Abstract: Composite bodies comprise a metallic member and a ceramic member integrally joined together by joining a projection of the ceramic member to a recess of the metallic member. Their joining strength is improved by substantially limiting brazing metal to an interface between the outer peripheral surface of the projection of the ceramic member and the innner peripheral surface of the recess of the metallic member. The joining strength is also improved by forming a groove around the outer periphery of the metallic member at the joined end. The joining strength is also improved by providing a space or an intermediate member between a tip end surface of the projection and a bottom surface of the recess and attaining the relation: ##EQU1## in which G, L.sub.1, .alpha., .alpha.', T.sub.S and T.sub.

Abstract: A high temperature turbine engine includes a hybrid ceramic/metallic rotor member having ceramic/metal joint structure. The disclosed joint is able to endure higher temperatures than previously possible, and aids in controlling heat transfer in the rotor member.

Abstract: The coated article includes a refractory metal substrate having an oxidation resistant intermetallic layer formed in situ thereon; e.g., a fused refractory metal silicide layer, and a ceramic layer applied on and adhering to the intermetallic layer to provide enhanced high temperature properties and improved resistance to premature catastrophic failure in high temperature oxidizing environments where dissimilar materials are present that may destructively react with the intermetallic layer.

Abstract: A ceramic thermal barrier coating system for superalloy components subjected to high operating temperatures, such as gas turbine engine airfoils, is disclosed which includes a titania doped interfacial layer between the metallic substrate and the ceramic overcoat in order to better resist failure by spalling.

Abstract: A runner is provided which consists of a radial turbine ceramic rotor with an integrated ceramic shaft and a non-ceramic compressor impeller which are connected by a releasable, thermally and mechanically loadable mechanical coupling in such a way that the releasable mechanical coupling is located with the compressor impeller. This coupling consists of a cylindrical slotted sleeve which, on the one hand, is fitted into a cylindrical fitting bore in the compressor impeller and, on the other hand, accepts the end of the ceramic shaft in a fitting bore. In addition, the coupling has a tie rod with a screw thread and a pair of conical clamping elements between the cylindrical sleeve and the compressor impeller.

Abstract: An erosion and corrosion resistant coating is formed of a plurality of alternating layers of metallic and ceramic materials. The two materials selected for the layers have complementary wear resistant characteristics, such that one is relatively ductile and the other is relatively brittle. The concentration of the two materials at the interface between adjacent layers is graded to improve the adhesion of the layers and to provide a more unified coating. Prefereably radio-frequency sputtering is employed to deposit the coating, since it does not produce excessive heating which could negate any prior heat treatment of the substrate onto which the coating is deposited.

Abstract: In a shaft composite structure wherein a ceramic shaft integrally formed with a ceramic turbine rotor is fixed to a metal sleeve integrally formed with a metal rotary shaft of a compressor impeller, a connection edge is located at a position corresponding to a recess for seal ring, and a thickness of tip portion of the metal sleeve is made thin to reduce a stiffness.Therefore, a stress concentration at the connection edge can be eliminated effectively and thus a reliable shaft composite structure can be obtained.

Abstract: A rotary gas seal in which a first member, e.g., a tip, cooperates with a second member to inhibit gas flow therebetween, the improvement wherein, the tip is provided with a ceramic or metallic coating bonded thereto, the surface of the coating having a plurality of laser-formed depressions and providing a wear-resistant, cutting surface capable of cutting into the second member. Also, a turbine or compressor blade having a tip surface adapted to cooperate with a sealing surface to form a seal between the blade and the sealing surface and a ceramic or metallic carbide coating bonded to said tip surface, the coating having a plurality of laser-formed depressions and providing a wear-resistant, cutting surface capable of cutting into the sealing surface.

Abstract: A turbine rotor having a ceramic turbine wheel having an improved resistance to cracking and breaking. The turbine wheel is made of a ceramic material having pores formed therein with a maximum diameter of 20 .mu.m distributed in the blade portion of the wheel at a porosity of 2 to 10 vol. %. Preferably, the volume porosity of the pores is gradually decreased from the blade surface to the interior of the blade portions.

