US3402914A

US3402914A - Method of controlling the permeability of a porous material, and turbine blade formed thereby

Info

Publication number: US3402914A
Application number: US431538A
Authority: US
Inventors: Donald J Kump; Norman F Lauziere
Original assignee: Curtiss Wright Corp
Current assignee: Curtiss Wright Corp
Priority date: 1965-02-10
Filing date: 1965-02-10
Publication date: 1968-09-24
Anticipated expiration: 1985-09-24

Description

Sept. 24, 1968 Dl L KUMP ET AL 3,402,914y

METHODOF CONTROLLING THE PERMEABILITY oF A PoRouS MATERIAL, AND TURBINE BLADE FORMED THEREBY Filed Feb. 1o, 1965 s sheets-sheet "1 BZDD Ammin. LEADIINE 01351 AEENT Sept. 24, 1968 Dl J. KUMP ET AL-` 3,402,914

OF CONTROLLIN 0F A POROUS ERIAL, AND TU THEREBY A 5 Sheets-Sheet z G E PERMEABILITY R E BLADE FORMED METHOD MAT Filed Feb. l0, 1965 INVENTORS DDNALD V. I NEIRMAN F. LAL! KLIMF ZIERE AEENT Sept. 24, 1968 D. J. KUMP ET Al. 3,402,914

METHOD 0F CONTROLLING THE FERME/ABILITY oF A Ponous MATERIAL, AND TURBINE BLADE FoRMED THEREBY Filed Feb. lO, 1965 3 Sheets-Sheet 5 .DEICI mmv-u2...

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| ann-MESH DBD DZD

n4 In zu an 4u 5|: En '7n en Em lun FERMEAE||L|TY% IIIF` SKIN FERMEABILITY PE mm www W A VWL mAF. N

AEENT United States Patent O 3,402,914 METHOD OF CONTROLLING THE PERMEABILITY OF A POROUS MATERIAL, AND TURBINE BLADE FORMED THEREBY Donald J. Kump, Hackensack, and Norman F. Lauziere,

Mahwah Township, Ramsey, NJ., assignors to Curtiss- Wright Corporation, a corporation of Delaware Filed Feb. 10, 1965, Ser. No. 431,538 6 Claims. (Cl. 253-39.15)

This invention relates to a method of controlling the permeability of a porous metal in discrete areas, and to transpiration cooled blades for turbine engines, formed by the process of the invention for providing more or less cooling in various portions of the blade in accordance with the requirements of localized regions.

Transpiration cooled turbine blades are known in the prior art, in which a hollow blade has a porous skin of metal fabric or pressed and sintered metal powder, with coolant being fed to the interior of the blade and bleeding through the porous sheath. Such blades commonly have no means of controlling the amount of coolant ow through any given area of the skin. However, in U.S. Patent No. 2,807,437 there is disclosed a turbine blade of sintered powdered metal made up of separate sections, which sections may be selectively coined before assembly to increase density and reduce porosity.

The present invention provides an improved method by means of which a porous sheath of airfoil contiguration may be mounted on a load-carrying strut, selected portions of the sheath being subsequently reduced in permeability by depositing material thereon to obstruct the pores of the sheath, thereby impeding the ow of coolant through the obstructed portions, whereby a higher proportion of coolant will ow through the unobstructed areas. Instead of depositing masking material on the surface of the skin, its permeability may also be reduced in the desired areas by shot-peening to close or diminish the pores by upsetting or deforming the material of the sheath.

It is an object of this invention to provide a method of controlling permeability of a porous material in selected areas.

Another object is to provide a method of adjusting the ow of coolant in a transpiration cooled turbine blade.

A further object of the invention is to provide a transpiration cooled blade having a porous skin, in which the permeability of the skin is reduced in areas exposed to lower temperatures.

