pipe wick 88 typically is a porous sintered metal or mesh which optionally may be mounted on the inner surface of leading edge 80.Layer 88 provides the conduit for the liquid metal to return from the condenser heat sink to the evaporator heat source when hollow inner cavity 89 within the cowl contains a cooling fluid In the preferred scramjet case, the leading edge is the evaporator and the condenser, not shown, is coupled to the hydrogen fueled by heat exchanger. Internal cooling of leading edge 80 is provided in this fashion.

Impingement cooling can be provided as depicted at Fig. S by the addition of nozzle 90 which can direct a cooling fluid on the inner surface of leading edge 80. The coolant flow normally is the vehicle fuel, which could be hydrogen, methane, or other hydrocarbon material. Additionally, cavity 89 within the cowl can direct the cooling fluid to a collection manifold after the spent impingement fluid is utilized to cool the cowl sidewalls.

With reference to Fig. 6, the impingement cooling adaptation is maintained, but layer 92 of (:VD diamond is attached to the inner surface of leading edge via braze line 94.

The high conductivity of the CVD diamond coating on the inside will help to reduce thermal gradients associated with the intense local cooling at the internal surface. It will be appreciated that other forms of internal cooling can be supplied to thejet engine component bearing the CVD diamond layer and is included within the precepts of the present invention.

In Fig. 7, free-standing diamond film 82, optionally with outer surface coating 86, is attached to leading edge 80. Actually, film 82, being structural, becomes the leading edge.

Referring now to the CVI) diamond layer attached to the jet engine component for thermal dissipation purposes, low pressure growth of diamond has been dubbed "chemical vapor deposition" or "CVD" in the field. Two predominant CVI) techniques have found favor in the literature One of these techniques involves the use of a dilute mixture of hydrocarbon gas (typically methane) and hydrogen wherein the hydrocarbon content usually is varied from about 0.1% to 2.54 of the total volumetric flow. The gas is introduced via a quartz tube located just above a hot tungsten filament which is electrically heated to a temperature ranging from between about 1750' to 2400'C.The gas mixture disassociates at the filament surface and diamonds are condensed onto a heated substrate placed just below the hot tungsten filament The substrate is held in a resistance heated boat (often molybdenum) and heated to a temperature in the region of about 500 to 1100'C, or the substrate can be heated by the filament.

The second technique involves the imposition of a plasma discharge of the foregoing filament process. The plasma discharge serves to increase the nucleation density, growth rate, and it is believed to enhance formation of diamond filrns as opposed to discrete diamond particles. Of the plasma systems that have been utilized in this area, there are three basic systems. One is a microwave plasma system, the second is an RF (inductively or capacitively coupled) plasma system, and the third is a d.c. plasma system.

The RF and microwave plasma systems utilize relatively complex and expensive equipment which usually requires complex tuning or matching networks to electrically couple electrical energy to the generated plasms Additionally, the diamond growth rate offered by these two systems can be quite modest.

With respect to conventional CVD processes useful in the present invention, hydrocarbon/hydrogen gaseous mixtures are fed into a CVI) reactor as an initial step.

Hydrocarbon sources can include the methane series gases, e.g. methane, ethane, propane; unsaturated hydrocarbons, e.g. ethylene, acetylene, cyclohexene, and benzene; and the like. Methane, however, is preferred. The molar ratio of hydrocarbon to hydrogen broadly ranges from about 1:10 to about 1:1,000 with about 1:100 being preferred. This gaseous mixture optionally may be diluted with an inert gas, e.g. argon. The gaseous mixture is at least partially decomposed thermally by one of several techniques known in the art. One of these techniques involves the use of a hot filament which normally is formed of tungsten, molybdenum, tantalum, or alloys thereof. U.S. Pat. No. 4,707,384 illustrates this process.

The gaseous mixture partial decomposition also can be conducted with the assistance of d.c. discharge or radio frequency electromagnetic radiation to generate a plasma, such as proposed in U.S. Pats. Nos. 4,749,587, 4,767,608, and 4,830,702; and U.S. Pat. No. 4,434,188 with respect to use of microwaves. The substrate may be bombarded with electrons during the CVI) decomposition process in accordance with U.S.

