JP2004076157A - THERMAL SPRAYING METHOD FOR MCrAlX COATING - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming an overlay coating on a substrate by cold-spraying MCrAlX alloy particles. <P>SOLUTION: A gas-dynamical thermal spraying method of the MCrAlX alloy particles is composed of a step of preparing a supersonic gas flow entraining therein solid phase MCrAlX alloy particles in which M is one or more selected among nickel, cobalt and iron and X is an element other than M, chromium and aluminum, and also keeping the particles in a temperature lower than the melting point of the particles, and a step of sticking the MCrAlX overlay coating on the substrate by colliding the solid phase particles in the supersonic gas flow against an unheated nickel- or cobalt-base superalloy substrate. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a method for forming an overlay coating on a substrate by cold spraying MCrAlX alloy particles.

MCrAlY overlay coatings, where M is selected from one or more of Ni, Co, and Fe, include gas turbine engine turbine airfoils and shrouds (such as blades and vanes) as high temperature corrosion and oxidation resistant coatings Applied to equipment such as turbine components. The shroud together forms an annular sealing surface that seals the turbine blade when the turbine blade tip rotates, as is well known. In the past, such MCrAlY overlay coatings have been applied by various techniques. For example, initially MCrAlY overlay coatings were applied using electron beam physical vapor deposition (EB-PVD). Thermal spray techniques have been developed to overcome some of the disadvantages associated with this EB-PVD deposition process. This thermal spraying technique includes low pressure plasma spraying (LPPS), high velocity flame spraying (HVOF), and atmospheric plasma spraying, which are widely used today.

In low-pressure plasma spraying, MCrAlY alloy powder particles are heated by a high-temperature plasma jet above the melting point and sprayed toward a substrate in a vacuum chamber that maintains a spraying environment at a low pressure lower than 1 atmosphere, typically lower than 50 Torr. . The heating and rate of the powder particles is achieved using a plasma torch designed and modified for operation in a reduced pressure atmosphere.

The high-speed flame spray coating method is a supersonic flame spraying process in which heat energy and kinetic energy are transferred to powder particles of MCrAlY alloy using a combustion torch instead of plasma. The particles are heated by the torch to a temperature above their melting point before impacting the substrate. This method is usually performed in a thermal spray environment in a local atmospheric atmosphere and the torch is operated manually or using an automated system. Usually the components to be coated are mounted on a table or drive system.

Thermal spray processes such as LPPS process, HVOF process, and atmospheric plasma spray process applied to MCrAlY overlay coating have several drawbacks. For example, a thermal spray coating applied on a hollow airfoil substrate obscures surface film cooling holes on the outer surface of the airfoil substrate. When an airfoil with an improved cooling mechanism is coated by thermal spraying, for example, a hollow air so that the acid exits through the concealed cooling holes by eroding away the coating above the cooling holes. It is necessary to open a cooling hole after the coating process, for example, by sending hot acid into the foil substrate. Alternatively, the MCrAlY coating can be drilled to expose the underlying cooling holes. Acid pumps and drilling operations are expensive and time consuming.

Thermal spray that requires expensive and time-consuming shot peening and polishing operations on the as-sprayed coating surface to achieve the airfoil surface finish required by engine manufacturers (eg, surface finish finer than 75 microinches) Such a thermal spray process is disadvantageous in that the as-grown MCrAlY overlay coating exhibits a rough surface (eg, rougher than 300 microinches).

Such a thermal spraying process is inefficient in that it has a low adhesion rate (the ratio of the initially sprayed particles to the particles attached to the substrate). For example, the deposition rate of HVOF processes is generally only 30% to 35%. Thermally sprayed particles can cost between $ 40 and $ 60 per pound, so a low deposition rate is very wasteful of expensive raw materials.

