EP0825275A1 - Process for coating nickel or cobalt-base superalloy substrate - Google Patents

Abstract

A substrate of nickel or cobalt-based alloy (2) is coated with another alloy at least over a restricted area by applying a powdered mixture of metals (1) which is then caused to react by controlled heating in a vessel filled with inert gas at up to 1.5 GPa pressure. The vessel has elements able to heat it to 1200 degrees C at 5-120 degrees C/minute to create a thermal gradient of 200 degrees C between opposite ends of the area, so that the reaction begins at one end of the mixture and is rapidly propagated therethrough, forming an intermetallic compound which bonds itself to the substrate.

Description

The present invention relates to a method for producing a contribution on a part of a turbomachine.

It is known in many applications to improve the service life of parts by applying a coating in a localized area so as to improve the properties of surface in this zone according to stresses or specific contacts. Examples of treatment techniques of this type are described by FR-A-2 397 259 which plans to deposit a layer of alloy by fusion welding resistant to cracking at the end of a blade then a layer of a hard alloy and / or resistant to oxidation-corrosion. We also know from FR-A-2 511 908 a process assembly by brazing-diffusion making it possible to report on a nickel or cobalt-based superalloy part a elementary part in the form of a pre-sintered blank formed from a mixture of two powders, one of which, called powder input, is present between 5 and 25% by weight of the mixture and has a nickel, chromium and boron or nickel, cobalt base, silicon and boron. Furthermore, according to US-A-4 705 203, a method of repairing surface defects of parts in superalloy has a plasma flame projection of two successive layers of different compositions, then one heat treatment during which only the first layer is melted and then the surface layer is removed.

The manufacturing techniques described by FR-A-2 511 908 in particular require the use of a homogeneous mixture of powders to prepare a self-brazable sintered material which can be used to produce a contribution by brazing on a localized area of superalloy part. In this case, the maximum temperature of use of the superalloy part must remain significantly lower than the brazing temperature. Research has also been carried out for the development of processes for the synthesis of materials, either metallic, intermetallic or ceramic by self-propagated combustion. US-4,778,649 describes for example a process for manufacturing a composite material comprising in particular a layer of copper alloy covered with a layer of mixture of Ti + B + Cu powders in which a reaction of synthesis of TiB ₂ by combustion self-propagating is triggered by compression and heating. There is thus obtained on a copper substrate, a TiB ₂ surface layer and an intermediate layer of a TiB ₂ + Cu mixture. Zr or Al as well as other borides or carbides can be used.

One of the objects of the invention is to obtain a recharging or a coating of turbomachine parts composed of a nickel-based or cobalt-based superalloy having either a polycrystalline structure, or a structure obtained by directed solidification, i.e. a structure monocrystalline.

• (a) dépôt sur au moins une zone localisée de la pièce d'un élément d'apport pris dans le groupe, d'une part, des poudres réactives dans des proportions correspondant à la formation d'un matériau intermétallique et, d'autre part, des poudres de superalliage à base de nickel ou de cobalt ;
• (b) mise en place de la pièce comportant le dépôt obtenue à l'étape (a) dans une chambre à haute pression alimentée en gaz neutre par un système de compression permettant d'assurer dans la chambre une pression hydrostatique de gaz neutre allant jusqu'à 1,5 GPa, ladite chambre formant également un four muni d'éléments chauffants permettant d'atteindre une température de 1200°C avec une vitesse de montée en température comprise entre 5°C/mn et 120°C/mn en assurant un gradient thermique de 200°C d'une extrémité à l'autre de la zone de pièce concernée, les températures étant contrôlées au moyen d'un système de mesure ;
• (c) réalisation d'une réaction de synthèse par combustion auto-protégée sous haute pression hydrostatique de gaz sur ledit élément d'apport dans des conditions déterminées de température et de pression de manière à assurer la densification de l'apport et la liaison métallurgique entre ledit apport et la surface concernée de la pièce en superalliage.