Pat. No. 4,740,263. In addition to the two predominant methods for CVI) diamond fabrication, other processes include flame or combustion, heat, photolysis, and hybrid filament plasma processes which can be used as is necessary, desirable, or convenient.

Regardless of the particular method used in generating the partially decomposed gaseous mixture, the substrate is maintained at an elevated CVI) diamond-forming temperature which typically ranges from about 500 to 1100' C and preferably in the range of about 850. to 950' C where diamond growth is at its highest rate in order to minimize grain size. Pressures in the range of from about 0.01 to 1000 Torr, advantageously about 100-800 Torr, are taught in the art, with reduced pressure being preferred.Details on CVD processes additionally can be reviewed by reference to Angus, et al., "Low-Pressure, Metastable Growth of Diamond and 'Diamondlike' Phases", Science, vol. 241, pages 913921 (August 19, 1988); and Bachmann, et al., "Diamond Thin Films", Chemical and Engineering News, pages 24-39 (May 15, 1989). The disclosures of all citations herein are expressly incorporated herein by reference.

A currently-preferred apparatus for manufacture of a layer of heat dissipative CYD diamond for application to the hypersonic leading edge of a scramjet engine is depicted at Figs. 8 and 9. Reactor 100 is conventional in structure and operation as described above.

Since the diamond layer for application to a jet engine component has a unique and asymmetric geometry, some challenge is faced in shaping the layer to possess acceptable uniformity and be free of residual stresses. Thus, the fixturing and method of forming the diamond layer is unique additionally. Reactor 100 utilizes a total of seven filaments, viz.

filaments 102a-102g. The seven filaments are separated by a distance of approximately 0.5 inch. Filament 102g is positioned at the tip of cowl leading edge 104 while filaments 102a102c are placed on one side and filaments 102d-102f are placed on the opposite side thereof. Separate power control for each filament set is provided by three separate electrical feed throughs 106a, 106b, and 106c. The design of reactor 100 is unique in its flexibility of filament arrangement. The length of each of the filaments may be adjusted simply by loosening screw 108 for filaments 102a-102c and sliding clamp 110 along support rod 112. This same arrangement applies for filaments 102d-102f and for filament 102g, and, thus, will not be described specifically herein.

The separation gap between the filaments and substrate, and the angle of the sets of three filaments also may be adjusted. Filament holder 114 is supported by clamp 110. The placement of the filaments can be altered by loosening screw 116 and repositioning holder 114. This can be done with all filament sets to yield the desired arrangement. The filaments preferably are tungsten wire and are held in place at their lower end by quartz sleeve 118. For simplicity, only one of the filaments of the sets of three has been illustrated at Fig. 8. Also, the lower sets of adjustment clamps and screws also has not been described specificaliy, but is to be provided in a similar manner.

The apparatus as described at Figs. 8 and 9 was utilized to grow diamond layer 120 on substrate 104 by stretching a screen mesh sheet (10 strands/cm by 100 strands/cm) of preferably Mo (though W or Ti can be used) over substrate 120 with the aid of bolts (not shown). Methane and hydrogen-(molar ratio of 118:2) then was flowed at a rate of 120 sccm with a total system pressure of 10 torr. Upon reaching steady state with respect to gas flows, concentrations, and partial pressures, the diamond-forming reactions were initiated by passage of 90 amps of current (15 amps per filament) at an applied 27 volts to achieve an incandescent state of tungsten filaments which were 6 inches in length and 0.015 inch diameter. Note, that only six filaments were used in this run. The filaments were spaced 0.5 inch apart and between 0.85 and 1.0 cm from the substrate surface.The substrate surface was heated to a temperature of approximately 700'-1,000'C and the diamond growth conditions maintained for 34 days to produce a diamond layer which was < 1 mm in thickness. Upon unbolting the screen mesh shcath from substrate 120, the desired diamond layer was readily separated and suitable for brazing or other attachment means to an actual cowl leading edge.

Brazing of the CVI? diamond can be accomplished using a variety of braze alloy compositions well known in the diamond art For example, braze alloys are shown in U.S. Pats. Nos. 3,894,673, 4,018,576, 4,527,998, 4,772,294, and 4,931,363, the disclosures of which are expressly incorporated herein by reference.