Abstract: In a gas generator of a gas turbine, the turbine is provided with more stages than aerodynamically necessary for reducing the turbine rotational speed. As a result thereof, the stresses of the turbine rotor are reduced, the latter can be made of ceramic material, and the turbine inlet temperature can be increased. In order to permit the compressor to continue to operate at optimum rotational speed, the compressor is coupled with the turbine by way of a transmission providing a speed-up. Owing to this arrangement, the thermal efficiency and therewith the economy of the gas turbine can be considerably increased and the heretofore occurring problems with the use of ceramic material in the turbine are solved in a simple manner.

Abstract: A ceramic rotor is produced by sequentially forming a ceramic rotary body portion, measuring the dynamic unbalance of the ceramic rotary body portion, grinding the ceramic rotary body portion to adjust the dynamic unbalance and then integrally coupling a rotary shaft to the ceramic rotary body portion.

Abstract: In a metal-ceramic combination wherein a monobloc ceramic member comprising a base, a protrusion integrally formed on the base and an easement portion on and around the root of the protrusion, is combined with a metallic member, an improved combination having an excellent strength in total is obtained by fitting the protrusion tightly into a recession or conduit of the metallic member, leaving clearance of 0.5 mm or more between the easement portion and a defined edge of joint interface of the said two members. The combination of the invention is particularly useful for engine parts to be subjected to high temperatures and repeated stresses such as a turbocharger rotor, piston, tappet, rocker arm, exhaust valve, cam and the like.

Abstract: A method of producing turbine rotor having a including vane wheel made of ceramics, a ceramic shaft formed integrally with the turbine wheel, and a metallic shaft bonded to the ceramic shaft. The hardness of a part of or the whole part of a compressor wheel-fitting shaft portion of the metallic shaft is made smaller than that of a portion of metallic shaft apart from the compressor wheel-fitting shaft, said portion being located on the turbine vane wheel side. Thereby, slackening between the compressor wheel and the fitting shaft is avoided.

Abstract: A ceramic radial turbine rotor made of a ceramic material having a strength s (kg/mm.sup.2) includes blade tips having a thickness t (mm). A product st.sup.2 of strength s and t.sup.2 (square of t) is representative of resistance to breakage of the rotor to foreign objects colliding against blades of the rotor. The product st.sup.2 fulfills a relation st.sup.2 .gtoreq.5.times.10.sup.4 vm+33. In this case, v is a circumferential speed of tip ends of inducers of blades of the rotating rotor when the blades are damaged by steel balls having a mass m (kg) colliding against the blades in a steel ball collision test of blades of a ceramic radial turbine rotor, and vm is a product of v and m.

Abstract: A method of producing a composite ceramic structure, including: preparing a formed ceramic piece which constitutes a portion of the composite ceramic structure; preparing a rubber mold having a molding surface defining a remaining portion of the composite ceramic structure; positioning the rubber mold in contact with a joining part of the formed ceramic piece from which the remaining portion of the composite ceramic structure extends; covering an exposed surface of the formed ceramic piece, and at least an end of the rubber mold adjacent to the joining part of the formed ceramic piece, with an elastic member; filling the rubber mold with a mass of ceramic powder such that the mass of ceramic powder contacts the joining part of the formed ceramic piece, the mass of ceramic powder being substantially identical in composition with a ceramic material of which the formed ceramic piece is formed; applying a static hydraulic pressure to an assembly of the formed ceramic piece and the mass of ceramic powder in the ru

Abstract: A centrifugal pump wherein the back shroud of a brittle impeller of ceramic or glass is coupled to the radially outwardly extending disc of a metallic adapter whose hub receives torque from the pump shaft. The adapter has a flange which surrounds the peripheral surface of the impeller or it has a collar which surrounds a complementary collar of the back shroud. The arrangement is such that the coupling between the adapter and the impeller does not subject the impeller to any tensional or other stresses which would be likely to affect the integrity of the brittle impeller. The disc of the adapter is adjacent the rear side of the back shroud so that the adapter does not interfere with the flow of conveyed material to, in and from the impeller.

Abstract: A turbine rotor has composite ceramic blades each having a bulb-shaped root with planar flanks which define an angle of convergence between them not exceeding ten degrees, and by which the root is held in a dovetail section socket in the periphery of the rotor disc by means of wedge-shaped members also disposed in the socket on opposite sides of the root. Each wedge-shaped member is part of an element including a platform which is disposed adjacent the curved portion of the blade radially outwards of the socket and which is joined to the wedge-shaped member by an integral strut. The platforms of all of the elements extend in a circumferential direction and combine to define a continuous ring forming part of the inner boundary of the gas flow path through the turbine.