The process for producing a contribution on a superalloy part meeting these conditions without incurring the drawbacks of prior known solutions is characterized by the following successive steps.

• (a) deposition on at least one localized area of the part of a filler element taken from the group, on the one hand, reactive powders in proportions corresponding to the formation of an intermetallic material and, on the other hand part, superalloy powders based on nickel or cobalt;
• (b) positioning of the part comprising the deposit obtained in step (a) in a high pressure chamber supplied with neutral gas by a compression system making it possible to ensure in the chamber a hydrostatic pressure of neutral gas up to '' at 1.5 GPa, said chamber also forming an oven provided with heating elements making it possible to reach a temperature of 1200 ° C. with a rate of temperature increase between 5 ° C./min. and 120 ° C./min. while ensuring a thermal gradient of 200 ° C from one end to the other of the zone of the part concerned, the temperatures being controlled by means of a measurement system;
• (c) carrying out a synthesis reaction by self-protected combustion under high hydrostatic gas pressure on said filler element under determined conditions of temperature and pressure so as to ensure the densification of the supply and the metallurgical bond between said contribution and the surface concerned of the superalloy part.

• la figure 1 représente une vue schématique en coupe d'un élément d'apport mis en place sur un substrat, selon un exemple du procédé de réalisation conforme à l'invention ;
• la figure 2 représente un diagramme des températures lors d'une réaction de synthèse par combustion auto-propagée dans ledit procédé ;
• la figure 3 représente une microphotographie à grossissement de 20 d'une zone de pièce comportant l'apport selon ledit procédé ;
• les figures 6 et 7 montrent des microphotographies et les courbes d'évolution des profils de concentration des éléments composants dans la zone d'interphase entre les matériaux de la pièce et de l'apport selon ledit procédé ;
• la figure 8 représente une vue schématique en coupe analogue à celle de la figure 1 d'un élément d'apport mise en place sur un substrat, selon un autre exemple du procédé de réalisation conforme à l'invention ;
• la figure 9 montre une microphotographie et les courbes d'évolution des profils de concentration des éléments composants de la zone de pièce comportant l'apport selon ledit procédé ;
• la figure 10 montre une microphotographie agrandie d'un détail de la zone représentée sur la figure 9 ;
• la figure 11 montre les courbes d'évolution des profils de concentration des éléments composants de la zone représentée sur la figure 10 ;
• la figure 12 montre une microphotographie agrandie d'un détail de la zone représentée sur la figure 10 ;
• la figure 13 montre une microphotographie agrandie d'un détail de la zone représentée sur la figure 9, proche de la zone représentée sur la figure 10 ;
• la figure 14 montre les courbes d'évolution des profils de concentration des éléments composants de la zone représentée sur la figure 13.

Other characteristics and advantages of the invention will be better understood on reading the following description of an embodiment of the invention, with reference to the appended drawings in which:

• Figure 1 shows a schematic sectional view of a filler element placed on a substrate, according to an example of the production method according to the invention;
• FIG. 2 represents a diagram of the temperatures during a synthesis reaction by self-propagated combustion in said method;
• FIG. 3 represents a micrograph with a magnification of 20 of a part area comprising the supply according to said method;
• FIGS. 6 and 7 show microphotographs and the curves of evolution of the concentration profiles of the component elements in the interphase zone between the materials of the part and of the contribution according to said method;
• 8 shows a schematic sectional view similar to that of Figure 1 of a filler element placed on a substrate, according to another example of the production method according to the invention;
• FIG. 9 shows a photomicrograph and the evolution curves of the concentration profiles of the component elements of the part area comprising the contribution according to said method;
• Figure 10 shows an enlarged photomicrograph of a detail of the area shown in Figure 9;
• FIG. 11 shows the curves of evolution of the concentration profiles of the component elements of the zone represented in FIG. 10;
• Figure 12 shows an enlarged photomicrograph of a detail of the area shown in Figure 10;
• Figure 13 shows an enlarged photomicrograph of a detail of the area shown in Figure 9, close to the area shown in Figure 10;
• FIG. 14 shows the curves of evolution of the concentration profiles of the component elements of the zone represented in FIG. 13.