Since certain changes may be made in carrying out the above-disclosed invention and in the constructions set forth, without departing from the scope of the invention, it is intended that all matter contained herein or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims (32)

CLAIMS:

1. A jet engine component having a surface which is in contact with a gas flow, said surface being coated with a layer of chemical vapor deposition (CVD) diamond.

2. The component of claim 1 wherein said CVD diamond layer ranges in thickness from between about 10 and 1,000 microns.

3. The component of claim 1 wherein said CVD diamond layer is brazed to said surface.

4. The component of claim 1 wherein said CVD diamond layer is overcoated with an oxidation-resistant coating.

5. The component of claim 4 wherein said coating is a siliceous coating.

6. The component of claim 5 wherein said coating is selected from silicon oxide, silicon carbide, and fused silica.

7. The component of claim 1 wherein surface is the leading edge of a scramjet engine cowl.

8. The component of claim 1 which has an interior cavity which contains a cooling fluid

9. The component of 1 which has an interior surface which also bears a layer of CVD diamond.

10. The component of 8 which has an interior surface which also bears a layer of CVD diamond.

11. The component of claim 1 wherein said CVD diamond layer is heat dissipative for creating a thermal flowpath away from said coated surface.

12. A method for creating a thermal flowpath away from a jet engine component surface in contact with a hot gas flow, which comprises coating said surface with a layer of chemical vapor deposition (CVD) diamond

13. The method of claim 12 wherein said CYD diamond layer ranges in thickness from between about 10 and 1,000.

14. The method of claim 12 wherein said CVD diamond layer is brazed to said surface.

15. The method of claim 12 wherein said CVD diamond layer is overcoated with an oxidation-rcsistant coating.

16. The method of claim 15 wherein said coating is a siliceous coating.

17. The method of claim 16 wherein said coating is selected from silicon oxide, silicon carbide, and fused silica

18. The method of claim 12 wherein surface is the leading edge of a scramjet engine cowl.

19. The method of claim 12 which has an interior cavity which contains a cooling fluid.

20 The method of 12 which has an interior surface which also bears a layer of CVI) diamond.

21. The method of 19 which has an interior surface which also bears a layer of CVI) diamond

22. The method of claim 12 wherein said CVI) diamond layer is made in a chemical vapor deposition (CVD) apparatus which comprises: a metallic screen mesh sheet affixed to said substrate which is disposed in said apparatus, said mesh sheet heatable to CYD dimond-forming temperature; a series of metallic filaments adjacent said mesh sheet, said filaments connected to a source of electrical current and being held between clamps which are adjustably held by support rods; wherein, said CVD diamond layer is made under CVI) diamond-forming conditions in said apparatus;; thereafter, said CvD diamond layer is removed from said mesh sheet; and said CvD diamond layer is attached to said jet engine component surface.

23. The method of claim 22 wherein said CVI? diamond layer is brazed to said jet engine component surface.

24. The method of claim 22 wherein said CVD diamond layer is mechanically attached to said jet engine component surface.

25. A method for protecting a jet engine component having a surface which is in contact with one or more of a flow of hot gas or gas laden with particulates, which comprises coating said surface with a layer of chemical vapor deposition (CVD) diamond

26. The method of claim 25 wherein said particulates comprises one or more of dust, dirt, water, or ice.

27. The method of claim 25 wherein said CVI? diamond layer is heat dissipative for creating a thermal flowpath away flom said coated surface.

28. The method of claim 25 wherein said CVI) diamond layer is made in a chemical vapor deposition (CVD) apparatus which comprises: a metallic screen mesh sheet affixed to said substrate which is disposed in said apparatus. said mesh sheet heatable to CVI? diamond-forming temperature; a series of metallic filaments adjacent said mesh sheet, said filaments connected to a source of electrical current and being held between clamps which are adjustably held by support rods; wherein, said CVI? diamond layer is made under CVD diamond-forming conditions in said apparatus; thereafter, said CVI? diamond layer is removed from said mesh sheet; and said CVI? diamond layer is attached to saidjet engine component surface.

29. The method of claim 28 wherein said CVI? diamond layer is brazed to said jet engine component surface.

30. The method of claim 28 wherein said CVD diamond layer is mechanically attached to said jet engine component surface.

31. A jet engine component substantially as hereinbefore described with reference to the accompanying drawings.

32. A method for creating a thermal flowpath substantially as hereinbefore described with reference to the accompanying drawings.