Abstract: A gas turbine engine blade has an abrasive material tip with a fused superalloy matrix and evenly distributed ceramic particulate. The matrix will have a desirable metallurgical structure characterized by fine dendrites and remanants of the original powder metal structure from which it was made. Due to the fusion of the tip, the peripheral edge will tend to be curved. To lessen the effect of thermal strains on such an abrasive tip, a sheath of a superalloy, such as a portion of the turbine blade substrate, extends along the side of the abrasive. The sheath may be present only in the thicker leading edge part of the blade airfoil.

Abstract: A ceramic-metal composite body comprises a ceramic member with a projection formed thereon and a metallic member with a depression or through hole formed therein. The ceramic member and the metallic member are bonded together by fitting the projection of the ceramic member into the depression or through hole of the metallic member. The difference between the outer diameter of the projection of the ceramic member and the inner diameter of the depression or through hole of the metallic member when the projection of the ceramic member is extracted from the depression or through hole of the metallic member is not less than 0.2% of the outer diameter of the projection of the ceramic member.

Abstract: A process provides a method for attaching a turbine blade to a blade support such as a rotor or rotor disc of a turbine. The root portion of the blade is formed to a shape approximately that of a groove in the surface of the rotor or rotor disc and the root portion of the blade is inserted within the groove. A composition comprising a particulate compound selected from the group consisting of a ceramic, graphite metal, metal alloy and mixtures thereof is positioned between the root portion of the blade and steeples, located one on either side of the groove.

Abstract: An airfoil-shaped blade assembly having a metallic core, thin coolant liner and ceramic blade jacket includes variable-size cooling passages and a circumferential stagnant air gap to provide a substantially cooler core temperature during high temperature operations.

Abstract: A turbine rotor unit and a method of producing the same are disclosed. This turbine rotor unit comprises a ceramic rotor, a ceramic shaft integrally united with the ceramic rotor and a metal shaft provided with a cylindrical portion fixing the ceramic shaft therein and is characterized by having a gap between a substantial portion of the inner peripheral surface of the cylinder portion located near the side of the ceramic rotor and the outer surface of the ceramic shaft. Further, the turbine rotor unit is produced by arranging on one end of the metal shaft a cylindrical portion wherein an inner diameter at its opening side is larger than that at the bottom side, inserting the ceramic shaft into the cylindrical portion, and fixing the ceramic shaft to the cylindrical portion at its small diameter side.

Abstract: Ceramic parts of complicated configurations with different thicknesses at different portions can be mass produced economically with high production yield and excellent quality using an injection molding process.

Abstract: In a turbine rotor composed of a ceramic turbine blade and a metal shaft with an end to be machined, martensite stainless steel or martensite heat-resistant steel which can be hardened in a gas or vacuum after having been heated beyond the quenching temperature thereof is used as the metal. The ceramic blade and the metal shaft are heat-connected by brazing or shrinkage fit at 800.degree. C., or more. The metal shaft hardened through the heat-connection is tempered only at the end to be machined or the metal shaft heated to the quenching temperature is quench hardened only in part other than the end to be machined, thus facilitating the machining of the metal shaft locally which keeping the remaining part thereof in a quench hardened condition.

Abstract: According to the present invention there is provided a thermal barrier coating wherein multilayers of (I) a ZrO.sub.2 layer containing a luminous activator and stabilized by Y.sub.2 O.sub.3, CaO, MgO or a mixture thereof and (II) a ZrO.sub.2 layer containing a luminous activator different from that used in (I) and stabilized by Y.sub.2 O.sub.3, CaO, MgO or a mixture thereof, or a ZrO.sub.2 layer not containing a luminous activator and stablized by Y.sub.2 O.sub.3 are stacked, and the layers at least under an uppermost layer opposite to a base member to be protected have a total thickness sufficient for exhibiting a thermal barrier effect. The present invention has as its object to provide a thermal barrier coating which allows non-destructive testing to determine whether it has a thickness sufficient for themal barrier effect.