Other objects and advantages will become apparent on reading the following specification in connection with the accompanying drawings, in which:

FIG. l is a graphie representation of a typical temperature distribution across a turbine rotor blade span of gas flow through the turbine passages, and of temperature distributions in portions of the blade;

FIG. 2 is a schematic representation of typical airfoil surface temperatures on the convex side of a transpiration cooled blade;

FIG. 3 is a similar schematic of the surface temperatures on the concave side of a transpiration cooled blade;

FIG. 4 is an elevation of the convex side of a turbine blade treated according to the invention;

FIG. 5 is an elevation of the concave side, partly broken away, of a blade according to the invention;

FIG. 6 is a cross-section taken on line 6 6 of FIG. 5;

FIG. 7 is a graph of particle size and thickness of masking material as it affects permeability; and

FIG. 8 is a schematized View in elevation of a stator blade and a rotor blade in juxtaposition as they might be apposed in an engine.

3,402,914 Patented Sept. 24, 1968 ice In FIG. l there is shown the pattern of distribution of combustion gas temperatures through a turbine passage between the radially inward root end of the rotor blades and the radially outward tip ends. It is to be understood that the temperatures shown are only for a given engine operating at a given load and are intended only to illustrate typical conditions in turbine engines. For example, the highest temperature, the profile of which is shown in full line, is approximately 2800 F., generally in the mid-region of the turbine passage but somewhat closer to the blade tips than to the root ends. The temperature of the gas at the root of the rotor blade, that is, the radially inward portion of the turbine passage, is approximately 1700 F., and about 2000 F. at the rotor blade tip, or radially outward portion of the passage. In a different engine the temperatures at comparable positions might be either higher or lower, depending on the design of the engine, its load-rating, and the load at which it might be operating at a given time.

The dashed line shows the temperature prole of the leading edge of a rotor blade of the known transpiration cooled type and comprising a strut member covered with a porous sheath of airfoil conguration, having internal passage means for the supply of coolant and having a generally equal tlow of coolant through all portions of the skin. It will be observed that the temperatures of the leading edge of the blade are several hundred degrees lower than those of the gas ow. However, the prole of the leading edge temperature is substantially parallel to that of the gas flow, so that the skin in that portion is subject to unequal expansion and thermal stresses, even though the maximum temperature reached may not in itself be high enough to damage or weaken the material.

The dotted line of FIG. l shows the temperature prole along the radial axis of the strut member from root to tip. This curve is generally parallel to the others, also having its maximum at about the same region between the root and the tip, so that the strut also is subject t0 differential expansion and thermal stresses.

Although FIG. 1 is described in terms of the positioning of a rotor blade, the curves are actually of the tem-v peratures found in a typical turbine passage, which may also have stator blades therein. The stator blades are subject to the same temperature conditions and FIG. 1 applied equally to stator blades, except that stator blades may have a root or support means at either or both ends. As shown in the drawing, the term blade root is therefore synonymous with the radially inward portion of the passage, and blade tip with the radially outward portion. It will be understood that the curves and temperatures shown are derived from a particular engine with specific parameters, and are intended to be exemplary only. For instance, in a higher rated engine the maximum temperature might be higher, and the curves might be more platykurtic or more leptokurtic; however, the general pattern would be similar.

FIG. 2 shows graphically the lines of distribution of specic temperatures on the surface of the convex side of a rot-or blade with equal transpiration cooling thro-ughout, as exemplified by the engine conditions of FIG. 1. The hottest portion of the convex side of the blade surface is the leading edge which is at 1600" F., except for a small cooler portion of short extent .close to the root. The temperature then drops to 1550 F. a short distance from the leading edge. The curve for l550 F. on the convex side originates near the root and tip corners of the leading edge, -and bellies out toward the trailing edge in the mid-region of the blade, the next curve for 1400 also originating near the leading edge corners and bellying still further in the mid-region toward the trailing edge.