The installation used for the implementation of the production of a contribution on a superalloy part of turbomachine according to the invention consists of a high pressure supplied with neutral gas by a system of compression and also forming an oven fitted with a heating and temperature measurement.

In an exemplary embodiment, the compressor used is consisting of three compression stages connected in series in which the gas is successively compressed. Pressure final gas reached is 1.5GPa and a pressure gauge controls the value of the gas pressure.

The high pressure chamber used includes the fittings suitable for conditions of use at high pressures and high temperatures such as multiple walls inserted in a shield and comprising an envelope of water cooling and all necessary access, electrical connections, gas passage and fittings sealing correspondents. Vacuum equipment about 1Pa is also attached. A rotation of the chamber also allows use in positions horizontal, vertical or inclined.

The heating system consists of a heating element under shape of a graphite coil and two electrodes in graphite placed at each end forming an oven placed in said room. The settings allow to ensure a gradient thermal of the order of 200 ° C on a part placed in the oven. Thermocouples are added to allow temperature measurements.

Variant embodiments can be made to the installation. Including energy supply equipment used to initiate the reaction can be added as than a tungsten wick, a graphite wick or a laser beam.

EXAMPLE A

This involves making a contribution on a superalloy part A based on nickel in order to restore to the profile desired by recharging using a mixture of nickel powders and aluminum, in equi-atomic proportions.

• (a1) réalisation d'un mélange homogène de la quantité adéquate des poudres de nickel et d'aluminium ;
• (a2) compactage à froid du mélange obtenu dans un moule adapté sous une charge de 40 MPa.

The nickel and aluminum powders used have a particle size of less than 150 μm. In the present application, step (a) of the process for producing a filler on a superalloy part comprising the deposition of a filler element on a part zone is carried out by the placement of an element compact 1 on the substrate 2 formed by said zone concerned with the part, as shown diagrammatically in FIG. 1. Said compact element 1 is obtained beforehand in two preliminary substeps comprising:

• (a1) production of a homogeneous mixture of the appropriate quantity of nickel and aluminum powders;
• (A2) cold compaction of the mixture obtained in a suitable mold under a load of 40 MPa.

As is known per se, cleaning operations of the substrate 2 are carried out prior to the installation of the compact element 1 and may include, depending on the condition of the part, new or used, of the degreasing, sanding, chemical deoxidation and / or thermochemical.

According to an alternative embodiment, the compact element 1 can also be obtained depending on the applications by techniques known per se of injection molding.

When installing the compact element 1 on the substrate 2, it is possible to maintain, for example by applying a capacitor discharge on the element concerned.

Other techniques known per se can be used to deposition, for example by direct deposition of powder on the substrate 2 in an electrophoretic medium.

The next step (b) is to introduce the part constituting the substrate 2 carrying the compact element 1 in a hydrostatic neutral gas high pressure chamber a heating enclosure.

Finally step (c) makes it possible to carry out a synthesis reaction on the compact element 1 so as to ensure its densification and the metallurgical link between said element 1 and the corresponding surface of the part constituting the substrate 2.

• pression de l'atmosphère de gaz neutre constitué dans cet exemple de réalisation par l'argon = 146MPa ;
• cycle de montée en température dans le four :
  • 50°C par minute jusqu'à 300°C ;
  • palier de 6 minutes à 300°C ;
  • 90°C par minute jusqu'à 800°C, sans palier ;
  • refroidissement à 50°C par minute jusqu'à 20°C.

