EP1878533A2 - Superalloy powder - Google Patents

Abstract

A nickel (Ni) or cobalt (Co) based superalloy powder is enriched with at least one melting element, boron (B), so that each grain of powder includes this element distributed among the other elements of the superalloy. The proportion of B in the superalloy is between 0.4 and 1.3 wt.%.

Description

The subject of the invention is a superalloy powder.

• une première poudre de superalliage de composition chimique voisine de celle du matériau à réparer, et
• une deuxième poudre à base de nickel (Ni) ou de cobalt (Co) contenant 2 à 6% en poids d'éléments fondants tels que le bore (B) ou le silicium (Si).

In the field of aeronautics or industrial turbines, the severe operating conditions imposed on certain parts, such as turbine blades and distributors, have led to the realization of these Ni or Co. Gold base superalloy parts, to assemble these parts. or to repair them by reloading (ie by localized deposition of material on the part), the current techniques of fusion welding prove to be unsuitable or even unusable. Also, as explained in the document FR 2 822 741 Diffusion-diffusion processes have been developed using so-called two-component mixtures of two metal powders. These mixtures include:

• a first superalloy powder of chemical composition close to that of the material to be repaired, and
• a second powder based on nickel (Ni) or cobalt (Co) containing 2 to 6% by weight of melting elements such as boron (B) or silicon (Si).

The presence of melting elements in the second powder makes it possible to lower the melting point thereof and to work at a temperature at which the second powder is liquid, while the first powder remains in the solid state.

These two-component mixtures nevertheless have disadvantages such as the difficulty of producing a homogeneous mixture of the two powders, the problems of segregation of the powders during the storage of the mixture, or the problems of proportioning the proportions of each powder in the mixture.

For example, when sintering a two-component mixture and the amount of flux in certain regions of the mixture is not sufficient, a porous sinter is obtained. Conversely, an excess of flux in certain regions of the mixture causes supercooling causing deformation of the sinter, which then does not meet the desired dimensions.

To overcome these problems, a solution described in FR 2 822 741 , plans to embed the grains of the second powder on the grains of the first powder, by mechano-synthesis. This technique of incrustation is however in practice limited: this technique is quite difficult to implement, especially because of the fineness of the second powder used, which causes hygiene problems. Moreover this technique only partially improves the homogeneity.

It is also known to chemically coat the grains of the superalloy powder with layers of Ni-B and / or Ni-Si. From an industrial point of view, this method is difficult to use because very long and very difficult to implement when the alloys consist of a large number of elements, in small proportion.

The aim of the invention is to propose an alternative to existing solutions, offering good results in terms of homogeneous distribution of the melting element or elements within the powder, which results, in particular, in the absence of deformation of the parts made by sintering.

To achieve this object, the subject of the invention is a superalloy powder according to claim 1 or claim 5.

It is not necessary to mix the powder of the invention with another powder as in FR 2 822 741 because the powder of the invention already has the final composition which is needed, both in terms of constituent elements of the superalloy and in terms of element (s) melting (s). In particular, the proportion of B and, optionally, Si is adapted for use of the powder without prior mixing step with another powder (as explained above, the proportion of melting elements has a determining influence on the behavior of the powder during the heat treatment thereof).

In addition, in the powder of the invention, said melting element is an integral part of the superalloy: it is not chemically deposited or mechanically inlaid on the surface of the superalloy grains, as in the known techniques mentioned above.

Finally, in the powder of the invention, the constituent elements of the superalloy, including the melting element, are present in each grain of powder and, consequently, are distributed within the powder in a perfectly homogeneous manner. This avoids the problems of localized porosity and supercooling related to a too low proportion, or too important, element melting in some regions of the powder.

Advantageously, in order to produce the powder of the invention, use is made of a technique for atomizing a precursor liquid mixture, comprising the elements of said superalloy and said at least one melting element.

• la figure 1 est une photographie d'une plaque réalisée par frittage à partir d'une poudre selon l'invention; et
• la figure 2 est une photographie d'une plaque réalisée par frittage à partir d'un mélange de poudres bicomposant.

The invention and its advantages will be better understood on reading the detailed description which follows. This description refers to the appended figures in which:

• Figure 1 is a photograph of a plate made by sintering from a powder according to the invention; and
• Figure 2 is a photograph of a plate made by sintering from a mixture of two-component powders.

Whatever the type of powder according to the invention, given by way of example below, each powder is a base Ni or Co superalloy powder, which comprises at least the three elements Ni, Co and Cr (Chrome).