When utilizing MCrAlY overlay coatings by HVOF or plasma spray processes, the surface of the airfoil substrate must be rough so that a mechanical bond is created between the coating and the substrate (eg, a surface greater than 200 microinches). Roughness). The required surface roughness of the substrate is achieved by an aggressive grit blasting operation (eg, 55-65 psi with 16 grit alumina particles). The grit particles are embedded in the substrate surface and require a grit particle removal operation as described, for example, in US Pat. No. 6,194,026.
Finally, the thermal spray process requires heating the substrate to a significant temperature prior to coating deposition. For example, when applying an MCrAlY overlay coating using an LPPS process, the process may be performed at least about 760-980 ° C. (1400-1800 ° F.) for at least 4 minutes after performing a reverse arc cleaning for at least 4 minutes prior to coating deposition. It is necessary to heat the substrate. Heating and reverse arc cleaning prior to coating spends 50% or more of the total time to coat the substrate.

An object of the present invention is to provide a method for cold spraying MCrAlX alloy particles to form an overlay coating on a substrate.

In the present invention, M is selected from one or more of Ni, Co, and Fe, and X is an element other than M, Cr, and Al, and preferably one or more of Y, rare earth elements, and reactive elements Providing a supersonic gas stream having a gas flow temperature entrained therein and entraining solid phase MCrAlX alloy particles therein and keeping the particles at a temperature below the melting point of the particles; and a solid phase in the supersonic gas stream A method is provided for gastrodynamic spraying of particles composed of MCrAlX alloys comprising the steps of impacting the particles against a nickel or cobalt based superalloy substrate to deposit an MCrAlX overlay coating on the substrate.

BEST MODE FOR CARRYING OUT THE INVENTION

In an exemplary embodiment of the present invention, the particles composed of MCrAlX alloy preferably have an average particle size (diameter) of about 20 μm or less, more preferably 10 μm or less, to substantially reduce the adhesion rate. Increase and substantially reduce coating surface roughness as sprayed.

In another exemplary embodiment of the present invention, an as-sprayed MCrAlX overlay coating is deposited on an unheated superalloy substrate in an atmospheric environment.

In another exemplary embodiment of the present invention, the as-sprayed MCrAlY overlay coating deposited on the superalloy substrate is heat treated to form a diffusion bond between the coating and the substrate.

The above advantages of the present invention will become more readily apparent by referring to the following detailed description and drawings.

Embodiments of the present invention relate to gas dynamic spraying of particles composed of MCrAlX alloys for depositing MCrAlX alloy overlay coatings on nickel or cobalt base superalloy substrates. MCrAlX alloy is a high temperature corrosion resistant coating that is applied as an overlay coating or layer on turbine components or non-turbine engine components such as airfoils, shroud blocks, and other turbine components including turbine blades and vanes And oxidation resistant alloys. By overlay coating, the as-sprayed coating is not bonded to the substrate by a metallurgical diffusion bond or diffusion layer between the coating and the substrate, but is bonded to the substrate by mechanical bonding to the substrate. It means that In these alloys, the M alloy element is selected from the group consisting of Ni, Co, and Fe, and combinations thereof. The X alloy element is composed of elements other than M, Cr, and Al. X is Y, rare earth elements such as Ce and / or La, and alkaline earth metals such as Si, Hf, Zr, K and / or Ca and / or Mg, and other reactive elements (where A reactive element refers to a stable sulfide, fluoride, phosphide, or other compound having a species such as S, B, and P) that impairs the oxidation resistance of the coating), And a group consisting of a combination of two or more Y, rare earth elements, and reactive elements.

In general, the MCrAlX coating is about 14% to about 35% Cr, about 4% to about 30% Al, about 0.1% to about 3% X, where X is selected from one or more of the above elements. ) And substantially the remainder of M (M is iron and / or nickel and / or cobalt).