This provides a reload by adding material to the affected area of the part. Said synthesis reaction allowing the constitution of a Ni-Al intermetallic compound material in the present exemplary embodiment is initiated at one end 3 of the element 1 when a tripping temperature is reached which is in this case 673 ° vs. The self-propagating exothermic combustion reaction then moves in the direction of arrow 4 indicated in FIG. 1 until it reaches the opposite end 5. In this case, the conditions applied are as follows:

• pressure of the neutral gas atmosphere constituted in this embodiment by argon = 146MPa;
• temperature rise cycle in the oven:
  • 50 ° C per minute up to 300 ° C;
  • step of 6 minutes at 300 ° C;
  • 90 ° C per minute up to 800 ° C, without plateau;
  • cooling at 50 ° C per minute to 20 ° C.

The diagram in Figure 2 shows the temperatures measured on the part and shows the ignition temperature of the auto-combustion reaction around 673 ° C. We also note that the propagation of a combustion front through the material of compact element 1 upon initiation of the reaction obtained thanks to the temperature gradient of 200 ° C established between the two ends of said element 1 is very fast. In this example, the reaction is complete and the propagation speed of the combustion front can be estimated at 20 mm / s. In general, the rate of propagation of the reaction is between 1 and 10cm per second depending on the operating conditions applied.

The results described below were observed on the coin recharged according to the process according to the invention.

In macroscopic observation, the filler material 1 has macroporosity with good adhesion over the entire length of the affected area of the room 2.

Under observation by light microscopy as shown on Figure 3, an intermediate phase is observed between the material A of the substrate and the intermetallic material NiAl. The NiAl material is porous but the part in contact with the material A is perfectly densified over a thickness of 0.7 mm approximately.

In observation by scanning electron microscopy, two types of analyzes were performed, one qualitative, the other quantitative by EDS probe.

• I   : NiAl
• II   : NiAl + Co,Cr
• III   : interphase
• IV   : zone de précipités
• V   : matériau A près de l'interphase
• VI   : matériau A

Qualitative analysis highlights the interphase between materials A and NiAl. Figures 4 and 5 show photomicrographs showing the appearance of the material obtained. There are six areas:

• I: NiAl
• II: NiAl + Co, Cr
• III: interphase
• IV: area of precipitates
• V: material A near the interphase
• VI: material A

The table below indicates the atomic percentages of the various elements constituting the material, the precision of the measurements carried out being ± 1%. The reference material A is indicated in the first column and the results of the point analyzes carried out in the six zones are reported in the following columns. AT ZONE VI ZONE V ZONE IV ZONE III ZONE II ZONE I AL 2.89 2.60 6.32 13.97 31.61 42.71 49.56 Ti 3.73 3.70 3.36 2.79 1.90 Cr 22.32 22.40 22.30 15.56 6.82 0.75 Co 11.95 11.90 11.81 8.18 4.51 1.09 Or 56.40 56.50 53.52 57.78 54.59 55.45 50.44 Mo 2.63 2.70 2.67 1.72 0.58 W 0.08 0.06 0.02 0.02

Figures 6 and 7 show the evolution of the concentration of the elements Al, Ni, Co, Cr, Ti along the interphase between materials A and NiAl. We note a regular decrease in aluminum concentration when switching from NiAl to A associated with an increase in the concentration of Cr, Co and Ti. As a result, a reaction of diffusion between the two materials A and NiAl has produced, the thickness of the interphase reaching about 20 µm (see zones II and III of figure 4).

• en zone I, sous charge de 100 g : 252
• en zone III, sous charge de 300 g : 410
• en zone VI, sous charge de 100 g : 298

Microhardness tests using the Vickers method carried out on the three materials A, NiAl and interphase gave the following results:

• in zone I, under 100 g load: 252
• in zone III, under 300 g load: 410
• in zone VI, under 100 g load: 298

It follows from these observations that the interphase obtained is consisting of a continuous solid solution between materials A and NiAl. No intermediate intermetallic compound has been observed. The introduction of chromium into the NiAl phase can justify the increase in hardness of the intermediate phase in zone III by effect of solid solution but the level of hardness confirms the absence of an intermetallic phase complex.