From' 1400 the temperature in4 the mid-region drops to about ;13'00 -'17350 nat' the Ytrailing edge. The coolest regions of the yconvex side of the blade, shown by the l100 and l200 lines originating near the leading edge corners and extending lacross the blade to the trailing edge, are generally triangular or trapezoidal areas at the root and tip regions, in which the root or tip end of the blade definesy one side of the triangle, with the base extending along the trailing edge and with the apex at `or near the leading'edge.

Thehottest portion of the convex side generally is therefore in the mid-region of the blade, with the temperature diminishing in a distinct gradient from the leading edge to the trailing edge, and with an even more marked gradient from the central portion of the span toward each of the blade ends, the temperature at the extreme root and tip being approximately lO0 F.

The temperature distribution for the concave surface of the blade is shown in FIG. 3 and is similar to the pattern for the convex side, except that the comparable coolest Zones at root and tip and tapering from the trailing edge toward the leading edge are smalle-r in area, having less extent along the trailing edge. Here again there is a gradient -of diminishing temperature from the leading edge to the trailing edge, and from the center of the span toward each of the ends, although these gradients are not the same as those of the convex side. For instance, a larger portion of the area of the concave side is at a temperature of approximately 1400". Nevertheless, the extreme tip and root ends and the trailing edge have temperatures comparable to those of the same portions on the convex side.

The temperature patterns for the stator vblades in a turbine passage are very similar to those of the rotor blades, except that the terms root end and tip end may not lbe applicable. As shown and discussed here, those terms are intended to indicate respectively the radially inward portion and the radially outward portions of the turbine passage.

From conside-ration of FIGS. 1 to 3 it becomes apparent that a transpiration cooled blade of known type, in which a porous skin passes coolant equally throughout, may be cooled sufiiciently that there is no likelihood of burning or melting any portion of the blade, or reaching the yield strength of its materials, in an engine wherein the gas temperature does not exceed about 2800" F., and consequently where no portion of the blade `reaches a temperature higher than about 1600 F. However, such a blade does not have a uniform temperature, and is thus subject to stresses which eventually cause cracking or deformation and render the -blade unserviceable.

When the coolant for transpiration blades is air bled from the compressor supply, a substantial proportion of the power output of the engine goes into providing the coolant at the requisite pressure. Therefore, if the permeability of the skin of a transpiration cooled blade is controlled in such a manne-r that there is little or no flow through the coolest areas, and a substantially reduced flow through the adjacent next coolest areas, the total coolant supply to the blade can be reduced and still maintain the |hottest portions within safe temperature limits, with a concomitant reduction in power consumption. Further, whether or not total flow is reduced, the coolant will nevertheless be directed principally to the hottest portions, and the blade may be used in a high rated engine with a gas flow of higher temperature wit-hout damage to the blade or reaching the yield point of the material. Either mode of operation results in a more uniform temperature over the entire blade, reducing thermal stresses and prolonging the operating life of the blade.

In FIG. 4' there is shown the convex side of a turbine blade 11', which may be either a stator or rotor blade. There is provided a strut member 12 having a transverse cross-section of generally airfoil configuration (shown in FIG. 6). The strut has mounting means 13, which may be the yconventional fir-tree root shown, or any other convenient attachment means for mounting and positioning the blade, and is shown here as disposed at the radially inward end of the blade. The mounting means may be formed integrally with the strut member, or fabricated separately and attached by Welding, brazing, or `other convenient means. The surface of the strut is provided with longitudinally extending ribs or lands 14 dening coolant passages 16 therebetween. Mounted on the root 13 or other attachment means is a shelf 17 which may be formed integrally with the root, or be a separate element subsequently attached as by brazing or welding. The under surface of the shelf is spaced apart from the remainder of the root or other attachment means, defining therewith passage means 18 communicating with blade passages 16 fo-r introduction of cooling air thereinto. A sheath or skin 19 of suitable porous material and of airfoil configuration encloses t-he strut member 12, being attached to the lands 14 thereof by welding, brazing, or other convenient means. The end of the blade opposite the mounting is occluded by a closure member 21, which may be integral with the strut or a separate element, so Uhat all coolant entering passages 16 through passage 18 must bleed through the porous skin into the gas stream. Closure 21 may be formed integrally with the strut 12, or may be a separate member attached thereto.