The present invention includes the steps of providing a supersonic gas stream having a gas flow temperature that entrains solid phase MCrAlX particles therein and maintains the MCrAlX particles at a temperature below the melting point of the particles, and solid phase particles in the supersonic gas stream. Struck against a nickel or cobalt base superalloy substrate to deposit a MCrAlX overlay coating on the substrate. The present invention may be practiced with other carrier gases such as air, nitrogen, and mixtures thereof, but preferably comprises a compressed carrier gas source 10 comprised of helium. The apparatus is shown in FIG. The compressed carrier gas is generally in the pressure range of 100 to 600 psig. For purposes of illustration and not limitation, a 400 psi helium high pressure cylinder is used to carry out the method of the present invention. The compressed carrier gas is supplied to gas preheater 12 and powder particle supplier 14 via conduits 13 and 15, respectively. Each valve 16 and 18 is provided in conduits 13 and 15 to shut off the gas.

The gas preheater 12 is used to bring the carrier gas (eg, He) to a temperature well below the melting point of the MCrAlX particles sprayed above the atmosphere so that the MCrAlX particles do not melt and remain in the solid phase in supersonic flow. Functions to preheat. The gas preheater is a conventional electrical resistance gas heater, or a gas preheat as described in US Pat. No. 5,302,414, the teachings of which are incorporated herein as part of this specification. It can be constituted by any other type of heater capable of heating compressed gas such as a vessel.

The compressed and preheated gas enters the chamber 22 from the gas preheater 12 via the conduit 24, whereas the powder particle supplier 14 passes the MCrAlX particles via the conduit 20 to the mixing chamber 22. It functions to supply while adjusting the powder discharge amount selected. The powder particle feeder 14 may be constituted by a drum-type feeder as described in US Pat. No. 5,302,414, which is incorporated herein as part of this specification. The present invention can be practiced with, but not limited to, rotating feed wheels, feed screws, or other powder particle feeders based on a fluidized feed bed.

The mixture of compressed carrier gas and MCrAlX powder particles flows through a supersonic (medium) nozzle 30 having a gas distribution baffle 30a, a converging (sonic) compartment 30b, and a diverging (supersonic) compartment 30c. Due to the flow through the nozzle 30, the carrier gas and the powder particles entrained therein are described in US Pat. No. 5,302,414, the teachings of which are hereby incorporated by reference. Thus, it is accelerated to a supersonic speed within a range of 350 to 1800 m / s (meter / second) corresponding to about 1 to 5.2 of Mach. The supersonic gas jet stream impinges on the unheated substrate S and deposits the MCrAlX overlay coating on the substrate. The nozzle 30 and the substrate S are attached in the air atmosphere in a state where the substrate is at the atmospheric temperature, that is, the substrate S does not need to be preheated.

The following examples are provided to further illustrate the present invention without limiting it. A substrate specimen made of a nickel-base superalloy called Rene'41 was sprayed according to the present invention and a CoNiCrAlY overlay coating was deposited on the substrate specimen. The Rene'41 nickel-base superalloy of the substrate is 19% Cr-11% Co-10% Mo-5% Fe-0.09% C-1.5% Al-3% Ti-balance Ni in weight%. Has a nominal composition. A plate-like substrate test piece having dimensions of 2 inches (about 5 cm) wide, 4 inches (about 10 cm) long and 1/8 inch (about 3.2 mm) thick, and is 40-60 psi prior to thermal spraying. Pretreatment was performed by grit blasting using 220 grit aluminum oxide particles at air pressure. CoNiCrAlY powders of different particle sizes, commercially available as CO-210-6 and CO-210-23 from Praxair Surface Technologies, were used. The coatings were analyzed after thermal spraying and heat treatment of a powder having a nominal composition of 31.4% Ni-20.5% Cr-9% Al-0.9% Y-balance Co in weight percent. Two different particle size powders were sprayed in different thermal spray tests, a powder having an average particle size of 6.4 μm (CO-210-6) and an average particle size of 14.8 μm (CO-210-23). . The average particle size means that half of the particles have a diameter greater than a predetermined dimension and the other half of the particles have a diameter smaller than a predetermined dimension.