EXAMPLE B

It is again a question of making a contribution on a piece in nickel-based superalloy B to reshape it to the profile desired by recharging using a mixture of powders nickel and aluminum in equi-atomic proportions with interposition of an intermediate superalloy underlayment C based on nickel.

As schematically shown in Figure 8, in step (a) of the process according to the invention, the compact element 1 is identical to the one that was used and previously described for example A and it is also obtained from the same way.

On the other hand, between the substrate 20 constituted by a part zone made of superalloy B and the compact element 1 is inserted another additional compact element 11 obtained by sintering from powders made of superalloy C based on nickel. The compositions of the superalloys are indicated below in percentages by weight:
B: Ni base; Cr 14; Co 9.5; Mo 4; Al 3; W4; Ti5; If 0.2; Mn0.2; C 0.17
C: Ni base; Co 16.5 to 19; Cr 10.4 to 12.2; MB 3.3 to 4.2; A1 2.85 to 3.15; Ti 2.45 to 2.8; If 1 to 1.3; B 0.68 to 0.8; C 0 to 0.06.

As before, in step (b), the part constituting the substrate 20 carry a sub-layer constituted by the element compact 11 and an outer layer formed by the element compact 1 is introduced into a high pressure chamber hydrostatic neutral gas forming a heating chamber.

The next step (c) again makes it possible to carry out a reaction synthesis on compact element 1 and we get a reloading by adding material to the affected area of the room.

• pression de l'atmosphère de gaz neutre constitué dans cet exemple de réalisation par l'argon : 110MPa ;
• cycle de montée en température dans le four :
  • 50°C par minute jusqu'à 300°C ;
  • palier de 6 minutes à 300°C ;
  • 90°C par minute jusqu'à 600°C, sans palier ;
  • refroidissement à 50°C par minute jusqu'à 20°C.

In this case, the conditions applied are:

• pressure of the neutral gas atmosphere constituted in this embodiment by argon: 110 MPa;
• temperature rise cycle in the oven:
  • 50 ° C per minute up to 300 ° C;
  • step of 6 minutes at 300 ° C;
  • 90 ° C per minute up to 600 ° C, without plateau;
  • cooling at 50 ° C per minute to 20 ° C.

The results described below were observed on the coin recharged according to the process according to the invention. In macroscopic observation, the assembly of the three parts, substrate 20 and filler elements 1 and 11 appear to be realized and solid.

Under observation by scanning electron microscopy, the micrograph shown in Figure 9 shows the appearance of the material obtained comprising seven zones for which the concentration profiles of the most important elements determined along line 12 are also shown.

Zone I corresponds to the NiAl intermetallic material. The area It is more clearly visible on the detail enlarged photomicrograph shown in Figure 10 and it corresponds to the interface between the NiAl material and the superalloy C with element concentration profiles Al, Ni, Co, Cr, Mo and Ti are also shown in the figure 11. The homogeneous band of zone II corresponds to the diffusion aluminum and chromium in particular with also a variation of the titanium concentration.

In zone III, the concentrations of Al, Ni, Co and Mo are constant while the concentrations of Cr and Ti vary continuously. On the micrograph of an enlarged part of this zone III represented in FIG. 12, we observe the multiphase nature of this zone with a single-phase zone predominantly white and a structured area acicular. Zone IV has a composition close to that of superalloy C with the presence of inclusions of light color corresponding to some variations for certain elements, molybdenum and chromium in particular.