The load-carrying strut may be formed of any of the various high-temperature alloys commonly used for turbine blades, such as those sold under the trademarks Inconel, Rene, Hastelloy, and the like. The porous sheath may be formed of any material lhaving suitable temperature resistance, such as pressed and sintered powdered metal, or a metal mesh member rolled and sintered. A particularly suitable material has been found to be that disclosed in U.S. Patent No. 3,067,982, wherein a continuous wire of small diameter is helically wound on a mandrel in a number of passes, then rolled and sintered to form a porous metal fabric.

It is to be understood that blades formed according to the invention need not have the precise means shown for providing coolant to the interior of the blade. Instead of a shelf spaced from the root to provide an entrance aperture, the root itself may have one or more lholes therethrough, or the air may be fed through passages in the rotor disk, and the attachment means may have any desired form.

As shown in FIG. 4, the skin on the convex side of the blade may have `one or more areas of reduced porosity of varying degrees. Such reduction of porosity may be achieved by shot-peening the selected portion of the skin to deform and densify the surface metal of the skin and thus occlude some or all the pores, or by spraying a powdered material at high temperature onto the skin. For total blockage of porosity a thin metal sheet may be affixed to the skin either on the interior or exterior surface thereof, -or a portion of the strut, of the desired configuration and location, may be left without air passages under the skin and have a smooth surface with the sheath aixed thereto.

The masking material to be deposited may be powdered ceramic, such as alumina, magnesia, titania, or zirconia; or it may be metal powder having suitable lhigh temperature characteristics, Examples of satisfactory metal powders for this purpose are the compositions sold under the trademarks Nicrobraz or Nicrobraz 150 (trademarks of the Wall Colmonoy Corporation), having approximately the following nominal compositions- Nicrobraz Percent Chromium 13.5

Boron 3.5

Carbon 0.8

Iron 4.5

Silicon 4.5 Nickel balance Nicrobraz 120: Percent Chromium 15.0 YBoron 3.5 Carbon max-- .15 Nickel balance Other sources market competing alloy powders of similar composition under other trade names, and these powyders of similar composition are also satisfactory for use as a masking material in the present invention.

The masking materials, whether ceramic or metal, may be deposited by any convenient means; the conventional methods of building up a metal part by oxyacetylene llame spraying or plasma arc spraying have been found very satisfactory, using the commercial equipment available for applying these methods. In this procedure the pulverized material is driven through an oxyacetylene flame or electrical plasma, whereby it reaches a temperature suiciently high to be discharged in the molten state, or at least in a suiciently plastic or tacky state to be adherent. Masking in a selected area need not be complete, that is, the degree of permeability remaining in a masked portion may be controlled by proper selection of particle size and the thickness of the masking layer deposited, as will be hereinafter described.

In FIG. 4 the convex side of the blade has a maskedV area 22 at the root end, which would be the radially inward end of a rotor blade, whether in the turbine portion or the compressor portion of a turbine engine. Area 22 is generally triangular or slightly trapezoidal, with extension along the trailing edge comparable to the base of a triangle, and tapers toward the apex which has a slight extension along the leading edge 23, with the hypotenuse approximately on the 1100 line shown in FIG. 2. Although the temperature lines of FIG. 2 are slightly curved, they are so nearly straight as to allow the use of straight edges in masking, if desired for convenience of fabrication in the masking procedure. Masked area 22 is substantially fully blocked, having a remaining permeability not over 5% of that of the untreated sheathing material 19. At the tip of the blade is shown a similar tapered masked area 26, dened by the radially outward end of the blade, the trailing edge 24, and the approximate 1100 line, with the apex close to the leadingedge 23. Area 26 may have the same residual porosity as area 22, not over 5% of that of the skin.