For purposes of illustration and not limitation, the spray parameters used in the test included the supersonic nozzle section 30a of FIG. 1 having a rectangular cross section with dimensions of a = 2 mm and b = 10 mm. The length L of the nozzle section 30c was 100 mm. 400 psi helium preheated to 400 ° C. in the preheater 12 of FIG. 1 was used as the compressed carrier gas. The nozzle section 30a had a nozzle height of 25 mm from the substrate test piece that was at atmospheric temperature. With these parameters, a particle velocity in a supersonic jet of 19-25 mm / sec of helium was achieved. The above drum-type feeder, similar in construction and operation to that described in US Pat. No. 5,302,414, was used so that a powder discharge rate of 3-5 Kg / hr was possible. The CoNiCrAlY overlay coating was deposited to a thickness of 0.004 (about 200 μm) to 0.008 inch (about 400 μm) on the unheated substrate specimen. The present invention is not limited to the above-described rectangular nozzles and spray parameters because nozzles 30 having a circular cross-section or other cross-sections or other nozzle dimensions and other spray parameters can be used in the practice of the present invention. .

The adhesion rate of the thermal spraying process using the above two different particle size dimensions is obtained by spraying a powder having a known weight on a plate-shaped specimen having an initial weight and obtaining the final weight of the sheet-shaped specimen after thermal spraying. The increase in the weight of each plate-like test piece due to the adhering powder was calculated, and the increase in the weight of each test piece was determined by dividing by the initial weight of the test piece on which the powder was sprayed and multiplying by 100. The adhesion rate is shown in FIG. As can be seen from FIG. 2, as the size of the powder particles decreased, the adhesion rate for the CoNiCrAlY powder increased. A maximum deposition rate of 55% was achieved for an average particle size of 6.4 μm. This provides a substantial improvement in deposition efficiency (eg, 1.7-1.8 times higher) for coating powders compared to that observed in thermal spraying using LPPS and HVOF processes. means. Since the powder particles do not dissolve in the thermal spraying process according to the present invention, it is possible to reuse the excessively sprayed MCrAlX powder, thereby further improving the utilization factor of the powder and further reducing the raw material cost.

The surface finish state of the CoNiCrAlY coating as sprayed was measured using a profilometer in a direction parallel to and perpendicular to the spraying direction. Multiple measurements (6 points in each direction) were averaged and the average surface finish was plotted as a function of powder particle size as shown in FIG. FIG. 3 reveals that the average particle size decreases and the surface finish improves. A surface finish of 243 microinches was achieved for the CoNiCrAlY coating using an average particle size of 6.4 μm. With respect to both sprayed particle sizes, the surface finish of the coating is equal to or better than that obtained using LPPS, HVOF, and atmospheric plasma spray processes where the surface finish of the coating is greater than 300 microinches. Met. As gas turbine engine manufacturers require a surface finish of 100 microinches or less, the improved surface finish achieved by the present invention is a similar MCrAlX coating sprayed by LPPS, HVOF, and atmospheric plasma spray processes. Fewer post-processing steps than coating.

For example, a typical coating post-processing step for a typical MCrAlX overlay coating deposited by LPPS is first a diffusion heat treatment (eg, 2-5 hours at 1080 ° C.) to form a diffusion bond between the coating and the substrate. In addition, an equilibrium phase is formed in the coating alloy. Next, shot peening is performed for 400 seconds to achieve a surface finish of about 125 microinches. The heat treated and peened coating must then be barrel polished for 3 hours to a surface finish finer than 75 microinches using a conventional media bowl polishing process.

In comparison, for a CoNiCrAlY overlay coating deposited by the above test using an average powder particle size of 6.4 μm with a coating surface finish of 243 microinches, the coated substrate was subjected to diffusion heat treatment (eg, 2 ° C. at 1080 ° C. 5 hours), a diffusion bond between the coating and the substrate was formed, and an equilibrium phase was formed in the coating alloy. However, only 210 seconds of shot peening was required to reduce the surface finish of the coating to 79 microinches. This means that the peening time is reduced by 47% compared to typical MCrAlY coatings deposited by LPPS. A final surface finish of 69 microinches on the CoNiCrAlY coating was obtained with a media bowl polishing time of only 30 minutes compared to the 3 hour final surface finish of a typical MCrAlY coating deposited by LPPS. This means that the polishing time is reduced by 84% compared to a typical MCrAlY coating deposited by LPPS.