The following zones V, VI and VII correspond to the interface between superalloys C and B. An enlarged detail is shown in the photomicrograph of Figure 13 and the figure 14 shows the concentration profiles of the different elements. Zone VI has a close average composition that of superalloy C with more aluminum and tungsten but less cobalt and silicon. This zone exhibits good homogeneity, the concentrations being all roughly constant. Around the grains constituting the phase VI, there is an acicular structure, of the type eutectic indicating partial fusion at grain boundaries of phase VII. Profiles indicate that this constituent contains Cr, Mo, Ti and Co with less Ni and Al than in superalloy C. In zone VII, the concentration of aluminum decreases, while chromium and molybdenum increase continuously.

It follows from these observations that good dissemination of different elements with the formation of a solid solution between superalloy C and the intermetallic material NiAl is found at the interface between these two materials.

In addition, the heat given off by the exothermic reaction of synthesis of the NiAl intermetallic compound is sufficient to affect the entire thickness of the compact sintered element 11 and cause the items to spread to the other side with appearance of an interface between superalloys C and B.

Claims (7)

Process for producing a contribution on a nickel or cobalt-based superalloy part, characterized by the following successive steps: (a) deposition on at least one localized area of the part (2 20) of a filler element (1; 1.11) taken from the group, on the one hand, reactive powders in proportions corresponding to the formation of an intermetallic material and, on the other hand, superalloy powders based on nickel or cobalt; (b) positioning of the part (2; 20) comprising the deposit obtained in step (a) in a high pressure chamber supplied with neutral gas by a compression system making it possible to ensure in the chamber a hydrostatic pressure of neutral gas up to 1.5 GPa, said chamber also comprising an oven composed of heating elements making it possible to reach a temperature of 1200 ° C. with a rate of temperature increase between 5 ° C. per minute and 120 ° C per minute by ensuring a thermal gradient of 200 ° C from one end to the other of the room area (2; 20) concerned, the temperatures being controlled by means of a measurement system; (c) carrying out a synthesis reaction by self-propagated combustion under high hydrostatic pressure of gas on said supply element under determined temperature and pressure conditions so as to ensure the densification of the supply (1; 1 , 11) and the metallurgical connection between said supply and the surface concerned of the superalloy part. Method of making a contribution on a piece in nickel or cobalt based superalloy depending on the claim 1 wherein said contribution constitutes a reloading of a localized part area and step (c) completed by simple room cooling is followed a surface leveling operation by machining finish. Method of making a contribution on a piece in nickel or cobalt based superalloy depending on the claim 1 wherein said contribution constitutes a protective coating on at least one area of the room, allowing to increase resistance to oxidation, corrosion and / or erosion. Method of making a contribution on a piece in nickel or cobalt based superalloy according to one of claims 1 to 3 wherein the final thickness of the deposit obtained on the part is between 20µm and 10mm. Method of making a contribution on a piece in nickel or cobalt based superalloy according to one any of claims 1, 2 and 4 wherein in step (a), the deposit is obtained by the installation of a compact element (1) obtained from the mixture of adequate amounts of nickel and aluminum powders of particle size less than 150 µm, in equi-atomic proportions, this mixture being placed in a suitable mold and cold compacted under a load of 40 MPa. Method of making a contribution on a piece in nickel or cobalt based superalloy depending on the claim 5 wherein in step (a), when putting in place of the compact element (1), another element additional compact (11) is inserted as an underlay on the surface of the affected area of the part forming the substrate (20), said additional element (11) being previously obtained by sintering powders in nickel-based superalloy. Method for producing an addition to a part made of nickel-based superalloy according to claim 6, in which the superalloy of the part forming the substrate (20) has the following nominal composition in weight percentages: Ni base, Cr 14; Co 9.5; Mo 4; Al 3; W4; Ti 5; If 0.2 Mn 0.2; C 0.17
and the compact additional element (11) has the following composition in weight percentages: Neither base; Co 16.5 to 19; Cr 10.4 to 12.2; MB 3.3 to 4.2; A1 2.85 to 3.15; Ti 2.45 to 2.8; If 1 to 1.3; B 0.68 to 0.8; C 0 to 0.06.

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