Abstract: Improved screw propellers especially useful in the propulsion of small boats are constructed at low cost from cast iron characterized by rounded graphite in a ferritic, pearlitic and/or acicular matrix. The propeller is exceptionally strong and may be driven by a prime mover at a speed up to 9,000 revolutions per minute without the blades losing their pitch or being easily damaged when submerged objects are struck at high speed. The disclosure is also concerned with outboard motors provided with the ductile iron propeller of the invention, and with small power boats having a propulsion unit which includes the ductile iron propeller of the invention. The propeller has certain preferred dimensions and characteristics, and should be constructed from ductile iron having the composition disclosed herein. The disclosed ductile iron propeller improves the operation of propulsion units of the type normally provided with inexpensive light weight propellers for the reasons noted herein.

Abstract: A turbine rotor including a turbine vane wheel made of ceramics, a ceramic shaft formed integrally with the turbine wheel, and a metallic shaft bonded to the ceramic shaft. The hardness of a part of or the whole part of a compressor wheel-fitting shaft portion of the metallic shaft is made smaller than that of a portion of metallic shaft apart from the compressor wheel-fitting shaft, said portion being located on the turbine vane wheel side. Thereby, slackening between the compressor wheel and the fitting shaft is avoided. Methods of producing the turbine rotor are also disclosed.

Abstract: A vane-type impeller having a plurality of abuttably-adjacent, interconnected components at least some of which are made of an abrasion-resistant ceramic material is improved by a layer of a resiliently-flexible material between at least each component made of an abrasion-resistant ceramic material and each component it is abuttably adjacent for increasing the capability of each component made of the abrasion-resistant material of withstanding impact forces.

Abstract: A rotor-shaft assembly includes a ceramic solid hubbed turbine rotor having an integral stub shaft interference fit within one end of a generally cylindrically shaped sleeve member. The sleeve member defines a hub portion adapted to mate with a piston ring seal and a coaxial bore therethrough. The interference fit, which is defined by the change in the diameter of the bore, schedules the compressive forces acting on the stub shaft. A metal shaft is brazed within the other end of the sleeve member in a torque transmitting relationship.

Abstract: A metal-ceramic composite fitting assembly is described in which an effective connection between a boss on the ceramic member and the metal shaft member is achieved by providing the shaft with a sleeve formed of a material having a coefficient of thermal elongation comparable to that of the ceramic member, which sleeve is joined to the shaft member and cooperates with a recess therein to engage the boss along its length and to impose thereon compressive gripping forces that increase in magnitude along the length of the boss.

Abstract: A power-transmitting ceramic to metal joint structure including a first shaft consisting essentially of a sintered ceramic material, one portion of the shaft defining a first mating surface; an intermediate insert consisting essentially of a sintered ceramic material, the insert having two opposite insert mating surfaces, the insert having a thickness between the opposite insert mating surfaces in the range of from about 1.5 to about 20% of a distance defined by the cross section of the first mating surface and a flexural strength of not less than about 70% of the sintered ceramic material comprising the first shaft; a second shaft consisting essentially of metal, one portion of the second shaft defining a second mating surface; and brazing filler means affixing the first mating surface to one of the insert mating surfaces and the second mating surface to the opposite insert mating surface, the aforementioned mating surfaces being affixed in abutting relationships.

Abstract: A rotor-shaft assembly which includes a ceramic, solid hubbed turbine rotor having an integral stub shaft brazed within one end of a generally cylindrically shaped sleeve member. A metal shaft is either brazed or cold press fitted within the other end of the sleeve member in a torque transmitting relationship. The stub shaft is formed with an annular relief therearound in order to reduce the compressive forces acting on the stub shaft by the sleeve member.

Abstract: There are disclosed a blade for use as part of an axial flow fan and a method of forming such a blade wherein a large concentration of silica particles are molded into the leading edge of a hollow, one-piece molded body which includes a core of reinforced, thermosetting resin having relatively low abrasion resistance.

Abstract: Disclosed herein is a metal-ceramic composite article which includes a metallic member made of a precipitation hardenable alloy and a ceramic member, wherein a projection of the ceramic member is fitted into a hole or a through hole formed in the metallic member and the metallic member of the composite article is hardened through precipitation hardening. A process for manufacturing such a metal-ceramic composite article is also disclosed. The manufacturing process includes the steps of: fitting a projection formed at a ceramic member into a hole formed in the metallic member made of a precipitation hardenable alloy in a state in which precipitation-hardening is not carried out to form a metal-ceramic joint body, and subjecting the thus formed metal-ceramic composite body to a precipitation hardening treatment to harden the metallic member.