Furthermore, the above thermal spray test demonstrates that non-aggressive grit blasting can be used by making the substrate surface, and that an acceptable green body bond strength (prior to diffusion heat treatment) of the MCrAlX overlay coating can be obtained. are doing. The present invention can also be practiced without preheating the substrate prior to spray deposition so that there is no need for grit removal, preheating and reverse arc cleaning required in the LPPS process. .

Test results show that MCrAlX overlay coating deposited on an airfoil substrate with surface film cooling holes on its outer surface straddles or plugs cooling holes, which is a feature of the MCrAlX coating deposited by LPPS and HVOF processes. It also demonstrates that there is nothing to do.

Although the invention has been shown and described with respect to several embodiments, it is to be understood that various other changes, modifications, and omissions in the structure and details of the invention may be practiced without departing from the spirit and scope of the invention. Those skilled in the art should understand.

It is the schematic of the thermal spraying apparatus for implementing the Example of this invention. It is an end view of the supersonic section of a nozzle. It is a graph which shows an adhesion rate and an average particle diameter about the CoNiCrAlY alloy powder sprayed by the Example of this invention. 4 is a graph showing surface finish and average particle size as deposited for a CoNiCrAlY alloy coating sprayed according to an example of the present invention.

Explanation of symbols

10 source 12 gas preheater 13,15 conduit 14 powder particle feeder 16,18 valve 20,24 conduit 22 chamber 30 nozzle 30a gas distribution baffle 30b convergence (sonic) compartment 30c divergence (supersonic) compartment S substrate

Claims (14)

a) Solid phase MCrAlX alloy particles in which M is selected from one or more of Ni, Co, and Fe, and combinations thereof, and X is an element other than M, Cr, and Al, and the melting point of the particles Providing a supersonic gas flow having a gas flow temperature that keeps the particles at a lower temperature; and b) impinging the solid phase particles in the supersonic gas flow against a nickel or cobalt base superalloy substrate, A method of coating a nickel or cobalt based superalloy substrate comprising depositing a MCrAlX overlay coating thereon. The method of claim 1, wherein the MCrAlX alloy particles are composed of X selected from the group consisting of Y, rare earth elements, reactive elements, and combinations thereof. The method of claim 1, wherein the particles have an average particle size of about 20 μm or less. 4. The method of claim 3, wherein the particles have an average particle size of about 10 μm or less. The method according to claim 1, wherein the gas flow temperature is in a range of 100 to 800 ° C. The method of claim 1, wherein the substrate is at ambient air temperature when subjected to a collision. The particles are selected from the group consisting of 14% to 35% Cr, 4% to 30% Al, 0.1% to 3% X, and Ni, Co, and Fe, and combinations thereof by weight percent. The method of claim 1 consisting essentially of the remainder. The method of claim 1 including the step of heat treating the as-sprayed MCrAlX overlay coating deposited on the superalloy substrate to form a diffusion bond between the coating and the substrate. The method according to claim 1, wherein the solid phase particles collide with an airfoil substrate. 8. A coated gas turbine engine component according to any one of claims 1 to 7, comprising a nickel or cobalt base superalloy substrate and a MCrAlX overlay coating sprayed thereon. The component according to claim 10, which is a turbine airfoil. The component according to claim 10, which is a shroud block constituting a part of a sealing surface for a tip of a turbine rotor blade of a gas turbine engine. The component according to claim 10, which is a turbine blade having an outer surface having a cooling hole and the coating sprayed on the surface without blocking the cooling hole. The component of claim 10, wherein the coating has a surface roughness of less than 300 microinches as measured by a profilometer.

Images