Toward midspan of the blade from area 26, that is, radially inward therefrom and contiguous therewith is another triangular masked area 27, generally defined by the trailing edge and the 1100 and l200 lines, with its apex near the leading edge of the blade. Area 27 may have a higher 4permeability than that of area 26, for example about 20% of the permeability of the sheathing Amaterial. Thus, area 27 will pass some coolant, but not -so much as the untreated portions of the skin. Another masked area 28 of reduced porosity but not complete occlusion is positioned toward the root end of the blade,

radially outward from area 22 and contiguous thereto.

Area 28A is shown as generally triangular, with its base along the trailing edge and its point at the leading edge, and bounded on the sides approximately by the 1100 and 1200 lines. It may also have about 20% of the porosity of the skin, or more or less according to design requirements.

FIG. 5 shows the concave side of the blade with four areas ofreduced permeability. Since the concave side of Va blade, whether stator or rotor in either the turbine portion or the compressor portion of a turbine engine, is the pressure side, it normally runs hotter than the con- Avex side, and for this reason the masked portions are here shown as smaller in area than those on the convex side. Area 29 Vis adjacent the tip end and is bounded on `its radially inward side approximately by the 1200 line edge 23. Radially inward there-from is another masked area 31 of higher porosity, more nearly rectangular in outline but having some taper from the trailing edge to the leading edge of the blade. The radially inward boundary of area 31 is approximately at the 1400* line.

Disposed at the root end of the concave side is another masked area 32, tapering from the trailing edge to the leading edge, and bounded on the sides by the root end of the blade and the 1200 line. Adjacent to area 32 in the radially outward direction is masked area 33, generally triangular in outline, having its apex at the leading edge, its base at the trailing edge, and its radially outward side approximately at the 1400 line.

The porosities of the masked areas on the concave side may be the same as the comparable areas on the convex side. On the other hand, they are not necessarily so. It is to be understood that the porosity of any masked area on either side of the blade may be such as is commensurate with design requirements, and is not limited to the specific values exemplified here. In a general way, however, the masked areas of greatest density and least porosity will usually be disposed at those portions of the blade where the lowest temperatures normally prevail, with masked areas of lesser density and higher porosity at portions of somewhat higher temperatures, and no masking of the portions of the blade where the highest temperatures normally occur.

Further, the number, location, size, and configuration of masked areas need not be the same as shown and described here by way of example. Such lfactors vary in different engine designs and also in the different stages of a compressor or turbine wheel, and their selection for efficient cooling will be governed by the design parameters in any given engine.

FIG. 6 shows a cross-section on an enlarged scale of the blade which has been described above. The leading edge 23 of the blade receives the rdirect impingement of the gas, whether the gas is air pumped by the compressor or is combustion gas driving a turbine. The leading edge is therefore generally the hottest portion, and it is essential that it should have adequate cooling. For this reason it is undesirable to have the skin attached to the strut at the leading edge, since such attachment would necessarily block porosity of the skin along the welding or brazing line. On the other hand, it is undesirable to leave a single coolant passage in the leading edge portion which is in free communication with both the concave and convex sides of the blade. Since the external gas pressure is greater on the concave side, and its velocity is higher on the convex side, the coolant supplied to such a single passage would bleed principally through the convex side of the leading edge, resulting in uneven cooling.

The solution to this problem is shown in FIG. 6. The nose of the strut 12 is prolonged forwardly in a thin section 34 toward the leading edge of the blade, leaving a coolant passage 16a on the concave side and another passage 16b on the convex side. Section 34 of the strut does not touch the skin, but stops short of it to leave a small gap, through which

passages

16a and 16b are in communication, and whereby the sheath 19 has no line of occluded permeability at the leading edge. Such a gap is very small, amounting to not more than about .010 in a blade of usual size. Hence, it functions as a restricted linear orifice, and although

passages

16a and 16b communicate, the gap is too small to allow all the coolant to be drawn through and bleed from the convex side.