Abstract: A metal-ceramic composite article produced by fitting a projection formed on a ceramic member into a hole formed in a metallic member having a hardened region and an unhardened region on its surface such that the ceramic member is monolithically bonded to the metallic member and the deformed region of the metallic member resulting from the fitting is located within its unhardened range, has a high bonding force between the ceramic member and the metallic member and is adapted to be used in engine parts, such as turbocharger rotor, gas turbine rotor and the like, and other structural parts exposed to high temperature or to repeating loads, by utilizing the heat resistance, wear resistance and high strength of the ceramic.

Abstract: A turbocharger for an internal combustion engine, in which the turbocharger has a turbine wheel made in one piece from a ceramic material and having an axially extending support portion which is inserted into a hollow shaft made from a metal material. The support portion of the turbine wheel has, at an end remote from the blade portions, a portion having an increased diameter and tightly fitted to the hollow shaft. An axial first annular slit is formed between the shaft and the support portion. A radial second annular slit is formed between facing surfaces of the shaft and the turbine wheel. These first and second slits are connected to each other and work to alleviate the effects of the different heat expansion coefficients of the metal and ceramic materials on the support portion of the turbine wheel.

Abstract: A radial-type ceramic turbine rotor comprising a blade member and a shaft bonded to the blade member, and having an axial hole extending through the blade member from its front surface towards the tip of the shaft, can be produced without forming cracks during dewaxing, ill-bonding of the blade member with the shaft, and lowering of the bonding strength, and has a high workability in the precise machining.

Abstract: A method of producing a composite ceramic structure, including: preparing a formed ceramic piece which constitutes a portion of the composite ceramic structure; preparing a rubber mold having a molding surface defining a remaining portion of the composite ceramic structure; positioning the rubber mold in contact with a joining part of the formed ceramic piece from which the remaining portion of the composite ceramic structure extends; covering an exposed surface of the formed ceramic piece, and at least an end of the rubber mold adjacent to the joining part of the formed ceramic piece, with an elastic member; filling the rubber mold with a mass of ceramic powder such that the mass of ceramic powder contacts the joining part of the formed ceramic piece, the mass of ceramic powder being substantially identical in composition with a ceramic material of which the formed ceramic piece is formed; applying a static hydraulic pressure to an assembly of the formed ceramic piece and the mass of ceramic powder in the ru

Abstract: A rotary component of a rotary device for heat engines, such as a turbine wheel of a gas turbine or a turbocharger, formed in an integral ceramic-fiber-reinforced sintered ceramic structure. The reinforcing ceramic fibers in the edges of the vanes of the rotary component are oriented radially to prevent the chipping of the edges of the vanes liable to occur in a direction perpendicular to the direction of thickness of the vanes. The rotary component is formed by molding a mixture of a ceramic powder, ceramic fibers and organic additive or additives in a mold having a cavity having the same shape as that of the rotary component except that the depth of sections of the cavity corresponding to the vanes is greater than the height of the vanes to be formed, sintering the molding, and cutting the vanes of the molding in a predetermined height.

Abstract: A metal-ceramic composite article obtained by press fitting a projection of a ceramic member into a hole formed in a metallic member has a high bonding force in the press-fitted portion and is free from separation between the ceramic member and the metallic member. The composite article exhibits high thermal resistance or wear resistance when used as a piston crown in a piston for an adiabatic engine or when used as a cam contacting surface of a tappet.

Abstract: A ceramic coated abrasion resistant member and method of making are described in which a plurality of thin plates of polycrystalline ceramic material of small size, for example, a square plate measuring 1.0 inch by 1.0 inch having a thickness less than 0.200 inch are bonded to a thicker substrate base member with a uniform layer of organic adhesive bonding material. The bonding material includes a thermosetting organic plastic adhesive and a coupling agent which forms covalent chemical bonds with the ceramic plates, base member and plastic adhesive. An organosilane, such as .gamma.-aminopropyl trimethoxy silane, may be used as the coupling agent. The ceramic material may be selected from the group consisting of aluminum oxide, zirconium oxide, silicon carbide, silicon nitride, and spinel ceramic materials. The substrate member is preferably metal, such as steel and the plastic adhesive may be an epoxy resin.