These powders were made using an atomization technique from a precursor liquid mixture comprising the elements of the superalloy (Ni, Co, Cr ...) and at least one melting element (B and optionally Si). This liquid mixture was obtained by melting alloys by induction, under vacuum, in a crucible equipped with a burette allowing the liquid mixture to flow at a low flow rate. Jets of inert gases under high pressure, flowing at a speed close to that of the sound, are used to spray the mixture leaving the burette. The mixture then disintegrates into fine droplets which then take a spheroidal shape under the effect of the surface tension and cool very rapidly in an atomization chamber. In our case, the inert gases used are, for example, argon or nitrogen.

Surprisingly, during cooling, there is no separation of the melting element or elements with the other elements of the alloy. All these elements remain within each droplet, and therefore each grain of powder.

Unless otherwise specified, the percentages given below are percentages by weight.

• 14 à 19,6% de Co ; 8,2 à 15,3% de Cr ; 2,6 à 4,7% de Mo ; 2,25 à 3,5% de Al ; 1,95 à 3,1% de Ti ; 0 à 2% de Si ; 0,4 à 1,3% de B ; et un solde en Ni.

According to a first type of superalloy powder according to the invention, base Ni, the superalloy enriched in melting elements, essentially comprises:

• 14 to 19.6% Co; 8.2 to 15.3% Cr; 2.6 to 4.7% Mo; 2.25-3.5% Al; 1.95 to 3.1% Ti; 0 to 2% Si; 0.4 to 1.3% B; and a balance in Ni.

The presence of impurities in the powder is not excluded (hence the use of the term "essentially"). For example, carbon (C), zirconium (Zr), and phosphorus (P) may be found in minute proportions, for example, on the order of 0.06% or less.

According to a first example (a) of the first type of superalloy powder according to the invention, the superalloy enriched in melting elements essentially comprises: 16.4 to 19.6% of Co; 8.2 to 12.8% Cr; 2.6 to 4.4% Mo; 2.25 to 3.3% Al; 1.95 to 2.9% Ti; 0.8 to 2% Si; 0.5 to 1.3% B; and a balance in Ni.

According to a second example (b) of the first type of superalloy powder according to the invention, the enriched superalloy essentially comprises: 14 to 16% of Co; 12 to 15.3% Cr; 3.35 to 4.7% Mo; 2.9 to 3.5% AI; 2.5 to 3.1% Ti; 0.4 to 1% of B; and a balance in Ni. In example (b), B is the only melting element.

According to a second type of superalloy powder according to the invention, of base Co, the enriched superalloy essentially comprises: 17.2 to 22.2% of Cr; 26.75 to 30% Ni; 0 to 1.5% Si; 0.8 to 1% of B; 0.1 to 0.5% C; 0 to 0.37% Zr; 0 to 3% of Ta; and a balance in Co.

The cobalt base powders of the second type may comprise impurities, such as phosphorus P, in minute proportions, for example of the order of 0.04% or less.

Table 1 below shows the compositions of the examples of powders (a) and (b), mentioned above, and of an example of powder (c) corresponding to the second type of superalloy powder according to the invention. Table 1 Ex Composition in% by weight Or Co Cr MB al Ti Yes B VS Zr P Your (at) based 16.4 8.2 2.6 2.25 1.95 0.8 0.5 0 0 0 0 19.6 12.8 4.4 3.3 2.9 2 1.3 0.06 0.05 0.01 0 (B) based 14 12 3.35 2.9 2.5 0 0.4 0 0 0 0 16 15.3 4.7 3.5 3.1 0 1 0.06 0.06 0.02 0 (vs) 26.75 based 17.2 0 0 0 0 0.8 0.1 0 0 - 30 22.2 0 0 0 1.5 1 0.5 0.37 0.04 -

All these examples of superalloy powder can be used in the implementation of any solder-diffusion process applied during the manufacture or repair of nickel-based alloy parts, cobalt, especially in the aeronautical field. It can be an assembly of parts, a filling of cracks, or cracks, on part or a reload of part surface to correct a superficial defect or to restore certain properties or geometrical dimensions of that -this.

Depending on the applications, the introduction of the filler powder can be carried out in different ways.

For the filling of cracks, the raw powder can be used mixed with a cementum, for example of the Nicrobraz 320 type. It will be noted that the mixture obtained can be used in the form of cords.