The trailing edge of strut 12 may be carried out to a sharp edge to support the sheathing all the way. However, at the point where the strut section becomes too thin it is impossible to provide coolant passages therein, which results in leaving a considerable proportion of the trailing edge of the skin without transpiration cooling, its porosity being occluded by being flat against the strut. It has been found in practice that the trailing edge of the sheathing is sufliciently rigid not to need internal strut support. Therefore, the trailing edge of the strut `is not extended out to a knife-edge but is cut short to some degree as shown, leaving a generally triangular coolant passage 16e in-the trailing edge of the blade. Also, if desired the trailing edge of the strut may have a thin section extended to the trailing edge, similar to section '34 in the nose portion and providing a coolant passage on each side, with the skin being attached at the extreme edge.

When shot-peening is used yto produce masked areas of reduced porosity in the sheath material, variation of the amount of residual porosity may be controlled by such factors as size, mass, and hardness of the shot, its velocity, and time of exposure to the peening operation, whereby the degree of closure of the pores may be varied. When it is elected to mask by depositing a pulverized material, variation in porosity is dependent on the size of particles and the thickness of the layer deposited. FIG. 7 is a graph showing the influence of these factors for such materials as the ceramics and metals described above.

Curves for four particle sizes `are shown. The coarsest material exemplified is one of which substantially all particles pass a l-mesh screen, that is, 99% or more, but are principally retained on the next liner screen of a standard series. Additional curves are shown for pulverized materials passing the 15C-mesh, 20G-mesh, and 300- mesh screens. It is not readily practicable to deposit a layer of masking material thinner than about .002 inch. It will therefore be seen that the 10U-mesh material has the widest range of controllability, in terms of permeability of the masking layer in proportion to permeability of the sheath material. That is, continuous variations in permeability of the masking layer may be obtained, from about 80% of that of the sheath material with a deposit about .00 thick, down to about with a deposit of about .040. Further deposit, within practical limits, of masking material of this size does not significantly reduce permeability.

Although the 10U-mesh material has the widest range, the 15G-mesh material has a useful range lower in the scale. About 50% of skin permeability is obtained with a deposit of approximately .002, with continuous reduction of permeability down to approximately 4% with a deposit of about .045 thickness. Again further increase in thickness of deposit does not yield a proportionate reduction of porosity. With the ZOO-mesh material, about 30% of skin porosity is obtained with a deposit of approximately .002 in thickness, and further reduction of porosity results with increasing thickness to approximately 4% at about .020. The 30G-mesh material has the shortest range of useful thicknesses, from about porosity at about .002 thickness to about 4% at about .015 thickness.

It will be apparent that reduction of skin permeability below about 4% cannot be obtained by the deposit of pulverized masking material in readily manageable thicknesses. However, this is good enough for most purposes; in the rare instances where zero permeability is desired it may be obtained by applying a thin sheet of impervious material of the desired size and configuration, or -by leaving a non-recessed portion of the strut member at the desired location and attaching the skin to it.

The l50mesh material is regarded as the most useful in most situations. It is seldom necessary to provide a masked area in which the permeability, although reduced, is greater than 50%, and with this particle size it is possible to reduce it as far as is conveniently possible. Further, the curve for the 15G-mesh material has a gentle slope in the mid-region, from 10% to 40% and from about .025 to about .004", rendering the procedure easily controllable.

In FIG. 8 there is shown a schematized representation of a stator blade and a rotor blade, modified according to the invention, as they would be positioned for use. The convex side of a stator blade 36 is shown, having masked areas of reduced porosity as described above. The stator blade may be supported at its radially outer end by a trunnion 37 or other convenient mounting means, and in some cases may also havemounting means 37a at its radially inner end. The stator blade directs gas flow as shown by the arrow to a rotor blade 11 positioned downstream from the stator blade, the concave side of the rotor blade asl described above being shown. It is to be understood that there 'may be more than one pair of such blades, as in a plural-stage compressor or turbine, and that masking according to the invention need not have precisely the form shown, since it may rvary according to the design parameters of the engine, and from one stage to another in a given engine.