Abstract: A gas turbine including a joint structure is disclosed. According to the joint structure, a ceramic shaft is received in a bore formed in an end portion of a metallic shaft. Brazing filler metal made of Ag-Cu alloy is distributed between the closely fitted surfaces of the ceramic shaft and bore wall, and it extends axially toward the open end of the bore up to a predetermined plane where a ring seal groove formed on the end portion of the metallic shaft lies. The open end of the bore is closed to prevent entrance of exhaust gas into the bore.

Abstract: A hybrid blade for a fluid flow engine has a U-shaped core of metal or a metal alloy and a ceramic outer jacket which forms together with a mounting plate a unitary, single piece structure. The legs of the core straddle the mounting plate and a heat insulating member is inserted between a crosspiece of the core and the mounting plate. This structure permits relative movement between the core and the jacket to compensate for different heat expansion coefficients.

Abstract: The connection of a ceramic rotary component to a metallic rotary component for a turbomachine such as a gas turbine engine wherein the ceramic rotary component comprises a sintered rotor disk of reaction bonded silicon nitride (RBSN) or silicon carbide sintered under no pressure and the metallic rotary component is formed by the hot isostatic pressing of a metallic powder. The metallic rotary component becomes bonded to the sintered rotor disk to form a secure connection therewith. The metallic powder has a coefficient of thermal expansion substantially equal to that of the ceramic rotary component.

Abstract: A hybrid gas turbine rotor having a silicon carbide ceramic turbine wheel portion and a nickel alloy steel shaft portion further includes a hollow silicon carbide ceramic stub shaft integral with the turbine wheel portion having a frustoconical outer surface tapering away from the wheel portion and a tubular end on the shaft portion having an inner frustoconical surface tapering toward the shaft portion at an angle corresponding to the outer surface taper angle. The shaft portion is connected to the wheel portion by shrink fitting the tubular end over the stub shaft so that the shrink fit is the sole medium whereby the wheel portion is supported on the shaft portion and torque is transferred therebetween.

Abstract: A three layer composite coating for gas turbine engine materials and other materials exposed to high temperatures, thermal cycling, and corrosive environments. The base layer is Aluminide or an MCrAlY composite, where M is a metal selected from the group consisting of nickel or cobalt, alone or in combination. The middle layer is a ceramic composite. The outer layer is composed of nickel oxide.

Abstract: A structural component which is coolable for use under high thermal load conditions, such as a turbine blade, has a metallic support core with cooling ducts separated by lands in its surface. The core and its cooling ducts and lands are enclosed by an inner layer of metal felt and an outer layer of heat insulating ceramic material which partially penetrates into the metal felt to form a bonding zone between the felt and the ceramic material. Thus, any heat passing through the ceramic layer is introduced into the large surface area of the metal felt enabling the latter to efficiently introduce the heat into a cooling medium flowing in the ducts, thereby preventing thermal loads from adversely affecting the metal core to any appreciable extent.

Abstract: Disclosed herein is a metal-ceramic composite body having a ceramic member with a small diameter portion and a large diameter portion which are formed by providing a ceramic member with a projection and a metallic member with a recessed portion or through hole. The ceramic member and the metallic member are bonded together by inserting the small diameter portion into the recessed portion or through hole such that a space being not less than the diameter of the small diameter portion is provided between the edge surface of the metallic member on the side of the ceramic member at the bonding portion and the back surface of the large diameter portion of the ceramic member. The thickness of the edge portion of the metallic member is gradually reduced toward the ceramic member at a radius of curvature of not smaller than 0.4 times as large as the diameter of the small diameter portion. A method of producing the metal-ceramic composite body is also disclosed herein.

Abstract: Disclosed herein is a heat resistant vaned stirrer for use in a high temperature atmosphere. To endure stirring operations in high temperature molten metals of 300.degree.-1200.degree. C., the stirrer vanes are formed of a carbon-ceramics composite material which is produced from coke powder blended with 10-50% by volume of ceramics powder and which has a bending strength higher than 200 kg/cm.

Abstract: A method of manufacturing a radial flow turbine rotor is disclosed, which comprises the steps of injection molding a rotor body including a conical shaft and a plurality of blades formed on the periphery of the shaft and at an angle to the axis of the shaft from a ceramic material using a mold having parting lines corresponding to blade edges such that projections are formed on the blade edges, sintering the molding thus obtained, and grinding the edge surfaces of the blades facing a casing. The blades are thus provided with projections on their inlet and outlet edges which face a fluid passage.