In some applications, and particularly in the case of the surface reloading of a workpiece, a supply can be made in the form of a compact filler. Said compact filler is obtained from the powder either by a manufacturing technique ensuring a sintering compaction thereof, or by means of injection molding techniques of metal powders.

FIG. 1 shows an example of a compact filler piece made by sintering from a superalloy powder according to the invention. This is a plate intended to be used to reload the surface of a room.

This plate was made from a powder of the aforementioned first type, according to the following steps: oven drying of the raw powder; distribution thereof in a mold adapted to the desired size and sintered thickness; placing the mold in an oven to heat treat it. As an example of heat treatment, one can perform (for an oven pressure of 0.13 Pa) a gradual increase in temperature up to 1160 ° C, then a hold at this temperature for about 10 min, followed by a gradual cooling.

Comparatively, a compact filler piece was made by sintering from a two-component powder mixture of known type, FIG. 2 shows the part obtained.

In practice, it has been found that the invention makes it possible to avoid the management and storage of several references of powders, and to avoid any step of mixing powders, critical from a hygiene and safety point of view.

In addition, because of the use of a single powder containing in each grain the composition necessary for the production of a plate (ie all the elements of the superalloy and at least one melting element), the sintering temperature is significantly reduced. relative to the temperature required for a two-component mixture. Thanks to the homogeneity of the powder and the reduction of the sintering temperature, a noticeable improvement in the homogeneity of the properties of the sintered plate and a good preservation of the dimensions and the shape thereof, in particular a respect of the wished dimensions and a good flatness.

Figure 2 illustrates, conversely, the deformation problems that can be encountered during sintering of a two-component mixture.

The homogeneity of the superalloy powder of the invention also results in an improvement of the mechanical properties of the zone reloaded with said plate.

According to another example of use of the powder of the invention, it is possible to produce a compact filler using known metal powder injection molding techniques. These techniques generally make it possible to obtain pieces of more complex shape than those made by simple molding followed by sintering.

To do this, the powder is mixed with a binder in a kneader. The binder includes, for example, polypropylene, ethylene, vinyl acetate and paraffin. The mixing time must be such as to obtain a plasticization of the mixture. The mixture is then cooled before being ground. The granulates thus obtained can be introduced into the hopper of a press and the injection can be carried out in molds of dimensions specific to the compact part to be produced. The mold blank is then chemically untied and the blank is sintered.

1. a) utilisation de la poudre mélangée à un cément, par exemple pour le rebouchage de criques;
2. b) utilisation de la poudre pour la réalisation de pièces d'apport compactes, en particulier de plaques, par frittage; et
3. c) utilisation de la poudre comme constituant d'un mélange pour moulage par injection de poudres métalliques.

Some examples of Table 1 powder have been found to be more suitable for some of the following uses: a, b and c:

1. a) use of the powder mixed with a cementum, for example for the filling of cracks;
2. b) use of the powder for the production of compact filler parts, in particular plates, by sintering; and
3. c) using the powder as a constituent of a mixture for injection molding of metal powders.

The preferred uses of each powder example are shown in Table 2 below. Table 2 Example Use a Use b Use c (at) Yes Yes Yes (B) Yes Yes (vs) Yes Yes

Claims (6)

Superalloy powder, characterized in that the superalloy is enriched with at least one melting element: B, so that each grain of powder comprises said at least one melting element distributed among the other elements of the superalloy, and in that this superalloy is composed of, in percentages by weight: - 17.2 to 23% of Cr; - 26.75 to 32.4% of Ni; 0 to 2.5% Si; 0 to 0.5% C; 0 to 0.4% Zr; 0 to 3% of Ta; 0 to 0.5% of Y; 0 to 8% of Al; - 0.8 to 1.2% of B; and - a balance in Co. Superalloy powder according to claim 1, characterized in that the flux-enriched superalloy is composed of, in percentages by weight: - 17.2 to 22.2% of Cr; 26.75 to 30% of Ni; 0 to 1.5% Si; 0.8 to 1% of B; 0.1 to 0.5% C; 0 to 0.37% of Zr; 0 to 3% of Ta; and - a balance in Co. Superalloy powder according to claim 1 or 2, characterized in that it is obtained by atomization of a liquid mixture composed of the elements of said superalloy and said at least one melting element. Use of a superalloy powder according to any one of claims 1 to 3 for producing parts, in particular plates, by sintering. Use of a superalloy powder according to any one of claims 1 to 3, mixed with a cementum. Use of a superalloy powder according to any one of claims 1 to 3 as a component of a metal powder injection molding mixture.

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