Although the invention is primarily useful in connection with blades in the turbine portion of an engine, in aircraft designed for high Mach number fiight speeds the load on the compressor portion is severe, and temperatures of compressor blades may be as high as l000 F. If these blades are made of light weight materials, such'as are commonly less heat resistant than the materials ordinarily used for turbine blades, it may be beneficial to provide transpiration cooling of variable distribution according to the invention. For blades in the turbine portion the coolant is commonly air bled from the compressor supply; for compressor blades it may be froma refrigerated source of coolant, or it may be fuel.

The invention has been described above in a preferred embodiment; however, it will be understood that various modifications may be made within the scope of the invention by those skilled in the art. It is intended to cover all such modifications in the appended claims.

What is claimed is:

1. A transpiration cooled blade for use in an environment wherein portions of said blade are subjected to different operating temperatures: comprising in combination a strut memberof generally airfoil configuration having on the surface thereof a plurality of lands extending in the generally radial direction of said blade; a permeable sheath member formed of porous mesh material surrounding said strut member and forming the operating surface of said blade and havingv a leading edge, a trailing edge, a concave side, a convex'side, a radially inward end, and a radially outward end; said sheath being attached to said lands and defining with said strut coolant passages between said lands; said blade having-supply passage means communicating with said coolant passages for supplying coolant thereto; said sheath having onV at least one of said sides at each end first masked portions of low permeability, said first masked portions being of generally triangular shape bounded by the blade ends and the trailing edge and tapering toward the leading edge; said sheath also having second masked portions contiguous to each of said first portions, said second masked portions being of higher permeability than said first portions and of generally triangular shape bounded by said first portions and the trailing edge and tapering toward the leading edge; each of said masked portions being formed ofv a layer of sintered particles adhering to said sheath; said sheath having an unmasked portion in the mid-region between said second masked portions, said unmasked portions being of higher permeability than said second portions, whereby said sheath will passv a larger proportion of said coolant lthrough the unmasked portions of said mid-region and successively'less through said'second andv said first masked portions toward said blade ends.

2. Thecombination recited in claim 1, wherein said sintered particles are selected from the group consisting of alumina, magnesia, titania, zirconia, Nicrobraz 120, and Nicrobraz 150.

3. The combination recited in claim 2, wherein said sintered particles have a size from 10G-mesh to 30G-mesh.

4. The combination recited in claim 3, wherein said rst masked portions are layers from about .010" to about .045" in thickness, and said second masked portions are layers from about .002 to 'about .025 in thickness.

5. The combination recited in claim 4, wherein said first and second masked portions are composed of particles of about ISO-mesh.

6. The combination recited in claim 1, wherein said strut member has a nose portion extending toward said sheath member in the leading edge portion of said blade, said nose portion defining with said sheath member a first coolant passage on one side of said nose portion and a second coolant passage on the other side of said nose portion, said nose portion also dening with said sheath member a restricted linear orifice communicating between said rst and second coolant passages.

References Cited UNITED STATES PATENTS 2,857,657 10/ 1958 Wheeler 29--156.8 3,067,982 12/1962 Wheeler 253-39.1 3,240,468 3/1966 Watts et al 253-39.15

FOREIGN PATENTS 619,634 3/ 1949 Great Britain. 722,514 1/ 1955 Great Britain.

EVERETTE A. POWELL, IR., Primary Examiner.

Claims

1. A TRANSPIRATION COOLED BLADE FOR USE IN AN ENVIRONMENT WHEREIN PORTIONS OF SAID BLADE ARE SUBJECTED TO